- Email: [email protected]
Catheter Ablation
Catheter Ablation (General Principles and Advances) Sabine Ernst, MD, PhD, FESC KEYWORDS Catheter ablation 3D image integration Remote navigation 3D mapping Simultaneous mapping Sequential mapping
KEY POINTS The underlying anatomy can be understood through three-dimensional reconstruction of tomographic imaging. Choosing the most appropriate acquisition system (simultaneous vs sequential) is necessary for the given arrhythmia. Recognizing the need for close collaboration with cardiac anesthesia ensures good hemodynamic support and adequate analgesia.
Cardiac arrhythmias are typically encountered after cardiac surgery and can occur in the immediate postsurgical period or, more often, decades after surgery. In the postoperative period, arrhythmias may complicate the patient’s course and prolong the stay in the intensive care unit.1,2 Late after surgery, cardiac arrhythmias are thought to stem mainly from the unavoidable scars left behind (eg, after an atriotomy, the cannulation sites for the cardiopulmonary bypass, or other scars inherent to the specific cardiac surgery [patch sutures]).3–5 However, age and progression of the structural/congenital heart disease, resulting in pressure increase and dilation, can lead to pronounced fibrosis, which in itself can promote focal and/or reentrant arrhythmia.6 The presence of frequently recurrent or sustained arrhythmias is associated with reduced quality of life, risk of development of heart failure symptoms caused by tachycardiomyopathy, higher thromboembolic risk, and reduced survival.7–9
Catheter ablation of postsurgical arrhythmias in patients with congenital heart disease is currently feasible and successful with the use of advanced image integration and ablation tools. This article reviews the general steps of preparation for such a procedure and discusses the available techniques as an alternative to long-term antiarrhythmic therapy. Fig. 1 summarizes a stepwise approach that helps clinicians to perform even complex ablation procedure successfully.
GENERAL PREPARATION OF PATIENTS WITH CONGENITAL HEART DISEASE PRESENTING WITH ARRHYTHMIAS In the first instance, 12-lead electrocardiogram (ECG) documentation is the key investigation to allow differentiation between atrial and ventricular, as well as regular (eg, atrial tachycardia) as opposed to irregular (eg, atrial fibrillation vs frequent atrial or ventricular ectopy or arrhythmias) arrhythmias. The 12-lead ECG allows a first localization of the origin of the documented arrhythmia,
Disclosures: S. Ernst is consulting for Stereotaxis Inc, Biosense Webster, and Spectrum Dynamics. Cardiology Department, National Heart and Lung Institute, Royal Brompton and Harefield Hospital, Imperial College, Sydney Street, London SW3 6NP, UK E-mail address: [email protected] Card Electrophysiol Clin - (2017) -–http://dx.doi.org/10.1016/j.ccep.2017.02.012 1877-9182/17/Ó 2017 Elsevier Inc. All rights reserved.
cardiacEP.theclinics.com
INTRODUCTION
2
Ernst
REVIEW ANATOMY and arrhythmia documentaon
ACCESS target chamber and start mapping process
IDENTIFY crical part for arrhythmia (characterisc signal or response to pacing maneuvers)
ABLATION to eliminate arrhythmia
VALIDATE (ablaon effect by pacing maneuvers)
Fig. 1. Stepwise approach to plan and execute a successful catheter ablation procedure in patients with congenital heart disease.
but, because of the possibly distorted cardiac anatomy, common ECG algorithms may not be sufficient. Holter recordings are especially valuable in intermittent arrhythmias and also allow documentation of the arrhythmias when more than 1 type of arrhythmia is present. Correlation with symptoms and potential consequences (eg, prolonged pauses after tachycardia termination) can be identified. However, the duration of Holter recordings (typically up to 7–14 days) may limit the yield of this diagnostic test if patients experience rare palpitations.10 Implantable loop recorder systems are an alternative, but lack the accuracy of P-wave detection and therefore differentiation of various atrial tachycardias may be based on cycle length analysis only.11,12
Standard Imaging Studies Because the arrhythmia could be an expression of worsening of the underlying congenital condition, careful transthoracic and, if necessary, transesophageal echocardiography should be performed to understand the relevant hemodynamic issues (eg, increase in pulmonary valve regurgitation in tetralogy of Fallot). Invasive hemodynamic studies may need to be considered either as stand-alone investigations or as part of the ablation procedure.
PREPARATION OF THE ABLATION PROCEDURE Detailed Knowledge of Individual Anatomy Understanding the individual three-dimensional (3D) anatomy is the cornerstone of any successful ablation procedure, even in patients without congenital conditions.13,14 Information on the dimensions of the cardiac chambers, the spatial relationship and angulations between different cardiac structures, and the presence of a patent foramen ovale are some examples of necessary information that may facilitate any procedure. In
patients with congenital heart disease, this detailed understanding of the specific anatomy becomes vitally important, and is in the author’s personal opinion an essential prerequisite for a successful ablation. Patients with congenital defects often have limited accessibility to their cardiac chambers because of complex intracardiac/ extracardiac anomaly and/or presence of intraatrial baffles or artificial materials. With this detailed knowledge of the individual anatomy and the use of advanced tools, these obstacles can be overcome and procedures can be performed as safely and successfully as possible with minimal fluoroscopy exposure.15
Review of Surgical Procedure Note Although knowing the underlying 3D anatomy is a necessary guide to insertion and navigation of the catheters, knowing the location and extent of surgical incisions and suture placement is of paramount importance in order to unveil the arrhythmia origin. Review of the surgical operation reports, if available, is valuable to understand the exact procedure performed in each individual and obtain information about the technique used (on/off pump, cannulation sites, location of patches). Cardiac surgeons have modified their technique over the years, so surgically created scars may be variable and, in the absence of surgical records, it may be difficult to reconstruct what has been done. This uncertainty is especially likely if preventive measures such as surgical mazelike ablations or incisions have been performed.16,17
ADVANCED TECHNIQUES Three-Dimensional Image Reconstruction In order to obtain a 3D reconstruction of the individual anatomy, the authors routinely perform a cardiac magnetic resonance (CMR) scan or, alternatively, a computed tomography (CT) scan when CMR is contraindicated.
Catheter Ablation Limitation of contrast flow in CT caused by long transit times necessitate long scan times and prolonged contrast bolus injections.18 In addition, patients with adult congenital heart disease (ACHD) are relatively young and most have already been exposed to several invasive (hemodynamic) procedures. Their lifetime burden with regard to radiation exposure is expected to be much higher than their peers who do not have ACHD, because they typically have had many hemodynamic studies in childhood and adulthood.19 For cardiac MRI, a free-breathing diaphragm– navigated balanced steady-state free-precession sequence with 3D reconstruction can be performed to image the whole heart.20
Three-Dimensional Imaging for Procedural Planning All preacquired 3D imaging DICOM (Digital Imaging and Communications in Medicine) data can then
be processed for 3D reconstructions and used during ablation procedures by integration with the mapping information (eg, using POLARIS software, Biosense Webster, Brussels, Belgium) (Fig. 2). Careful 3D assessment and procedural planning are necessary to access the most likely target chamber. Asking for a larger field of view (particularly when using nonfluoroscopic techniques such as CMR) allows review of the whole vascular tree, which can be integrated in the overall 3D reconstruction. Obstruction of the iliac vessels can also be present with multiple collaterals too small to navigate a catheter through. In the presence of completely occluded femoral venous access, alternative routes (eg, a superior approach using jugular or subclavian veins) need to be considered. In case of inferior vena cava interruptions, vessels of the azygos system can be used, which is made easy using remote magnetic navigation (discussed later).21 Another example is the surgically created access limitation from a superior vein via the superior
Fig. 2. Image integration from cardiac MRI during a magnetically remote controlled ablation procedure in a patient with atrial isomerism and situs inversus and transposition of the great arteries. Retrograde navigation across the aortic valve is shown with the soft magnetic catheter aligning parallel to the applied magnetic field vector (yellow). Ao, aorta; AP, anteroposterior; LA, left atrium; LV, left ventricle; IVC, inferior vena cava; PA, pulmonary artery; RA, right atrium; RV, right ventricle.
3
4
Ernst vena cava (SVC) after a Glenn operation. Careful review of 3D imaging with a wide imaging window allows assessment of the patency of the superior pathways. Access planning for patients after baffle operations is also key, because the target chamber might be located behind the baffle, necessitating either transbaffle puncture or remote magnetic navigation.22–26 Dimensions and, if available, scar/fibrosis information need to be reviewed carefully to predict reentrant circuits.
Vascular Access: Femoral Vascular access in patients with complex ACHD can be challenging or even impossible using the standard femoral venous access because of extensive scarring (eg, after vascular cut-down procedures during/before surgery). Ultrasonography guidance for vascular access is helpful to gain safe and reliable access.
Vascular Access: Alternative If unavoidable, alternative access such as transhepatic punctures to gain access to the right-sided atrium can be performed, but carry a high bleeding risk on sheath removal.27 Careful risk/benefit assessment should be performed and alternatives like retrograde remote approaches should be considered. Transapical ventricular access could be another option, as well as access via punctures through the ventricular septum.28,29
INTRAPROCEDURAL CONSIDERATIONS Dedicated Anesthetic Monitoring Patients with ACHD conditions undergoing invasive electrophysiology (EP) studies are typically exposed to longer procedure times and more difficult or more numerous arrhythmias compared with their peers without ACHD. They also can have more hemodynamic consequences of sustained arrhythmias and, therefore, need careful intraprocedural monitoring.30 A dedicated cardiac anesthetist who is well trained in the special requisites of complex EP procedures should be present throughout the ablation procedure to allow the operators to concentrate on the task of arrhythmia management. Depending on the nature of the arrhythmia, conscious sedation may be indicated rather than general anesthesia. Patients with high pulmonary artery pressure or changing shunting volumes need extremely careful monitoring.31 A collaborative approach that is focused on the primary outcome of the ablation (ie, elimination of all arrhythmias by ablation) is key and communication of applied medications (including choice of
sedative drugs, hemodynamic support, and so forth) is vital. At the end of the procedure, patients may need to be completely awake to expose them to enough sympathetic stimulation to exert further arrhythmias. In contrast, all 3D mapping systems require minimal patient movement, which can be difficult to obtain, especially in longer procedures when the patient is not fully sedated. In addition, monitoring of the fluid balance is another important feature that needs special consideration. Because most ablations are nowadays performed using irrigated-tip ablation catheters, patients can be exposed to a substantial amount of fluids during an invasive EP procedure. Diuretics may be necessary to avoid fluid overload, which may impair respiratory function in the periprocedural period. Adequate analgesia during and after an invasive EP procedure is equally important and helps the operator to perform an effective procedure without voluntary or involuntary movements of the patient on the catheter laboratory table. Postprocedural pain control is also mandatory to avoid local access site complications (extensive hematomas).
Three-Dimensional Electroanatomic Mapping A 3D electroanatomic mapping system is used to (1) localize the catheters without the need for radiographs, (2) calculate 3D displays of electrical activation sequences (activation maps) and of local voltage (voltage maps), and (3) display in 3 dimensions the anatomy of a heart chamber using sequential localization of the catheter.32 The 3D electroanatomic maps are superimposed on the reconstructed 3D surfaces of each cardiac structure (see Fig. 2). These point-by-point mapping systems require a stable arrhythmia and reaching all sites of interest, which then results in a meaningful 3D reconstruction of the activation sequence of a given arrhythmia. Inability to achieve a complete map may result in inconclusive maps and unsuccessful ablation attempts.
Multielectrode High-Resolution Mapping In order to hasten the mapping process, multielectrode mapping has been introduced to shorten the time required for mapping of a given arrhythmia. However, critical for these systems is that the arrhythmia must be stable enough, with little cycle length variation.33 Also, because direct contact is required, the risk of mechanical alteration or termination is higher. Fig. 3 shows an example of the Rhythmia system (Boston Scientific), which collects a large number of points with a dedicated multielectrode basket catheter. Comparison of neighboring points and various other stability
Catheter Ablation
Fig. 3. A patient with enlarged RA after Fontan operation with multipolar sequential mapping of an atrial tachycardia (265 milliseconds cycle length). Note the enlarged RA shown on the fluoroscopy image and the multipolar catheter in the coronary sinus (CS) positioned in a large loop. The multielectrode basket is highlighted with a yellow arrow. The critical part of the tachycardia is located between the superior vena cava (SVC) and the roof of the RA toward the pulmonary artery. ABL, ablation catheter.
criteria (including cycle length stability) allows rapid mapping of several thousand points on a 3D reconstruction. However, larger cohorts of patients with ACHD have not yet been investigated with this system.
Simultaneous Mapping System Simultaneous mapping systems have been introduced to the invasive EP arena: contact mapping using multielectrode baskets or noninvasive body surface mapping combined with 3D imaging. For the latter, data on patients with ACHD now exist.34 This system records simultaneously from 252 surface ECG electrodes and displays the electrical information of each cardiac activation on a 3D epicardial reconstruction of either the biatrial or biventricular chambers. This system allows the mapping of multiple arrhythmias or even very rare arrhythmias (eg, ventricular ectopy triggering ventricular fibrillation) while the patient is still on the ward. Mapping can be performed for several hours and provocation such as physical exercise on a stationary bike or with various common stimulants (food, social interaction, pharmacologic, and so forth) is performed on the ward, rather than in the catheter laboratory. Because this system is an exclusive mapping system, intraprocedural navigation to the site of origin can be challenging. However, compatibility with remote magnetic navigation has been shown.
Catheter Ablation Techniques The thickness of a chronically volume-overloaded or scarred myocardium can present an insurmountable obstacle to successful catheter ablation even in the presence of perfect 3D mapping and subsequent understanding of the underlying tachycardia substrate. Recently, the introduction of so-called irrigated tip catheters with increased lesion depth has improved the ability to create transmural lesions, but, in situations with limited catheter-tissue contact (eg, in the presence of a massively dilated atrial chamber) or increased/ reduced blood flow, lesion formation continues to be problematic.35
Remote Navigation by Magnetic Navigation In order to overcome the dominant problem in ACHD EP procedures, which is access to the target chamber, a remote controlled navigation system has been successfully used by several centers in patients with ACHD. Because the catheter tip is flexible and aligns in an outer magnetic field, the navigation of the mapping and ablation catheter, even through usual access vessels (eg, of the azygos system) or retrogradely across the aortic valve, can be achieved (see Fig. 2).22 The magnetic navigation system (Niobe, Stereotaxis Inc, St Louis) consists of 2 computer-controlled permanent magnets (composed of the magnetic rare earth neodymium, Bor, and iron) positioned
5
6
Ernst on either side of the fluoroscopy table resulting in a uniform magnetic field (0.08 T) of about 15 cm in diameter in the area of the patient’s chest.36 The flexible mapping catheter is equipped at its tip with small magnets that align parallel to the externally controlled direction of the magnetic field. In combination with a 3D mapping system such as CARTO RMT (Biosense Webster, Brussels, Belgium), the magnetic field directions (vectors) needed for sequential 3D reconstruction are applied from a remote position inside the control room. In addition, the magnetic navigation system allows integration of the preacquired 3D image directly on the reference fluoroscopy displays. Registration of all 3 systems (magnetic navigation, 3D mapping system [CARTO], and conventional fluoroscopy) allows superimposition of all information on the same reference image with depiction of the ablation catheter tip in real time.21
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SUMMARY A structured approach to arrhythmia ablation in patients with congenital heart disease involves the review of the anatomy and surgical notes, 3D reconstruction of the cardiac endocardial surfaces, 3D electroanatomic mapping, and (if necessary) facilitated access and movement of the ablation catheter using remote magnetic navigation technology. The recent advances in imaging and ablation tools can now offer solutions and successful ablation of even the most complex postsurgical arrhythmias.
13.
14.
REFERENCES 1. Chung MK. Cardiac surgery: postoperative arrhythmias. Crit Care Med 2000;28(10 Suppl):N136–44. 2. England MR, Gordon G, Salem M, et al. Magnesium administration and dysrhythmias after cardiac surgery. A placebo-controlled, double-blind, randomized trial. JAMA 1992;268(17):2395–402. 3. Mantovan R, Gatzoulis MA, Pedrocco A, et al. Supraventricular arrhythmia before and after surgical closure of atrial septal defects: spectrum, prognosis and management. Europace 2003;5(2):133–8. 4. Nabar A, Timmermans C, Medeiros A, et al. Radiofrequency ablation of atrial arrhythmias after previous open-heart surgery. Europace 2005;7(1):40–9. 5. Gatzoulis MA, Freeman MA, Siu SC, et al. Atrial arrhythmia after surgical closure of atrial septal defects in adults. N Engl J Med 1999;340(11):839–46. 6. de Jong S, van Veen TA, van Rijen HV, et al. Fibrosis and cardiac arrhythmias. J Cardiovasc Pharmacol 2015;57(6):630–8. 7. Gatzoulis MA, Balaji S, Webber SA, et al. Risk factors for arrhythmia and sudden cardiac death late
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after repair of tetralogy of Fallot: a multicentre study. Lancet 2000;356(9234):975–81. Roubertie F, Thambo JB, Bretonneau A, et al. Late outcome of 132 Senning procedures after 20 years of follow-up. Ann Thorac Surg 2011;92(6):2206–13 [discussion: 2213–4]. von Olshausen K, Witt T, Schmidt G, et al. Ventricular tachycardia as a cause of sudden death in patients with aortic valve disease. Am J Cardiol 1987;59(12): 1214–5. Locati ET, Vecchi AM, Vargiu S, et al. Role of extended external loop recorders for the diagnosis of unexplained syncope, pre-syncope, and sustained palpitations. Europace 2014;16(6):914–22. Volosin K, Stadler RW, Wyszynski R, et al. Tachycardia detection performance of implantable loop recorders: results from a large ‘real-life’ patient cohort and patients with induced ventricular arrhythmias. Europace 2013;15(8):1215–22. Podd SJ, Sugihara C, Furniss SS, et al. Are implantable cardiac monitors the ’gold standard’ for atrial fibrillation detection? A prospective randomized trial comparing atrial fibrillation monitoring using implantable cardiac monitors and DDDRP permanent pacemakers in post atrial fibrillation ablation patients. Europace 2016;18(7):1000–5. Sithamparanathan S, Padley SP, Rubens MB, et al. Great vessel and coronary artery anatomy in transposition and other coronary anomalies: a universal descriptive and alphanumerical sequential classification. JACC Cardiovasc Imaging 2013;6(5): 624–30. Gerlis LM, Ho SY, Somerville J. A postmortem review of congenital cardiac malformations in a series of 180 adults, over the age of 16 years, born between 1865 and 1980. Cardiovasc Pathol 1999; 8(5):263–72. Ueda AS, Mantziari L, Gujic M, et al. Contribution of remote magnetic navigation to supraventricular tachycardia ablation in complex congenital heart diseases. Circ Arrhythm Electrophysiol 2013;6: 606–13. Uemura H. Surgical aspects of atrial arrhythmia: right atrial ablation and anti-arrhythmic surgery in congenital heart disease. Herzschrittmacherthe Elektrophysiol 2016;27(2):137–42. Stulak JM, Dearani JA, Puga FJ, et al. Right-sided Maze procedure for atrial tachyarrhythmias in congenital heart disease. Ann Thorac Surg 2006; 81(5):1780–4 [discussion: 1784–5]. Siripornpitak S, Pornkul R, Khowsathit P, et al. Cardiac CT angiography in children with congenital heart disease. Eur J Radiol 2013;82(7):1067–82. Glatz AC, Purrington KS, Klinger A, et al. Cumulative exposure to medical radiation for children requiring surgery for congenital heart disease. J Pediatr 2014;164(4):789–94.e10.
Catheter Ablation 20. Keegan J, Jhooti P, Babu-Narayan SV, et al. Improved respiratory efficiency of 3D late gadolinium enhancement imaging using the continuously adaptive windowing strategy (CLAWS). Magn Reson Med 2014;71(3):1064–74. 21. Ernst S, Chun JK, Koektuerk B, et al. Magnetic navigation and catheter ablation of right atrial ectopic tachycardia in the presence of a hemi-azygos continuation: a magnetic navigation case using 3D electroanatomical mapping. J Cardiovasc Electrophysiol 2009;20(1):99–102. 22. Ueda A, Suman-Horduna I, Mantziari L, et al. Contemporary outcomes of supraventricular tachycardia ablation in congenital heart disease: a single-center experience in 116 patients. Circ Arrhythm Electrophysiol 2013;6(3):606–13. 23. Krause U, Backhoff D, Klehs S, et al. Transbaffle catheter ablation of atrial re-entrant tachycardia within the pulmonary venous atrium in adult patients with congenital heart disease. Europace 2016;18(7): 1055–60. 24. Schwagten B, Cuypers J, Szili-Torok T. The magnetic navigation system allows avoidance of puncturing a baffle during ablation of a postincisional macroreentrant tachycardia. Cardiol Young 2009;19(2):216–9. 25. El-Said HG, Ing FF, Grifka RG, et al. 18-year experience with transseptal procedures through baffles, conduits, and other intra-atrial patches. Catheter Cardiovasc Interv 2000;50(4):434–9 [discussion: 440]. 26. Dave AS, Aboulhosn J, Child JS, et al. Transconduit puncture for catheter ablation of atrial tachycardia in a patient with extracardiac Fontan palliation. Heart Rhythm 2010;7(3):413–6. 27. Singh SM, Neuzil P, Skoka J, et al. Percutaneous transhepatic venous access for catheter ablation procedures in patients with interruption of the inferior
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vena cava. Circ Arrhythm Electrophysiol 2011;4(2): 235–41. Kliger C, Jelnin V, Sharma S, et al. CT angiographyfluoroscopy fusion imaging for percutaneous transapical access. JACC Cardiovasc Imaging 2014; 7(2):169–77. Vaseghi M, Macias C, Tung R, et al. Percutaneous interventricular septal access in a patient with aortic and mitral mechanical valves: a novel technique for catheter ablation of ventricular tachycardia. Heart Rhythm 2013;10(7):1069–73. Seal R. Adult congenital heart disease. Paediatr Anaesth 2011;21(5):615–22. Bennett JM, Ehrenfeld JM, Markham L, et al. Anesthetic management and outcomes for patients with pulmonary hypertension and intracardiac shunts and Eisenmenger syndrome: a review of institutional experience. J Clin Anesth 2014;26(4):286–93. Knackstedt C, Schauerte P, Kirchhof P. Electroanatomic mapping systems in arrhythmias. Europace 2008;10(suppl 3):iii28–34. Anter E, McElderry TH, Contreras-Valdes FM, et al. Evaluation of a novel high-resolution mapping technology for ablation of recurrent scar-related atrial tachycardias. Heart Rhythm 2016;13(10):2048–55. Ernst S, Saenen J, Rydman R, et al. Utility of noninvasive arrhythmia mapping in patients with adult congenital heart disease. Card Electrophysiol Clin 2015;7(1):117–23. Everett TH 4th, Lee KW, Wilson EE, et al. Safety profiles and lesion size of different radiofrequency ablation technologies: a comparison of large tip, open and closed irrigation catheters. J Cardiovasc Electrophysiol 2008;20(3):325–35. Faddis MN, Blume W, Finney J, et al. Novel, magnetically guided catheter for endocardial mapping and radiofrequency catheter ablation. Circulation 2002; 106(23):2980–5.
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KEY POINTS The underlying anatomy can be understood through three-dimensional reconstruction of tomographic imaging. Choosing the most appropriate acquisition system (simultaneous vs sequential) is necessary for the given arrhythmia. Recognizing the need for close collaboration with cardiac anesthesia ensures good hemodynamic support and adequate analgesia.
Cardiac arrhythmias are typically encountered after cardiac surgery and can occur in the immediate postsurgical period or, more often, decades after surgery. In the postoperative period, arrhythmias may complicate the patient’s course and prolong the stay in the intensive care unit.1,2 Late after surgery, cardiac arrhythmias are thought to stem mainly from the unavoidable scars left behind (eg, after an atriotomy, the cannulation sites for the cardiopulmonary bypass, or other scars inherent to the specific cardiac surgery [patch sutures]).3–5 However, age and progression of the structural/congenital heart disease, resulting in pressure increase and dilation, can lead to pronounced fibrosis, which in itself can promote focal and/or reentrant arrhythmia.6 The presence of frequently recurrent or sustained arrhythmias is associated with reduced quality of life, risk of development of heart failure symptoms caused by tachycardiomyopathy, higher thromboembolic risk, and reduced survival.7–9
Catheter ablation of postsurgical arrhythmias in patients with congenital heart disease is currently feasible and successful with the use of advanced image integration and ablation tools. This article reviews the general steps of preparation for such a procedure and discusses the available techniques as an alternative to long-term antiarrhythmic therapy. Fig. 1 summarizes a stepwise approach that helps clinicians to perform even complex ablation procedure successfully.
GENERAL PREPARATION OF PATIENTS WITH CONGENITAL HEART DISEASE PRESENTING WITH ARRHYTHMIAS In the first instance, 12-lead electrocardiogram (ECG) documentation is the key investigation to allow differentiation between atrial and ventricular, as well as regular (eg, atrial tachycardia) as opposed to irregular (eg, atrial fibrillation vs frequent atrial or ventricular ectopy or arrhythmias) arrhythmias. The 12-lead ECG allows a first localization of the origin of the documented arrhythmia,
Disclosures: S. Ernst is consulting for Stereotaxis Inc, Biosense Webster, and Spectrum Dynamics. Cardiology Department, National Heart and Lung Institute, Royal Brompton and Harefield Hospital, Imperial College, Sydney Street, London SW3 6NP, UK E-mail address: [email protected] Card Electrophysiol Clin - (2017) -–http://dx.doi.org/10.1016/j.ccep.2017.02.012 1877-9182/17/Ó 2017 Elsevier Inc. All rights reserved.
cardiacEP.theclinics.com
INTRODUCTION
2
Ernst
REVIEW ANATOMY and arrhythmia documentaon
ACCESS target chamber and start mapping process
IDENTIFY crical part for arrhythmia (characterisc signal or response to pacing maneuvers)
ABLATION to eliminate arrhythmia
VALIDATE (ablaon effect by pacing maneuvers)
Fig. 1. Stepwise approach to plan and execute a successful catheter ablation procedure in patients with congenital heart disease.
but, because of the possibly distorted cardiac anatomy, common ECG algorithms may not be sufficient. Holter recordings are especially valuable in intermittent arrhythmias and also allow documentation of the arrhythmias when more than 1 type of arrhythmia is present. Correlation with symptoms and potential consequences (eg, prolonged pauses after tachycardia termination) can be identified. However, the duration of Holter recordings (typically up to 7–14 days) may limit the yield of this diagnostic test if patients experience rare palpitations.10 Implantable loop recorder systems are an alternative, but lack the accuracy of P-wave detection and therefore differentiation of various atrial tachycardias may be based on cycle length analysis only.11,12
Standard Imaging Studies Because the arrhythmia could be an expression of worsening of the underlying congenital condition, careful transthoracic and, if necessary, transesophageal echocardiography should be performed to understand the relevant hemodynamic issues (eg, increase in pulmonary valve regurgitation in tetralogy of Fallot). Invasive hemodynamic studies may need to be considered either as stand-alone investigations or as part of the ablation procedure.
PREPARATION OF THE ABLATION PROCEDURE Detailed Knowledge of Individual Anatomy Understanding the individual three-dimensional (3D) anatomy is the cornerstone of any successful ablation procedure, even in patients without congenital conditions.13,14 Information on the dimensions of the cardiac chambers, the spatial relationship and angulations between different cardiac structures, and the presence of a patent foramen ovale are some examples of necessary information that may facilitate any procedure. In
patients with congenital heart disease, this detailed understanding of the specific anatomy becomes vitally important, and is in the author’s personal opinion an essential prerequisite for a successful ablation. Patients with congenital defects often have limited accessibility to their cardiac chambers because of complex intracardiac/ extracardiac anomaly and/or presence of intraatrial baffles or artificial materials. With this detailed knowledge of the individual anatomy and the use of advanced tools, these obstacles can be overcome and procedures can be performed as safely and successfully as possible with minimal fluoroscopy exposure.15
Review of Surgical Procedure Note Although knowing the underlying 3D anatomy is a necessary guide to insertion and navigation of the catheters, knowing the location and extent of surgical incisions and suture placement is of paramount importance in order to unveil the arrhythmia origin. Review of the surgical operation reports, if available, is valuable to understand the exact procedure performed in each individual and obtain information about the technique used (on/off pump, cannulation sites, location of patches). Cardiac surgeons have modified their technique over the years, so surgically created scars may be variable and, in the absence of surgical records, it may be difficult to reconstruct what has been done. This uncertainty is especially likely if preventive measures such as surgical mazelike ablations or incisions have been performed.16,17
ADVANCED TECHNIQUES Three-Dimensional Image Reconstruction In order to obtain a 3D reconstruction of the individual anatomy, the authors routinely perform a cardiac magnetic resonance (CMR) scan or, alternatively, a computed tomography (CT) scan when CMR is contraindicated.
Catheter Ablation Limitation of contrast flow in CT caused by long transit times necessitate long scan times and prolonged contrast bolus injections.18 In addition, patients with adult congenital heart disease (ACHD) are relatively young and most have already been exposed to several invasive (hemodynamic) procedures. Their lifetime burden with regard to radiation exposure is expected to be much higher than their peers who do not have ACHD, because they typically have had many hemodynamic studies in childhood and adulthood.19 For cardiac MRI, a free-breathing diaphragm– navigated balanced steady-state free-precession sequence with 3D reconstruction can be performed to image the whole heart.20
Three-Dimensional Imaging for Procedural Planning All preacquired 3D imaging DICOM (Digital Imaging and Communications in Medicine) data can then
be processed for 3D reconstructions and used during ablation procedures by integration with the mapping information (eg, using POLARIS software, Biosense Webster, Brussels, Belgium) (Fig. 2). Careful 3D assessment and procedural planning are necessary to access the most likely target chamber. Asking for a larger field of view (particularly when using nonfluoroscopic techniques such as CMR) allows review of the whole vascular tree, which can be integrated in the overall 3D reconstruction. Obstruction of the iliac vessels can also be present with multiple collaterals too small to navigate a catheter through. In the presence of completely occluded femoral venous access, alternative routes (eg, a superior approach using jugular or subclavian veins) need to be considered. In case of inferior vena cava interruptions, vessels of the azygos system can be used, which is made easy using remote magnetic navigation (discussed later).21 Another example is the surgically created access limitation from a superior vein via the superior
Fig. 2. Image integration from cardiac MRI during a magnetically remote controlled ablation procedure in a patient with atrial isomerism and situs inversus and transposition of the great arteries. Retrograde navigation across the aortic valve is shown with the soft magnetic catheter aligning parallel to the applied magnetic field vector (yellow). Ao, aorta; AP, anteroposterior; LA, left atrium; LV, left ventricle; IVC, inferior vena cava; PA, pulmonary artery; RA, right atrium; RV, right ventricle.
3
4
Ernst vena cava (SVC) after a Glenn operation. Careful review of 3D imaging with a wide imaging window allows assessment of the patency of the superior pathways. Access planning for patients after baffle operations is also key, because the target chamber might be located behind the baffle, necessitating either transbaffle puncture or remote magnetic navigation.22–26 Dimensions and, if available, scar/fibrosis information need to be reviewed carefully to predict reentrant circuits.
Vascular Access: Femoral Vascular access in patients with complex ACHD can be challenging or even impossible using the standard femoral venous access because of extensive scarring (eg, after vascular cut-down procedures during/before surgery). Ultrasonography guidance for vascular access is helpful to gain safe and reliable access.
Vascular Access: Alternative If unavoidable, alternative access such as transhepatic punctures to gain access to the right-sided atrium can be performed, but carry a high bleeding risk on sheath removal.27 Careful risk/benefit assessment should be performed and alternatives like retrograde remote approaches should be considered. Transapical ventricular access could be another option, as well as access via punctures through the ventricular septum.28,29
INTRAPROCEDURAL CONSIDERATIONS Dedicated Anesthetic Monitoring Patients with ACHD conditions undergoing invasive electrophysiology (EP) studies are typically exposed to longer procedure times and more difficult or more numerous arrhythmias compared with their peers without ACHD. They also can have more hemodynamic consequences of sustained arrhythmias and, therefore, need careful intraprocedural monitoring.30 A dedicated cardiac anesthetist who is well trained in the special requisites of complex EP procedures should be present throughout the ablation procedure to allow the operators to concentrate on the task of arrhythmia management. Depending on the nature of the arrhythmia, conscious sedation may be indicated rather than general anesthesia. Patients with high pulmonary artery pressure or changing shunting volumes need extremely careful monitoring.31 A collaborative approach that is focused on the primary outcome of the ablation (ie, elimination of all arrhythmias by ablation) is key and communication of applied medications (including choice of
sedative drugs, hemodynamic support, and so forth) is vital. At the end of the procedure, patients may need to be completely awake to expose them to enough sympathetic stimulation to exert further arrhythmias. In contrast, all 3D mapping systems require minimal patient movement, which can be difficult to obtain, especially in longer procedures when the patient is not fully sedated. In addition, monitoring of the fluid balance is another important feature that needs special consideration. Because most ablations are nowadays performed using irrigated-tip ablation catheters, patients can be exposed to a substantial amount of fluids during an invasive EP procedure. Diuretics may be necessary to avoid fluid overload, which may impair respiratory function in the periprocedural period. Adequate analgesia during and after an invasive EP procedure is equally important and helps the operator to perform an effective procedure without voluntary or involuntary movements of the patient on the catheter laboratory table. Postprocedural pain control is also mandatory to avoid local access site complications (extensive hematomas).
Three-Dimensional Electroanatomic Mapping A 3D electroanatomic mapping system is used to (1) localize the catheters without the need for radiographs, (2) calculate 3D displays of electrical activation sequences (activation maps) and of local voltage (voltage maps), and (3) display in 3 dimensions the anatomy of a heart chamber using sequential localization of the catheter.32 The 3D electroanatomic maps are superimposed on the reconstructed 3D surfaces of each cardiac structure (see Fig. 2). These point-by-point mapping systems require a stable arrhythmia and reaching all sites of interest, which then results in a meaningful 3D reconstruction of the activation sequence of a given arrhythmia. Inability to achieve a complete map may result in inconclusive maps and unsuccessful ablation attempts.
Multielectrode High-Resolution Mapping In order to hasten the mapping process, multielectrode mapping has been introduced to shorten the time required for mapping of a given arrhythmia. However, critical for these systems is that the arrhythmia must be stable enough, with little cycle length variation.33 Also, because direct contact is required, the risk of mechanical alteration or termination is higher. Fig. 3 shows an example of the Rhythmia system (Boston Scientific), which collects a large number of points with a dedicated multielectrode basket catheter. Comparison of neighboring points and various other stability
Catheter Ablation
Fig. 3. A patient with enlarged RA after Fontan operation with multipolar sequential mapping of an atrial tachycardia (265 milliseconds cycle length). Note the enlarged RA shown on the fluoroscopy image and the multipolar catheter in the coronary sinus (CS) positioned in a large loop. The multielectrode basket is highlighted with a yellow arrow. The critical part of the tachycardia is located between the superior vena cava (SVC) and the roof of the RA toward the pulmonary artery. ABL, ablation catheter.
criteria (including cycle length stability) allows rapid mapping of several thousand points on a 3D reconstruction. However, larger cohorts of patients with ACHD have not yet been investigated with this system.
Simultaneous Mapping System Simultaneous mapping systems have been introduced to the invasive EP arena: contact mapping using multielectrode baskets or noninvasive body surface mapping combined with 3D imaging. For the latter, data on patients with ACHD now exist.34 This system records simultaneously from 252 surface ECG electrodes and displays the electrical information of each cardiac activation on a 3D epicardial reconstruction of either the biatrial or biventricular chambers. This system allows the mapping of multiple arrhythmias or even very rare arrhythmias (eg, ventricular ectopy triggering ventricular fibrillation) while the patient is still on the ward. Mapping can be performed for several hours and provocation such as physical exercise on a stationary bike or with various common stimulants (food, social interaction, pharmacologic, and so forth) is performed on the ward, rather than in the catheter laboratory. Because this system is an exclusive mapping system, intraprocedural navigation to the site of origin can be challenging. However, compatibility with remote magnetic navigation has been shown.
Catheter Ablation Techniques The thickness of a chronically volume-overloaded or scarred myocardium can present an insurmountable obstacle to successful catheter ablation even in the presence of perfect 3D mapping and subsequent understanding of the underlying tachycardia substrate. Recently, the introduction of so-called irrigated tip catheters with increased lesion depth has improved the ability to create transmural lesions, but, in situations with limited catheter-tissue contact (eg, in the presence of a massively dilated atrial chamber) or increased/ reduced blood flow, lesion formation continues to be problematic.35
Remote Navigation by Magnetic Navigation In order to overcome the dominant problem in ACHD EP procedures, which is access to the target chamber, a remote controlled navigation system has been successfully used by several centers in patients with ACHD. Because the catheter tip is flexible and aligns in an outer magnetic field, the navigation of the mapping and ablation catheter, even through usual access vessels (eg, of the azygos system) or retrogradely across the aortic valve, can be achieved (see Fig. 2).22 The magnetic navigation system (Niobe, Stereotaxis Inc, St Louis) consists of 2 computer-controlled permanent magnets (composed of the magnetic rare earth neodymium, Bor, and iron) positioned
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Ernst on either side of the fluoroscopy table resulting in a uniform magnetic field (0.08 T) of about 15 cm in diameter in the area of the patient’s chest.36 The flexible mapping catheter is equipped at its tip with small magnets that align parallel to the externally controlled direction of the magnetic field. In combination with a 3D mapping system such as CARTO RMT (Biosense Webster, Brussels, Belgium), the magnetic field directions (vectors) needed for sequential 3D reconstruction are applied from a remote position inside the control room. In addition, the magnetic navigation system allows integration of the preacquired 3D image directly on the reference fluoroscopy displays. Registration of all 3 systems (magnetic navigation, 3D mapping system [CARTO], and conventional fluoroscopy) allows superimposition of all information on the same reference image with depiction of the ablation catheter tip in real time.21
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SUMMARY A structured approach to arrhythmia ablation in patients with congenital heart disease involves the review of the anatomy and surgical notes, 3D reconstruction of the cardiac endocardial surfaces, 3D electroanatomic mapping, and (if necessary) facilitated access and movement of the ablation catheter using remote magnetic navigation technology. The recent advances in imaging and ablation tools can now offer solutions and successful ablation of even the most complex postsurgical arrhythmias.
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