Imaging for Atrial Fibrillation

Imaging for Atrial Fibrillation Darryl P. Leong, MBBS (Hons), MPH, PhD, Victoria Delgado, MD, PhD, and Jeroen J. Bax, MD, PhD Abstract: Atrial fibrillation (AF) is the most common clinically significant arrhythmia and is associated with considerable increase in morbidity and mortality. Its appropriate evaluation and management are therefore of paramount importance. Cardiac imaging plays a crucial role in this regard. Imaging permits the identification of cardiovascular conditions that predispose to the development and perpetuation of AF. Furthermore, imaging provides important information to refine strategies to prevent thromboembolic complications of the arrhythmia and allows characterization of the arrhythmogenic substrate itself. This capacity places imaging in a pivotal position in the workup and treatment of AF. This review provides a critical appraisal of the role of currently available imaging techniques for evaluating patients with AF. In addition, the importance of imaging in guiding AF therapy with respect to the prescription of anticoagulation, cardioversion, and radiofrequency catheter ablation techniques are summarized. (Curr Probl Cardiol 2012; 37:7-33.) trial fibrillation (AF) is the most common clinically significant arrhythmia, occurring in 1%-2% of the general population.1 The lifetime risk for the development of AF in the Framingham cohort was 25% among those aged over 40 years.2 In addition, among individuals in Western Europe aged 55 years and above, the prevalence of AF is

A

Sources of Funding: Dr Leong is supported by the National Health and Medical Research Council of Australia, the National Heart Foundation of Australia, and the Royal Australasian College of Physicians and is the recipient of the Earl Bakken Electrophysiology Fellowship. Dr Bax received grants from Biotronik, Medtronic, Boston Scientific Corporation, St Jude Medical, and GE Healthcare. Dr Delgado received consultant fees from St Jude Medical. Dr Leong has nothing to disclose. Curr Probl Cardiol 2012;37:7-33. 0146-2806/$ – see front matter doi:10.1016/j.cpcardiol.2011.08.004

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5.5%.3 The clinical consequences of AF are well known and include increased risk of death, stroke, other thromboembolic complications, and heart failure.4 Aging is one of the most important risk factors for developing AF. The incidence of AF increases with advancing age to 9.7 per 1000 person-years among those aged over 70 years.5 In addition, chronic cardiovascular diseases, such as hypertension and ischemic and valvular heart disease, carry an increased risk of AF and modify the arrhythmogenic substrate favoring perpetuation of this arrhythmia.6,7 Therefore, aging populations and improved survival of individuals with chronic diseases are likely to contribute to a greater burden of disease attributable to AF in the future. The increased morbidity and mortality associated with AF has promoted ongoing research to understand the underlying mechanisms of this arrhythmia and to develop effective therapies.1,8 Recent developments in stroke prevention and new approaches in antiarrhythmic therapy have influenced the clinical management of patients with AF, which has been focused on the prevention of AF-related complications, control of ventricular rate, and treatment of concomitant cardiac disease.1 Cardiac imaging plays a pivotal role in the evaluation and management of AF (Fig 1). Imaging permits the identification of conditions that predispose to the development and perpetuation of AF, such as left ventricular (LV) dysfunction or valvular heart disease. Furthermore, imaging provides important information to refine stroke prevention strategies and permits characterization of the arrhythmogenic substrate that may lead to improved outcome of specific AF therapies, such as radiofrequency catheter ablation (RFCA) procedures. Table 1 summarizes the role of noninvasive imaging techniques in the evaluation of AF patients. This review provides a critical appraisal of the role of currently available imaging techniques for evaluating patients with AF. The importance of imaging in characterizing pathologic left atrial (LA) substrate and comorbid conditions (structural heart disease) underlying this arrhythmia is described. In addition, the role of imaging in guiding AF therapy with respect to the prescription of anticoagulation, cardioversion, and RFCA techniques is summarized.

Normal Left Atrial Structure and Function Structural remodeling of the LA, including dilatation of the LA vestibule or the pulmonary veins, has been related to the presence of AF.9 In addition, LA structural remodeling has been linked to LA dysfunction 8

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FIG 1. Flow diagram illustrating the role of cardiac imaging in the evaluation and treatment of AF. Adapted with permission from Camm et al. Figure 3 from Guidelines for the management of atrial fibrillation: The Task Force for the Management of Atrial Fibrillation of the European Society of Cardiology (ESC) Eur Heart J (2010) 31(19): 2369-2429.1 LA, left atrial; LASEC, left atrial spontaneous echocardiographic contrast. (Color version of figure is available online.) TABLE 1. Role of different imaging modalities in patients with AF Imaging modality Role

TTE

TEE

CMR

MDCT

Nuclear imaging

Assessment of LA size Assessment of LA function Evaluation of underlying heart disease Valvular heart disease Coronary artery disease Hypertensive heart disease Congestive heart failure Identification of LA thrombus RFCA procedures Preablation Intra-ablation* Postablation

⫹⫹ ⫹⫹⫹

⫹⫹ ⫹⫹⫹

⫹⫹⫹ ⫹⫹

⫹⫹⫹ ⫹⫹

— —

⫹⫹⫹ ⫹⫹ ⫹⫹ ⫹⫹⫹ —

⫹⫹⫹ — — — ⫹⫹⫹

⫹⫹ ⫹⫹⫹ ⫹ ⫹⫹⫹ ⫹⫹

⫹⫹ ⫹⫹⫹ ⫹ ⫹ ⫹⫹

— ⫹⫹⫹ — ⫹⫹ —

⫹ — ⫹⫹

⫹⫹ ⫹⫹⫹ —

⫹⫹⫹ — ⫹⫹

⫹⫹⫹ — —

— — —

Abbreviations: CMR, cardiovascular magnetic resonance; LA, left atrial; MDCT, multidetector row computed tomography; RFCA, radiofrequency catheter ablation; TTE, transthoracic echocardiography; TEE, transesophageal echocardiography. *Intracardiac echocardiography is a novel echocardiographic modality that may be used during AF catheter ablation.

that may further increase the risk of atrial arrhythmias. Therefore, characterization of the anatomy, geometry, and function of the LA with imaging techniques may help to understand the pathophysiological factors underlying this arrhythmia. Curr Probl Cardiol, January 2012

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FIG 2. left atrial (LA) anatomy correlates with noninvasive imaging. (A) Longitudinal section through the heart that permits visualization of the interatrial septum from the LA. The black arrow indicates the crescentic edge of the fossa ovalis. On 3-dimensional TEE (B), these anatomical details can be noted together with the surrounding structures, such as the RSPV, the mitral valve, and the CS. The anterior wall of the LA is displayed in (C). The aortic root is retracted forward and the right and left atrial appendages (LAAs) are deflected laterally. The BB is located at the interatrial groove and the curved arrows indicate the bifurcations of this bundle as it approaches the appendages. The dotted line indicates the “unprotected” LA wall. The imaging correlate of these structures can be appreciated with MDCT (D). The aortic root is colored red. The LA is located posteriorly. MDCT provides superior image quality and permits identification of the pulmonary veins, LAA, right atrial appendage, and the SVC. (Adapted with permission.84). Ao, aorta; BB, Bachmann’s bundle; CS, coronary sinus; LAA, left atrial appendage; LIPV, left interior pulmonary vein; LSVP/LS, left superior pulmonary vein; RAA, right atrial appendage; RIPV, right inferior pulmonary vein; RSPV/RS, right superior pulmonary vein; SVC, superior vena cava. (Color version of figure is available online.)

The LA is separated from the right atrium by the interatrial septum. This structure comprises the foramen ovale—a flap valve formed by an inferior muscular rim, the infolded right atrial wall superiorly, and a “fibrofatty sandwich of atrial and ventricular musculature” anteriorly.10 In most cases, 2 pulmonary veins from each lung drain into the LA at the atrial roof (Fig 2). Common pulmonary vein ostia or extrapulmonary veins may be observed as normal variants.10 In addition, at the anterior wall of the LA, the Bachmann’s bundle is located, close to the sinoatrial node at 10

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the insertion of the crista terminalis into the atrial roof and anterior to the superior vena caval ostium (Fig 2). Electrical depolarization of the LA occurs normally via this muscular tract that links the left and right atria. These communicating fibers may also be found at the anterior margin of the foramen ovale. The LA appendage (LAA) is a narrow, blind-ended structure arising from the LA free wall, protruding superiorly and leftward. The LAA is multilobed in 80% of cases11 and features pectinate muscles within it (Fig 3). These structures may be differentiated from LAA thrombus by their linear appearance. In addition, assessment of the spatial relationships of the LAA is important before percutaneous closure interventions of this structure. The LAA lies in close relation to the ostium of the left superior pulmonary vein, from which it is separated by a ridge. The LAA is also in proximity to the left circumflex coronary artery within the atrioventricular groove (Fig 3). Current 3-dimensional imaging techniques, such as 3-dimensional transesophageal echocardiography (TEE), multidetector row computed tomography (MDCT), and cardiac magnetic resonance (CMR), provide probably the most accurate approach to assess these anatomical aspects and are important tools to guide transcatheter-based therapies. Furthermore, changes in the dimensions of the LA are important markers of LA structural remodeling and changes in the arrhythmogenic substrate. LA dimensions and structure are commonly assessed with transthoracic echocardiography (TTE) or TEE. LA volume may be estimated from 2-dimensional TTE by the modified Simpson’s method, the area-length technique, or the prolate ellipsoid approach (Fig 4). However, 2-dimensional imaging techniques may lack accuracy by introducing geometric assumptions in the calculation of the LA dimensions. In contrast, 3-dimensional imaging techniques, such as real-time 3-dimensional TTE, MDCT, and CMR, may provide more exact and detailed assessment of the dimensions, structure, and spatial relationships of the LA, crucial for risk stratification and clinical decision-making of patients with AF (Fig 5). Several imaging modalities have been proposed to assess LA function, which may be divided into 3 phases: reservoir, conduit, and contractile phase. Phasic changes in LA volume may be measured with TTE, CMR, or MDCT12-14 (Fig 6). The reservoir function, which reflects LA filling during LV systole, may be evaluated by the difference between its maximal volume (at LV end-systole, 1 frame before mitral valve opening) and its minimal volume (at LV end-diastole) and expressed as a percentage of minimal LA volume. The conduit function is assessed by Curr Probl Cardiol, January 2012

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FIG 3. Visualization of the left atrial appendage (LAA) with noninvasive imaging techniques. (A) Anatomical section through the ostium (OS) of the LAA (double arrowhead). The spatial relationship of the LAA with the circumflex coronary artery (Cx), left pulmonary veins (superior [LSPV] and inferior [LIPV]), and mitral valve can be visualized. On 2-dimensional TEE (B), a 45°-60° midesophageal view permits visualization of the long axis of the LAA and the relationship with the circumflex coronary artery, the left superior pulmonary vein, and the ridge that separates them. The pectinate muscles are located within the body of the LAA (arrows). With 3-dimensional TEE, the exact relationship between the LAA and the left superior pulmonary vein can be visualized. (D) Longitudinal section of the heart through the ridge (black arrow) and the pointed profile of this structure formed by the infolding of the atrial wall. MDCT reconstructions provide accurate evaluation of these structures. (E) Longitudinal section of the heart visualized with MDCT. The left superior pulmonary vein is separated by the ridge from the LAA. The circumflex coronary artery is in close relationship with the left appendage and the mitral annulus. (Adapted with permission.84,85) CS, coronary sinus; Cx, circumflex coronary artery; LAA, left atrial appendage; LIPV/LI, left interior pulmonary vein; LSVP/LS, left superior pulmonary vein; OS, ostium. (Color version of figure is available online.)

the difference between maximal LA volume at LV end-systole and its volume at the onset of atrial contraction (marked by the P-wave on the electrocardiogram) and can be expressed as a percentage of maximal LA volume. Finally, the contractile function is evaluated by calculating the difference between LA volume at the onset of atrial contraction and its minimum volume at LV end-diastole and can be expressed as a percentage of its volume at the onset of atrial contraction. 12

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FIG 4. Assessment of left atrial dimensions. Two-dimensional techniques for estimating LA linear diameters and volume,86 where L is the longer of L1 and L2, and A2CH and A4CH are the areas of the atrium traced at end-ventricular systole in the apical 2- and 4-chamber views, respectively, and h is the disk height. A, parasternal long axis view; B, apical 4-chamber view; C, apical 2-chamber view. (Color version of figure is available online.)

Echocardiographic techniques have provided various LA function indexes. Pulse-wave Doppler echocardiography at the tips of the mitral valve leaflets and at the pulmonary vein ostia provides information on hemodynamics between the LA and LV, and upstream to the LA, respectively. Measurement of the peak transmitral A-wave velocity and velocity-time integral in late diastole with pulsed-wave Doppler echocardiography has been used as indexes of LA function (Fig 7). In addition, the ratio between peak transmitral E-wave velocity and peak septal mitral annular tissue velocity in early diastole (the E/E= ratio) has been well validated as a noninvasive measure of LV filling pressure, a parameter that reflects indirectly the pressure overload of the LA. More novel indexes for the assessment of LA function include measurement of late diastolic tissue velocity at the septal mitral annulus (A= velocity), LA strain (or deformation), and strain rate (Fig 7). These parameters may be measured by either tissue Doppler techniques or speckle tracking echocardiography and provide direct information of LA myocardial properties. These various methods of evaluation of LA structure, dimensions, and function have all been engaged in the assessment of patients with AF. The following text expands on the application of cardiovascular imaging to the clinical setting. Masood Akhtar: The authors do an excellent job of describing the anatomy and various structures that help to guide electrophysiologists to identify Curr Probl Cardiol, January 2012

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FIG 5. Three-dimensional techniques for the evaluation of left atrial size and geometry. (A) Representative short-axis cine cardiac magnetic resonance image at the level of the left atrium at end-ventricular systole. LA volume may be estimated by summation of the volumes of contiguous slices spanning the left atrium. (B-E) Cropped 3-dimensional transthoracic echocardiography data set. The left atrium is demonstrated in the 4-chamber (B), 2-chamber (C), short-axis (D) views, and as a sliced 3-dimensional image (E). A volume-rendered computed tomography image of the left atrium and pulmonary veins is displayed in (F), with orthogonal sections through the left atrium in the 4-chamber (G), 2-chamber (H), and short axis (I) views. Ao, aorta; LA, left atrium; LIPV, left inferior pulmonary vein; LSPV, left superior pulmonary vein; LV, left ventricle; PA, pulmonary artery; RA, right atrium; RIPV, right inferior pulmonary vein; RSPV, right superior pulmonary vein. (Color version of figure is available online.)

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FIG 6. Graphical representation of phasic changes in LA volume during the cardiac cycle. (Adapted with permission.14) (See text for elaboration.)

FIG 7. Transthoracic echocardiographic techniques for evaluating LA function. (A) Tissue Doppler imaging of the septal mitral annulus, with A= indicated (blue arrows). (B) Speckletracking strain of the left atrium, with dotted curve representing the average of 6 segments and the yellow arrow indicating the peak strain. (C) Strain rate of the left atrium by tissue Doppler imaging (white arrows). (Color version of figure is available online.)

landmarks and their role, if any. When it comes to function, however, only the left atrium as a whole is addressed. For example, I did not learn much about the function of LAA. Maybe the expression of role rather than function will describe what is presented here more accurately.

Evaluation of Conditions Predisposing to Atrial Fibrillation AF frequently coexists with other cardiac conditions, such as coronary artery disease (CAD) or valvular heart disease. The recognition and Curr Probl Cardiol, January 2012

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appropriate treatment of such conditions may halt or reverse LA remodeling and thus ameliorate AF and prevent progression of the arrhythmia to sustained forms of AF. Cardiac imaging plays a pivotal role in the diagnosis and evaluation of these various comorbidities that predispose to AF. TTE is the imaging modality most commonly employed for the initial evaluation of individuals presenting with AF, owing to its versatility, safety, and ability to assess myocardial and valvular structure and function. CMR, MDCT, and radionuclide techniques offer information that is complementary to TTE and may be useful in the evaluation of the conditions described subsequently.

Valvular Heart Disease Valvular heart disease is observed in approximately 1 in 5 first-detected cases of AF.15 Mitral valve disease may promote LA dilatation directly through the volume or pressure load presented to the LA. Longstanding aortic stenosis results in LV hypertrophy, myocardial fibrosis, and diastolic dysfunction, which impose a pressure load on the LA. Because of high temporal resolution, both 2-dimensional and Doppler echocardiographic techniques are well suited to the identification and quantification of valvular heart disease.16 In addition, CMR is a comprehensive imaging modality used to assess valvular morphology and function and hemodynamic consequences of valvular dysfunction with LV and LA volumes measurement and tissue characterization.17 Steady-state free precession cine CMR sequences are commonly used for morphologic and functional evaluation of cardiac structures, whereas velocity-encoded phase imaging permits accurate assessment of blood flow. Instantaneous flow velocities across the cardiac valve can be measured with “through-plane” sequences and integration of these velocities along the cardiac cycle provides flow volume per heart beat. Furthermore, separate analysis in systole and diastole permits calculation of forward and regurgitant volumes.18

Coronary Artery Disease In patients with AF, a high prevalence of CAD is reported.19 Among individuals with first-presentation AF and no past history of ischemic heart disease, the subsequent incidence of coronary events was 31 per 1000 person-years.20 CAD should therefore be excluded in new-presentation AF unless the pretest probability is low. Noninvasive imaging modalities permit direct evaluation of the luminal narrowing of the coronary arteries (anatomical imaging) or assessment of the hemodynamic consequences of obstructive CAD (functional imaging). 16

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The high negative-predictive value of MDCT for detection of significant CAD makes this imaging technique a valuable gatekeeper for invasive coronary angiography.21,22 It is the noninvasive imaging modality of choice for the detection of coronary atherosclerosis in populations with low or intermediate risk for CAD and provides information on plaque burden, composition and positive arterial remodeling. In addition, technological advances have improved the accuracy of CMR to characterise coronary atherosclerotic plaques.23 Furthermore, CMR imaging, single-photon emission computed tomography, positron emission tomography, and stress echocardiography are the imaging modalities to evaluate the functional consequences of obstructive CAD (myocardial ischemia). The sensitivity and specificity of these imaging modalities to detect obstructive CAD are between 80% and 90%.24 Although all noninvasive cardiac imaging techniques have demonstrated utility in the identification of ischemic heart disease, the choice of approach adopted should be individualized and also guided by local expertise. In addition, there is growing evidence that sequential or combined noninvasive imaging techniques may provide complementary information along the ischemic cascade in the evaluation of patients for CAD.25

Hypertensive Heart Disease Hypertension has long been recognized as an independent risk factor for the development of AF.26 The mechanisms by which hypertension causes AF are complex and may involve neurohormonal changes, LV diastolic dysfunction and hypertrophy, LA distension, fibrosis, and associated electrophysiological abnormalities. Diastolic LV dysfunction may be the earliest manifestation of hypertensive heart disease, preceding morphologic changes that result from prolonged hypertension. TTE is the modality of choice for the evaluation of diastolic LV function. Three-dimensional imaging techniques, such as CMR, MDCT, and 3-dimensional echocardiography, can offer evidence to support the diagnosis of hypertensive heart disease through accurate measurement of LA volume and LV mass.27

Heart Failure Congestive heart failure is among the most potent risk factors for the development of AF.26 The pathophysiological mechanisms linking LV dysfunction and AF share some common ground with hypertensive heart disease. Curr Probl Cardiol, January 2012

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Two-dimensional TTE remains the mainstay of evaluation of systolic LV function in clinical practice. In addition, tissue Doppler imaging, strain imaging, contrast echocardiography, and 3-dimensional echocardiography have provided important information on LV hemodynamics and mechanics. Notably, global LV longitudinal and circumferential strain by speckle tracking echocardiography incorporate characterization of the LV myocardium in addition to the evaluation of contractile function28 and have been shown to confer additive prognostic value to conventional echocardiographic parameters.29,30 CMR is now regarded as the noninvasive gold standard in the quantification of LV volumes, ejection fraction, and mass, owing to its high spatial resolution and signal-to-noise ratio, and its 3-dimensional nature. It is a highly reproducible technique for the evaluation of systolic LV function and for the identification of LV remodeling. In summary, although TTE is indicated in the initial workup of patients presenting with AF for the first time,31 further imaging may be useful in the evaluation of underlying myocardial, valvular, or coronary artery disease. The choice of modality in these circumstances must be individualized and should also be guided by local expertise.

Masood Akhtar: The exact part played by these so-called predisposing factors, particularly CAD, is not clear. It is also not proven, for instance, that AF will be abolished if CAD was found and fixed. Although CAD may cause subclinical atrial damage/fibrosis, coexistence of CAD and AF may simply be due to a high prevalence of both in a given population. Valvular disease, hypertension, atrial stretch, and dilatation predisposing to AF are more convincing and already well accepted. I wonder if the authors have any hypothesis as to what predisposes patients to the so-called lone AF.

Imaging to Understand the Mechanisms Underlying AF and Thromboembolism Cardiac imaging has been a cardinal tool in the examination of the mechanisms that underlie AF and its complication, thromboembolism. LA remodeling refers to “changes in atrial properties and function that promote AF.”32 These changes include ion channel remodeling, cellular microscopic changes, and macroscopic remodeling on both structural and functional level. LA dilatation is clearly associated with the development of AF. In a population-based study, Vaziri et al found an increase in LA size to be an independent predictor of the subsequent risk of occurrence of AF.33 The 18

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role of AF itself in causing LA dilatation and stretch, which may then promote further AF, has long been recognized using cardiac imaging.34 More recent experimental evidence from a canine model of AF suggests that the arrhythmia itself may cause atrial fibrosis.35 As will be subsequently expanded on, there are emerging imaging approaches for the identification and quantification of LA fibrosis.36,37 Cardiac imaging techniques, such as CMR and MDCT, that permit visualization of periatrial structures have drawn attention to the potential role of periatrial fat in the pathogenesis of AF.38,39 Thromboembolism in AF is a complex pathophysiological process with diverse etiological factors. Adverse LA remodeling and mechanical dysfunction have been implicated in the prothrombotic milieu. The relationship between these factors and LA thrombosis or clinical thromboembolism has been reported using TEE. Fatkin et al showed that the measurement of LA spontaneous echocardiographic contrast and LAA emptying velocity are closely related to the presence of LA thrombus in patients with AF.40 The LAA has been implicated as the most common LA source of thrombus.41 Therefore, there has been great research interest in the value of closing this structure to prevent the development of thrombus there.42,43 Pre- and intraprocedural imaging to define patient suitability for LAA closure and to guide the procedure are likely to play important roles in the advancement of this therapeutic alternative to anticoagulation.44

Imaging in AF Treatment: Guiding Anticoagulation The decision to recommend anticoagulation for the prevention of thromboembolic complications in the individual with AF demands an understanding of the risks and benefits of anticoagulation vs the degree of thromboembolic risk. In the clinical setting, evaluation of thromboembolic risk is most frequently performed by scoring systems, such as the congestive heart failure, hypertension, age, diabetes, CHADS2 score.45 These clinical aids may only have limited discriminatory ability, however.46 There is emerging evidence that cardiac imaging may further refine such risk prediction strategies. In a study of AF patients who had undergone TEE, Kamp et al demonstrated that LAA emptying velocity ⱕ20 cm/s was an independent predictor of future thromboembolic events.47 In research illustrating how the findings of these studies might be incorporated in a clinical practice framework, Thambidorai et al have shown that TTE and TEE added incremental predictive value for the combined endpoint of LA thrombus and clinical thromboembolism, respectively.48 Although most work on the identification of high-risk Curr Probl Cardiol, January 2012

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characteristics for subsequent thromboembolism has employed echocardiographic imaging, complementary imaging techniques may offer particular advantages in this regard. For instance, using CMR, Beinart et al demonstrated that LAA dimensions are an independent predictor of stroke among patients with AF.49 Although noninvasive imaging to refine thromboembolic risk prediction in AF is appealing, its role in clinical practice remains to be defined in adequately sized cohorts or a randomized trial.

Masood Akhtar: This section on thromboembolism in AF is fairly well covered by the authors. Although TTE and TEE have been the usual tools for detection of atrial thrombus, the added tools, such as LA emptying velocity and CMR, provide additional and independent predictive information. The question arises that, if early and precise diagnosis of soft LA thrombus is made with newer technologies, would it change our management approach from the routine long-term anticoagulation to intervention to prevent impending embolization and then start anticoagulation?

Imaging in AF Treatment: Guiding Cardioversion Before electrical cardioversion, detection of intracardiac thrombus is the main indication of cardiac imaging. In contrast, after electrical cardioversion, recovery of LA function and monitoring of LA remodeling are the main focus of imaging modalities. TEE has a well-established role in the exclusion of LA thrombus before AF cardioversion. In a randomized, multicenter study comparing TEEguided cardioversion to cardioversion following 3 weeks of anticoagulation, the TEE-guided strategy proved at least as clinically effective as the nonimaging approach.50 There is also evidence to suggest that LA imaging may offer predictive value in the identification of individuals in whom cardioversion is likely to offer long-term freedom from AF. The measurement of LAA emptying velocity by TEE has been shown to be an important predictor of long-term freedom from AF recurrence following cardioversion.51 Novel echocardiographic techniques evaluating the function of the LA myocardial wall have been shown to predict AF recurrences after successful cardioversion. Dell’Era et al evaluated the LA mechanical properties with speckle tracking echocardiography in patients undergoing cardioversion of persistent AF.52 These investigators reported significant functional LA remodeling following successful cardioversion and improvement in LA function reflected by an increase in LA strain. In addition, LA synchrony 20

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as measured with speckle tracking echocardiography was predictive of freedom from AF at 1-year follow-up. After electrical cardioversion, imaging studies have clearly demonstrated the occurrence of stunning–transient LA mechanical dysfunction.53,54 This phenomenon has been related to increased risk for thrombus formation and, accordingly, therapeutic anticoagulation is recommended for at least 4 weeks following cardioversion to prevent thromboembolism.1,55 Thomas et al examined the time course of recovery of LA mechanical function following cardioversion using transmitral A-wave velocity as an index of LA contractility.56 Improvements in LA mechanical function were reported at 4 weeks after successful cardioversion, thus providing mechanistic support for the observation of elevated thromboembolic risk during this postcardioversion period.57

Imaging in AF Treatment: Precatheter Ablation In AF patients who are candidates for RFCA techniques, cardiac imaging plays a central role before, during, and after this therapeutic approach. These procedures aim to electrically isolate pulmonary veins from the LA. The reported efficacy of these procedures in patients with paroxysmal AF is approximately 70%.58 Despite the largely proven safety of pulmonary vein isolation procedures, the 3%-5% overall complication rate indicates that accurate selection and evaluation of candidates for these procedures are mandatory. In this regard, cardiac imaging plays a pivotal role. TTE may serve to identify AF patients who are less likely to experience a favorable response to catheter ablation. Among patients with persistent AF, McCready et al found LA size to be the sole independent predictor of AF recurrence.59 Using tissue Dopplerderived strain, Tops et al have shown an independent, positive relationship between baseline LA mechanical deformation and subsequent reverse structural LA remodeling as a surrogate for procedural efficacy following AF ablation.60 The authors speculate that degree of LA deformation may reflect the underlying extent of LA fibrosis, which is likely to be a determinant of the ability of the left atrium to reverse remodel after successful RFCA. In addition to the measurement of LA size, which as previously discussed may be predictive of AF ablation success, MDCT offers important anatomical information before the ablation procedure. There is considerable variation in LA and pulmonary vein geometry, and pulmonary vein number, among both patients with AF and healthy individuCurr Probl Cardiol, January 2012

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als.61 With its high spatial resolution, MDCT is well suited to illustrate these variants and guide the approach undertaken to ablation.62,63 Masood Akhtar: Significant variations in anatomy can be seen in the left atrium. In a recent study (Preliminary results: 96 Radiological Society of North-America scientific assembly 2010: Abstract SSJ 05-01; published online December 3, 2010), image processing and analysis were performed on 515 consecutive patients (74.8% male, median age 58, range 51-66 years) with AF and CT scans performed before LA ablation. Most patients’ LA anatomies fell into 1 of 3 categories. Patients with 2 left pulmonary veins and 2 right pulmonary veins were, not unexpectedly, the most common with 332 patients (64.5%). Patients with 2 left pulmonary veins and 3 right pulmonary veins were the next most commonly seen type with 90 patients (17.5%). Also seen commonly were patients with 1 left pulmonary veins and 2 right pulmonary veins, 63 patients (12.2%). We observed 13 patients with 2 left pulmonary veins and 4 right pulmonary veins (2.5%) and 9 with 1 left pulmonary vein and 3 right pulmonary veins (1.7%) were also seen. Figure 1 shows examples of these. The remaining 8 (1.6%) patients showed less common anatomical varieties, including 3 left pulmonary veins and 2 or 3 right pulmonary veins, common right pulmonary veins, common inferior pulmonary veins, etc.

Furthermore, CMR exhibits particular strengths in imaging the left atrium, particularly as part of the workup for AF ablation. As a 3-dimensional modality with high spatial resolution and signal-to-noise ratio, CMR permits accurate measurement of LA volume.64 It is also able to visualize the number and location of pulmonary veins. Indeed, in a head-to-head comparison of CMR with MDCT, Hamdan et al found close agreement between the 2 modalities in the evaluation of pulmonary vein anatomy and caliber.65 In addition, the capacity to characterize myocardial tissue with high spatial resolution is unique to CMR. Gadolinium-diethylenetriaminepenta acetic acid (DTPA) is a paramagnetic contrast agent that has been used to delineate areas of expanded extracellular space using CMR. The presence of significant LA fibrosis as assessed with late-gadolinium enhancement (LGE-CMR) has been related with the outcomes of RFCA. In a study of 81 patients undergoing AF ablation, Oakes et al demonstrated the feasibility of LGE-CMR of the LA.36 Using a pixel intensity-based threshold technique to identify and quantify regions of LGE within the LA myocardium (Fig 8), these authors observed a close linear relationship between extent of LGE and atrial tissue voltage on electroanatomical mapping as a surrogate for myocardial fibrosis. Greater degree of baseline LA wall LGE (⬎15%) was associated with an elevated odds of AF recurrence after catheter ablation (odds ratio 4.88, 95% confidence 22

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FIG 8. Delayed enhancement cardiac magnetic resonance of the left atrium to quantify myocardial fibrosis. After CMR cropping, LA epicardium and endocardium are manually planimetered to create a region of interest. Areas of delayed enhancement are highlighted by an algorithm on the basis of pixel intensity. (Reproduced with permission.36) Ao, aorta; LA, left atrium. (Color version of figure is available online.)

interval 1.73-13.74). Furthermore, Kuppahally et al extended these findings and showed that the presence of mild, rather than more extensive, baseline LA LGE is associated with favorable structural and functional reverse remodeling after RFCA.66 In this study, LA remodeling was evaluated echocardiographically by measuring LA dimensions and LA strain and strain rate (using velocity vector imaging). Finally, recent evidence implicates periatrial fat and its local effects in the pathogenesis of AF. Using CMR to quantify periatrial fat, Wong et al have shown that its preablation burden is associated with AF recurrence during follow-up.67

Imaging in AF Treatment: During Catheter Ablation Catheter ablation for AF involves the creation of lesions within the left atrium to disrupt the electrophysiological milieu responsible for the development of the arrhythmia. There exists considerable heterogeneity in approaches described to perform AF ablation, including electrical Curr Probl Cardiol, January 2012

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isolation of the pulmonary veins from the LA body, ablation of complex fractionated electrical signals, and other linear ablative strategies to create more extensive conduction block and substrate modification. Given the aforementioned variability in both LA anatomy and ablative techniques, precise catheter navigation during the ablation procedure is critical to ensure appropriate lesion delivery. Guidance of AF ablation intraprocedurally is frequently performed by the integration of 3-dimensional datasets (MDCT or CMR) acquired preprocedurally with point-by-point electroanatomical mapping of the left atrium in the electrophysiology laboratory. This approach to catheter guidance has superseded purely electroanatomic mapping systems in AF ablation owing to the advantages that will be subsequently presented.68 Tops et al demonstrated the feasibility of fusion of MDCT and electroanatomic data to generate a 3-dimensional map to guide catheter position during AF ablation.69 This approach has been adopted to demonstrate a reduction in intraprocedural fluoroscopy times and improved outcomes over contact mapping techniques alone.70 Martinek et al confirmed these findings in a study of 100 AF patients undergoing catheter ablation, in which integration of MDCT and electroanatomic data were associated with superior procedural success.71 Intracardiac echocardiography, in which the echocardiographic probe is positioned transvenously within the right atrium, has a well-established role in the intraprocedural guidance of transseptal puncture for AF ablation. In addition, preliminary research suggests a potential role for 3-dimensional mapping of the LA using intracardiac echocardiography, as a real-time accompaniment to preprocedural MDCT and intraprocedural electroanatomical mapping (Fig 9).72 Rotational angiography is an imaging approach to visualize LA anatomy and surrounding structures that may be undertaken within the electrophysiology laboratory. Although experience with this technique is limited, its development may overcome variation in LA dimensions attributable to differing loading conditions or atrial rhythm between preprocedural scans and intraprocedural electroanatomical mapping.73 Current fluoroscopy-guided AF ablation may be associated with significant radiation exposure, for both the patient and the staff within the electrophysiology laboratory. There exists experimental evidence to suggest the feasibility of CMR catheter guidance for ablation procedures.74,75 This approach, although promising, has undergone limited testing to date in humans and remains an area of potential advancement in the field (Fig 10). 24

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FIG 9. Real-time integration of intracardiac echocardiography and MDCT to guide RFCA. The LA endocardial contours are traced in real-time (A) to obtain a 3-dimensional reconstruction of the left atrium (B). In addition, the pulmonary veins are localized (C) and incorporated in the volume rendering of the left atrium (D). Manual coregistration of the 3-dimensional LA volume obtained with intracardiac echocardiography and MDCT is performed to obtain the final 3-dimensional rendering of the left atrium to guide the procedure (E). (Adapted with permission.72) Add PV, additional pulmonary vein; LCO, left common ostium; RIVP, right inferior pulmonary vein; RSPV, right superior pulmonary vein. (Color version of figure is available online.)

FIG 10. Difference in visibility of (A) active (capable of receiving magnetic resonance signal) and (B) passive catheters on magnetic resonance images in a canine model. (Reproduced with permission.74)

In addition to guidance of the ablation procedure, imaging plays a crucial role in the identification and management of periprocedural complications. Cardiac perforation and tamponade are among the most precipitous acute complications of AF ablation, and with a reported Curr Probl Cardiol, January 2012

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incidence of approximately 1%, are among the most common periprocedural adverse events.76 Owing to its portability and ability to guide therapeutic pericardiocentesis in real-time, TTE serves a crucial role in the identification and treatment of this adverse outcome.

Imaging in AF Treatment: Postcatheter Ablation Cardiac imaging can fulfill 2 important roles following catheter ablation for AF. It enables detection of late complications and the assessment of structural and functional outcomes of the ablation procedure on the left atrium. Pulmonary vein stenosis is a complication that may develop either early or late following AF ablation. In a multicenter survey, its incidence has been reported in approximately 1.5% of patients undergoing ablation,76 although accurate estimation of its true frequency is hampered by variation in ablation technique and follow-up protocol. The severity of pulmonary vein stenosis is frequently categorized according to anatomic severity by MDCT, with mild stenosis defined as ⬍50% luminal narrowing, moderate stenosis 50%-69%, and severe stenosis ⱖ70%.77 Although studies correlating these anatomic thresholds with their functional (pulmonary venous flow velocity) consequence are scarce, successful treatment of severe stenosis by these criteria appears effective at reversal of patient symptoms.78 CMR is a theoretically attractive imaging modality with which to detect and quantify pulmonary vein stenosis, as it may offer both anatomical and function information. Goo et al have recently demonstrated the feasibility of measuring pulmonary vein flow velocity by phase contrast CMR.79 At the present time, however, the role of CMR in evaluating this condition remains to be defined, particularly given the high spatial resolution of MDCT for measurement of pulmonary vein caliber and the high temporal resolution of echocardiography to identify elevated flow velocities. A reduction in LA size has been generally reported following AF ablation using heterogeneous ablation techniques and imaging modalities.80,81 The exact mechanism underlying the observed reduction in LA size remains uncertain. Although some studies have found reduction in LA size only among those without recurrent AF,81 suggesting that the arrhythmia itself promotes LA enlargement, others have reported reverse LA remodeling in those both with and without AF recurrence.80 It has been proposed that atrial fibrosis induced by the ablation results in reduction in LA size. A recent meta-analysis of studies involving radiofrequency catheter ablation for AF indicates that LA volume 26

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decreases in those without AF recurrence after ablation but not statistically significantly so in those with AF recurrence.82 Using the LGE-CMR technique previously described, McGann et al evaluated the effect of AF ablation on LA scarring.83 These authors observed a significant positive relationship between the quantity of scarring caused by the ablation and the subsequent freedom from AF. These findings provide potentially important insights into the mechanisms of AF and the prediction of a favorable response to its ablation.

Conclusion and Future Directions Multimodality cardiac imaging has to date enabled a thorough understanding of normal and pathologic LA structure and function. The mechanisms underlying their AF can be fully characterized and treatment approaches tailored accordingly. Moreover, observational research has yielded potentially important insight into the predictive value of imaging findings for future cardiovascular outcomes. These studies give rise to intriguing hypotheses that imaging may improve the outcome of patients with, or at risk of, AF. Such hypotheses, with notable exceptions, remain to be proven in the setting of randomized clinical trials. This level of evidence would add significant weight to the incorporation of imaging into patient management guidelines and algorithms.

Masood Akhtar: The authors describe some of the currently used techniques for preprocedure anatomical delineation, intraprocedure catheter navigation, and postprocedure identification of possible complications. Significant advancement in these technologies is providing further help to physicians in managing this complex arrhythmia. 3D transesophageal and intracardiac echocardiography are likely to be of significant benefit in the future. Caution is, however, needed in interpreting some of the most commonly used techniques during catheter ablation techniques, such as 3D-3D and 3D-2D image integration to help navigate catheters during the ablation procedures. Many of these techniques use the principle of rigid body registration, which although ideal in a structure such as brain, could potentially cause significant errors of interpretation in a moving structure, such as heart, due to deformities created by cardiac cycle motion and respiration.

REFERENCES 1.

2.

Camm AJ, Kirchhof P, Camm AJ, et al. Guidelines for the management of atrial fibrillation: the Task Force for the Management of Atrial Fibrillation of the European Society of Cardiology (ESC). Eur Heart J 2010;31:2369-429. Lloyd-Jones DM, Wang TJ, Leip EP, et al. Lifetime risk for development of atrial fibrillation: the Framingham Heart Study. Circulation 2004;110:1042-6.

Curr Probl Cardiol, January 2012

27

3.

18.

Heeringa J, van der Kuip DA, Hofman A, et al. Prevalence, incidence and lifetime risk of atrial fibrillation: the Rotterdam study. Eur Heart J 2006;27:949-53. Stewart S, Hart CL, Hole DJ, et al. A population-based study of the long-term risks associated with atrial fibrillation: 20-year follow-up of the Renfrew/Paisley study. Am J Med 2002;113:359-64. Krahn AD, Manfreda J, Tate RB, et al. The natural history of atrial fibrillation: incidence, risk factors, and prognosis in the Manitoba Follow-Up Study. Am J Med 1995;98:476-84. Lau DH, Mackenzie L, Kelly DJ, et al. Hypertension and atrial fibrillation: evidence of progressive atrial remodeling with electrostructural correlate in a conscious chronically instrumented ovine model. Heart Rhythm 2010;7:1282-90. John B, Stiles MK, Kuklik P, et al. Reverse remodeling of the atria after treatment of chronic stretch in humans: implications for the atrial fibrillation substrate. J Am Coll Cardiol 2010;55:1217-26. Lane DA, Lip GY. Quality of life in older people with atrial fibrillation. J Interv Card Electrophysiol 2009;25:37-42. Knackstedt C, Visser L, Plisiene J, et al. Dilatation of the pulmonary veins in atrial fibrillation: a transesophageal echocardiographic evaluation. Pacing Clin Electrophysiol 2003;26:1371-8. Ho SY, Sanchez-Quintana D, Cabrera JA, et al. Anatomy of the left atrium: implications for radiofrequency ablation of atrial fibrillation. J Cardiovasc Electrophysiol 1999;10:1525-33. Veinot JP, Harrity PJ, Gentile F, et al. Anatomy of the normal left atrial appendage: a quantitative study of age-related changes in 500 autopsy hearts: implications for echocardiographic examination. Circulation 1997;96:3112-5. Wen Z, Zhang Z, Yu W, et al. Assessing the left atrial phasic volume and function with dual-source CT: comparison with 3T MRI. Int J Cardiovasc Imaging 2010;26(suppl 1):83-92. Eshoo S, Boyd AC, Ross DL, et al. Strain rate evaluation of phasic atrial function in hypertension. Heart 2009;95:1184-91. Spencer KT, Mor-Avi V, Gorcsan J, 3rd, et al. Effects of aging on left atrial reservoir, conduit, and booster pump function: a multi-institution acoustic quantification study. Heart 2001;85:272-7. Nieuwlaat R, Capucci A, Camm AJ, et al. Atrial fibrillation management: a prospective survey in ESC member countries: the euro Heart Survey on atrial fibrillation. Eur Heart J 2005;26:2422-34. Bonow RO, Carabello BA, Chatterjee K, et al. ACC/AHA 2006 guidelines for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (writing Committee to Revise the 1998 guidelines for the management of patients with valvular heart disease) developed in collaboration with the Society of Cardiovascular Anesthesiologists endorsed by the Society for Cardiovascular Angiography and Interventions and the Society of Thoracic Surgeons. J Am Coll Cardiol 2006;48:e1-148. Christiansen JP, Karamitsos TD, Myerson SG. Assessment of valvular heart disease by cardiovascular magnetic resonance imaging: a review. Heart Lung Circ 2011;20:73-82. Roes SD, Hammer S, van der Geest RJ, et al. Flow assessment through four heart

28

Curr Probl Cardiol, January 2012

4.

5.

6.

7.

8. 9.

10.

11.

12.

13. 14.

15.

16.

17.

19.

20. 21.

22.

23. 24. 25.

26.

27.

28.

29. 30.

31.

valves simultaneously using 3-dimensional 3-directional velocity-encoded magnetic resonance imaging with retrospective valve tracking in healthy volunteers and patients with valvular regurgitation. Invest Radiol 2009;44:669-75. Nucifora G, Schuijf JD, Tops LF, et al. Prevalence of coronary artery disease assessed by multislice computed tomography coronary angiography in patients with paroxysmal or persistent atrial fibrillation. Circ Cardiovasc Imaging 2009;2:100-6. Miyasaka Y, Barnes ME, Gersh BJ, et al. Coronary ischemic events after first atrial fibrillation: risk and survival. Am J Med 2007;120:357-63. Schuetz GM, Zacharopoulou NM, Schlattmann P, et al. Meta-analysis: noninvasive coronary angiography using computed tomography versus magnetic resonance imaging. Ann Intern Med 2010;152:167-77. Hamon M, Biondi-Zoccai GG, Malagutti P, et al. Diagnostic performance of multislice spiral computed tomography of coronary arteries as compared with conventional invasive coronary angiography: a meta-analysis. J Am Coll Cardiol 2006;48:1896-910. Corti R, Fuster V. Imaging of atherosclerosis: magnetic resonance imaging. Eur Heart J 2011;32:1709-19b. Bax JJ, van der Wall EE, de Roos A, et al., editors. Clinical Nuclear Cardiology. State of the Art and Future Directions. Philadelphia: Mosby, 2005. van Werkhoven JM, Heijenbrok MW, Schuijf JD, et al. Combined non-invasive anatomical and functional assessment with MSCT and MRI for the detection of significant coronary artery disease in patients with an intermediate pre-test likelihood. Heart 2010;96:425-31. Benjamin EJ, Levy D, Vaziri SM, et al. Independent risk factors for atrial fibrillation in a population-based cohort. The Framingham Heart Study. JAMA 1994;271:840-4. Leong DP, De Pasquale CG, Selvanayagam JB. Heart failure with normal ejection fraction: the complementary roles of echocardiography and CMR imaging. J Am Coll Cardiol Imaging 2010;3:409-20. Roes SD, Mollema SA, Lamb HJ, et al. Validation of echocardiographic twodimensional speckle tracking longitudinal strain imaging for viability assessment in patients with chronic ischemic left ventricular dysfunction and comparison with contrast-enhanced magnetic resonance imaging. Am J Cardiol 2009;104:312-7. Cho GY, Marwick TH, Kim HS, et al. Global 2-dimensional strain as a new prognosticator in patients with heart failure. J Am Coll Cardiol 2009;54:618-24. Stanton T, Leano R, Marwick TH. Prediction of all-cause mortality from global longitudinal speckle strain: comparison with ejection fraction and wall motion scoring. Circ Cardiovasc Imaging 2009;2:356-64. Douglas PS, Khandheria B, Stainback RF, et al. ACCF/ASE/ACEP/ASNC/SCAI/ SCCT/SCMR 2007 appropriateness criteria for transthoracic and transesophageal echocardiography: a report of the American College of Cardiology Foundation Quality Strategic Directions Committee Appropriateness Criteria Working Group, American Society of Echocardiography, American College of Emergency Physicians, American Society of Nuclear Cardiology, Society for Cardiovascular Angiography and Interventions, Society of Cardiovascular Computed Tomography, and the Society for Cardiovascular Magnetic Resonance endorsed by the American College of Chest Physicians and the Society of Critical Care Medicine. J Am Coll Cardiol 2007;50:187-204.

Curr Probl Cardiol, January 2012

29

32.

33.

34.

35. 36.

37.

38.

39. 40.

41.

42.

43.

44.

45.

46.

30

Kirchhof P, Bax J, Blomstrom-Lundquist C, et al. Early and comprehensive management of atrial fibrillation: proceedings from the 2nd AFNET/EHRA consensus conference on atrial fibrillation entitled ’research perspectives in atrial fibrillation Europace 2009;11:860-85. Vaziri SM, Larson MG, Benjamin EJ, et al. Echocardiographic predictors of nonrheumatic atrial fibrillation. The Framingham Heart Study. Circulation 1994;89:724-30. Sanfilippo AJ, Abascal VM, Sheehan M, et al. Atrial enlargement as a consequence of atrial fibrillation. A prospective echocardiographic study. Circulation 1990;82:792-7. Avitall B, Bi J, Mykytsey A, et al. Atrial and ventricular fibrosis induced by atrial fibrillation: evidence to support early rhythm control. Heart Rhythm 2008;5:839-45. Oakes RS, Badger TJ, Kholmovski EG, et al. Detection and quantification of left atrial structural remodeling with delayed-enhancement magnetic resonance imaging in patients with atrial fibrillation. Circulation 2009;119:1758-67. Kuppahally SS, Akoum N, Burgon NS, et al. Left atrial strain and strain rate in patients with paroxysmal and persistent atrial fibrillation: relationship to left atrial structural remodeling detected by delayed-enhancement MRI. Circ Cardiovasc Imaging 2010;3:231-9. Thanassoulis G, Massaro JM, O’Donnell CJ, et al. Pericardial fat is associated with prevalent atrial fibrillation: the Framingham Heart Study. Circ Arrhythm J Electrophysiol 2010;3:345-50. Wong CX, Abed HS, Molaee P, et al. Pericardial Fat is Associated with atrial fibrillation Severity and ablation Ooutcome. J Am Coll Cardiol 2011 (in press). Fatkin D, Kelly RP, Feneley MP. Relations between left atrial appendage blood flow velocity, spontaneous echocardiographic contrast and thromboembolic risk in vivo. J Am Coll Cardiol 1994;23:961-9. Stoddard MF, Dawkins PR, Prince CR, et al. Left atrial appendage thrombus is not uncommon in patients with acute atrial fibrillation and a recent embolic event: a transesophageal echocardiographic study. J Am Coll Cardiol 1995;25:452-9. Ostermayer SH, Reisman M, Kramer PH, et al. Percutaneous left atrial appendage transcatheter occlusion (PLAATO system) to prevent stroke in high-risk patients with non-rheumatic atrial fibrillation: results from the international multi-center feasibility trials. J Am Coll Cardiol 2005;46:9-14. Holmes DR, Reddy VY, Turi ZG, et al. Percutaneous closure of the left atrial appendage versus warfarin therapy for prevention of stroke in patients with atrial fibrillation: a randomised non-inferiority trial. Lancet 2009;374:534-42. Wang Y, Di Biase L, Horton RP, et al. Left atrial appendage studied by computed tomography to help planning for appendage closure device placement. J Cardiovasc Electrophysiol 2010;21:973-82. Gage BF, Waterman AD, Shannon W, et al. Validation of clinical classification schemes for predicting stroke: results from the National Registry of Atrial Fibrillation. JAMA 2001;285:2864-70. Fang MC, Go AS, Chang Y, et al. Comparison of risk stratification schemes to predict thromboembolism in people with nonvalvular atrial fibrillation. J Am Coll Cardiol 2008;51:810-5. Curr Probl Cardiol, January 2012

47.

48.

49.

50.

51.

52.

53.

54.

55.

56.

57.

58.

59.

60.

Kamp O, Verhorst PM, Welling RC, et al. Importance of left atrial appendage flow as a predictor of thromboembolic events in patients with atrial fibrillation. Eur Heart J 1999;20:979-85. Thambidorai SK, Murray RD, Parakh K, et al. Utility of transesophageal echocardiography in identification of thrombogenic milieu in patients with atrial fibrillation (an ACUTE ancillary study). Am J Cardiol 2005;96:935-41. Beinart R, Heist EK, Newell JB, et al. Left atrial appendage dimensions predict the risk of stroke/TIA in patients with atrial fibrillation. J Cardiovasc Electrophysiol 2011;22:10-5. Klein AL, Grimm RA, Murray RD, et al. Use of transesophageal echocardiography to guide cardioversion in patients with atrial fibrillation. N Engl J Med 2001; 344:1411-20. Antonielli E, Pizzuti A, Pálinkás A, et al. Clinical value of left atrial appendage flow for prediction of long-term sinus rhythm maintenance in patients with nonvalvular atrial fibrillation. J Am Coll Cardiol 2002;39:1443-9. Dell’Era G, Rondano E, Franchi E, et al. Atrial asynchrony and function before and after electrical cardioversion for persistent atrial fibrillation. Eur J Echocardiogr 2010;11:577-83. Grimm RA, Stewart WJ, Maloney JD, et al. Impact of electrical cardioversion for atrial fibrillation on left atrial appendage function and spontaneous echo contrast: characterization by simultaneous transesophageal echocardiography. J Am Coll Cardiol 1993;22:1359-66. Dogan A, Gedikli O, Ozaydin M, et al. Mitral annular velocity by Doppler tissue imaging for the evaluation of atrial stunning after cardioversion of atrial fibrillation. Int J Cardiovasc Imaging 2009;25:113-20. Fuster V, Ryden LE, Cannom DS, et al. ACC/AHA/ESC Guidelines for the management of patients with atrial fibrillation— executive summary: 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 fibrillation). J Am Coll Cardiol 2006;2006( 48):854-906. Thomas MD, Kalra PR, Jones A, et al. Time course for recovery of atrial mechanical and endocrine function post DC cardioversion for persistent atrial fibrillation. Int J Cardiol 2005;102:487-91. Mancini GB, Goldberger AL. Cardioversion of atrial fibrillation: consideration of embolization, anticoagulation, prophylactic pacemaker, and long-term success. Am Heart J 1982;104:617-21. Wilber DJ, Pappone C, Neuzil P, et al. Comparison of antiarrhythmic drug therapy and radiofrequency catheter ablation in patients with paroxysmal atrial fibrillation: a randomized controlled trial. JAMA 2010;303:333-40. McCready JW, Smedley T, Lambiase PD, et al. Predictors of recurrence following radiofrequency ablation for persistent atrial fibrillation. Europace 2011;13(3):355-61. Tops LF, Delgado V, Bertini M, et al. Left atrial strain predicts reverse remodeling after catheter ablation for atrial fibrillation. J Am Coll Cardiol 2011;57:324-31.

Curr Probl Cardiol, January 2012

31

61.

62.

63.

64.

65.

66.

67. 68. 69.

70.

71.

72.

73.

74.

75.

32

Thorning C, Hamady M, Liaw JV, et al. CT evaluation of pulmonary venous anatomy variation in patients undergoing catheter ablation for atrial fibrillation. Clin Imaging 2011;35:1-9. Wongcharoen W, Tsao HM, Wu MH, et al. Morphologic characteristics of the left atrial appendage, roof, and septum: implications for the ablation of atrial fibrillation. J Cardiovasc Electrophysiol 2006;17:951-6. Jongbloed MR, Dirksen MS, Bax JJ, et al. Atrial fibrillation: multi-detector row CT of pulmonary vein anatomy prior to radiofrequency catheter ablation—initial experience. Radiology 2005;234:702-9. Järvinen V, Kupari M, Hekali P, et al. Assessment of left atrial volumes and phasic function using cine magnetic resonance imaging in normal subjects. Am J Cardiol 1994;73:1135-8. Hamdan A, Charalampos K, Roettgen R, et al. Magnetic resonance imaging versus computed tomography for characterization of pulmonary vein morphology before radiofrequency catheter ablation of atrial fibrillation. Am J Cardiol 2009; 104:1540-6. Kuppahally SS, Akoum N, Badger TJ, et al. Echocardiographic left atrial reverse remodeling after catheter ablation of atrial fibrillation is predicted by preablation delayed enhancement of left atrium by magnetic resonance imaging. Am Heart J 2010;160:877-84. Wong CX, Abed HS, Molaee P, et al. Pericardial fat is associated with atrial fibrillation severity and ablation outcome. J Am Coll Cardiol 2011;57:1745-51. Knackstedt C, Schauerte P, Kirchhof P. Electro-anatomic mapping systems in arrhythmias. Europace 2008;10(suppl 3):iii28-34. Tops LF, Bax JJ, Zeppenfeld K, et al. Fusion of multislice computed tomography imaging with three-dimensional electroanatomic mapping to guide radiofrequency catheter ablation procedures. Heart Rhythm 2005;2:1076-81. Kistler PM, Rajappan K, Jahngir M, et al. The impact of CT image integration into an electroanatomic mapping system on clinical outcomes of catheter ablation of atrial fibrillation. J Cardiovasc Electrophysiol 2006;17:1093-101. Martinek M, Nesser HJ, Aichinger J, et al. Impact of integration of multislice computed tomography imaging into three-dimensional electroanatomic mapping on clinical outcomes, safety, and efficacy using radiofrequency ablation for atrial fibrillation. Pacing Clin Electrophysiol 2007;30:1215-23. den Uijl DW, Tops LF, Tolosana JM, et al. Real-time integration of intracardiac echocardiography and multislice computed tomography to guide radiofrequency catheter ablation for atrial fibrillation. Heart Rhythm 2008;5:1403-10. Nölker G, Gutleben KJ, Marschang H, et al. Three-dimensional left atrial and esophagus reconstruction using cardiac C-arm computed tomography with image integration into fluoroscopic views for ablation of atrial fibrillation: accuracy of a novel modality in comparison with multislice computed tomography. Heart Rhythm 2008;5:1651-7. Nazarian S, Kolandaivelu A, Zviman MM, et al. Feasibility of real-time magnetic resonance imaging for catheter guidance in electrophysiology studies. Circulation 2008;118:223-9. Nordbeck P, Bauer WR, Fidler F, et al. Feasibility of real-time MRI with a novel carbon catheter for interventional electrophysiology. Circ Arrhythm J Electrophysiol 2009;2:258-67. Curr Probl Cardiol, January 2012

76.

77. 78.

79.

80. 81.

82.

83.

84. 85. 86.

Cappato R, Calkins H, Chen SA, et al. Worldwide survey on the methods, efficacy, and safety of catheter ablation for human atrial fibrillation. Circulation 2005; 111:1100-5. Baranowski B, Saliba W. Our approach to management of patients with pulmonary vein stenosis following AF ablation. J Cardiovasc Electrophysiol 2011;22(3):364-7. Packer DL, Keelan P, Munger TM, et al. Clinical presentation, investigation, and management of pulmonary vein stenosis complicating ablation for atrial fibrillation. Circulation 2005;111:546-54. Goo HW, Al-Otay A, Grosse-Wortmann L, et al. Phase-contrast magnetic resonance quantification of normal pulmonary venous return. J Magn Reson Imaging 2009;29:588-94. Hof IE, Velthuis BK, Chaldoupi SM, et al. Pulmonary vein antrum isolation leads to a significant decrease of left atrial size. Europace 2011;13(3):371-5. Marsan NA, Tops LF, Holman ER, et al. Comparison of left atrial volumes and function by real-time three-dimensional echocardiography in patients having catheter ablation for atrial fibrillation with persistence of sinus rhythm versus recurrent atrial fibrillation three months later. Am J Cardiol 2008;102:847-53. Jeevanantham V, Ntim W, Navaneethan SD, et al. Meta-analysis of the effect of radio frequency catheter ablation on left atrial size, volumes and function in patients with atrial fibrillation. Am J Cardiol 2011;105:1317-26. McGann CJ, Kholmovski EG, Oakes RS, et al. New magnetic resonance imagingbased method for defining the extent of left atrial wall injury after the ablation of atrial fibrillation. J Am Coll Cardiol 2008;52:1263-71. Ho SY, McCarthy KP. Anatomy of the left atrium for interventional electrophysiologists. Pacing Clin Electrophysiol 2010;33:620-7. Su P, McCarthy KP, Ho SY. Occluding the left atrial appendage: anatomical considerations. Heart 2008;94:1166-70. Lang RM, Bierig M, Devereux RB, et al. Recommendations for chamber quantification: a report from the American Society of Echocardiography’s Guidelines and Standards Committee and the Chamber Quantification Writing Group, developed in conjunction with the European Association of Echocardiography, a branch of the European Society of Cardiology. J Am Soc Echocardiogr 2005;18:1440-63.

Curr Probl Cardiol, January 2012

33