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Computed Tomography Imaging of Left Atrium and Pulmonary Veins for Radiofrequency Ablation of Atrial Fibrillation
Computed Tomography Imaging of Left Atrium and Pulmonary Veins for Radiofrequency Ablation of Atrial Fibrillation Jadranka Stojanovska, MD, and Paul Cronin, MD, MS
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trial fibrillation is the most common sustained supraventricular arrhythmia. The prevalence and the incidence increases with advancing age and with the presence of cardiovascular disease.1 It is associated with increased morbidity and mortality due to hemodynamic deterioration secondary to increased heart rate, loss of atrioventricular synchrony, and progressive dysfunction of the left atrium, which may increase the risk of stroke and other embolic events secondary to atrial thrombi.2 Atrial fibrillation is more frequent in patients with hypertension or structural heart disease such as underlying valve disease (especially rheumatic and mitral valve)3,4 and coronary artery disease. It is more frequent in patients with cardiopulmonary disease resulting in hypoxia or hypercapnia such as chronic obstructive pulmonary disease, or in patients with metabolic disease such as diabetes mellitus and hyperthyroidism. Atrial fibrillation has a strong association of with other arrhythmias such as Wolff—Parkinson–White syndrome, atrioventricular nodal reentrant tachycardias, and sick sinus syndrome. In addition, it may occur in healthy patients in times of stress, following surgery, strenuous exercise, or with stimulants such as coffee or alcohol.5
Introduction Atrial Fibrillation Classification of atrial fibrillation has been proposed by the American College of Cardiology/American Heart Association/European Society of Cardiology6 and it consists of the following: paroxysmal atrial fibrillation, self-terminating that can last up to 7 days, persistent atrial fibrillation that lasts longer than 7 days but can be terminated by cardioversion, and permanent atrial fibrillation that persists longer than 1
Department of Radiology, Division of Cardiothoracic Radiology, University of Michigan Medical Center, Ann Arbor, Michigan. Address reprint requests to Paul Cronin, MD, MS, Department of Radiology, Division of Cardiothoracic Radiology, University of Michigan Hospitals, B1 132G Taubman Center/0302, 1500 East Medical Center Drive, Ann Arbor, Michigan 48109-0030. E-mail: [email protected]
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0037-198X/08/$-see front matter © 2008 Elsevier Inc. All rights reserved. doi:10.1053/j.ro.2008.01.010
year. In addition, “lone” atrial fibrillation is described as paroxysmal, persistent, or permanent atrial fibrillation in patients without structural heart disease. Atrial fibrillation occurs when multiple ectopic electrical foci fire independently, sending as many as 300 discharges per minute to the atrioventricular (AV) node (Fig. 1). The pathologic background involves the development of ectopic beats secondary to ectopic foci of electrical activity, up to 94% of which originate within the pulmonary veins7; although the ectopic beats can also originate from the walls of the superior vena cava (SVC), both atria, crista terminalis, ostium of the coronary sinus, and interatrial septum. The myocardium of the left atrium extends a variable length into the pulmonary veins with the myocardial sleeves of the superior and left pulmonary veins longer than those of the inferior and right pulmonary veins.7 The pulmonary vein musculature is also highly anisotropic with abrupt fiber orientation changes, muscular breaks, and fibrous encapsulation of the muscle bundles and is innervated by the autonomic nervous system with autonomic nerves concentrated in ganglionic plexi around the great vessels such as the pulmonary veins. This suggests an important role for the genesis of atrial fibrillation.8 Tan and coworkers indicated in their study that the pulmonary vein antrum within 5 mm of the pulmonary vein–left atrium junction, rather than elsewhere in the atria or more distally in the pulmonary veins, is the most densely innervated and therefore the optimal location for autonomic nerve modulation procedures.9 The main symptoms associated with atrial fibrillation are related to the rapid ventricular rate that may cause hypotension, induce angina, or lead to loss of atrioventricular synchrony. The major complication is the formation of the atrial thrombi with severe risk of systemic embolization such as stroke. The initial diagnosis is made by the lack of P-waves, an atrial rate of 300 to 600 beats per minute, and an irregular ventricular response on electrocardiograph (ECG).
Management There are two goals of therapy in atrial fibrillation: alleviation of the symptoms and reducing the risk of stroke. There are
CT imaging for radiofrequency ablation of atrial fibrillation
Figure 1 Long axis or four-chamber graphic of the heart showing the basic cardiac anatomy and components of the cardiac conduction system. (Color version of figure is available online.)
multiple treatment options for atrial fibrillation including antiarrhythmic drug,10 electrical and mechanical cardioversion, transvenous AV junction ablation, surgical treatments including the Cox–Maze procedure that is best performed in patients requiring open heart surgery for another reason, and more recently, radiofrequency ablation techniques. If the patient is hemodynamically compromised, electrical cardioversion is the treatment of choice. Cardioversion restores mechanical atrial contraction over time. However, patients are anticoagulated for up to 3 weeks before and 4 weeks after cardioversion, with an international ratio of 2.0 to 3.0, if the duration of atrial fibrillation is greater than 48 hours, to reduce the risk of systemic embolization. The American College of Cardiology/American Heart Association Task Force and the European Society of Cardiology Committee for Practice Guidelines recommend anticoagulation for newly discovered atrial fibrillation, recurrent paroxysmal atrial fibrillation, and recurrent persistent or permanent atrial fibrillation.6 In hemodynamically stable patients, pharmacological agents such as beta-blockers are used to slow the ventricular response and to maintain sinus rhythm. However, the Sotalol-Amiodarone Atrial Fibrillation Efficacy Trial, a multicenter, double-blind, randomized, placebo-controlled study designed to compare the effects of sotalol and amiodarone on long-term maintenance of sinus rhythm, quality of life, and exercise tolerance in patients with persistent atrial fibrillation after drug or direct current (DC) cardioversion with 12 months follow-up concluded that neither sotalol nor amiodarone treatment was associated with an improvement in exercise capacity, regardless of rhythm status throughout the follow-up.11
155 veins and the left atrium.17 If the treatment is successful, long-term anticoagulation is unnecessary. This is in contrast to the cardioversion, where long-term anticoagulation is required. The catheter-based pulmonary vein ablation technique is used to electrically disconnect the pulmonary veins from the left atrium and is increasingly being used by interventional electrophysiologists. This technique was first described in 199418 using point ablation of site-specific arrhythmogenic foci in the pulmonary veins. This initially had a low success rate of 4% but has subsequently been shown to have a success rate of approximately 47%. However, this may require repeat procedures of multiple veins with a high risk of pulmonary vein stenosis. An advancement of this technique was empirical ablation of all pulmonary vein ostia if feasible. This reduced the development of recurrent atrial fibrillation and the need for repeat procedures. Newer trends include the radiofrequency ablation MAZE and extraostial ablation. With the radiofrequency ablation MAZE procedure, wide area lesions in the posterior wall/roof of the left atrium circumferentially encircling the pulmonary veins are created using radiofrequency energy (Fig. 2).17 This technique has somewhat fallen out of favor because scar tissue induced by the procedure can be proarrhythmic as can incomplete or nontransmural lesions by predisposing to reentrant flutter circuits. This technique may also be complicated by atrioesophageal fistula. The newest technique, using circumferential extraostial (Fig. 3) ablation, shows significantly better outcomes.15 The procedure is long, lasting several hours, and is performed under general anesthesia requiring endotracheal intubation.
Catheter Ablation Catheter-based radiofrequency ablation is the preferred therapeutic method and an evolving procedure for the treatment of paroxysmal atrial fibrillation in patients who do not respond to anti-arrhythmic drugs.12-16 Radiofrequency catheter ablation including cryoablation and the Cox–Maze procedure are aimed at causing anatomic scars to disrupt electrical communication between the ectopic foci of the pulmonary
Figure 2 Three-dimensional endocardial model of the left atrium in a 54-year-old man with atrial fibrillation. White line demonstrates the typical posterior left atrial ablation lines for a MAZE procedure. The gray dotted line indicates the position of the esophagus. RSPV indicates right superior pulmonary vein; RIPV, right inferior pulmonary vein; LSPV, left superior pulmonary vein; LIPV, left inferior pulmonary vein.
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Figure 3 Three-dimensional endocardial model of the left atrium in a 58-year-old man with atrial fibrillation. White line demonstrates the typical posterior left atrial ablation lines for an extraostial ablation procedure. These are circumferential lesions placed around the right superior and inferior veins and left superior and inferior veins. RSPV indicates right superior pulmonary vein; RIPV, right inferior pulmonary vein; LSPV, left superior pulmonary vein; LIPV, left inferior pulmonary vein.
In this technique, access to the pulmonary veins and the left atrium is gained via the right atrium through a patent foramen ovale or fossa ovalis puncture using a transfemoral approach, under fluoroscopic guidance. Guide wires are introduced through the trans-septal puncture followed by catheters and sheaths. Ablation is usually performed during normal sinus rhythm. First, the anatomy of the left atrium and the position of the pulmonary vein ostia are identified by selective angiography and then the pulmonary veins are mapped. Current ablation electrodes only cover a few millimeters of space; therefore, multiple individual ablation lesions are required to create the intended contiguous circumferential lesion.15,17
Preablation Imaging Knowledge of the detailed anatomy of the left atrium and pulmonary vein ostia is crucial for the effectiveness of radiofrequency ablation. It is also important to know the ostial orientation and diameter. It can be difficult and time consuming to locate the ostia with conventional angiography at the time of ablation. Therefore, imaging before the procedure is important to answer these questions. Conventional angiography, intracardiac echocardiography, transesophageal echocardiography, computed tomography, more recently multidetector computed tomography (MDCT) and magnetic resonance angiography (MRA) are modalities which have been used to determine ostial orientation and diameter before the ablation procedure. However, no technique has yet been widely accepted as the gold standard for measurement of pulmonary veins.13 Conventional angiography is an invasive method that does not allow good visualization of the
J. Stojanovska and P. Cronin pulmonary veins secondary to overlapping structures.19 Intracardiac echocardiography (ICE) is an essential tool used for safe trans-septal access, identification of anatomical structures relevant to the ablation, the placement and navigation of circular mapping catheters, and titration of energy delivery during ablation.20-22 However, it does not allow visualization of the left atrium/pulmonary veins relationship and often fails to visualize multiple right-sided pulmonary vein ostia that can be detected using computed tomography (CT).13,22 Intracardiac echocardiography can also visualize the esophagus in relation to the posterior left atrial structures. Kenigsberg and coworkers showed that intracardiac echocardiography provides rapid, real-time localization of the esophagus during left atrial ablation.23 Transesophageal echocardiography is the method used at most institutions to assess the left atrial/ left atrial appendage for thrombus, which is an absolute contraindication to the ablation procedure.24 However, transesophageal echocardiography does not allow visualization of the inferior pulmonary veins. Noninvasive imaging modalities, including MRA MDCT, which can depict the three-dimensional anatomy of the pulmonary veins and left atrium, provide a valuable road map before catheter ablation. The advantages of cardiac CT/MRA are as follows: (1) imaging the anatomic characteristics of the pulmonary vein and left atrium before the procedure; (2) assessing the anatomic relationship of the left atrium, esophagus, and adjacent vascular structures; (3) understanding the morphological remodeling of pulmonary vein and left atrium in atrial fibrillation; and (4) detecting postprocedural complications.20 MRA has its own advantages over CT including lack of ionizing radiation and higher temporal resolution. However, the long scan time, expense, and contraindications to magnetic resonance imaging, including the presence of defibrillator/pacemaker, can limit its utility. At our institution, left atrium and pulmonary vein mapping using helical CT scanners has been performed since the invention of the MDCT scanner, and we have performed these mapping studies using 4-, 8-, 16-, and 64-slice scanners. Currently all patients are scanned on a 64-slice scanner. Some institutions use ECG-gating and some institutions do not. At our institution, retrospective ECG-gating is used were possible. As patients undergoing radiofrequency ablation procedures typically have paroxysmal atrial fibrillation, their rhythm may be atrial fibrillation, ie, fast and/or irregular or sinus rhythm at the time of their CT. ECG-gating is used for patients in sinus rhythm and non-ECG-gating is used for patients in atrial fibrillation. In general, one-third to one-half of our patients cannot undergo ECG-gated examinations. ECG-gating improves both the quality of three-dimensional images and the ability to detect thrombus within the left atrium and/or left atrial appendage. Furthermore, there is both phasic change in pulmonary vein ostial diameters and phasic change in ostial positions during the cardiac cycle; therefore, ECG-gating allows assessment of the pulmonary veins at a single phase of the R-R interval such as 75% R-R, ie, end diastole when there is least cardiac motion. Alternatively, the pulmonary veins can be assessed at 85% R-R, ie, late atrial diastole when the pulmonary vein ostial diameters are max-
CT imaging for radiofrequency ablation of atrial fibrillation
Figure 4 Axial CT image of a right superior pulmonary vein obtained in a 44-year-old man with atrial fibrillation before radiofrequency procedure. Axial CT image shows right superior pulmonary vein (arrow).
imal. Test bolus timing with a region of interest placed in the left atrium is employed. Fifteen milliliters of nonionic intravenous contrast material followed by a 20 mL saline chase are injected to determine the peak enhancement within the left atrium. Scans are initiated with a delay equal to the time to peak enhancement plus 6 seconds after beginning injection of the remaining 100 mL of nonionic intravenous contrast material. We use 115 mL of nonionic intravenous contrast material in total (including 15 mL for the test bolus timing) administered with a power injector at a rate of 4 mL/s through an antecubital vein. The collimation used is 1.25 mm, and a 0.625-mm reconstruction interval. The heart or the entire thorax may be scanned. We scan from the lung bases to the apices during a single breath-hold. Including the
Figure 5 Multiplanar reformatted (MPR) CT image of a right superior normal pulmonary vein obtained in a 42-year-old man with atrial fibrillation before radiofrequency procedure. MPR CT scan shows right superior pulmonary vein (arrow).
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Figure 6 Three-dimensional model of left atrium and pulmonary veins in a 64-year-old man with atrial fibrillation. This image shows right superior pulmonary vein (RSPV), right inferior pulmonary vein (RIPV), left superior pulmonary vein (LSPV), left inferior pulmonary vein (LIPV), and left atrium (LA).
superior thorax, not just the left atrium and central pulmonary veins allows visualization of aberrant pulmonary venous drainage to the brachiocephalic veins or SVC. The bottom-up direction minimizes respiratory motion should the patient inhale or exhale toward the end of the scan and minimizes streak artifact from contrast in the SVC and brachiocephalic veins. Imaging is performed using 120 kVp and 320 mA tube current. For an average-sized adult male patient, the effective
Figure 7 Semiautomated analysis software using “Vessel Analysis” technique that allows the user to track, extract, visualize, and measure the veins. Short-axis view of the right superior pulmonary vein ostium with a minimum diameter of 23.7 mm and a maximum diameter of 27 mm.
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158 radiation dose per pulmonary vein scan, assuming 320 mA tube current, is approximately 10 mSv.25 The acquired images can be reviewed as axial data (Fig. 4), as multiplanar reformatted images (Fig. 5), or using advanced processing such as volume rendering or endocardiac views.
Pulmonary Vein Advanced Processing Three-dimensional models of the left atrium, left atrial appendage, and pulmonary veins are routinely reconstructed to guide electrophysiologists before atrial fibrillation ablation procedures. Surface-rendered views (vessel analysis) and endocardiac views (navigator electrophysiology [EP]) of the left
atrium and the pulmonary veins are obtained using CardEP™ software (GE Medical System, Milwaukee, WI) on GE Advantages Windows workstations. The vessel analysis software is a semi-automated analysis tool based on the advanced vessel analysis technique that allows the user to track, extract, visualize, and measure the veins. The software initially generates a three-dimensional model of the left atrium and pulmonary veins (Fig. 6). The user then identifies the pulmonary vein ostium and the software generates minimum, mean, and maximum pulmonary vein ostial diameter measurements. This software provides short-axis, cross-sectional (Fig. 7), long-axis (Fig. 8), and
Figure 8 Vessel analysis software that allows the user to track, extract, and visualize the pulmonary veins. (A) Long-axis view of right superior pulmonary vein (RSPV). (B) Left superior pulmonary vein (LSPV). (C) Right inferior pulmonary vein (RIPV) and (D) left inferior pulmonary vein (LIPV).
CT imaging for radiofrequency ablation of atrial fibrillation
Figure 9 Three-dimensional endocardiac/endoluminal model of left atrium and pulmonary veins in a 62-year-old man with atrial fibrillation. This image shows the right superior pulmonary vein (RSPV), right inferior pulmonary vein (RIPV), left superior pulmonary vein (LSPV), left inferior pulmonary vein (LIPV), and left atrial appendage (LAA).
rotating curved views of the pulmonary veins, which allows measurement of pulmonary vein diameter, cross-sectional area, and distance to first branch. These views give the electrophysiologists an “angiograph” view of the left atrium and the pulmonary veins. The pulmonary veins are best visualized from a dorsocranial view with right posterior oblique and left posterior oblique angulation. This posterior view allows better visualization of the left atrium and the pulmonary veins as these are posterior structures. Endoluminal/endocardiac views using GE CardEP ™ software, Navigator EP protocol, are also routinely rendered (Fig. 9). Theses views allow visualization of the pulmonary vein ostia but also give a better sense of pulmonary vein orientation, geometry of pulmonary vein branches, and common ostia. If studies are performed with retrospective ECG-gating, data from the entire cardiac cycle are available to reconstruct four-dimensional (time-resolved imaging). These images can also be viewed in cine mode to globally assess left atrial function (Fig. 10). Also, left atrial end-diastolic volume, endsystolic volume, stroke volume, and ejection fraction can be calculated.
159 the superior than the inferior pulmonary veins. Normally, there are two superior pulmonary veins, one right and one left, and two inferior pulmonary veins, one right and one left (Fig. 11). The right superior vein drains the right upper and middle lobe. The left superior vein drains the left upper lobe, including the lingula. The inferior veins drain their respective lower lobes. The course of the pulmonary veins is distinct from the course of the pulmonary arteries and bronchi. The superior veins take an oblique course caudally as they pass medially, whereas the inferior veins take virtually a horizontal course centrally and a vertical course distally. The right superior pulmonary vein is usually the largest pulmonary vein. It passes posterior to the superior vena cava and anterior to the right pulmonary artery. As it courses caudally, it passes under the right pulmonary artery to enter the most superior and lateral aspect of the left atrium. The left superior pulmonary vein runs anterior to but in close relationship with the left pulmonary artery. It joins the left atrium near the left atrial appendage. As well as coursing horizontally, the inferior pulmonary veins pass forward as they pass medially, to enter the left atrium at its most inferior and lateral aspect. They lie in a plane considerably posterior to the superior pulmonary veins. The superior pulmonary vein ostia are significantly larger than the inferior pulmonary vein ostia. Cronin and coworkers reported on 200 patients with atrial fibrillation and found the mean diameter of the right superior pulmonary vein ostia was 17.6 mm; the left superior pulmonary vein ostia was 16.6 mm, compared with 17.1 mm for the right inferior pulmo-
Pulmonary Vein and Left Atrium Anatomy During embryological development, the pulmonary vein confluence is incorporated into the dorsal wall of the left atrium. This is followed by musculization or atrialization of the venous part of the atrial wall. Myocardium is found around AV junctions and within the media of the pulmonary veins. These myocardial sleeves are more developed around
Figure 10 Three-dimensional model of left atrium in a 52-year-old woman with atrial fibrillation. This model can be viewed in cine mode to globally assess left atrial function and also can be used to calculate left atrial function such as end-diastolic volume, end-systolic volume, stroke volume, and ejection fraction. (Color version of figure is available online.)
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Figure 11 Multiplanar reformatted CT scans of normal pulmonary veins obtained in 65-year-old man with atrial fibrillation before a radiofrequency procedure. Axial CT scans show (A) right superior pulmonary vein (arrow), (B) left superior pulmonary vein (arrow), (C) right inferior pulmonary vein, and (D) left superior pulmonary vein.
nary vein ostia, and 14.8 mm for the left inferior pulmonary vein ostia.26 There was no significant difference between the average diameters of right and left pulmonary vein ostia. In another study, the mean pulmonary vein diameters at the ostia were as follows: right superior, 11.9 mm; left superior, 10 mm; right inferior, 12.7 mm; and left inferior, 9.5 mm.27 The pulmonary vein trunk is defined as the distance from the ostium to the first-order branch. The superior pulmonary veins tend to have a longer trunk, 16 (15.3, 16.7) mm, than the inferior pulmonary veins, 10.2 (9.7, 10.7) mm. The superior veins are also overlapped by the descending proximal pulmonary artery, which may make visualization of the first branch difficult. Scharf and coworkers found greater variation in pulmonary vein length than in diameter.28
Pulmonary Vein and Left Atrium Variants Pulmonary vein anatomy is more variable than pulmonary arterial anatomy, and developmental anomalies are common. When variations occur, the right side tends to have accessory veins (one or more), and the left side tends to have conver-
gent veins (a short or long common trunk), which drains into the left atrium. The common anomalies include a common left or right pulmonary vein in 4.5 to 14% of individuals (Fig. 12).26,29 Conjoined veins or common trunk occurs when the superior and inferior veins converge to form a single atriopulmonary venous junction. A single common left vein is much more common than a common right vein. In our experience, with several hundred patients, a common right vein has only been identified in two patients. When present, a common pulmonary vein trunk has a significantly larger diameter, on average 24.3 mm, compared with the other pulmonary veins, and a significantly shorter trunk, 9.8 mm on average.26 Supernumerary or accessory veins are common. An accessory vein has its own independent atriopulmonary venous junction separate from the superior and inferior pulmonary veins. The most common is a separate right middle pulmonary vein, which drains the middle lobe directly to the left atrium (Fig. 13). This is estimated to occur in 10.5 to 26% of individuals.26,29,30 Tsao and coworkers reported that the right
CT imaging for radiofrequency ablation of atrial fibrillation
Figure 12 A 53-year-old woman with atrial fibrillation. Three-dimensional model of the left atrium and pulmonary veins, which shows a common left trunk (arrow). This is a common anomaly occurring in 4.5 to 14% of patients.
middle lobe vein may drain directly into the left atrium in 23% of patients, share a common ostium to the proximal part of the right superior pulmonary vein in 69% of patients, and share a common ostium to the proximal right inferior pulmonary vein in 8% of patients.31 Cronin and coworkers found that in 84% of patients the right middle lobe vein drained into the right superior pulmonary vein; in 11% of
Figure 13 A 56-year-old man with atrial fibrillation and direct drainage of a middle lobe pulmonary vein into left atrium. Endocardial view with annotation shows a right superior and inferior pulmonary vein and separate drainage of middle pulmonary vein into the left atrium. These images show the right superior pulmonary vein (RSPV), middle lobe pulmonary vein (MLPV), right inferior pulmonary vein (RIPV), left superior pulmonary vein (LSPV), and left inferior pulmonary vein (LIPV).
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Figure 14 A 58-year-old man with atrial fibrillation. Three-dimensional model shows a pulmonary vein with separate direct drainage to the left atrium of superior segment of the right lower lobe separate from the right inferior pulmonary vein. These images show the right superior pulmonary vein (RSPV), superior segment of the right lower lobe pulmonary vein (ssRIPV), right inferior pulmonary vein (RIPV), left superior pulmonary vein (LSPV), and left inferior pulmonary vein (LIPV).
patients it drained directly into the left atrium (Fig. 13), and in 5.5% of patients it drained into the right inferior pulmonary vein.26 The middle lobe pulmonary vein ostia are significantly smaller than the superior or inferior pulmonary vein ostia, on average 8.6 mm, as are middle lobe pulmonary vein trunks, on average 8.4 mm.26 Accessory veins are much more infrequent on the left; usually draining all or part of the lingula. These veins have been referred to as “middle veins”, and in our experience only one of these veins has been identified. Other accessory veins occur. The other most notable accessory vein on the right is an accessory vein, draining the superior segment of the right lower lobe directly to the left atrium (Fig. 14). A “top vein”, which enters the roof of the left atrium superomedial to the right superior pulmonary vein, is also described.17 When present, an accessory pulmonary vein has a significantly smaller diameter, on average 7.7 mm compared with the other pulmonary veins, and a significantly shorter trunk, on average, 7.7 mm.26 Given their small size, it is often difficult to identify accessory veins at fluoroscopy, and they may be overlooked and therefore untreated. In one study, 3% of patients had two anomalies and 0.5% of patients had three anomalies.26 A variety of anomalous pulmonary and systemic connections exist; drainage can be partial or total (Figs. 15 and 16). These abnormal pulmonary–systemic venous connections are best classified based on their embryologic derivation and the anatomy of the anomalous connection. Based on this classification, four types are described: (1) supracardiac (a) into derivatives of the right cardinal system (superior vena cava or azygos vein) (b) into derivatives of the left cardinal system (a persistent left superior vena cava, vertical vein, or left brachiocephalic vein); (2) cardiac (a) into derivatives of the left cardinal system (the coronary sinus) (b) into the right atrium; (3) infra-
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Figure 15 Axial image of a pulmonary venous anomaly, a right pulmonary-systemic connection in a 54-year-old man with atrial fibrillation. The axial image shows the pulmonary venous anomaly with the right superior vein draining into the superior vena cava (arrow) just above the insertion into the right atrium. Various anomalous pulmonary–systemic connections exist, and drainage can be partial or total. These abnormal pulmonary–systemic venous connections are best classified according to embryologic derivation and the anatomy of the anomalous connection. Four types are defined in text.
cardiac (a) into the umbilicovitelline system (the portal vein or ductus venosus) (b) into the inferior vena cava, and (4) mixed, a combination of two or more of the anomalies described above may also occur.25 An ostial branch does not have an atrio-pulmonary venous junction but empties into the proximal portion of a vein within 5 mm of the atrio-pulmonary venous junction
Figure 16 Multiplanar reformatted image of a pulmonary venous anomaly, a left pulmonary-systemic connection in a 53-year-old man with atrial fibrillation. The left superior pulmonary vein drains into left brachiocephalic vein via a left vertical vein.
Figure 17 Axial CT scans of an ostial branch in a 43-year-old man with atrial fibrillation before radiofrequency procedure. The axial image shows the middle lobe pulmonary vein draining into the right inferior pulmonary vein but forming an ostial branch with the right inferior pulmonary vein as it enters within 5 mm of the right inferior pulmonary vein atrio-pulmonary venous junction.
(Fig. 17). Because ostial branches drain into a vein within 5 mm of the atrio-pulmonary venous junction, they are also at risk, but less so now that point ablations within the pulmonary veins are performed less.
Interpretation The evaluation of the left atrium before ablation procedures includes assessment for the presence of left atrial/left atrial appendage thrombus, left atrial dimensions and volumes, as well as the relationship with adjacent structures, especially assessing the relation of the posterior wall of the left atrium and the esophagus, which may help avoid the most serious complication, atrioesophageal fistula. Abnormalities of the left atrium or the interatrial septum, including left atrium diverticulum, interatrial septal aneurysms, and atrial septal defects, should be reported. An intraatrial accessory septum is a thin septum extending from the fossa ovalis region anteriorly and superiorly along the atrial wall (Fig. 18). The presence of thrombi in the left atrium and/or left atrial appendage should be identified as this is a complete contraindication to a radiofrequency ablation procedure; although currently transesophageal echo remains the standard of reference to exclude thrombus. It is also important to report to the electrophysiologist any systemic venous variants, particularly azygous continuation of the inferior vena cava, where the right atrium is not accessible inferiorly. Incidental findings should also be reported. These findings include the following: lung carcinoma, indeterminate lung nodules, pneumonia, bronchiectasis, emphysema, pulmonary fibrosis, sarcoidosis, enlarged lymph nodes, coronary artery disease, thoracic aortic aneurysms, hiatal hernias, and pleural and pericardial effusions.
CT imaging for radiofrequency ablation of atrial fibrillation Despite mapping of the left atrium and pulmonary veins, evaluation of the pulmonary venous anatomy, anatomic variants, diameter of the pulmonary vein ostium, and distance to the first branch before ablation procedures, radiofrequency ablation procedures have been shown to cause atrial scarring that theoretically may result in left atrium dysfunction. This left atrium dysfunction can further predispose the patient to thromboembolism and may also decrease cardiac output, particularly in patients with heart failure.32,33 Therefore, it is becoming increasingly important to establish values for left atrial function. This allows accurate assessment of left atrial dimensions and function and provides standardization for follow-up studies, especially in postablation patients where the left atrium function impairment may occur and lead to prolonged use of anticoagulant therapy. So far, several studies have reported results comparing cardiovascular magnetic resonance imaging to established normal values of the left atrium on echocardiography.34-38
Postablation Imaging There are no established recommendations for CT follow-up post radiofrequency ablation procedures. If an intraostial vein procedure has been performed, CT at one or more intervals, typically between 3 and 12 months following the ablation to screen for pulmonary vein stenosis, is generally performed. However, if a radiofrequency MAZE or extraostial procedure is performed, follow-up CT is only acquired if there is clinical suspicion of a complication.
Pulmonary Vein Stenosis Electric isolation of pulmonary vein ostia is shown to be safe and rarely causes symptomatic stenosis.28 Postprocedure pulmonary vein stenosis may occur in 40 to 100% of patients.39 Scharf and coworkers demonstrated that 3% of patients have stenosis of up to 65% luminal diameter narrowing but were asymptomatic. They also showed that some patients have pulmonary vein dilation after radiofrequency ablation. However, severe pulmonary vein stenosis is described in
Figure 18 CT of an intraatrial accessory septum in a 62-year-old woman with atrial fibrillation before radiofrequency procedure. The axial CT image shows a thin septation extending anteriorly along the interatrial septum (arrow).
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Figure 19 Three-dimensional volume-rendered image in a 53-yearold man with atrial fibrillation shows minor (not functionally significant) left inferior pulmonary vein stenosis (arrow).
11% of patients by Robbins and coworkers40 and has been reported to cause pulmonary venoocclusive disease in three patients.39,41 Clinically, this may present with dyspnea on exertion, manifest as focal pulmonary edema on chest radiographs or CT, or pulmonary vein luminal narrowing on CT pulmonary vein imaging (Figs. 19 and 20). Robbins and coworkers describe two patients with postprocedural venoocclusive disease: one with severe stenosis of all four pulmonary veins, and another patient with severe stenosis of three pulmonary veins and complete occlusion of the other pulmonary vein several months post radiofrequency ablation.40 However, both patients were successfully treated with angioplasty, followed by resolution of symptoms. Scanavacca and coworkers also describe severe venoocclusive disease of the left pulmonary veins post radiofrequency ablation, treated with angioplasty, and followed by complete resolution of symptoms.41 Postablation stenosis is not predicted by the initial pulmonary vein size or total duration of radiofrequency energy
Figure 20 Three-dimensional volume-rendered image in a 55-yearold man with atrial fibrillation who developed significant stenosis in the right and left superior pulmonary veins post ablation requiring stent placement. The image shows a stent within the right and left superior pulmonary veins (arrows).
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Figure 21 Axial CT scan of a 45-year-old man with atrial fibrillation post radiofrequency procedure. (A) Axial image at the level of the left atrium shows “atrioesophageal fistula” with absent anterior wall of the esophagus and gas in the mediastinum extending into the left atrium (arrow). Also, other mediastinal gas (arrowhead). (B) Axial image at the level of the left ventricle shows gas within the left ventricle (arrow).
application delivered to the vein, but by catheter position. The more distal the catheter from the ostium, the greater the degree of narrowing created.42 The left inferior pulmonary vein is most susceptible to the development of narrowing, due to the more medial location of its ostia, located more posteriorly and therefore inside the cardiac silhouette on standard imaging and fluoroscopic projections. As a consequence, more energy may be delivered inside the vein distal to the ostium. Preprocedure CT is helpful to clearly identify the position of the left inferior pulmonary vein ostium. Pulmonary vein stenosis may be associated with pulmonary vein thrombosis.39 Thrombus formation has been reported to occur from day 1 to 3 months after radiofrequency ablation with an embolism rate of 2% despite adequate anticoagulation therapy. Therefore, patients receive anticoagulation during the procedure and for approximately 1 month afterwards.43 CT angiography or MRA can be used to noninvasively demonstrate pulmonary vein occlusion. Infarction may result in wedge-shaped parenchymal consolidation. CT may also show interlobular septal thickening and groundglass opacity secondary to localized pulmonary venous hypertension. Reactive regional mediastinal lymph node enlargement may occur secondary to mediastinal inflammation and fibrosis from thermal injury.44 One case of pulmonary vein dissection has been described highlighting the need for careful placement of mapping and ablation catheters within the pulmonary veins.45
Atrioesophageal Fistula Atrioesophageal fistula is a known but rare complication of posterior left atrial ablation (MAZE procedure) in which there is injury to the posterior wall of the left atrium and possible injury to the anterior wall of the esophagus related to thermal injury during the procedure. The outcomes are devastating and mortality rates are high, exceeding 50%. In 2004, Pappone and coworkers reported the first two cases following radiofrequency catheter ablation from two different centers. One patient died of multiple embolic events and the other survived after emergency cardiac and esophageal
surgery (Fig. 21).46 The evolution of radiofrequency catheterbased ablation (RFCA) away from point ablations within the veins, to circumferential pulmonary vein ablation, and posterior left atrial ablation accounts for the rising incidence of atrioesophageal fistula, as no cases were reported when point ablations were performed. The causes of morbidity and mortality include the following: systemic thromboembolic disease, massive air emboli, septic emboli, endocarditis, mediastinitis, overwhelming sepsis, and massive hematemesis. Signs and symptoms occur 10 to 20 days postablation. These include (complete) dysphagia, odynophagia, (pleuritic) chest pain, (high) fever, and elevated white blood cell count, especially if there is mediastinitis. When the posterior left atrial wall is breached, air and bacteria from the esophagus can enter the left atrium and blood, causing signs and symptoms of endocarditis, sepsis, and systemic emboli, either air or septic (Fig. 21B). Alternatively, the posterior wall of the left atrium may slough off and the patient exsanguinate before they can be transferred to a hospital. This may explain why contrast extravasation from the left atrium has not been reported. Chest CT with thin-section collimation and intravenous contrast is the modality of choice for diagnosis. At our institution chest CT is performed as per our pulmonary vein protocol as described above but without the advanced postprocessing. The findings are those of mediastinitis and/or endocarditis. Early findings may be subtle and careful comparison with the preprocedure examination may be helpful. The mediastinitis is centered on the posterior left atrialesophageal region. Findings include inflammatory changes within the mediastinal fat and the presence of small fluid collections or gas locules between the esophagus and posterior left atrium (Fig. 21A).
Conclusion Radiofrequency ablation of pulmonary veins and left atrium is an established but evolving procedure for the treatment of atrial fibrillation. CT angiography of left atrium and pulmo-
CT imaging for radiofrequency ablation of atrial fibrillation nary vein has become an important tool to assess the anatomy of the pulmonary veins and the left atrium before the procedure, reducing the time of the procedure. Also, postprocedure assessment for complications such as pulmonary vein stenosis, thrombosis, and atrioesophageal fistula with CT angiography can also be performed noninvasively.
References 1. Heeringa J, Van der Kuip DA, Hofman A, et al: Prevalence, incidence and lifetime risk of strial fibrillation: the Rotterdam study. Eur Heart J 27(8):949-953, 2006 2. Chugh SS, Blackshear JL, Shen WK, et al: Epidemiology and natural history of atrial fibrillation: clinical implications. J Am Coll Cardiol 37:371, 2001 3. Gohmen PM, Dushe S, Liu J, et al: Ablation of atrial firbilation in valvular heart surgery: are results determined by underlying valve disease? J Heart Valve Dis 16(1):76-83, 2007 4. Tanabe K, Yamaguchi K, Tani T, et al: Left atrial volume: predictor of atrial fibrillation in patients with degenerative mitral regurgitation. J Heart Valve Dis 16(1):8-12, 2007 5. Pelosi F, Morady F: Evaluation and management of atrial fibrillation. Med Clin North Am 85(2):225-244, 2001 6. Fuster V, Ryden LE, Cannom DS, et al: CC/AHA/ESC 2006 Guidelines for the Management of Patients With Atrial Fibrillation: A Report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the European Society of Cardiology Committee for Practice Guidelines (Writing Committee to Revise the 2001 Guidelines for the Management of Patients with Atrial Fibrilation). J Am Coll Cardiol 48(4):e149-e246, 2006 7. Haissauguerre M, Jais P, Shah DC, et al: Spontaneous initiation of atrial fibrillation by ectopic beats originating in the pulmonary veins. N Engl J Med 339(10):659-666, 1998 8. Tan AY, Li H, Waschsmann-Hogiu S, et al: Autonomic innervation and segmental muscular disconnections at the human pulmonary veinatrial junction: implications for catheter ablation of atrial-pulmonary vein junction. J Am Coll Cardiol 48:132-143, 2006 9. Tan AY, Chen P-S, Chen LS, et al: Autonomic nerves in pulmonary veins. Heart Rhythm 4:S57-S60, 2007 10. Page RL: Medical management of atrial fibrillation: future directions. Heart Rhythm 4(3):S91-S93, 2007 (suppl 1) 11. Atwood JE, Myers JN, Tang XC, et al: Exercise capacity in atrial fibrillation: a substudy of the Sotalol-Amiodarone Atrial Fibrilation Efficacy Trial (SAFE-T). Am Heart J 153(4):566-572, 2007 12. Sra J, Narayan G, Krum D, et al: Computed tomography-fluoroscopy image integration-guided catheter ablation of atrial fibrillation. J Cardiovasc Electrophysiol 18(4):409-414, 2007 13. Wood MA, Wittkamp M, Henrry D, et al: A comparison of pulmonary vein ostial anatomy by computerized tomography. Echocardiography and venography in patients with atrial fibrillation having radiofrequency catheter ablation. Am J Cardiol 93:49-53, 2004 14. Sra J, Krum D, Malloy A, et al: Registration of three-dimensional left atrial computed tomographic images with projection images obtained using fluoroscopy. Circulation 112(24):3677-3679, 2005 15. Nilsson B, Chen X, Perhson S, et al: Recurrence of pulmonary vein conduction and atrial fibrillation after pulmonary vein isolation for atrial fibrillation: a randomized trial of the ostial versus the extraostial ablation strategy. Am Heart J 152:537, 2006 16. Malchano ZJ, Neuzil P, Cury RC, et al: Integration of cardiac CT/MR imaging with three-dimensional electroanatomical mapping to guide catheter manipulation in the left atrium, implications for catheter ablation of atrial fibrillation. J Cardiovasc Electrophysiol 17:1221-1229, 2006 17. Lacomis JM, Goitein O, Deible C, et al: CT of the pulmonary veins. J Thoracic Imaging 22:63-76, 2007 18. Haissaguerre M: Successful catheter ablation of atrial fibrillation. J Cardiovasc Electrophysiol 5:1045-1052, 1994 19. Maksimovic R, Dill T, Ristic AD, et al: Imaging in percutaneous ablation for atrial fibrillation. Eur Radiol 16:2491-2504, 2006
165 20. Wazni OM, Tsao HM, Chen SA, et al: Cardiovascular imaging in the management of atrial fibrilation. J Am Coll Cardiol 48(10):2077-2084, 2006 21. Wong SH, Scott GC, Conolly SM, et al: Feasibility of noncontrast intracardiac ultrasound ablation and imaging catheter for treatment of atrial fibrillation. IEEE Trans Ultrason Ferroeelectr Freq Control 53(12):2394-2405, 2006 22. Cabera JA, Sanchez-Quintana D, et al: Ultrasonic characterization of the pulmonary venous wall: echographic and histological correlation. Circulation 106(8):968-973, 2002 23. Kenigsberg DN, Lee BP, Grizzard JD, et al: Accuracy of intracardiac echocardiography for assessing the esophageal course along the posterior left atrium: a comparison to magnetic resonance imaging. J Cardiovasc Electrophysiol 18(2):169-173, 2007 24. Lacomis JM, Wigginton W, Fuhrman C, et al: Multi-detector row CT of the left atrium and pulmonary veins before radio-frequency catheter ablation for atrial fibrillation. Radiographics 23:S35-S48, 2003 25. Cronin P, Sneider MB, Kazerooni EA, et al: MDCT of the left atrium and pulmonary veins in planning radiofrequency ablation for atrial fibrillation: a how-to guide. AJR Am J Roentgenol 183(3):767-778, 2004 26. Cronin P, Kelly AM, Desjardins B, et al: Normative analysis of pulmonary vein drainage patterns on multidetector CT with measurements of pulmonary vein ostial diameter and distance to first bifurcation. Acad Radiol 14(2):178-188, 2007 27. Kim YH, Marom EM, Herndon JE 2nd, et al: Pulmonary vein diameter, cross-sectional area, and shape: CT analysis. Radiology 235(1):43-49, 2005 28. Scharf C, Sneider M, Case I, et al: Anatomy of the pulmonary veins in patients with atrial fibrillation and effects of segmental ostial ablation analyzed by computed tomography. J Cardiovasc Electrophysiol 14(2): 150-155, 2003 29. Marom EM, Herndon JE, Kim YH, et al: Variations in pulmonary venous drainage to the left atrium: implications for radiofrequency ablation. Radiology 230(3):824-829, 2004 30. Budorick NE, McDonald V, Flisak ME, et al: The pulmonary veins. Semin Roentgenol 24(2):127-140, 1989 31. Tsao HM, Wu MH, Yu WC, et al: Role of right middle pulmonary vein in patients with paroxysmal atrial fibrillation. J Cardiovasc Electrophysiol 12(12):1353-1357, 2001 32. Naccarelli GV, Hynes BJ, Wolbrette DL, et al: Atrial fibrillation in heart failure: prognostic significance and management. J Cardiovasc Electrophysiol 14:S281-S286, 2003 33. Thomas L, Thomas SP, Hoy M, et al: Comparison of left atrial volume and function after linear ablation and after cardioversion for chronic atrial fibrillation. Am J Cardiol 93:165-170, 2004 34. Sievers B, Kirchberg S, Franken U, et al: Determination of normal gender-specific left atrial dimensions by cardiovascular magnetic resonance imaging. J Cardiovasc Magn Reson 7(4):677-683, 2005 35. Anderson JL, Horne BD, Pennell DJ: Atrial dimensions in health and left ventricular disease using cardiovascular magnetic resonance. J Cardiovasc Magn Reson 7(4):671-675, 2005 36. Raman SV, Ng VY, Neff MA, et al: Volumetric cine CMR to quantify atrial structure and function in patients with atrial dysrhythmias. J Cardiovasc Magn Reson 7(3):539-543, 2005 37. Therkelsen SK, Groenning BA, Svendsen JH, et al: Atrial and ventricular volume and function in persistent and permanent atrial fibrillation, a magnetic resonance imaging study. J Cardiovasc Magn Reson 7(2): 465-473, 2005 38. Bowman AW, Kovacs SJ: Prediction and assessment of the time-varying effective pulmonary vein area via cardiac MRI and Doppler echocardiography. Am J Physiol Heart Circ Physiol 288(1):H280-H286, 2005 [Epub 2004 Sep 9] 39. Ravenel JG, McAdams P: Pulmonary venous infarction after radiofrequency ablation for atrial fibrillation. AJR Am J Roentgenol 178:664666, 2002 40. Robbins IM, Colvin EV, Doyle TP, et al: Pulmonary vein stenosis after catheter ablation of atrial fibrillation. Circulation 98(17):1769-1775, 1998
166 41. Scanavacca MI, Kajita LJ, Vieira M, et al: Pulmonary vein stenosis complicating catheter ablation of focal atrial fibrillation. J Cardiovasc Electrophysiol 11(6):677-681, 2000 42. Oral H, Knight BP, Tada H, et al: Pulmonary vein isolation for paroxysmal and persistent atrial fibrillation. Circulation 105(9):1077-1081, 2002 43. Ho SY, Cabrera JA, Tran VH, et al: Architecture of the pulmonary veins: relevance to radiofrequency ablation. Heart 86(3):265-270, 2001
J. Stojanovska and P. Cronin 44. Thakur RK, Klein GJ, Yee R, et al: Embolic complications after radiofrequency catheter ablation. Am J Cardiol 74:278-279, 1994 45. Wu CC, Tai CT, Lin YK, et al: Pulmonary vein dissection during mapping of atrial fibrillation. J Cardiovasc Electrophysiol 12:505, 2001 46. Pappone C, Oral H, Santinelli V, et al: Atrio-esophageal fistula as a complication of percutaneous transcatheter ablation of atrial fibrillation. Circulation 109:2724-2726, 2004
A
trial fibrillation is the most common sustained supraventricular arrhythmia. The prevalence and the incidence increases with advancing age and with the presence of cardiovascular disease.1 It is associated with increased morbidity and mortality due to hemodynamic deterioration secondary to increased heart rate, loss of atrioventricular synchrony, and progressive dysfunction of the left atrium, which may increase the risk of stroke and other embolic events secondary to atrial thrombi.2 Atrial fibrillation is more frequent in patients with hypertension or structural heart disease such as underlying valve disease (especially rheumatic and mitral valve)3,4 and coronary artery disease. It is more frequent in patients with cardiopulmonary disease resulting in hypoxia or hypercapnia such as chronic obstructive pulmonary disease, or in patients with metabolic disease such as diabetes mellitus and hyperthyroidism. Atrial fibrillation has a strong association of with other arrhythmias such as Wolff—Parkinson–White syndrome, atrioventricular nodal reentrant tachycardias, and sick sinus syndrome. In addition, it may occur in healthy patients in times of stress, following surgery, strenuous exercise, or with stimulants such as coffee or alcohol.5
Introduction Atrial Fibrillation Classification of atrial fibrillation has been proposed by the American College of Cardiology/American Heart Association/European Society of Cardiology6 and it consists of the following: paroxysmal atrial fibrillation, self-terminating that can last up to 7 days, persistent atrial fibrillation that lasts longer than 7 days but can be terminated by cardioversion, and permanent atrial fibrillation that persists longer than 1
Department of Radiology, Division of Cardiothoracic Radiology, University of Michigan Medical Center, Ann Arbor, Michigan. Address reprint requests to Paul Cronin, MD, MS, Department of Radiology, Division of Cardiothoracic Radiology, University of Michigan Hospitals, B1 132G Taubman Center/0302, 1500 East Medical Center Drive, Ann Arbor, Michigan 48109-0030. E-mail: [email protected]
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year. In addition, “lone” atrial fibrillation is described as paroxysmal, persistent, or permanent atrial fibrillation in patients without structural heart disease. Atrial fibrillation occurs when multiple ectopic electrical foci fire independently, sending as many as 300 discharges per minute to the atrioventricular (AV) node (Fig. 1). The pathologic background involves the development of ectopic beats secondary to ectopic foci of electrical activity, up to 94% of which originate within the pulmonary veins7; although the ectopic beats can also originate from the walls of the superior vena cava (SVC), both atria, crista terminalis, ostium of the coronary sinus, and interatrial septum. The myocardium of the left atrium extends a variable length into the pulmonary veins with the myocardial sleeves of the superior and left pulmonary veins longer than those of the inferior and right pulmonary veins.7 The pulmonary vein musculature is also highly anisotropic with abrupt fiber orientation changes, muscular breaks, and fibrous encapsulation of the muscle bundles and is innervated by the autonomic nervous system with autonomic nerves concentrated in ganglionic plexi around the great vessels such as the pulmonary veins. This suggests an important role for the genesis of atrial fibrillation.8 Tan and coworkers indicated in their study that the pulmonary vein antrum within 5 mm of the pulmonary vein–left atrium junction, rather than elsewhere in the atria or more distally in the pulmonary veins, is the most densely innervated and therefore the optimal location for autonomic nerve modulation procedures.9 The main symptoms associated with atrial fibrillation are related to the rapid ventricular rate that may cause hypotension, induce angina, or lead to loss of atrioventricular synchrony. The major complication is the formation of the atrial thrombi with severe risk of systemic embolization such as stroke. The initial diagnosis is made by the lack of P-waves, an atrial rate of 300 to 600 beats per minute, and an irregular ventricular response on electrocardiograph (ECG).
Management There are two goals of therapy in atrial fibrillation: alleviation of the symptoms and reducing the risk of stroke. There are
CT imaging for radiofrequency ablation of atrial fibrillation
Figure 1 Long axis or four-chamber graphic of the heart showing the basic cardiac anatomy and components of the cardiac conduction system. (Color version of figure is available online.)
multiple treatment options for atrial fibrillation including antiarrhythmic drug,10 electrical and mechanical cardioversion, transvenous AV junction ablation, surgical treatments including the Cox–Maze procedure that is best performed in patients requiring open heart surgery for another reason, and more recently, radiofrequency ablation techniques. If the patient is hemodynamically compromised, electrical cardioversion is the treatment of choice. Cardioversion restores mechanical atrial contraction over time. However, patients are anticoagulated for up to 3 weeks before and 4 weeks after cardioversion, with an international ratio of 2.0 to 3.0, if the duration of atrial fibrillation is greater than 48 hours, to reduce the risk of systemic embolization. The American College of Cardiology/American Heart Association Task Force and the European Society of Cardiology Committee for Practice Guidelines recommend anticoagulation for newly discovered atrial fibrillation, recurrent paroxysmal atrial fibrillation, and recurrent persistent or permanent atrial fibrillation.6 In hemodynamically stable patients, pharmacological agents such as beta-blockers are used to slow the ventricular response and to maintain sinus rhythm. However, the Sotalol-Amiodarone Atrial Fibrillation Efficacy Trial, a multicenter, double-blind, randomized, placebo-controlled study designed to compare the effects of sotalol and amiodarone on long-term maintenance of sinus rhythm, quality of life, and exercise tolerance in patients with persistent atrial fibrillation after drug or direct current (DC) cardioversion with 12 months follow-up concluded that neither sotalol nor amiodarone treatment was associated with an improvement in exercise capacity, regardless of rhythm status throughout the follow-up.11
155 veins and the left atrium.17 If the treatment is successful, long-term anticoagulation is unnecessary. This is in contrast to the cardioversion, where long-term anticoagulation is required. The catheter-based pulmonary vein ablation technique is used to electrically disconnect the pulmonary veins from the left atrium and is increasingly being used by interventional electrophysiologists. This technique was first described in 199418 using point ablation of site-specific arrhythmogenic foci in the pulmonary veins. This initially had a low success rate of 4% but has subsequently been shown to have a success rate of approximately 47%. However, this may require repeat procedures of multiple veins with a high risk of pulmonary vein stenosis. An advancement of this technique was empirical ablation of all pulmonary vein ostia if feasible. This reduced the development of recurrent atrial fibrillation and the need for repeat procedures. Newer trends include the radiofrequency ablation MAZE and extraostial ablation. With the radiofrequency ablation MAZE procedure, wide area lesions in the posterior wall/roof of the left atrium circumferentially encircling the pulmonary veins are created using radiofrequency energy (Fig. 2).17 This technique has somewhat fallen out of favor because scar tissue induced by the procedure can be proarrhythmic as can incomplete or nontransmural lesions by predisposing to reentrant flutter circuits. This technique may also be complicated by atrioesophageal fistula. The newest technique, using circumferential extraostial (Fig. 3) ablation, shows significantly better outcomes.15 The procedure is long, lasting several hours, and is performed under general anesthesia requiring endotracheal intubation.
Catheter Ablation Catheter-based radiofrequency ablation is the preferred therapeutic method and an evolving procedure for the treatment of paroxysmal atrial fibrillation in patients who do not respond to anti-arrhythmic drugs.12-16 Radiofrequency catheter ablation including cryoablation and the Cox–Maze procedure are aimed at causing anatomic scars to disrupt electrical communication between the ectopic foci of the pulmonary
Figure 2 Three-dimensional endocardial model of the left atrium in a 54-year-old man with atrial fibrillation. White line demonstrates the typical posterior left atrial ablation lines for a MAZE procedure. The gray dotted line indicates the position of the esophagus. RSPV indicates right superior pulmonary vein; RIPV, right inferior pulmonary vein; LSPV, left superior pulmonary vein; LIPV, left inferior pulmonary vein.
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Figure 3 Three-dimensional endocardial model of the left atrium in a 58-year-old man with atrial fibrillation. White line demonstrates the typical posterior left atrial ablation lines for an extraostial ablation procedure. These are circumferential lesions placed around the right superior and inferior veins and left superior and inferior veins. RSPV indicates right superior pulmonary vein; RIPV, right inferior pulmonary vein; LSPV, left superior pulmonary vein; LIPV, left inferior pulmonary vein.
In this technique, access to the pulmonary veins and the left atrium is gained via the right atrium through a patent foramen ovale or fossa ovalis puncture using a transfemoral approach, under fluoroscopic guidance. Guide wires are introduced through the trans-septal puncture followed by catheters and sheaths. Ablation is usually performed during normal sinus rhythm. First, the anatomy of the left atrium and the position of the pulmonary vein ostia are identified by selective angiography and then the pulmonary veins are mapped. Current ablation electrodes only cover a few millimeters of space; therefore, multiple individual ablation lesions are required to create the intended contiguous circumferential lesion.15,17
Preablation Imaging Knowledge of the detailed anatomy of the left atrium and pulmonary vein ostia is crucial for the effectiveness of radiofrequency ablation. It is also important to know the ostial orientation and diameter. It can be difficult and time consuming to locate the ostia with conventional angiography at the time of ablation. Therefore, imaging before the procedure is important to answer these questions. Conventional angiography, intracardiac echocardiography, transesophageal echocardiography, computed tomography, more recently multidetector computed tomography (MDCT) and magnetic resonance angiography (MRA) are modalities which have been used to determine ostial orientation and diameter before the ablation procedure. However, no technique has yet been widely accepted as the gold standard for measurement of pulmonary veins.13 Conventional angiography is an invasive method that does not allow good visualization of the
J. Stojanovska and P. Cronin pulmonary veins secondary to overlapping structures.19 Intracardiac echocardiography (ICE) is an essential tool used for safe trans-septal access, identification of anatomical structures relevant to the ablation, the placement and navigation of circular mapping catheters, and titration of energy delivery during ablation.20-22 However, it does not allow visualization of the left atrium/pulmonary veins relationship and often fails to visualize multiple right-sided pulmonary vein ostia that can be detected using computed tomography (CT).13,22 Intracardiac echocardiography can also visualize the esophagus in relation to the posterior left atrial structures. Kenigsberg and coworkers showed that intracardiac echocardiography provides rapid, real-time localization of the esophagus during left atrial ablation.23 Transesophageal echocardiography is the method used at most institutions to assess the left atrial/ left atrial appendage for thrombus, which is an absolute contraindication to the ablation procedure.24 However, transesophageal echocardiography does not allow visualization of the inferior pulmonary veins. Noninvasive imaging modalities, including MRA MDCT, which can depict the three-dimensional anatomy of the pulmonary veins and left atrium, provide a valuable road map before catheter ablation. The advantages of cardiac CT/MRA are as follows: (1) imaging the anatomic characteristics of the pulmonary vein and left atrium before the procedure; (2) assessing the anatomic relationship of the left atrium, esophagus, and adjacent vascular structures; (3) understanding the morphological remodeling of pulmonary vein and left atrium in atrial fibrillation; and (4) detecting postprocedural complications.20 MRA has its own advantages over CT including lack of ionizing radiation and higher temporal resolution. However, the long scan time, expense, and contraindications to magnetic resonance imaging, including the presence of defibrillator/pacemaker, can limit its utility. At our institution, left atrium and pulmonary vein mapping using helical CT scanners has been performed since the invention of the MDCT scanner, and we have performed these mapping studies using 4-, 8-, 16-, and 64-slice scanners. Currently all patients are scanned on a 64-slice scanner. Some institutions use ECG-gating and some institutions do not. At our institution, retrospective ECG-gating is used were possible. As patients undergoing radiofrequency ablation procedures typically have paroxysmal atrial fibrillation, their rhythm may be atrial fibrillation, ie, fast and/or irregular or sinus rhythm at the time of their CT. ECG-gating is used for patients in sinus rhythm and non-ECG-gating is used for patients in atrial fibrillation. In general, one-third to one-half of our patients cannot undergo ECG-gated examinations. ECG-gating improves both the quality of three-dimensional images and the ability to detect thrombus within the left atrium and/or left atrial appendage. Furthermore, there is both phasic change in pulmonary vein ostial diameters and phasic change in ostial positions during the cardiac cycle; therefore, ECG-gating allows assessment of the pulmonary veins at a single phase of the R-R interval such as 75% R-R, ie, end diastole when there is least cardiac motion. Alternatively, the pulmonary veins can be assessed at 85% R-R, ie, late atrial diastole when the pulmonary vein ostial diameters are max-
CT imaging for radiofrequency ablation of atrial fibrillation
Figure 4 Axial CT image of a right superior pulmonary vein obtained in a 44-year-old man with atrial fibrillation before radiofrequency procedure. Axial CT image shows right superior pulmonary vein (arrow).
imal. Test bolus timing with a region of interest placed in the left atrium is employed. Fifteen milliliters of nonionic intravenous contrast material followed by a 20 mL saline chase are injected to determine the peak enhancement within the left atrium. Scans are initiated with a delay equal to the time to peak enhancement plus 6 seconds after beginning injection of the remaining 100 mL of nonionic intravenous contrast material. We use 115 mL of nonionic intravenous contrast material in total (including 15 mL for the test bolus timing) administered with a power injector at a rate of 4 mL/s through an antecubital vein. The collimation used is 1.25 mm, and a 0.625-mm reconstruction interval. The heart or the entire thorax may be scanned. We scan from the lung bases to the apices during a single breath-hold. Including the
Figure 5 Multiplanar reformatted (MPR) CT image of a right superior normal pulmonary vein obtained in a 42-year-old man with atrial fibrillation before radiofrequency procedure. MPR CT scan shows right superior pulmonary vein (arrow).
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Figure 6 Three-dimensional model of left atrium and pulmonary veins in a 64-year-old man with atrial fibrillation. This image shows right superior pulmonary vein (RSPV), right inferior pulmonary vein (RIPV), left superior pulmonary vein (LSPV), left inferior pulmonary vein (LIPV), and left atrium (LA).
superior thorax, not just the left atrium and central pulmonary veins allows visualization of aberrant pulmonary venous drainage to the brachiocephalic veins or SVC. The bottom-up direction minimizes respiratory motion should the patient inhale or exhale toward the end of the scan and minimizes streak artifact from contrast in the SVC and brachiocephalic veins. Imaging is performed using 120 kVp and 320 mA tube current. For an average-sized adult male patient, the effective
Figure 7 Semiautomated analysis software using “Vessel Analysis” technique that allows the user to track, extract, visualize, and measure the veins. Short-axis view of the right superior pulmonary vein ostium with a minimum diameter of 23.7 mm and a maximum diameter of 27 mm.
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158 radiation dose per pulmonary vein scan, assuming 320 mA tube current, is approximately 10 mSv.25 The acquired images can be reviewed as axial data (Fig. 4), as multiplanar reformatted images (Fig. 5), or using advanced processing such as volume rendering or endocardiac views.
Pulmonary Vein Advanced Processing Three-dimensional models of the left atrium, left atrial appendage, and pulmonary veins are routinely reconstructed to guide electrophysiologists before atrial fibrillation ablation procedures. Surface-rendered views (vessel analysis) and endocardiac views (navigator electrophysiology [EP]) of the left
atrium and the pulmonary veins are obtained using CardEP™ software (GE Medical System, Milwaukee, WI) on GE Advantages Windows workstations. The vessel analysis software is a semi-automated analysis tool based on the advanced vessel analysis technique that allows the user to track, extract, visualize, and measure the veins. The software initially generates a three-dimensional model of the left atrium and pulmonary veins (Fig. 6). The user then identifies the pulmonary vein ostium and the software generates minimum, mean, and maximum pulmonary vein ostial diameter measurements. This software provides short-axis, cross-sectional (Fig. 7), long-axis (Fig. 8), and
Figure 8 Vessel analysis software that allows the user to track, extract, and visualize the pulmonary veins. (A) Long-axis view of right superior pulmonary vein (RSPV). (B) Left superior pulmonary vein (LSPV). (C) Right inferior pulmonary vein (RIPV) and (D) left inferior pulmonary vein (LIPV).
CT imaging for radiofrequency ablation of atrial fibrillation
Figure 9 Three-dimensional endocardiac/endoluminal model of left atrium and pulmonary veins in a 62-year-old man with atrial fibrillation. This image shows the right superior pulmonary vein (RSPV), right inferior pulmonary vein (RIPV), left superior pulmonary vein (LSPV), left inferior pulmonary vein (LIPV), and left atrial appendage (LAA).
rotating curved views of the pulmonary veins, which allows measurement of pulmonary vein diameter, cross-sectional area, and distance to first branch. These views give the electrophysiologists an “angiograph” view of the left atrium and the pulmonary veins. The pulmonary veins are best visualized from a dorsocranial view with right posterior oblique and left posterior oblique angulation. This posterior view allows better visualization of the left atrium and the pulmonary veins as these are posterior structures. Endoluminal/endocardiac views using GE CardEP ™ software, Navigator EP protocol, are also routinely rendered (Fig. 9). Theses views allow visualization of the pulmonary vein ostia but also give a better sense of pulmonary vein orientation, geometry of pulmonary vein branches, and common ostia. If studies are performed with retrospective ECG-gating, data from the entire cardiac cycle are available to reconstruct four-dimensional (time-resolved imaging). These images can also be viewed in cine mode to globally assess left atrial function (Fig. 10). Also, left atrial end-diastolic volume, endsystolic volume, stroke volume, and ejection fraction can be calculated.
159 the superior than the inferior pulmonary veins. Normally, there are two superior pulmonary veins, one right and one left, and two inferior pulmonary veins, one right and one left (Fig. 11). The right superior vein drains the right upper and middle lobe. The left superior vein drains the left upper lobe, including the lingula. The inferior veins drain their respective lower lobes. The course of the pulmonary veins is distinct from the course of the pulmonary arteries and bronchi. The superior veins take an oblique course caudally as they pass medially, whereas the inferior veins take virtually a horizontal course centrally and a vertical course distally. The right superior pulmonary vein is usually the largest pulmonary vein. It passes posterior to the superior vena cava and anterior to the right pulmonary artery. As it courses caudally, it passes under the right pulmonary artery to enter the most superior and lateral aspect of the left atrium. The left superior pulmonary vein runs anterior to but in close relationship with the left pulmonary artery. It joins the left atrium near the left atrial appendage. As well as coursing horizontally, the inferior pulmonary veins pass forward as they pass medially, to enter the left atrium at its most inferior and lateral aspect. They lie in a plane considerably posterior to the superior pulmonary veins. The superior pulmonary vein ostia are significantly larger than the inferior pulmonary vein ostia. Cronin and coworkers reported on 200 patients with atrial fibrillation and found the mean diameter of the right superior pulmonary vein ostia was 17.6 mm; the left superior pulmonary vein ostia was 16.6 mm, compared with 17.1 mm for the right inferior pulmo-
Pulmonary Vein and Left Atrium Anatomy During embryological development, the pulmonary vein confluence is incorporated into the dorsal wall of the left atrium. This is followed by musculization or atrialization of the venous part of the atrial wall. Myocardium is found around AV junctions and within the media of the pulmonary veins. These myocardial sleeves are more developed around
Figure 10 Three-dimensional model of left atrium in a 52-year-old woman with atrial fibrillation. This model can be viewed in cine mode to globally assess left atrial function and also can be used to calculate left atrial function such as end-diastolic volume, end-systolic volume, stroke volume, and ejection fraction. (Color version of figure is available online.)
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Figure 11 Multiplanar reformatted CT scans of normal pulmonary veins obtained in 65-year-old man with atrial fibrillation before a radiofrequency procedure. Axial CT scans show (A) right superior pulmonary vein (arrow), (B) left superior pulmonary vein (arrow), (C) right inferior pulmonary vein, and (D) left superior pulmonary vein.
nary vein ostia, and 14.8 mm for the left inferior pulmonary vein ostia.26 There was no significant difference between the average diameters of right and left pulmonary vein ostia. In another study, the mean pulmonary vein diameters at the ostia were as follows: right superior, 11.9 mm; left superior, 10 mm; right inferior, 12.7 mm; and left inferior, 9.5 mm.27 The pulmonary vein trunk is defined as the distance from the ostium to the first-order branch. The superior pulmonary veins tend to have a longer trunk, 16 (15.3, 16.7) mm, than the inferior pulmonary veins, 10.2 (9.7, 10.7) mm. The superior veins are also overlapped by the descending proximal pulmonary artery, which may make visualization of the first branch difficult. Scharf and coworkers found greater variation in pulmonary vein length than in diameter.28
Pulmonary Vein and Left Atrium Variants Pulmonary vein anatomy is more variable than pulmonary arterial anatomy, and developmental anomalies are common. When variations occur, the right side tends to have accessory veins (one or more), and the left side tends to have conver-
gent veins (a short or long common trunk), which drains into the left atrium. The common anomalies include a common left or right pulmonary vein in 4.5 to 14% of individuals (Fig. 12).26,29 Conjoined veins or common trunk occurs when the superior and inferior veins converge to form a single atriopulmonary venous junction. A single common left vein is much more common than a common right vein. In our experience, with several hundred patients, a common right vein has only been identified in two patients. When present, a common pulmonary vein trunk has a significantly larger diameter, on average 24.3 mm, compared with the other pulmonary veins, and a significantly shorter trunk, 9.8 mm on average.26 Supernumerary or accessory veins are common. An accessory vein has its own independent atriopulmonary venous junction separate from the superior and inferior pulmonary veins. The most common is a separate right middle pulmonary vein, which drains the middle lobe directly to the left atrium (Fig. 13). This is estimated to occur in 10.5 to 26% of individuals.26,29,30 Tsao and coworkers reported that the right
CT imaging for radiofrequency ablation of atrial fibrillation
Figure 12 A 53-year-old woman with atrial fibrillation. Three-dimensional model of the left atrium and pulmonary veins, which shows a common left trunk (arrow). This is a common anomaly occurring in 4.5 to 14% of patients.
middle lobe vein may drain directly into the left atrium in 23% of patients, share a common ostium to the proximal part of the right superior pulmonary vein in 69% of patients, and share a common ostium to the proximal right inferior pulmonary vein in 8% of patients.31 Cronin and coworkers found that in 84% of patients the right middle lobe vein drained into the right superior pulmonary vein; in 11% of
Figure 13 A 56-year-old man with atrial fibrillation and direct drainage of a middle lobe pulmonary vein into left atrium. Endocardial view with annotation shows a right superior and inferior pulmonary vein and separate drainage of middle pulmonary vein into the left atrium. These images show the right superior pulmonary vein (RSPV), middle lobe pulmonary vein (MLPV), right inferior pulmonary vein (RIPV), left superior pulmonary vein (LSPV), and left inferior pulmonary vein (LIPV).
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Figure 14 A 58-year-old man with atrial fibrillation. Three-dimensional model shows a pulmonary vein with separate direct drainage to the left atrium of superior segment of the right lower lobe separate from the right inferior pulmonary vein. These images show the right superior pulmonary vein (RSPV), superior segment of the right lower lobe pulmonary vein (ssRIPV), right inferior pulmonary vein (RIPV), left superior pulmonary vein (LSPV), and left inferior pulmonary vein (LIPV).
patients it drained directly into the left atrium (Fig. 13), and in 5.5% of patients it drained into the right inferior pulmonary vein.26 The middle lobe pulmonary vein ostia are significantly smaller than the superior or inferior pulmonary vein ostia, on average 8.6 mm, as are middle lobe pulmonary vein trunks, on average 8.4 mm.26 Accessory veins are much more infrequent on the left; usually draining all or part of the lingula. These veins have been referred to as “middle veins”, and in our experience only one of these veins has been identified. Other accessory veins occur. The other most notable accessory vein on the right is an accessory vein, draining the superior segment of the right lower lobe directly to the left atrium (Fig. 14). A “top vein”, which enters the roof of the left atrium superomedial to the right superior pulmonary vein, is also described.17 When present, an accessory pulmonary vein has a significantly smaller diameter, on average 7.7 mm compared with the other pulmonary veins, and a significantly shorter trunk, on average, 7.7 mm.26 Given their small size, it is often difficult to identify accessory veins at fluoroscopy, and they may be overlooked and therefore untreated. In one study, 3% of patients had two anomalies and 0.5% of patients had three anomalies.26 A variety of anomalous pulmonary and systemic connections exist; drainage can be partial or total (Figs. 15 and 16). These abnormal pulmonary–systemic venous connections are best classified based on their embryologic derivation and the anatomy of the anomalous connection. Based on this classification, four types are described: (1) supracardiac (a) into derivatives of the right cardinal system (superior vena cava or azygos vein) (b) into derivatives of the left cardinal system (a persistent left superior vena cava, vertical vein, or left brachiocephalic vein); (2) cardiac (a) into derivatives of the left cardinal system (the coronary sinus) (b) into the right atrium; (3) infra-
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Figure 15 Axial image of a pulmonary venous anomaly, a right pulmonary-systemic connection in a 54-year-old man with atrial fibrillation. The axial image shows the pulmonary venous anomaly with the right superior vein draining into the superior vena cava (arrow) just above the insertion into the right atrium. Various anomalous pulmonary–systemic connections exist, and drainage can be partial or total. These abnormal pulmonary–systemic venous connections are best classified according to embryologic derivation and the anatomy of the anomalous connection. Four types are defined in text.
cardiac (a) into the umbilicovitelline system (the portal vein or ductus venosus) (b) into the inferior vena cava, and (4) mixed, a combination of two or more of the anomalies described above may also occur.25 An ostial branch does not have an atrio-pulmonary venous junction but empties into the proximal portion of a vein within 5 mm of the atrio-pulmonary venous junction
Figure 16 Multiplanar reformatted image of a pulmonary venous anomaly, a left pulmonary-systemic connection in a 53-year-old man with atrial fibrillation. The left superior pulmonary vein drains into left brachiocephalic vein via a left vertical vein.
Figure 17 Axial CT scans of an ostial branch in a 43-year-old man with atrial fibrillation before radiofrequency procedure. The axial image shows the middle lobe pulmonary vein draining into the right inferior pulmonary vein but forming an ostial branch with the right inferior pulmonary vein as it enters within 5 mm of the right inferior pulmonary vein atrio-pulmonary venous junction.
(Fig. 17). Because ostial branches drain into a vein within 5 mm of the atrio-pulmonary venous junction, they are also at risk, but less so now that point ablations within the pulmonary veins are performed less.
Interpretation The evaluation of the left atrium before ablation procedures includes assessment for the presence of left atrial/left atrial appendage thrombus, left atrial dimensions and volumes, as well as the relationship with adjacent structures, especially assessing the relation of the posterior wall of the left atrium and the esophagus, which may help avoid the most serious complication, atrioesophageal fistula. Abnormalities of the left atrium or the interatrial septum, including left atrium diverticulum, interatrial septal aneurysms, and atrial septal defects, should be reported. An intraatrial accessory septum is a thin septum extending from the fossa ovalis region anteriorly and superiorly along the atrial wall (Fig. 18). The presence of thrombi in the left atrium and/or left atrial appendage should be identified as this is a complete contraindication to a radiofrequency ablation procedure; although currently transesophageal echo remains the standard of reference to exclude thrombus. It is also important to report to the electrophysiologist any systemic venous variants, particularly azygous continuation of the inferior vena cava, where the right atrium is not accessible inferiorly. Incidental findings should also be reported. These findings include the following: lung carcinoma, indeterminate lung nodules, pneumonia, bronchiectasis, emphysema, pulmonary fibrosis, sarcoidosis, enlarged lymph nodes, coronary artery disease, thoracic aortic aneurysms, hiatal hernias, and pleural and pericardial effusions.
CT imaging for radiofrequency ablation of atrial fibrillation Despite mapping of the left atrium and pulmonary veins, evaluation of the pulmonary venous anatomy, anatomic variants, diameter of the pulmonary vein ostium, and distance to the first branch before ablation procedures, radiofrequency ablation procedures have been shown to cause atrial scarring that theoretically may result in left atrium dysfunction. This left atrium dysfunction can further predispose the patient to thromboembolism and may also decrease cardiac output, particularly in patients with heart failure.32,33 Therefore, it is becoming increasingly important to establish values for left atrial function. This allows accurate assessment of left atrial dimensions and function and provides standardization for follow-up studies, especially in postablation patients where the left atrium function impairment may occur and lead to prolonged use of anticoagulant therapy. So far, several studies have reported results comparing cardiovascular magnetic resonance imaging to established normal values of the left atrium on echocardiography.34-38
Postablation Imaging There are no established recommendations for CT follow-up post radiofrequency ablation procedures. If an intraostial vein procedure has been performed, CT at one or more intervals, typically between 3 and 12 months following the ablation to screen for pulmonary vein stenosis, is generally performed. However, if a radiofrequency MAZE or extraostial procedure is performed, follow-up CT is only acquired if there is clinical suspicion of a complication.
Pulmonary Vein Stenosis Electric isolation of pulmonary vein ostia is shown to be safe and rarely causes symptomatic stenosis.28 Postprocedure pulmonary vein stenosis may occur in 40 to 100% of patients.39 Scharf and coworkers demonstrated that 3% of patients have stenosis of up to 65% luminal diameter narrowing but were asymptomatic. They also showed that some patients have pulmonary vein dilation after radiofrequency ablation. However, severe pulmonary vein stenosis is described in
Figure 18 CT of an intraatrial accessory septum in a 62-year-old woman with atrial fibrillation before radiofrequency procedure. The axial CT image shows a thin septation extending anteriorly along the interatrial septum (arrow).
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Figure 19 Three-dimensional volume-rendered image in a 53-yearold man with atrial fibrillation shows minor (not functionally significant) left inferior pulmonary vein stenosis (arrow).
11% of patients by Robbins and coworkers40 and has been reported to cause pulmonary venoocclusive disease in three patients.39,41 Clinically, this may present with dyspnea on exertion, manifest as focal pulmonary edema on chest radiographs or CT, or pulmonary vein luminal narrowing on CT pulmonary vein imaging (Figs. 19 and 20). Robbins and coworkers describe two patients with postprocedural venoocclusive disease: one with severe stenosis of all four pulmonary veins, and another patient with severe stenosis of three pulmonary veins and complete occlusion of the other pulmonary vein several months post radiofrequency ablation.40 However, both patients were successfully treated with angioplasty, followed by resolution of symptoms. Scanavacca and coworkers also describe severe venoocclusive disease of the left pulmonary veins post radiofrequency ablation, treated with angioplasty, and followed by complete resolution of symptoms.41 Postablation stenosis is not predicted by the initial pulmonary vein size or total duration of radiofrequency energy
Figure 20 Three-dimensional volume-rendered image in a 55-yearold man with atrial fibrillation who developed significant stenosis in the right and left superior pulmonary veins post ablation requiring stent placement. The image shows a stent within the right and left superior pulmonary veins (arrows).
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Figure 21 Axial CT scan of a 45-year-old man with atrial fibrillation post radiofrequency procedure. (A) Axial image at the level of the left atrium shows “atrioesophageal fistula” with absent anterior wall of the esophagus and gas in the mediastinum extending into the left atrium (arrow). Also, other mediastinal gas (arrowhead). (B) Axial image at the level of the left ventricle shows gas within the left ventricle (arrow).
application delivered to the vein, but by catheter position. The more distal the catheter from the ostium, the greater the degree of narrowing created.42 The left inferior pulmonary vein is most susceptible to the development of narrowing, due to the more medial location of its ostia, located more posteriorly and therefore inside the cardiac silhouette on standard imaging and fluoroscopic projections. As a consequence, more energy may be delivered inside the vein distal to the ostium. Preprocedure CT is helpful to clearly identify the position of the left inferior pulmonary vein ostium. Pulmonary vein stenosis may be associated with pulmonary vein thrombosis.39 Thrombus formation has been reported to occur from day 1 to 3 months after radiofrequency ablation with an embolism rate of 2% despite adequate anticoagulation therapy. Therefore, patients receive anticoagulation during the procedure and for approximately 1 month afterwards.43 CT angiography or MRA can be used to noninvasively demonstrate pulmonary vein occlusion. Infarction may result in wedge-shaped parenchymal consolidation. CT may also show interlobular septal thickening and groundglass opacity secondary to localized pulmonary venous hypertension. Reactive regional mediastinal lymph node enlargement may occur secondary to mediastinal inflammation and fibrosis from thermal injury.44 One case of pulmonary vein dissection has been described highlighting the need for careful placement of mapping and ablation catheters within the pulmonary veins.45
Atrioesophageal Fistula Atrioesophageal fistula is a known but rare complication of posterior left atrial ablation (MAZE procedure) in which there is injury to the posterior wall of the left atrium and possible injury to the anterior wall of the esophagus related to thermal injury during the procedure. The outcomes are devastating and mortality rates are high, exceeding 50%. In 2004, Pappone and coworkers reported the first two cases following radiofrequency catheter ablation from two different centers. One patient died of multiple embolic events and the other survived after emergency cardiac and esophageal
surgery (Fig. 21).46 The evolution of radiofrequency catheterbased ablation (RFCA) away from point ablations within the veins, to circumferential pulmonary vein ablation, and posterior left atrial ablation accounts for the rising incidence of atrioesophageal fistula, as no cases were reported when point ablations were performed. The causes of morbidity and mortality include the following: systemic thromboembolic disease, massive air emboli, septic emboli, endocarditis, mediastinitis, overwhelming sepsis, and massive hematemesis. Signs and symptoms occur 10 to 20 days postablation. These include (complete) dysphagia, odynophagia, (pleuritic) chest pain, (high) fever, and elevated white blood cell count, especially if there is mediastinitis. When the posterior left atrial wall is breached, air and bacteria from the esophagus can enter the left atrium and blood, causing signs and symptoms of endocarditis, sepsis, and systemic emboli, either air or septic (Fig. 21B). Alternatively, the posterior wall of the left atrium may slough off and the patient exsanguinate before they can be transferred to a hospital. This may explain why contrast extravasation from the left atrium has not been reported. Chest CT with thin-section collimation and intravenous contrast is the modality of choice for diagnosis. At our institution chest CT is performed as per our pulmonary vein protocol as described above but without the advanced postprocessing. The findings are those of mediastinitis and/or endocarditis. Early findings may be subtle and careful comparison with the preprocedure examination may be helpful. The mediastinitis is centered on the posterior left atrialesophageal region. Findings include inflammatory changes within the mediastinal fat and the presence of small fluid collections or gas locules between the esophagus and posterior left atrium (Fig. 21A).
Conclusion Radiofrequency ablation of pulmonary veins and left atrium is an established but evolving procedure for the treatment of atrial fibrillation. CT angiography of left atrium and pulmo-
CT imaging for radiofrequency ablation of atrial fibrillation nary vein has become an important tool to assess the anatomy of the pulmonary veins and the left atrium before the procedure, reducing the time of the procedure. Also, postprocedure assessment for complications such as pulmonary vein stenosis, thrombosis, and atrioesophageal fistula with CT angiography can also be performed noninvasively.
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