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Radiofrequency Catheter Ablation for the Management of Cardiac Tachyarrhythmias
Radiofrequency Catheter Ablation for the Management of Cardiac Tachyarrhythmias MARK WOOD, MD,
KENNETH ELLENBOGEN, MD,
ABSTRACT: Radiofrequency catheter ablation techniques allow for safe and highly effective curative therapy of a variety of cardiac dysrhythmias. The technique involves the delivery of a high-frequency, alternating electrical current through an intravascular catheter to sites of arrhythmogenic myocardium. This current induces resistive electrical heating of the tissue, resulting in discrete areas of myocardial destruction through coagulation and desiccation. Dysrhythmias most commonly treated with these techniques are atrioventricular nodal reentry and tachycardias related to accessory atrioventricular bypass tracts. For these dysrhythmias, success rates of 90% to 95% are achievable with a low (2% to 4%) risk of complications. Radiofrequency catheter ablation techniques also have been used to treat ventricular tachycardias, atrial flutter, ectopic atrial tachycardia, and sinus node reentry, albeit with lower success rates. These techniques are still evolving, alternate energy sources (such as microwave and laser) and improved catheter technology should enhance the technique's safety and efficacy for a wider range of dysrhythmias. KEY INDEXING TERMS: Dysrhythmias; Cardiac tachyarrhythmias; Radiofrequency catheter ablation. [Am J Med Sci 1993;306(4):241-247.]
R
ecently developed radiofrequency catheter ablation (RFA) techniques provide curative therapy for many forms of supraventricular and ventricular tachyarrhythmias. These techniques currently are revolutionizing the field of cardiac electrophysiology similar to the impact of percutaneous transluminal coronary angioplasty on the specialty of cardiac catheterization. Using percutaneous catheter techniques to From the Medical College of Virginia, Richmond, Virginia, and McGuire Veterans Administration Hospitals, Richmond, Virginia. Correspondence: Mark Wood, MD, Co-Director, Cardiac Electrophysiology, Department of Cardiac Electrophysiology, Medical College of Virginia, MCV Box 53, Richmond, VA 232.98. THE AMERICAN JOURNAL OF THE MEDICAL SCIENCES
BRUCE STAMBLER, MD
selectively destroy arrhythmogenic myocardial tissue, RFA techniques provide safe, well-tolerated, and costeffective therapeutic results previously obtainable only with cardiac surgery. This paper reviews the history, fundamental principles, and clinical aspects of RF A procedures. History
Medical management of common forms of paroxysmal supraventricular tachycardias is rarely totally satisfactory because of clinical arrhythmia recurrences, intolerance to drug therapy, and difficulties with medical compliance. Previously, the only alternatives to drug therapy included surgical obliteration of arrhythmogenic myocardium or possibly the use of antitachycardia pacemaker systems. For most patients, the cost, risks, and morbidity associated with these surgical approaches were prohibitive. In 1982, Gallagher 1 first reported the use of transluminal direct-current catheter ablation techniques to interrupt atrioventricular (AV) nodal conduction in nine patients with debilitating supraventricular tachycardias. The direct current technique involves delivery of 50 to 400 joule shocks from a standard external defibrillator between a large surface skin electrode and the ablation catheter tip positioned in proximity to the targeted myocardium. The high-energy impulse damages myocardium by the production of intense heat (temperature to 1,700° C), electrical fields, and barotrauma (up to 11 atmospheres).2,3 Although highly effective in abolishing AV nodal and accessory AV pathway function, the diffuse nature of the myocardial injury is unsuitable for controlled modification of A V nodal conduction and carries a significant risk of global depression of left-ventricular function, myocardial rupture and tamponade, ventricular tachyarrhythmias, and sudden death after the procedure. 4,5 The search for safer and more controllable energy sources drew from 70 years of surgical experience with radiofrequency energy, first introduced as electrosurgical cautery in 1911 and later adapted for focal lesion production in neurosurgical and oncologic procedures. In 1987, Borggrefe6 first reported the successful use of catheter-directed radiofrequency energy to abolish accessory pathway function in humans. Subsequently, large clinical studies have documented the safety and
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efficacy of the RFA technique for a variety of cardiac arrhythmias. Biophysics
The radiofrequency energy used in catheter ablation techniques is a high frequency alternating electrical current with frequency in the range of 300 kHz to 1.5 MHz. When this current is passed through biologic tissues between low resistance electrodes, resistive heating occurs within the tissue because of the tissue's intrinsic electrical impedance. Depending upon the current intensity and electrical waveform, three electrosurgical effects may result: 1) electrosurgical cutting-vaporization of tissue by intense local heat production and abrupt expansive steam formation within the tissue, 2) electro surgical cautery (fulguration)tissue burning and charring from intense local heat production causing dense eschar formation, or 3) electrosurgical desiccation-tissue destruction by coagulation and dehydration as intra- and extracellular water is driven away by less intense tissue heating. Radiofrequency catheter ablation -techniques use unmodulated sinusoidal waveforms of 300 to 750 kHz to produce discrete zones of electrosurgical desiccation around a catheter electrode contacting the cardiac endocardium. The high electrical frequencies prevent direct electrical stimulation and possibly fibrillation of the myocardium. The heat generated within the tissue is directly proportional to the square of the current intensity and duration of current application and inversely proportional to the 4th power of the distance from the active electrode. 7 Using conventional electrodes (3 to 4 mm diameter tip), the volume of myocardium undergoing active, resistive heating is small and confined to a radius of less than 1 mm around the electrode surface. s Passive heat conduction away from the zone of active resistive heating extends the volume of myocardial damage. Myocardial tissue temperatures above 46 to 49 0 C are required for permanent lesion formation. s Tissue temperature declines in inverse proportion to the distance from the electrode. 9 For any given electrode diameter, there exists a theoretical maximum lesion size. 1o This results from a maximum achievable electrode-tissue interface temperature of 100 0 C, above which tissue charring and coagulum formation raise the electrical impedance and limit further current flow. For 6F catheter tip electrodes, the maximum lesion depth is 7.5 mm. 10 Other factors influencing lesion size are current intensity and duration, electrode-tissue contact pressure, convective heat loss from local blood flow, and the tissue compositionY The half-time for lesion generation under stable in vitro conditions is approximately 7 to 9 seconds. 12 Histologically, cardiac radiofrequency lesions are well-demarcated, ovoid or spherical zones of central coagulation necrosis with a peripheral rim of hemorrhagic necrosis and granulation tissue. 13
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Procedures
Preparation for RF A is similar to that for other invasive percutaneous vascular procedures. The patient fasts overnight but is well-hydrated. All antiarrhythmic medications are discontinued five half-lives before the procedure to permit induction of the tachycardia. For the initial evaluation of supraventricular tachycardias, electrode catheters are positioned in the right atrium, right ventricul~r apex, and right ventricular inflow region to record the His bundle potential and in the coronary sinus to map left-atrial and left-ventricular activation sequences. Ablation of ventricular foci may require as few as one ventricular catheter in addition to the ablation catheter. The patient generally is heparinized for the duration of the procedure. Once electrophysiologic studies define the mechanism and site of arrhythmogenesis, the ablation catheter is positioned under fluoroscopic and electrocardiographic guidance to the desired location. The ablation catheter typically is 6 to 7F in diameter, with steerable tips to allow maximal control (Figure 1). Once positioned, radio frequency energy is delivered between the catheter tip and a large patch electrode on the patient's chest. Current delivery is terminated after 5 to 10 seconds if the desired electrophysiologic effect is not observed and the catheter is then repositioned. Should therapeutic results occur, the current is continued for a total of 20 to 60 seconds to produce a maximal lesion. Radiofrequency current generally is produced using standard neurosurgical lesion generators (Figures 1); however, generators designed specifically for ablation of cardiac arrhythmias are now available. Generally, energy deliveries of 20 to 50 watts (40 to 60 V, 400 to 600 rnA) are used, depending on the site of application.
Figure 1. Radiofrequency lesion generator suitable for neurosurgical and cardiologic applications. The large surface patch electrode is shown to the left and the steerable radiofrequency ablation catheter to the right. The steering mechanism deflects the catheter tip through 270 0 from the catheter's long axis. October 1993 Volume 306 Number 4
Wood, Ellenbogen, and Stambler
Table 1. Cardiac Arrhythmias Treated by Radiofrequency Catheter Ablation AV nodal reentry AV reciprocating tachycardias Wolff-Parkinson-White syndrome Concealed accessory bypass tracts Mahaim type AV bypass tracts Ventricular tachycardias Associated with chronic CAD Right ventricular outflow tract tachycardia Idiopathic monomorphic VT Bundle branch reentrant VT Ectopic atrial tachycardia Atrial flutter Sinus node reentrant tachycardia
Cardiac dysrhythmias treated with radiofrequency catheter ablation techniques. A V = atrioventricular; CAD = coronary artery disease; VT = ventricular tachycardia.
Treatment of Specific Arrhythmias. Arrhythmias successfully treated with RFA techniques are listed in Table 1. By far, tachyarrhythmias associated with AV nodal reentry and accessory AV bypass tracts are the most commonly treated. For reentrant tachyarrhythmias, RF A techniques require localization and interruption of a critical limb of the reentrant circuit. For automatic rhythms or those believed to involve very small reentrant circuits, RF A lesions may be directed toward the sites of earliest myocardial activation during the tachycardias. Accessory Atrioventricular Bypass Tracts. With demonstrable ante grade accessory pathway conduction (Wolff-Parkinson-White syndrome), catheter mapping of the earliest site of ventricular activation along the AV annulus defines the ventricular insertion of the pathway. For concealed accessory pathways or during orthodromic reciprocating tachycardia, the site of earliest retrograde atrial activation or shortest ventricleto-atrial conduction times are sought to approximate the atrial insertion. For left-sided accessory pathways, the mitral valve annulus is accessed by catheter positioning retrogradely across the aortic valve or transseptally from the right to left atria. Right-sided pathways are approached transvenously, either from the superior or inferior vena cavae. The ablation catheter frequently is wedged beneath the AV valve against the annulus for stability (Figure 2). Electrocardiographic criteria predicting effective catheter positions include local ventricular electrograms preceding surface QRS complex during antegrade preexcitation or local atrial-to-ventricular conduction times up to 40 msec (Figure 3), recording electrical activity from the pathway itself (Figure 4), and electrogram stability and local ventricular-to-atrial conduction times ofless than 60 msec during retrograde accessory pathway conduction (Figure 5).14,15 Successful energy delivery to these sites results in a loss of preexcitation on a surface electrocardiogram (Figure THE AMERICAN JOURNAL OF THE MEDICAL SCIENCES
Figure 2. Right anterior oblique 30° projection of intracardiac catheter positions for left lateral accessory pathway ablation. Catheters are located in the right atrium (RA), His position (HS), right ventricle (RV), and coronary sinus (CS). The ablation catheter (AB) crosses the aortic valve retrogradely to rest beneath the mitral valve annulus in proximity to the middle poles of the CS catheter.
6), the termination of reciprocating tachycardia, and the abolition of retrograde accessory pathway conduction. Atrioventricular Nodal Reentry. Atrioventricular nodal reentrant tachycardias may be eliminated by the
Figure 3. Intracardiac electro grams demonstrating ventricular activation before preexcited surface electrocardiogram QRS (delta wave) onset in a patient with a right-anterior free-wall accessory pathway. During atrial pacing the first two beats are preexcited. Ventricular activation precedes the surface delta wave by 40 msec on the AB catheter. Ventricular preexcitation is spontaneously lost on the third paced beat. The AB catheter now records ventricular activation 40 msec after QRS onset. The atrial-ventricular time of 230 msec with a clear His bundle recording is now visible from the His catheter recordings. I, II, III, VI = surface electrocardiogram leads; AB = ablation catheter located on the anterior right-ventricular free wall near the tricuspid annulus; HBI and HB2 = His bundle catheter; S = pacing stimulus; A = atrial electrogram; V = ventricular electrogram; and H = His bundle recordings.
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Radiofrequency Catheter Ablation
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Figure 4. Surface electrocardiogram and ablation catheter recordings from a second patient with a right-anterior free-wall accessory pathway. The ablation catheter rests on the tricuspid annulus, thereby recording atrial and ventricular activation. The first beat is not preexcited and separate atrial and ventricular electrograms are recorded. The second and third beats are preexcited by a surface electrocardiogram. These beats record continuous electrical activity from the AB catheter and a prominent spike preceding surface ventricular activation by 45 msec. This spike is consistent with electrical activity from the accessory pathway itself. AP = accessory pathway; I, II, III, VI = surface electrocardiogram leads; AB = ablation catheter located on the anterior right-ventricular free wall near the tricuspid annulus; HBI and HB2 = His bundle catheter; S = pacing stimulus; A = atrial electrogram; V = ventricular electrogram; and H = His bundle recordings.
interruption of either the ante grade or retrograde limb of the reentrant circuit. Radiofrequency ablation techniques have shown the rapidly conducting retrograde limb (fast pathway) and the slowly conducting antegrade limb (slow pathway) to be anatomically distinct and therefore amenable to selective injury.16 The area of fast pathway conduction is localized proximal to the catheter position recording the largest His bundle potential in the right-anteroseptal A V junction. Radiofrequency lesions delivered to this area typically terminate AV nodal reentry by the elimination of dual AV nodal physiology and/or retrograde A V nodal conduction. Because this technique may result in marked P-R prolongation and up to a 10% to 20% risk of complete heart block, techniques for slow pathway ablation are now favored. 16 The area of slow pathway conduction is remote from the bundle of His and usually lies posteriorly between the coronary sinus os and the tricuspid valve annulus. Lesions may be delivered empirically to this anatomic region or may be directed toward catheter positions recording "slow pathway" potentials during sinus rhythm. 17.18 These potentials are slurred low amplitude signals after the local atrial electrogram and may be dissociated from local atrial and ventricular activity during atrial pacing (Figure 7). Lesions delivered to this area typically eliminate dual AV nodal physiology with minimal or no alteration of antegrade or retrograde AV nodal conduction times and rarely produce heart block. 18 Ventricular Tachycardias. Large studies detailing the efficacy of RF A for ventricular tachyarrhythmias are not available. Because most common forms of vent ricular tachycardia are thought to be reentrant in nature, ablation sites are directed toward intraventricular
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Figure 5. Early retrograde atrial activation through a right-anterior free-wall accessory pathway in the same patient as in Figure 3. The first beat is non-preexcited sinus rhythm. The second and third beats are ventricularly paced and demonstrate a short ventricle-to-atrium conduction time of 35 msec as recorded from the AB catheter. I, II, III, V I = surface electrocardiogram leads; AB = ablation catheter located on the anterior right-ventricular free wall near the tricuspid annulus; HBI and HB2 = His bundle catheter; S = pacing stimulus; A = atrial electrogram; V = ventricular electrogram; and H = His bundle recordings.
catheter positions recording diastolic electrical activity during sinus rhythm or ventricular tachycardia (VT; zone of slow co'n duction), or positions from which ventricular pacing exactly reproduces the spontaneous VT morphology on a 12-lead electrocardiogram (Figure 8).19
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Figure 6. Loss of preexcitation during radio frequency energy delivery to a right posteroseptal accessory pathway. I, A VF, and VI = surface electrocardiogram leads; and CS prox, CS mid, and CS distal = proximal, mid, and distal coronary sinus electrograms, respectively. There is an abrupt loss of pre excitation on surface electrocardiograms (labelled) and a concomitant prolongation of atrial-to-ventricular activation times in all coronary sinus leads, reflecting the altered sequence of ventricular activation. October 1993 Volume 306 Number 4
Wood, Ellenbogen, and Stambler
Figure 7. Electrogram's and catheter positions recording A V nodal slow pathway potentials. Left: The third and fourth tracings from the top arise from HB and AB catheters, respectively. The arrow identifies the slow pathway potential after a large atrial electrogram. The slow potential is dissociated from the local atrial electrogram by a premature atrial-pacing stimulus. Right: Right anterior oblique view of catheter positions for slow pathway recording. Catheters from top to bottom are in His bundle position, coronary sinus, slow pathway ablation (arrow), and right ventricle. LRA = low right atrium; I, II, III, V 1 = surface electrocardiogram leads; AB = ablation catheter located on the anterior right-ventricular free wall near the tricuspid annulus; HBl and HB2 = His bundle catheter; S = pacing stimulus; A = atrial electrogram; V = ventricular electrogram; and H = His bundle recordings. Reproduced with permission from the American Heart Association from Hassaguirre et al. l8
"Pace mapping" and recording the earliest sites of ventricular activation during VT may identify sites of small reentrant circuits or foci of automatic ventricular tachycardias for ablation. Bundle-branch reentrant VT may be eliminated by a selective injury to the right bundle branch. 20 Atrial Oysrhythmias. Persistent atrial flutter has been eliminated by radio frequency energy delivery to areas of prolonged, fractionated electrical activity in the posterior right atrium, which presumably identifies the area of slow conduction in the reentrant circuit. 21 To date, reports of atrial flutter ablation are preliminary and suggest limited rates of success. Because atrial fibrillation involves multiple continuously changing electrical wave fronts throughout the atria, direct treatment of this dysrhythmia with RFA is not possible. Radiofrequency catheter ablation may, however, provide palliative control of the ventricular response to refractory atrial fibrillation by interrupting AV conduction at the level of the AV junction or His bundle. A ventricular pacemaker then is inserted to control the ventricular rate. Ectopic atrial tachycardias 22 and sinus node reentry have been treated successfully with RF A techniques (unpublished personal observations). Efficacy and Safety. The success rates for the treatment of most common forms of supraventricular tachycardias are remarkably high. In the first large series, reported by Jackman et al,23 164 (99%) of 166 patients had a successful ablation of accessory bypass THE AMERICAN JOURNAL OF THE MEDICAL SCIENCES
tract function. Subsequently, Calkins et aF4 have reported successful procedures in 94% of 250 patients with accessory pathways. Recurrence of accessory pathway function may occur in 7% to 9% ofpatients. 23 Success rates appear to be equally high for the treatment of AV nodal reentrant tachycardias; however, the rate of recurrence may be less. In an early report, Calkins et aF5 achieved the successful elimination of AV nodal reentrant tachycardias in 42 (95%) of 44 patients. Recently, Haissaguerre et aFs reported 100% success in 64 patients treated with the slow pathway approach. In this series, no recurrence of tachycardia was seen in up to 16 months of follow-up. No large series have been reported on the efficacy of RFA for ventricular tachycardias. Klein et al 26 successfully eliminated VT in 15 of 16 patients with structurally normal hearts. Small series suggest more limited efficacy in the treatment of VT complicating chronic coronary-artery disease. 27 In this setting, sustained VT for accurate mapping may not be tolerated hemodynamically, and the small lesions produced by radiofrequency techniques may lack the volumes to destroy
Figure 8. Right ventricular pace mapping in a patient with arrhythmogenic right ventricular dysplasia (ARVD). A: 12-lead electrocardiogram and rhythm strips of induced ventricular tachycardia in a 27 -year-old man with ARVD. B: Pacing from a catheter position in the anterolateral free wall near the right ventricular outflow tract exactly reproduces the ventricular tachycardia morphology in all leads.
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Radiofrequency Catheter Ablation
intramural or large reentrant circuits. For other dysrhythmias treated with RFA, only small series and case reports are available. Radiofrequency catheter ablation techniques have been performed on adults and children as young as 10 months. 28 An initial study of the financial aspects of RF A suggests that the procedure is cost-effective compared with surgical or long-term medical therapy. Kalbfleisch et al 29 estimated the cost of RF A techniques to be comparable with 2 years of medical therapy for poorly controlled supraventricular tachycardias. In our team's facility, the cost of an uncomplicated RF A procedure approaches $12,000 to $15,000. Complications and Safety. The procedural complication rate for RFA techniques is 2% to 4% in most large series. 23 ,24 Common to all RF A procedures are potential complications from vascular access (hematoma, bleeding, and thrombosis) and catheter manipulation. The latter may result in cardiac perforation and tamponade, aortic valve trauma, or catheter misplacement into the coronary arteries. 16 These more serious complications are rare, however. Serum creatinine kinase levels may rise after RF A but infrequently exceed normal limits. 23 ,24 The advent of slow pathway modification for AV nodal reentry has reduced the risk of heart block from 10% to 20% in early experience to 0% in a recent large series. 18 Complete AV block also may complicate the ablation of parahisian accessory pathways. Ventricular function is not altered after RF A procedures but trauma to the aortic and mitral valves has been reported. 3D Radiation exposure to both patients and medical staff may be significant (7.26 rem and 99 mrem, respectively) during a prolonged fluoroscopy sometimes required for accurate catheter placement. 31 The long-term effects are not known; however, abbreviated approaches to the procedure, the single catheter technique, pulsed fluoroscopy, the development of improved catheter and mapping technology, and growing operator experience all may combine to dramatically limit future radiation exposure. 32,33 Indications. For the management of various supraventricular tachycardias, RFA may be indicated in the setting of: 1) life-threatening dysrhythmias (eg, a rapid ventricular response to atrial fibrillation in patients with accessory pathways), 2) medically refractory dysrhythmias, 3) drug intolerance, 4) medical noncompliance, or 5) initial diagnostic electrophysiologic study. For patients with favorable responses to medical therapy, for extremely intermittent and well-tolerated dysrhythmias, and for elderly patients, the potential risks and benefits must seriously be considered. Pregnancy may be the only absolute contraindication to RF A procedures, given the potential for significant radiation exposure. Indications for ablation of ventricular tachyarrhythmias are much less clear. Patients with structurally normal hearts and symptomatic VT may be most amenable. 26 The role of RF A in treatment of VT as-
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sociated with chronic coronary-artery disease is under investigation. At centers experienced with the technique, RF A may be considered for those with drug refractory incessant VT or recurrent hemodynamically stable VT. Future Directions. The limited lesion volumes obtainable with RFA contribute to the safety of the technique, but also may limit efficacy in the elimination of intramural or large diffuse reentry circuits. Alternate energy sources, such as laser, microwave, ultrasound, and cryoablation techniques, may prove necessary for some applications and are under development. Current radiofrequency ablation catheter technology is in its infancy, and a continued evolution to include tissuetemperature monitoring capabilities, improved torque control, and enhanced steerability should follow. Finally, RFA has considerably advanced the understanding of many tachyarrhythmias, most notably AV nodal reentry. Further definition of pathophysiologic mechanisms should enable more refined and efficient approaches to tachycardia mapping and ablation. References 1. Gallagher JJ, Svenson RH, Kasell JH, German LD, Bardy GH, Broughton A, Critelli G: Catheter technique for closed-chest ablation of the atrioventricular conduction system. N Engl J Med 306:194-200,1982. 2. Lemery R, Leung TK, Lavallee E, Girard A, Talajic M, Ray D, Montpetit M: In vitro and in vivo effects within the coronary sinus of nonarcing and arcing shocks using a new system of lowenergy DC ablation. Circulation 83:279-293, 1991. 3. Boyd EGCA, Holt PM: The biophysics of catheter ablation techniques. Journal of Electrophysiology 1:62-77, 1987. 4. Warin JF, Haissaguerre M, D'lvernois C, Metager PC, Montserrat P: Catheter ablation of accessory pathways: Technique and results in 248 patients. PACE 13:1609-1614, 1990. 5. Abott JA, Eldar M, Segar JJ: Noninvasive assessment of myocardial function following attempted catheter ablation of ventricular tachycardia (abstract). Circulation 72:111·388, 1985. 6. Borggrefe M, Budde T, Podczeck A, Breithardt G: High frequency alternating current ablation of an accessory pathway in humans. J Am Coli CardioI10:576-582, 1987. 7. Organ LW: Electrophysiologic principles of radiofrequency lesion making. Applied Neurophysiology 39:69-76, 1976/77. 8. Haines DE, Watson DD, Verow AF: Electrode radius predicts lesion radius during radiofrequency energy heating. Circ Res 67: 124-129, 1990. 9. Haines DE, Watson DD: Tissue heating during radiofrequency catheter ablation: A thermodynamic model and observations in isolated perfused and superficial canine right ventricular free wall. PACE 12:962-976, 1989. 10. Haines DE, Verow AF: Observations on electrode tissue interface temperature and effect on electrical impedance during radiofrequency ablation of ventricular myocardium. Circulation 82:10341038,1990. 11. Hoyt RH, Huang SK, Marcus FI, Odell RS: Factors influencing· trans-catheter radio frequency ablation of the myocardium. Journal of Applied Cardiology 1:469-486, 1986. 12. Haines DE: Determinants of lesion site during radio frequency catheter ablation: The role of electrode-tissue contact pressure and duration of energy delivery. Journal of Cardiovascular Electrophysiology 2:509-515, 1991. 13. Huang SK, Bharati S, Lev M, Marcus FI: Electrophysiologic and histologic observations of chronic atrioventricular block induced by closed-chest catheter desiccation with radiofrequency energy. PACE 10:805-816, 1987. October 1993 Volume 306 Number 4
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14. Calkins H, Kim Y, Schmaltz S, Sousa J, EI-Atassi R, Leon A, Kadish A, Langberg JL, Morady F: Electrogram criteria for identification of appropriate target sites for radiofrequency catheter ablation of accessory atrioventricular connections. Circulation 85:565-573, 1992. 15. Silka MJ, Kron J, Halperin BD, Griffith K, Crandall B, Oliver RP, Walance CG, McAnulty JH: Analysis of local electrogram characteristics correlated with successful radiofrequency catheter ablation of accessory atrioventricular pathways. PACE 15:10001007,1992. 16. Jazayeri MR, Hempe SL, Sra JS, Dhala AA, Blanck Z, Deshpande SS, Avitall B, Krumm DP, Gilbert CJ, Akhtar M: Selective transcatheter ablation of the fast and slow pathways using radiofrequency energy in patients with atrioventricular nodal reentrant tachycardia. Circulation 85:1318-1328, 1992. 17. Kay GN, Epstein AE, Dailey SM, Plumb VJ: Selective radiofrequency ablation of the slow pathway for the treatment of atrioventricular nodal reentrant tachycardia. Circulation 85: 1675-1688, 1992. 18. Haissaguerre M, Gaito F, Fischer B, Commenges D, Montserrat P, D'lvernois C, Lemetayer P, Warin J-F: Elimination of atrioventricular nodal reentrant tachycardia using discrete slow potentials to guide application of radiofrequency energy. Circulation 85:2162-2175, 1992. 19. Kuck KH, Schluter M, Geigh M, Siebels J: Successful catheter ablation of human ventricular tachycardia with radiofrequency current guided by an endocardial map of the area of slow conduction. PACE 14:1060-1071, 1991. 20. Langberg JL, Dessai J, Dullet N, Scheinman MM: Treatment of macro reentrant ventricular tachycardia with radiofrequency ablation of the right bundle branch. Am J Cardiol63: 1010-1013, 1989. 21. Feld G, Chen P-S, Fleck P, Boyce K: Radiofrequency catheter ablation oftype I atrial flutter in humans (abstract). PACE 15: 548,1992. 22. Ehlert FA, Goldberger JJ, Deal BT, Benson DW, Kadish AH: Radiofrequency current catheter ablation for drug refractory automatic supraventricular tachycardia (abstract). PACE 15:549, 1992. 23. Jackman WM, Wang X, Friday KJ, Roman CA, Moulton KP, Beckman KJ, McClelland JH, Twidale N, Hazlitt HA, Prior MI,
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Margolis PD, Colame JD, Overholt ED, Lazzara R: Catheter ablation of accessory atrioventricular pathways (Wolff-Parkinson-White Syndrome) by radiofrequency current. N Engl J Med 324:1605-1611, 1991. Calkins H, Langberg J, Sousa J, EI-Atassi R, Leon A, Kow W, Kalbfeisch S, Morady F: Radiofrequency catheter ablation of accessory atrioventricular connections in 250 patients. Circulation 85:1337-1346, 1992. Calkins H, Sousa J, EI-Atassi R, Rosenheck S, DeBuiteir M, Kow WH, Kadish AH, Langberg J, Morady F: Diagnosis and cure of the W olff-Parkinson-White syndrome or paroxysmal supraventricular tachycardias during a single electrophysiologic test. N Engl J Med 324:1612-1618, 1991. Klein LS, Shih H-T, Hackett K, Zipes D, Miles WM: Radiofrequency catheter ablation of ventricular tachycardia in patients without structural heart disease. Circulation 85:1666-1674, 1992. Gursoy S, Schlutter M, Chiladalsis I, Kuck K-H: Radiofrequency energy ablation of sustained monomorphic ventricular tachycardia in patients with underlying heart disease: Which site to ablate (abstract)? PACE 15:549, 1992. Van Hare GF, Lesh MD, Scheinman M, Langberg JJ: Percutaneous radio frequency catheter ablation for supraventricular arrhythmias in children. JAm Coll Cardiol17:1613-1620, 1991. Kalbfeisch SJ, Calkins H, Langberg JJ, EI-Atassi R, Leon A, Borganelli M, Morady F: Comparison of the cost of radiofrequency catheter modification of the atrioventricular node and medical therapy for drug-refractory atrioventricular node reentrant tachycardia. JAm Coll Cardiol19:1583-1587, 1992. Minich LL, Sider AR, Dick M: Doppler detection of valvular regurgitation after radiofrequency ablation of accessory connections. Am J Cardiol70:116-117, 1992. Calkins H, Niklason L, Sousa J, EI-Atassi R, Langberg J, Morady F: Radiation exposure during radiofrequency catheter ablation of accessory atrioventricular connections. Circulation 84:23762382, 1991. Kuck K-H, Schluter M: Single-catheter approach to radiofrequency current ablation of left sided accessory pathways in patients with Wolff Parkinson White Syndrome. Circulation 84: 2366-2375, 1991. Leatter RA, Leitch JW, Klein GJ, Guiradon GM, Yee R, Kim YH: Radiofrequency catheter ablation of accessory pathways: A learning experience. Am J Cardiol68:1651-1655.
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KENNETH ELLENBOGEN, MD,
ABSTRACT: Radiofrequency catheter ablation techniques allow for safe and highly effective curative therapy of a variety of cardiac dysrhythmias. The technique involves the delivery of a high-frequency, alternating electrical current through an intravascular catheter to sites of arrhythmogenic myocardium. This current induces resistive electrical heating of the tissue, resulting in discrete areas of myocardial destruction through coagulation and desiccation. Dysrhythmias most commonly treated with these techniques are atrioventricular nodal reentry and tachycardias related to accessory atrioventricular bypass tracts. For these dysrhythmias, success rates of 90% to 95% are achievable with a low (2% to 4%) risk of complications. Radiofrequency catheter ablation techniques also have been used to treat ventricular tachycardias, atrial flutter, ectopic atrial tachycardia, and sinus node reentry, albeit with lower success rates. These techniques are still evolving, alternate energy sources (such as microwave and laser) and improved catheter technology should enhance the technique's safety and efficacy for a wider range of dysrhythmias. KEY INDEXING TERMS: Dysrhythmias; Cardiac tachyarrhythmias; Radiofrequency catheter ablation. [Am J Med Sci 1993;306(4):241-247.]
R
ecently developed radiofrequency catheter ablation (RFA) techniques provide curative therapy for many forms of supraventricular and ventricular tachyarrhythmias. These techniques currently are revolutionizing the field of cardiac electrophysiology similar to the impact of percutaneous transluminal coronary angioplasty on the specialty of cardiac catheterization. Using percutaneous catheter techniques to From the Medical College of Virginia, Richmond, Virginia, and McGuire Veterans Administration Hospitals, Richmond, Virginia. Correspondence: Mark Wood, MD, Co-Director, Cardiac Electrophysiology, Department of Cardiac Electrophysiology, Medical College of Virginia, MCV Box 53, Richmond, VA 232.98. THE AMERICAN JOURNAL OF THE MEDICAL SCIENCES
BRUCE STAMBLER, MD
selectively destroy arrhythmogenic myocardial tissue, RFA techniques provide safe, well-tolerated, and costeffective therapeutic results previously obtainable only with cardiac surgery. This paper reviews the history, fundamental principles, and clinical aspects of RF A procedures. History
Medical management of common forms of paroxysmal supraventricular tachycardias is rarely totally satisfactory because of clinical arrhythmia recurrences, intolerance to drug therapy, and difficulties with medical compliance. Previously, the only alternatives to drug therapy included surgical obliteration of arrhythmogenic myocardium or possibly the use of antitachycardia pacemaker systems. For most patients, the cost, risks, and morbidity associated with these surgical approaches were prohibitive. In 1982, Gallagher 1 first reported the use of transluminal direct-current catheter ablation techniques to interrupt atrioventricular (AV) nodal conduction in nine patients with debilitating supraventricular tachycardias. The direct current technique involves delivery of 50 to 400 joule shocks from a standard external defibrillator between a large surface skin electrode and the ablation catheter tip positioned in proximity to the targeted myocardium. The high-energy impulse damages myocardium by the production of intense heat (temperature to 1,700° C), electrical fields, and barotrauma (up to 11 atmospheres).2,3 Although highly effective in abolishing AV nodal and accessory AV pathway function, the diffuse nature of the myocardial injury is unsuitable for controlled modification of A V nodal conduction and carries a significant risk of global depression of left-ventricular function, myocardial rupture and tamponade, ventricular tachyarrhythmias, and sudden death after the procedure. 4,5 The search for safer and more controllable energy sources drew from 70 years of surgical experience with radiofrequency energy, first introduced as electrosurgical cautery in 1911 and later adapted for focal lesion production in neurosurgical and oncologic procedures. In 1987, Borggrefe6 first reported the successful use of catheter-directed radiofrequency energy to abolish accessory pathway function in humans. Subsequently, large clinical studies have documented the safety and
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efficacy of the RFA technique for a variety of cardiac arrhythmias. Biophysics
The radiofrequency energy used in catheter ablation techniques is a high frequency alternating electrical current with frequency in the range of 300 kHz to 1.5 MHz. When this current is passed through biologic tissues between low resistance electrodes, resistive heating occurs within the tissue because of the tissue's intrinsic electrical impedance. Depending upon the current intensity and electrical waveform, three electrosurgical effects may result: 1) electrosurgical cutting-vaporization of tissue by intense local heat production and abrupt expansive steam formation within the tissue, 2) electro surgical cautery (fulguration)tissue burning and charring from intense local heat production causing dense eschar formation, or 3) electrosurgical desiccation-tissue destruction by coagulation and dehydration as intra- and extracellular water is driven away by less intense tissue heating. Radiofrequency catheter ablation -techniques use unmodulated sinusoidal waveforms of 300 to 750 kHz to produce discrete zones of electrosurgical desiccation around a catheter electrode contacting the cardiac endocardium. The high electrical frequencies prevent direct electrical stimulation and possibly fibrillation of the myocardium. The heat generated within the tissue is directly proportional to the square of the current intensity and duration of current application and inversely proportional to the 4th power of the distance from the active electrode. 7 Using conventional electrodes (3 to 4 mm diameter tip), the volume of myocardium undergoing active, resistive heating is small and confined to a radius of less than 1 mm around the electrode surface. s Passive heat conduction away from the zone of active resistive heating extends the volume of myocardial damage. Myocardial tissue temperatures above 46 to 49 0 C are required for permanent lesion formation. s Tissue temperature declines in inverse proportion to the distance from the electrode. 9 For any given electrode diameter, there exists a theoretical maximum lesion size. 1o This results from a maximum achievable electrode-tissue interface temperature of 100 0 C, above which tissue charring and coagulum formation raise the electrical impedance and limit further current flow. For 6F catheter tip electrodes, the maximum lesion depth is 7.5 mm. 10 Other factors influencing lesion size are current intensity and duration, electrode-tissue contact pressure, convective heat loss from local blood flow, and the tissue compositionY The half-time for lesion generation under stable in vitro conditions is approximately 7 to 9 seconds. 12 Histologically, cardiac radiofrequency lesions are well-demarcated, ovoid or spherical zones of central coagulation necrosis with a peripheral rim of hemorrhagic necrosis and granulation tissue. 13
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Procedures
Preparation for RF A is similar to that for other invasive percutaneous vascular procedures. The patient fasts overnight but is well-hydrated. All antiarrhythmic medications are discontinued five half-lives before the procedure to permit induction of the tachycardia. For the initial evaluation of supraventricular tachycardias, electrode catheters are positioned in the right atrium, right ventricul~r apex, and right ventricular inflow region to record the His bundle potential and in the coronary sinus to map left-atrial and left-ventricular activation sequences. Ablation of ventricular foci may require as few as one ventricular catheter in addition to the ablation catheter. The patient generally is heparinized for the duration of the procedure. Once electrophysiologic studies define the mechanism and site of arrhythmogenesis, the ablation catheter is positioned under fluoroscopic and electrocardiographic guidance to the desired location. The ablation catheter typically is 6 to 7F in diameter, with steerable tips to allow maximal control (Figure 1). Once positioned, radio frequency energy is delivered between the catheter tip and a large patch electrode on the patient's chest. Current delivery is terminated after 5 to 10 seconds if the desired electrophysiologic effect is not observed and the catheter is then repositioned. Should therapeutic results occur, the current is continued for a total of 20 to 60 seconds to produce a maximal lesion. Radiofrequency current generally is produced using standard neurosurgical lesion generators (Figures 1); however, generators designed specifically for ablation of cardiac arrhythmias are now available. Generally, energy deliveries of 20 to 50 watts (40 to 60 V, 400 to 600 rnA) are used, depending on the site of application.
Figure 1. Radiofrequency lesion generator suitable for neurosurgical and cardiologic applications. The large surface patch electrode is shown to the left and the steerable radiofrequency ablation catheter to the right. The steering mechanism deflects the catheter tip through 270 0 from the catheter's long axis. October 1993 Volume 306 Number 4
Wood, Ellenbogen, and Stambler
Table 1. Cardiac Arrhythmias Treated by Radiofrequency Catheter Ablation AV nodal reentry AV reciprocating tachycardias Wolff-Parkinson-White syndrome Concealed accessory bypass tracts Mahaim type AV bypass tracts Ventricular tachycardias Associated with chronic CAD Right ventricular outflow tract tachycardia Idiopathic monomorphic VT Bundle branch reentrant VT Ectopic atrial tachycardia Atrial flutter Sinus node reentrant tachycardia
Cardiac dysrhythmias treated with radiofrequency catheter ablation techniques. A V = atrioventricular; CAD = coronary artery disease; VT = ventricular tachycardia.
Treatment of Specific Arrhythmias. Arrhythmias successfully treated with RFA techniques are listed in Table 1. By far, tachyarrhythmias associated with AV nodal reentry and accessory AV bypass tracts are the most commonly treated. For reentrant tachyarrhythmias, RF A techniques require localization and interruption of a critical limb of the reentrant circuit. For automatic rhythms or those believed to involve very small reentrant circuits, RF A lesions may be directed toward the sites of earliest myocardial activation during the tachycardias. Accessory Atrioventricular Bypass Tracts. With demonstrable ante grade accessory pathway conduction (Wolff-Parkinson-White syndrome), catheter mapping of the earliest site of ventricular activation along the AV annulus defines the ventricular insertion of the pathway. For concealed accessory pathways or during orthodromic reciprocating tachycardia, the site of earliest retrograde atrial activation or shortest ventricleto-atrial conduction times are sought to approximate the atrial insertion. For left-sided accessory pathways, the mitral valve annulus is accessed by catheter positioning retrogradely across the aortic valve or transseptally from the right to left atria. Right-sided pathways are approached transvenously, either from the superior or inferior vena cavae. The ablation catheter frequently is wedged beneath the AV valve against the annulus for stability (Figure 2). Electrocardiographic criteria predicting effective catheter positions include local ventricular electrograms preceding surface QRS complex during antegrade preexcitation or local atrial-to-ventricular conduction times up to 40 msec (Figure 3), recording electrical activity from the pathway itself (Figure 4), and electrogram stability and local ventricular-to-atrial conduction times ofless than 60 msec during retrograde accessory pathway conduction (Figure 5).14,15 Successful energy delivery to these sites results in a loss of preexcitation on a surface electrocardiogram (Figure THE AMERICAN JOURNAL OF THE MEDICAL SCIENCES
Figure 2. Right anterior oblique 30° projection of intracardiac catheter positions for left lateral accessory pathway ablation. Catheters are located in the right atrium (RA), His position (HS), right ventricle (RV), and coronary sinus (CS). The ablation catheter (AB) crosses the aortic valve retrogradely to rest beneath the mitral valve annulus in proximity to the middle poles of the CS catheter.
6), the termination of reciprocating tachycardia, and the abolition of retrograde accessory pathway conduction. Atrioventricular Nodal Reentry. Atrioventricular nodal reentrant tachycardias may be eliminated by the
Figure 3. Intracardiac electro grams demonstrating ventricular activation before preexcited surface electrocardiogram QRS (delta wave) onset in a patient with a right-anterior free-wall accessory pathway. During atrial pacing the first two beats are preexcited. Ventricular activation precedes the surface delta wave by 40 msec on the AB catheter. Ventricular preexcitation is spontaneously lost on the third paced beat. The AB catheter now records ventricular activation 40 msec after QRS onset. The atrial-ventricular time of 230 msec with a clear His bundle recording is now visible from the His catheter recordings. I, II, III, VI = surface electrocardiogram leads; AB = ablation catheter located on the anterior right-ventricular free wall near the tricuspid annulus; HBI and HB2 = His bundle catheter; S = pacing stimulus; A = atrial electrogram; V = ventricular electrogram; and H = His bundle recordings.
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Radiofrequency Catheter Ablation
II n m V,
A
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/AP
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Figure 4. Surface electrocardiogram and ablation catheter recordings from a second patient with a right-anterior free-wall accessory pathway. The ablation catheter rests on the tricuspid annulus, thereby recording atrial and ventricular activation. The first beat is not preexcited and separate atrial and ventricular electrograms are recorded. The second and third beats are preexcited by a surface electrocardiogram. These beats record continuous electrical activity from the AB catheter and a prominent spike preceding surface ventricular activation by 45 msec. This spike is consistent with electrical activity from the accessory pathway itself. AP = accessory pathway; I, II, III, VI = surface electrocardiogram leads; AB = ablation catheter located on the anterior right-ventricular free wall near the tricuspid annulus; HBI and HB2 = His bundle catheter; S = pacing stimulus; A = atrial electrogram; V = ventricular electrogram; and H = His bundle recordings.
interruption of either the ante grade or retrograde limb of the reentrant circuit. Radiofrequency ablation techniques have shown the rapidly conducting retrograde limb (fast pathway) and the slowly conducting antegrade limb (slow pathway) to be anatomically distinct and therefore amenable to selective injury.16 The area of fast pathway conduction is localized proximal to the catheter position recording the largest His bundle potential in the right-anteroseptal A V junction. Radiofrequency lesions delivered to this area typically terminate AV nodal reentry by the elimination of dual AV nodal physiology and/or retrograde A V nodal conduction. Because this technique may result in marked P-R prolongation and up to a 10% to 20% risk of complete heart block, techniques for slow pathway ablation are now favored. 16 The area of slow pathway conduction is remote from the bundle of His and usually lies posteriorly between the coronary sinus os and the tricuspid valve annulus. Lesions may be delivered empirically to this anatomic region or may be directed toward catheter positions recording "slow pathway" potentials during sinus rhythm. 17.18 These potentials are slurred low amplitude signals after the local atrial electrogram and may be dissociated from local atrial and ventricular activity during atrial pacing (Figure 7). Lesions delivered to this area typically eliminate dual AV nodal physiology with minimal or no alteration of antegrade or retrograde AV nodal conduction times and rarely produce heart block. 18 Ventricular Tachycardias. Large studies detailing the efficacy of RF A for ventricular tachyarrhythmias are not available. Because most common forms of vent ricular tachycardia are thought to be reentrant in nature, ablation sites are directed toward intraventricular
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Figure 5. Early retrograde atrial activation through a right-anterior free-wall accessory pathway in the same patient as in Figure 3. The first beat is non-preexcited sinus rhythm. The second and third beats are ventricularly paced and demonstrate a short ventricle-to-atrium conduction time of 35 msec as recorded from the AB catheter. I, II, III, V I = surface electrocardiogram leads; AB = ablation catheter located on the anterior right-ventricular free wall near the tricuspid annulus; HBI and HB2 = His bundle catheter; S = pacing stimulus; A = atrial electrogram; V = ventricular electrogram; and H = His bundle recordings.
catheter positions recording diastolic electrical activity during sinus rhythm or ventricular tachycardia (VT; zone of slow co'n duction), or positions from which ventricular pacing exactly reproduces the spontaneous VT morphology on a 12-lead electrocardiogram (Figure 8).19
AVF
CS PROX
CSMID
II
\ CS DISTAL
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I RVA
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Figure 6. Loss of preexcitation during radio frequency energy delivery to a right posteroseptal accessory pathway. I, A VF, and VI = surface electrocardiogram leads; and CS prox, CS mid, and CS distal = proximal, mid, and distal coronary sinus electrograms, respectively. There is an abrupt loss of pre excitation on surface electrocardiograms (labelled) and a concomitant prolongation of atrial-to-ventricular activation times in all coronary sinus leads, reflecting the altered sequence of ventricular activation. October 1993 Volume 306 Number 4
Wood, Ellenbogen, and Stambler
Figure 7. Electrogram's and catheter positions recording A V nodal slow pathway potentials. Left: The third and fourth tracings from the top arise from HB and AB catheters, respectively. The arrow identifies the slow pathway potential after a large atrial electrogram. The slow potential is dissociated from the local atrial electrogram by a premature atrial-pacing stimulus. Right: Right anterior oblique view of catheter positions for slow pathway recording. Catheters from top to bottom are in His bundle position, coronary sinus, slow pathway ablation (arrow), and right ventricle. LRA = low right atrium; I, II, III, V 1 = surface electrocardiogram leads; AB = ablation catheter located on the anterior right-ventricular free wall near the tricuspid annulus; HBl and HB2 = His bundle catheter; S = pacing stimulus; A = atrial electrogram; V = ventricular electrogram; and H = His bundle recordings. Reproduced with permission from the American Heart Association from Hassaguirre et al. l8
"Pace mapping" and recording the earliest sites of ventricular activation during VT may identify sites of small reentrant circuits or foci of automatic ventricular tachycardias for ablation. Bundle-branch reentrant VT may be eliminated by a selective injury to the right bundle branch. 20 Atrial Oysrhythmias. Persistent atrial flutter has been eliminated by radio frequency energy delivery to areas of prolonged, fractionated electrical activity in the posterior right atrium, which presumably identifies the area of slow conduction in the reentrant circuit. 21 To date, reports of atrial flutter ablation are preliminary and suggest limited rates of success. Because atrial fibrillation involves multiple continuously changing electrical wave fronts throughout the atria, direct treatment of this dysrhythmia with RFA is not possible. Radiofrequency catheter ablation may, however, provide palliative control of the ventricular response to refractory atrial fibrillation by interrupting AV conduction at the level of the AV junction or His bundle. A ventricular pacemaker then is inserted to control the ventricular rate. Ectopic atrial tachycardias 22 and sinus node reentry have been treated successfully with RF A techniques (unpublished personal observations). Efficacy and Safety. The success rates for the treatment of most common forms of supraventricular tachycardias are remarkably high. In the first large series, reported by Jackman et al,23 164 (99%) of 166 patients had a successful ablation of accessory bypass THE AMERICAN JOURNAL OF THE MEDICAL SCIENCES
tract function. Subsequently, Calkins et aF4 have reported successful procedures in 94% of 250 patients with accessory pathways. Recurrence of accessory pathway function may occur in 7% to 9% ofpatients. 23 Success rates appear to be equally high for the treatment of AV nodal reentrant tachycardias; however, the rate of recurrence may be less. In an early report, Calkins et aF5 achieved the successful elimination of AV nodal reentrant tachycardias in 42 (95%) of 44 patients. Recently, Haissaguerre et aFs reported 100% success in 64 patients treated with the slow pathway approach. In this series, no recurrence of tachycardia was seen in up to 16 months of follow-up. No large series have been reported on the efficacy of RFA for ventricular tachycardias. Klein et al 26 successfully eliminated VT in 15 of 16 patients with structurally normal hearts. Small series suggest more limited efficacy in the treatment of VT complicating chronic coronary-artery disease. 27 In this setting, sustained VT for accurate mapping may not be tolerated hemodynamically, and the small lesions produced by radiofrequency techniques may lack the volumes to destroy
Figure 8. Right ventricular pace mapping in a patient with arrhythmogenic right ventricular dysplasia (ARVD). A: 12-lead electrocardiogram and rhythm strips of induced ventricular tachycardia in a 27 -year-old man with ARVD. B: Pacing from a catheter position in the anterolateral free wall near the right ventricular outflow tract exactly reproduces the ventricular tachycardia morphology in all leads.
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Radiofrequency Catheter Ablation
intramural or large reentrant circuits. For other dysrhythmias treated with RFA, only small series and case reports are available. Radiofrequency catheter ablation techniques have been performed on adults and children as young as 10 months. 28 An initial study of the financial aspects of RF A suggests that the procedure is cost-effective compared with surgical or long-term medical therapy. Kalbfleisch et al 29 estimated the cost of RF A techniques to be comparable with 2 years of medical therapy for poorly controlled supraventricular tachycardias. In our team's facility, the cost of an uncomplicated RF A procedure approaches $12,000 to $15,000. Complications and Safety. The procedural complication rate for RFA techniques is 2% to 4% in most large series. 23 ,24 Common to all RF A procedures are potential complications from vascular access (hematoma, bleeding, and thrombosis) and catheter manipulation. The latter may result in cardiac perforation and tamponade, aortic valve trauma, or catheter misplacement into the coronary arteries. 16 These more serious complications are rare, however. Serum creatinine kinase levels may rise after RF A but infrequently exceed normal limits. 23 ,24 The advent of slow pathway modification for AV nodal reentry has reduced the risk of heart block from 10% to 20% in early experience to 0% in a recent large series. 18 Complete AV block also may complicate the ablation of parahisian accessory pathways. Ventricular function is not altered after RF A procedures but trauma to the aortic and mitral valves has been reported. 3D Radiation exposure to both patients and medical staff may be significant (7.26 rem and 99 mrem, respectively) during a prolonged fluoroscopy sometimes required for accurate catheter placement. 31 The long-term effects are not known; however, abbreviated approaches to the procedure, the single catheter technique, pulsed fluoroscopy, the development of improved catheter and mapping technology, and growing operator experience all may combine to dramatically limit future radiation exposure. 32,33 Indications. For the management of various supraventricular tachycardias, RFA may be indicated in the setting of: 1) life-threatening dysrhythmias (eg, a rapid ventricular response to atrial fibrillation in patients with accessory pathways), 2) medically refractory dysrhythmias, 3) drug intolerance, 4) medical noncompliance, or 5) initial diagnostic electrophysiologic study. For patients with favorable responses to medical therapy, for extremely intermittent and well-tolerated dysrhythmias, and for elderly patients, the potential risks and benefits must seriously be considered. Pregnancy may be the only absolute contraindication to RF A procedures, given the potential for significant radiation exposure. Indications for ablation of ventricular tachyarrhythmias are much less clear. Patients with structurally normal hearts and symptomatic VT may be most amenable. 26 The role of RF A in treatment of VT as-
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sociated with chronic coronary-artery disease is under investigation. At centers experienced with the technique, RF A may be considered for those with drug refractory incessant VT or recurrent hemodynamically stable VT. Future Directions. The limited lesion volumes obtainable with RFA contribute to the safety of the technique, but also may limit efficacy in the elimination of intramural or large diffuse reentry circuits. Alternate energy sources, such as laser, microwave, ultrasound, and cryoablation techniques, may prove necessary for some applications and are under development. Current radiofrequency ablation catheter technology is in its infancy, and a continued evolution to include tissuetemperature monitoring capabilities, improved torque control, and enhanced steerability should follow. Finally, RFA has considerably advanced the understanding of many tachyarrhythmias, most notably AV nodal reentry. Further definition of pathophysiologic mechanisms should enable more refined and efficient approaches to tachycardia mapping and ablation. References 1. Gallagher JJ, Svenson RH, Kasell JH, German LD, Bardy GH, Broughton A, Critelli G: Catheter technique for closed-chest ablation of the atrioventricular conduction system. N Engl J Med 306:194-200,1982. 2. Lemery R, Leung TK, Lavallee E, Girard A, Talajic M, Ray D, Montpetit M: In vitro and in vivo effects within the coronary sinus of nonarcing and arcing shocks using a new system of lowenergy DC ablation. Circulation 83:279-293, 1991. 3. Boyd EGCA, Holt PM: The biophysics of catheter ablation techniques. Journal of Electrophysiology 1:62-77, 1987. 4. Warin JF, Haissaguerre M, D'lvernois C, Metager PC, Montserrat P: Catheter ablation of accessory pathways: Technique and results in 248 patients. PACE 13:1609-1614, 1990. 5. Abott JA, Eldar M, Segar JJ: Noninvasive assessment of myocardial function following attempted catheter ablation of ventricular tachycardia (abstract). Circulation 72:111·388, 1985. 6. Borggrefe M, Budde T, Podczeck A, Breithardt G: High frequency alternating current ablation of an accessory pathway in humans. J Am Coli CardioI10:576-582, 1987. 7. Organ LW: Electrophysiologic principles of radiofrequency lesion making. Applied Neurophysiology 39:69-76, 1976/77. 8. Haines DE, Watson DD, Verow AF: Electrode radius predicts lesion radius during radiofrequency energy heating. Circ Res 67: 124-129, 1990. 9. Haines DE, Watson DD: Tissue heating during radiofrequency catheter ablation: A thermodynamic model and observations in isolated perfused and superficial canine right ventricular free wall. PACE 12:962-976, 1989. 10. Haines DE, Verow AF: Observations on electrode tissue interface temperature and effect on electrical impedance during radiofrequency ablation of ventricular myocardium. Circulation 82:10341038,1990. 11. Hoyt RH, Huang SK, Marcus FI, Odell RS: Factors influencing· trans-catheter radio frequency ablation of the myocardium. Journal of Applied Cardiology 1:469-486, 1986. 12. Haines DE: Determinants of lesion site during radio frequency catheter ablation: The role of electrode-tissue contact pressure and duration of energy delivery. Journal of Cardiovascular Electrophysiology 2:509-515, 1991. 13. Huang SK, Bharati S, Lev M, Marcus FI: Electrophysiologic and histologic observations of chronic atrioventricular block induced by closed-chest catheter desiccation with radiofrequency energy. PACE 10:805-816, 1987. October 1993 Volume 306 Number 4
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14. Calkins H, Kim Y, Schmaltz S, Sousa J, EI-Atassi R, Leon A, Kadish A, Langberg JL, Morady F: Electrogram criteria for identification of appropriate target sites for radiofrequency catheter ablation of accessory atrioventricular connections. Circulation 85:565-573, 1992. 15. Silka MJ, Kron J, Halperin BD, Griffith K, Crandall B, Oliver RP, Walance CG, McAnulty JH: Analysis of local electrogram characteristics correlated with successful radiofrequency catheter ablation of accessory atrioventricular pathways. PACE 15:10001007,1992. 16. Jazayeri MR, Hempe SL, Sra JS, Dhala AA, Blanck Z, Deshpande SS, Avitall B, Krumm DP, Gilbert CJ, Akhtar M: Selective transcatheter ablation of the fast and slow pathways using radiofrequency energy in patients with atrioventricular nodal reentrant tachycardia. Circulation 85:1318-1328, 1992. 17. Kay GN, Epstein AE, Dailey SM, Plumb VJ: Selective radiofrequency ablation of the slow pathway for the treatment of atrioventricular nodal reentrant tachycardia. Circulation 85: 1675-1688, 1992. 18. Haissaguerre M, Gaito F, Fischer B, Commenges D, Montserrat P, D'lvernois C, Lemetayer P, Warin J-F: Elimination of atrioventricular nodal reentrant tachycardia using discrete slow potentials to guide application of radiofrequency energy. Circulation 85:2162-2175, 1992. 19. Kuck KH, Schluter M, Geigh M, Siebels J: Successful catheter ablation of human ventricular tachycardia with radiofrequency current guided by an endocardial map of the area of slow conduction. PACE 14:1060-1071, 1991. 20. Langberg JL, Dessai J, Dullet N, Scheinman MM: Treatment of macro reentrant ventricular tachycardia with radiofrequency ablation of the right bundle branch. Am J Cardiol63: 1010-1013, 1989. 21. Feld G, Chen P-S, Fleck P, Boyce K: Radiofrequency catheter ablation oftype I atrial flutter in humans (abstract). PACE 15: 548,1992. 22. Ehlert FA, Goldberger JJ, Deal BT, Benson DW, Kadish AH: Radiofrequency current catheter ablation for drug refractory automatic supraventricular tachycardia (abstract). PACE 15:549, 1992. 23. Jackman WM, Wang X, Friday KJ, Roman CA, Moulton KP, Beckman KJ, McClelland JH, Twidale N, Hazlitt HA, Prior MI,
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Margolis PD, Colame JD, Overholt ED, Lazzara R: Catheter ablation of accessory atrioventricular pathways (Wolff-Parkinson-White Syndrome) by radiofrequency current. N Engl J Med 324:1605-1611, 1991. Calkins H, Langberg J, Sousa J, EI-Atassi R, Leon A, Kow W, Kalbfeisch S, Morady F: Radiofrequency catheter ablation of accessory atrioventricular connections in 250 patients. Circulation 85:1337-1346, 1992. Calkins H, Sousa J, EI-Atassi R, Rosenheck S, DeBuiteir M, Kow WH, Kadish AH, Langberg J, Morady F: Diagnosis and cure of the W olff-Parkinson-White syndrome or paroxysmal supraventricular tachycardias during a single electrophysiologic test. N Engl J Med 324:1612-1618, 1991. Klein LS, Shih H-T, Hackett K, Zipes D, Miles WM: Radiofrequency catheter ablation of ventricular tachycardia in patients without structural heart disease. Circulation 85:1666-1674, 1992. Gursoy S, Schlutter M, Chiladalsis I, Kuck K-H: Radiofrequency energy ablation of sustained monomorphic ventricular tachycardia in patients with underlying heart disease: Which site to ablate (abstract)? PACE 15:549, 1992. Van Hare GF, Lesh MD, Scheinman M, Langberg JJ: Percutaneous radio frequency catheter ablation for supraventricular arrhythmias in children. JAm Coll Cardiol17:1613-1620, 1991. Kalbfeisch SJ, Calkins H, Langberg JJ, EI-Atassi R, Leon A, Borganelli M, Morady F: Comparison of the cost of radiofrequency catheter modification of the atrioventricular node and medical therapy for drug-refractory atrioventricular node reentrant tachycardia. JAm Coll Cardiol19:1583-1587, 1992. Minich LL, Sider AR, Dick M: Doppler detection of valvular regurgitation after radiofrequency ablation of accessory connections. Am J Cardiol70:116-117, 1992. Calkins H, Niklason L, Sousa J, EI-Atassi R, Langberg J, Morady F: Radiation exposure during radiofrequency catheter ablation of accessory atrioventricular connections. Circulation 84:23762382, 1991. Kuck K-H, Schluter M: Single-catheter approach to radiofrequency current ablation of left sided accessory pathways in patients with Wolff Parkinson White Syndrome. Circulation 84: 2366-2375, 1991. Leatter RA, Leitch JW, Klein GJ, Guiradon GM, Yee R, Kim YH: Radiofrequency catheter ablation of accessory pathways: A learning experience. Am J Cardiol68:1651-1655.
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