Antitachycardia pacing and low-energy cardioversion for ventricular tachycardia termination: A clinical perspective

Antitachycardia pacing and low-energy cardioversion for ventricular tachycardia termination: A clinical perspective When incorporated into tiered therapy implantable cardioverter defibrillators (ICDs), antitachycardia pacing (ATP) techniques have proved useful for termination of sustained monomorphic ventricular tachycardias (VT) and have the advantages of rapid delivery, absence of patient discomfort, and minimal battery drain. The efficacy of low-energy cardioversion (LEC) is similar to that of pacing techniques for VT termination, but LEC has the disadvantages of patient discomfort, atrial proarrhythmia, and greater battery drain compared with ATP. Acceleration of VT occurs with similar frequency with each technique. Neither technique should be used without back-up defibrillation capability in an ICD. VT termination algorithms are currently empiric and require repetitive arrhythmia induction and trials of ATP or LEC. Future studies of the risk and benefits of each technique are likely to define optimal programming strategies in tiered therapy ICDs. (AM HEART J 1994;127:1038-48.)

N. A. Mark E&es III, MD, Connor J. Haugh, MD, Paul J. Wang, MD, and Antonis S. Manolis, MD Boston, Mass.

Pacing techniques for termination of ventricular tachycardia (VT) were described and incorporated into implantable pacemakers capable of manually activated or automatic tachycardia termination more than a decade ago.l-7 However, antitachycardia pacing (ATP) has gained significant clinical utility for treatment of VT only in the past few years with refinement of pacing algorithms8-26 and incorporation into tiered therapy, third-generation implantable cardioverter defibrillators (ICDS).~~-~~ Shortly after the feasibility and effectiveness of low-energy defibrillation in humans were demonstrated by Mirowski in 1973,37 modifications of the technique were made to deliver low-energy cardioversion (LEC) shocks for the termination of VT.38-42 Despite the development and implantation in humans of a device capable of synchronized cardioversion, the implantable cardioverter, only with incorporation of LEC into ICDs has this technique become clinically useful. For both antitachycardia pacemakers and the im-

From The Cardiac Arrhythmia Service, New England Medical pital, and the Department of Medicine/Division of Cardiology, versity School of Medicine. Reprint Service, NEMCH

requests: N. A. Mark Estes III, MD, Director, New England Medical Center Hospital, Box No. 197, Boston, MA 02111.

Copyright ‘i’ 1994 0002.8703/94/$3.00

1038

by Mosby-Year + 0 4/O/63021

Book,

Inc.

Center Tufts

HosUni-

Cardiac Arrhythmia 750 Washington St.,

plantable cardioverter, investigators and clinicians recognized the need for backup high-energy shock therapy to ensure termination of VT not responsive to ATP or LEC and for defibrillation. Basic and clinical investigation on ATP and LEC have contributed to the evolution of both techniques as useful therapies for treatment of VT in tiered therapy ICDs when patients are appropriately selected and evaluated. This article will provide a clinical perspective on ATP and LEC by reviewing prior basic and clinical reports of the two techniques, including the few comparative published studies,43-47summarizing results with their application in tiered therapy ICDs, and developing guidelines for clinical use. ATP: BACKGROUND

AND BASIC CONSIDERATIONS

The initial observations regarding use of pacing techniques for prevention of ventricular arrhythmias were made in the late 1960s when several investigators reported on the prevention of ventricular premature beats, tachycardia, and fibrillation by overdrive atria1 or ventricular pacing at physiologic rates in the setting of bradycardia.48-51 Although this technique has some utility in the setting of bradycardia-dependent ventricular arrhythmias such as torsades de pointes, its clinical application has been very limited because of the unproved and unpredictable long-term efficacy. l8 Similarly, pacing techniques for hemodynamic stabilization during VT,

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such as ventricular triggered atria1 pacing and paired ventricular pacing, have had extremely limited clinical application for hemodynamic stabilization of the patient with incessant VT.la 52,53 Observations on resetting17, 54 and entrainment7 indicate that single capture termination methods (single extrastimulus) and multiple capture termination techniques (multiple extrastimuli, multicapture bursts) of ATP for VT termination are dependent on failure of impulse conduction at a critical area of slowed conduction in a reentrant circuit, which results in tachycardia termination.15, I63l8 Although single extrastimulus techniques are the least effective for tachycardia termination because in many instances they do not penetrate the reentrant circuit, they are the least likely to result in tachycardia acceleration.15>16,l8 Multiple capture techniques, including double extrastimuli and multicapture bursts, have efficacy rates that are considerably high for tachycardia termination.18, 4o This results from the ability of the initial stimuli to peel back refractoriness between the site of stimulation and the critical area of slowed conduction in the reentrant circuit, allowing subsequent stimuli to induce block in the tachycardia circuit.7* 16-18Evaluation of numerous types of multicapture ATP sequences, including fixed burst, shifting or scanning burst, autodecremental or ramp pacing, incremental-decremental scan, and other techniques have demonstrated a higher efficacy rate and risk of acceleration with multicapture techniques. Numerous studies have confirmed a decrease in efficacy and an increase in acceleration as the tachycardia cycle length shortens.15-21In addition, it has been observed that there is no clearly superior mode of multicapture ATP with regard to efficacy or acceleration.15-21 ATP: CLINICAL

RESULTS

Fisher et a1.54initially reported that single extrastimuli were effective for VT termination in 48% of 290 episodes of slow, hemodynamically tolerated VT with only one episode of acceleration. However, subsequent observations indicated that only 1 of 20 patients examined on multiple occasions had VT terminated consistently with single capture techniques.15sl8 Comparisons of single, double, and multicapture techniques by Naccarelli et a1.40demonstrated respective efficacy rates of 18%) 42%) and 61% with acceleration rates of 0 % , 15 % , and 18%. On the basis of higher efficacy rates with multiple capture techniques, they have become the dominant pacing algorithm used in pacemakers18and ICDS.~~-~~ Initial reports of the outcome of antitachycardia pacing with implanted pacemakers without a back-up

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defibrillator included isolated case reports and small series without long term follow-up or survival data.3, 5,7,8 As recently summarized by Roth and Fisher l8 there are 24 reports of separately implanted permanent pacemakers that use ATP for VT in a total of 212 patients. Although the results were considered “good to excellent” in 64 % of the patients, these patients were highly selected with slow hemodynamically tolerated tachycardias that were repetitively terminated by ATP without acceleration.18 Furthermore, the desirability of back-up cardioversion and defibrillation capability has been stressed in all recent reports.‘s* 55-57 Before the development of tiered therapy ICDs, multiple investigators used independent antitachycardia pacemakers with a separately implanted ICD.55-57 The 52 patients described in these series had more than 11,287 episodes of VT; ATP was successful in 50% to 89% of the episodes, and shock therapy was delivered for a total of 554 episodes.lss5557 With this combined device therapy, the antitachycardia pacemaker has only a few seconds to detect and terminate the tachycardia before the ICD is committed to shock therapy. This severely limits both the duration of the burst and the number of attempts of ATP. Furthermore, there are multiple adverse interactions between the pacemaker and ICD that make the clinical utility of this combination extremely limited.55-57 However, when ATP is incorporated into a tiered therapy ICD, multiple ATP attempts can be allowed by the device before shock therapy. Reports of tiered therapy ICDs that incorporate ATP, LEC, and defibrillation capabilities have emphasized successrates of 59 % to 99 4’, for VT termination (Fig. 1) and failure rates of 3 9-Oto 30 % (Fig. 2) with acceleration rates of 1% to 24 % with ATP.27-36 Most of these patients were selected on the basis of sustained VT as the presenting arrhythmia and on the basis of reproducible induction and termination of the arrhythmia with pacing techniques. In a recent series of 527 implantations of a tiered therapy ICD, 71.5% had sustained VT as the presenting arrhythmia.35 Of 82,117 episodes of VT detected by this noncommitted device, 64,590 reverted spontaneously and 25,797 (28.5%) resulted in therapy delivery by the device. Of these 25,797 episodes, 92% reverted with ATP with an acceleration rate of 2%. Shock therapy was needed in only 1945 episodes. In another recent report of a different tiered therapy device, of the 533 patients who received the device, 421 (79%) had sustained monomorphic VT as the presenting arrhythmia.36 Of the patients in this clinical study, tiered therapy with ATP was activated in 66%)

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Fig. 1. A 12-lead ECG is shown with sustainedmonomorphic VT with a cycle length of 400 msec.Eight beats of burst pacing with an 8 msecdecrement between eachstimulus result in termination of the tachycardia before resumption of the patient’s native rhythm (dual chamber pacing).

whereas 34% had one zone therapy with only a defibrillation shock programmed. In 14,141 episodes of VT detected by the device, 79 % were terminated by ATP and 10% were terminated with low-energy shocks. In these and other reports of ATP incorporated into ICDs, the dominant pacing strategies used have included fixed burst pacing or autodecremental (or ramp) pacing. With the former technique a limited number of stimuli (typically 5 to 15) are delivered at rates faster than the tachycardia.15-21 With the latter technique the first stimulus in the train is delivered at an adaptive percentage of the tachycardia cycle length (typically 85 % to 97 % ), and each subsequent extrastimulus is delivered at progressively shorter decrements (approximately 8 to 10 msec or 3%).1521,~~~s Before device implantation, at the time of implantation, and before the patient is discharged from the hospital, ATP therapy is refined by repetitive induction of the clinical VT and empiric programming. For autodecremental pacing, titration of the initial coupling interval, the decrement between stimuli within each train, the number of stimuli in each train, the number of trains, and minimal pacing intervals

are programmed. Several comparative trials of multicapture pacing techniques have shown no clear advantage of one form of ATP over any other.1g-22Accordingly, choice of pacing technique has become a matter of physician preference, with individualization based on empiric trials for each tachycardia. In these series, antiarrhythmic agents have continued to be used in 18 % to 62 % of patients to decrease the frequency of spontaneous arrhythmias, render the VT slower, make it more reliably paceterminable, and decrease the probability of acceleration. With increased recognition of the adverse effects of antiarrhythmic agents, more appropriate patient selection, refinements of the capabilities of the ICDs, and more physician experience in programming tiered therapy devices, a trend for limited drug use has evolved.28 Reports of drug use in 62 % of patients with initial tiered therapy devices, including amiodarone use in 42 % of the patients, contrast with recent reports of antiarrhythmic drug use in only 18% of patients with ICDS.‘~~~~>~~These observations in integrated pacing-cardioversion-defibrillation systems indicate that with appropriate patient selection and careful programming of the device,

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Fig. 2. A 12-lead ECG is shown during sustained monomorphic VT with a cycle length of 350 msec. A 10 beat burst of ventricular pacing results in persistence of the tachycardia for 4 beats before a slower tachycardia (cycle length 620 msec) with a different morphology develops.

most well tolerated pace termination. LEC: BACKGROUND

tachycardias

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to

AND BASIC CONSIDERATIONS

The feasibility of terminating sustained VT with LEC (defined as 15 joules) has been demonstrated in experimental and clinical studies.37-47 On the basis of favorable observations with temporary transvenous leads for endocardial LEC, a permanently implanted LEC device was developed and used in clinical investigations. Synchronization of the shock within the QRS complex was found to be critical, because energy delivered outside of ventricular depolarization can precipitate ventricular fibrillation or accelerate VT.58 Synchronized direct current shocks terminate VT by creation of conduction block within the reentrant circuit. As with permanent antitachycardia pacemakers, backup high-energy shock capability is needed for definitive treatment when LEC is not effective or acceleration occurs. In addition, a more rapid VT or ventricular fibrillation may occur in a patient in whom an LEC device is placed for relatively slow, stable monomorphic VT. LEC has several advantages in the clinical treatment of VT,

including the relatively rapid delivery of therapy, the reduction in battery drain, and less patient discomfort compared with high-energy shocks. Limitations of the technique include failure of cardioversion, decreased tachycardia acceleration, and induction of atria1 arrhythmias. In current ICDs the typical time after detection to delivery of a 1 joule shock is approximately 0.5 second compared with more than 6.5 seconds for defibrillation shock. Detailed comparisons of patient perception of discomfort with LEC have not been performed. However, energies of 10.5 joule have been described as minimally uncomfortable and well tolerated.45 LEC with energies of 0.5 to 3.0 joules are less well tolerated, and some patients are unable to distinguish this from higher energy shocks. It has been found that LEC is more likely to be successful with higher energies within the range of 0.05 to 3 joules (Fig. 3)44 and with slower tachycardias.43-47 Tachycardia acceleration occurs in 7.5 % to 21% of episodes of VT (Fig. 4)43-47 but occurs more commonly with tachycardias with rapid rates and may be caused by the more critical timing of synchronization with rapid ventricular arrhythmias.

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of sustainedmonomorphic VT with a cycle length (CL) of 410msec.A 5 joule LEC is given by the device, resulting in termination of the tachycardia and resumption of the patient’s dual-chamber pacing.

The incidence of induction of atria1 arrhythmias with LEC has been reported to be as high as 23 % .43Most commonly atria1 fibrillation and atria1 flutter are reported, which may be induced by delivery of energy during atria1 repolarization. LEC: CLINICAL

RESULTS

Initial investigations of LEC, which had noted efficacy rates of up to 90 % , were performed in patients selected on the basis of slow monomorphic tachycardia.3aa39In a prospective trial of consecutive, nonselected patients undergoing electrophysiologic studies for VT,44 the efficacy of LEC (0.03 to 2.2 joules) and moderate energy (incremental 0.5 to 10 joules) was 56 % and 72 % , respectively.44 In this consecutive series of patients, the overall efficacy rate (0.03 to 10 joules) was 62% with accelerations occurring in 8% of episodes, which indicates a more limited efficacy of the technique in unselected patients. A prospectively evaluated algorithm of sequential transvenous ATP followed by LEC (0.5 to 2.7 joules) and moderate-energy cardioversion (2.7 to 10 joules) was reported to result in termination of 85% of VT episodes with a cycle length >270 msec with an acceleration rate of

12 % . In contrast, the efficacy rate for the algorithm for arrhythmias with a cycle length <270 msec was only 40 % , with 47 % of episodes accelerating.47 With the development of tiered therapy ICDs that incorporate ATP and LEC and defibrillation capabilities, the relative role of each in algorithms for VT treatment has become an important issue. A prospective, randomized crossover study of LEC and ATP noted an 83% efficacy rate for LEC (0.5 to 2.7 joules) and an 80% efficacy rate of burst pacing (p > 0.1).43 The incidence of acceleration was similar with LEC (11%) and ATP (6%); p > 0.2. However, LEC was complicated by a 23% rate of atria1 arrhythmias compared with 3 % for ATP. Furthermore, 57 % of patients reported significant discomfort after LEC, whereas there were no reports of discomfort with ATP. In a second prospective randomized repeat crossover comparison of ATP with LEC (0.4 to 2.0 joules),45 efficacy rates were 63 % for ATP (autodecremental overdrive) and 75% with LEC (p = 0.53). Acceleration rates were 17% and 21% for ATP and LEC, respectively (p = 0.88). Efficacy and acceleration rates were similar, and on the basis of the crossover design, the investigators concluded that

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Fig. 4. A 12-lead ECG is shownwith a marker channel from a third generation tiered therapy device dur-

ing sustainedmonomorphic VT with a cycle length of 390msec.A 0.5 joule LEC acceleratesthe tachycardia to a cycle length of 240 msec.With this tachycardia, intermittent failure of the patient’s permanent separately implanted dual chamberpacemakerto sensethe tachycardia results in intermittent spikesfrom the ventricular lead. response to one therapy does not predict response to the other. GUIDELINES

FOR USE OF ATP AND LEC

Although LEC and ATP have similar efficacy and acceleration rates on the basis of these comparative studies, the advantages of lower risk of atria1 proarrhythmia, less patient discomfort, and considerably less battery drain have made ATP the dominant strategy for VT termination in tiered therapy devices. Unless LEC is demonstrated to be more efficacious and safer in a given patient, ATP remains preferable as the initial therapy. ATP should be limited to five or fewer attempts because additional efforts are likely to be unsuccessful. It is reasonable to follow a limited number of ATP attempts with LEC provided this algorithm is reproducibly effective in tachycardia termination (Fig. 5). It should be emphasized that trying to recognize a beneficial or proarrhythmic effect from either therapy without reproducible monomorphic VT may not be possible because a given tachycardia may not be reproducibly induced to allow testing of therapy.45 Empiric pro-

gramming of ATP or LEC without repetitive testing is not advised because of a low probability of efficacy and considerable risk of arrhythmia acceleration. Both LEC and ATP should be used only with backup defibrillation, and results generally are best with VT cycle lengths >300 msec. Programming the lowest effective LEC energy minimizes patient discomfort. Generally, patients are lesslikely to be made uncomfortable if the LEC pulses are 50.5 joule. In tiered therapy ICDs, ATP and LEC should be programmed as therapy in the zone defined by the lower and upper rate limit for sustained monomorphic VT for which therapies have been proved to be effective. Multicapture techniques of ATP are preferable to single capture methods with no clear advantage to autodecremental, fixed burst, or other forms of pacing. Generally, to minimize the risk of ischemia, hemodynamic deterioration, or adverse effects on arrhythmia termination, these therapies should be given for 1 minute or less to terminate the tachycardia before maximal device shock is delivered. These therapies should not be programmed in the zone of more rapid tachycardia in which an ICD would detect

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Fig. 5. A 12-lead ECG is shown with a marker channel from a tiered therapy device during sustained monomorphic VT with a cycle length of 390 msec.Burst pacing with an 8 msecdecrement between each stimulus within the burst is unsuccessfulin terminating the VT. A 3 joule LEC is successfulin reestablishing the patient’s native rhythm with dual chamber pacing. Notice that the time for detection of VT after unsuccessfulpacing, charging of the capacitors to 3 joules, and delivery of the shocktakes lessthan 3.8 seconds.

ventricular fibrillation and in which initial therapy should be a maximal shock. Although ATP and LEC therapies remain guided by individualized and empiric testing in each patient, both therapies have proved clinical utility in reducing high-energy shock in ICDs. Additional studies are needed to further define the risks and benefits of each therapy and facilitate optimal device programming. REFERENCES 1. Wellens HJJ. Value and limitations of programmed electrical stimulation of the heart in the study and treatment of tachycardias. Circulation 1978;57:845-53. 2. Hartzler GO. Treatment of recurrent ventricular tachycardia by patient activated radiofrequency ventricular stimulation. Mayo Clin Proc 1979;54:75-82. 3. Ruskin JN, Garan H, Poulin F, Hawthorne JW. Permanent radiofrequency ventricular pacing for management of drugresistant ventricular tachycardia. Am J Cardiol 1980;46:31721. 4. Fisher JD, Mehra R, Furman S. Termination of ventricular tachycardia with bursts of rapid ventricular pacing. Am J Cardiol 1978;11:94-102. 5. Rothmsn MT, Keefe JM. Clinical results with Omni-Orthcor, an implantable antitachycardia pacing system. PACE 1984; 7:1306-12.

6. Griffin JC, Sweeney M. The management of paroxysmal tachycardia using the Cybertach-60. PACE 1984;7:1291-5. 7. Waldo AL, Maclean WA, Karp RB, Kouchoukos NT, James TN. Entrainment and interruption of atria1 flutter with atria1 pacing: studies in man following open heart surgery. Circulation 1977;56:737-45. 8. Fisher JD, Kim SG, Furman S, Matos JA. Role of implantable pacemakers in control of recurrent ventricular tachycardia. Am J Cardiol 1982;49:194-206. 9. Fisher JD, Kim SG, Waspe LE, Matos JA. Mechanisms for the success and failure of pacing for termination of ventricular tachycardia: clinical and hypothetical considerations. PACE 1983;6:1094-105. 10. Fisher JD, Kim SG, Matos JA, Waspe LE. Pacing for ventricular tachycardia. PACE 1984,7:12X90. 11. Sowton E. Clinical results with Tachylog antitachycardia pacemaker. PACE 1984;7:1313-7. 12. Keren G, Miura DS, Somberg JC. Pacing termination of ventricular tachycardia: influence of antiarrhythmic-slowed ectopic rate. AM HEART J 1984;107:638-43. 13. Liideritz B, Gerckens U, Manz M. Automatic implantable cardioverter/defibrillator (AICD) and antitachycardia pacemaker (Tachylog): combined use in ventricular tachyarrhythmias. PACE 1986;9:1356-60. 14. Newman DM, Less MA, Herre JM, Langberg JJ, Scheinman MM, Griffin JC. Permanent antitachycardia pacemaker therapy for ventricular tachycardia. PACE 1989;12:1387-95. 15. Fisher JD, Kim SG, Matos JA, Ostrow E. Comparative effectiveness of pacing techniques for termination of well-tolerated sustained ventricular tachycardia. PACE 1983;6:915-22.

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JD, Kim SG, Mercando AD. Electrical devices for treatment of arrhythmias. Am J Cardiol 1988;61:45A-57A. 17. Almendral JM, Rosenthal ME, Stamato NJ, Marchlinski FE, Buxton AE, Framer LH, Miller JM, Josephson ME. Analysis of the resetting phenomenon in sustained uniform ventricular tachycardia: incidence and relation to termination, J Am Co11 Cardiol 1986;8:294-300. 18. Roth JA, Fisher JD. Basic concepts in tachycardia management by pacing. In: Estes NAM, Manolis AS, Wang PJ, eds. The implantable cardioverter-defibrillator: a comprehensive textbook. New York: Marcel Dekker, 1994 (in press). 19. Cook JR, Kirchhoffer JB, Fitzgerald TF, Lajzer-DA. Comparison of decremental and burst overdrive pacing as treatment for ventricular tachycardia associated with coronary artery disease. Am J Cardiol 1992;70:311-5. 20. Gillis AM, Leitch JW, Wyse DG, Sheldon RS, Yee R, Klein GJ, Mitchell LB. Randomized comparative trial of modes of ventricular tachvcardia pace termination [Abstract]. PACE 1992;

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D, Dorian P, Hardy J. A randomized prospective comnarison of ventricular antitachycardia pacing modalities [Abstract]. PACE 1992;15:506. 22. Klein H, Hofmann R, Troster J, Trappe HJ, Kielblock B. Efficacy of various antitachycardia pacing modes with ICD therapy [Abstract]. PACE 1992;15:506. 23. Luderitz B, D’Alnoncourt CN, Steinbeck G, Beyer J. Therapeutic pacing in tachyarrythmias by implanted pacemakers. PACE 1982;5:366-71. 24. Liideritz B. The impact of antitachycardia pacing with defibrillation. PACE 1991;14:312-6. 25. Hammill S, Stanton M, Packer D. The effect of therapy type (autodecremental, burst, cardioversion) on subsequent ventricular tachycardia cycle length in patients with implantable antitachycardia pacing-cardioversion-defibrillation device [Abstract]. PACE 1991;14:623. 26. Charos GS, Haffajee CI, Gold RL, Bishop RL, Berkovits BV, Alpert JS. A theoretically and practically more effective method for interruption of ventricular tachycardia: selfadapting autodecremental overdrive pacing. Circulation 1986; 73:309-15. L. Experi27. Fromer M, Schlapfer J, Fischer A, Kappenberger ence with a new implantable pacer-cardioverter-defibrillator for the therapy of recurrent sustained ventricular tachyarrhythmias: a step toward a universal tachyarrhythmia control device. PACE 1991;14:1288-98. C, Poole JE, Kudenchuk PJ, Dolack GL, 28. Bardy GH, Troutman Johnson G. Hofer B. Clinical experience with a tiered therapy multiprogrammable antiarrhythmia device. Circulation 1992; 85:1689-98. 29. Saksena S, Mehta D, Krol RB, Tullo NG, Saxena A, Kaushik R, Neglia J. Experience with a third generation implantable cardioverter defibrillator. Am J Cardiol 1991;67:1375-

M, Brachmann J, Block M, Siebels J, Hoffmann E, Almendral J, Ohm OJ, den Dulk K, Coumel P, Camm AJ. Efficacy of automatic multimodal device therapy for ventricular tachyarrhythmias as delivered by a new implantable pacing cardioverter-defibrillator: results of a European multicenter study of 102 implants. Circulation 1992;86:363-73. Wann PJ. The Telectronics 4210 imnlantable cardioverterdefib;illator. In: Estes NAM, ManolisAS, Wang PJ, eds. The implantable cardioverter-defibrillator: a comprehensive textbook. New York: Marcel Dekker, 1994 (in press). Estes NAM III. CPI PRx implantable cardioverter-defibrillator. In: Estes NAM, Manolis AS, Wang PJ, eds. The implantable cardioverterdefibrillator: a comprehensive textbook. New York: Marcel Dekker, 1994 (in press). Mirowski M, Mower MM, Gott VL, Brawley K. Feasibility and effectiveness of low-energy catheter defibrillation in man. Circulation 1973;47:79-84. Zipes DP, Jackman WM, Heger JJ, Chilson JA, Browne KF, Naccarelli GV, Rahilly GJ Jr., Prystowsky EN. Clinical transvenous cardioversion of recurrent life-threatening ventricular arrhythmias: low energy synchronized cardioversion of ventricular tachycardia and termination of ventricular fibrillation in patients using a catheter electrode. AM HEART J 1982; 1-_

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JW, Gillis AM, Wyse DG, Yee R, Klein GJ, Guiraudon G, Sheldon RS, Duff HJ, Kieser TM, Mitchell LB. Reduction in defibrillator shocks with an implantable device combining antitachvcardia nacing and shock therapy. J Am Co11 Cardiol i99i;i8:i45-51. 31. Reiter M. Ventritex Cadence tiered therapy defibrillator device descrintion and clinical experience. In: Estes NAM, Manolis AS, Wang PJ, eds. The &plantable cardioverter-defibrillator: a comprehensive textbook. New York: Marcel Dekker, 1994 (in press). 32. Block M, Borggrefe M, Hammel D, Hief C, Scheld HH, Schwammenthal E, Breithardt G. Pacer-Cardioverter-Defibrillator (PCD): utilization, efficacy, and complications of antitachycardia pacing [Abstract]. J Am Co11 Cardiol 1991;17: 54A. 33. Ellenbogen K, Welch W, Luceri R, Jackman W, Singer I, Dorian P, Saksena S, Brachman J, Renker M. Clinical evaluation of the Guardian ATP 4210 implantable pacemaker/defibrillator: worldwide experience [Abstract]: PACE 1991; 14:623.

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S, Shah Y, Pantopoulos D. A prospective randomized studv of the clinical efficacv and safetv of tramavenous cardioversion for termination of ventricular tachycardia. Circulation 1985;71:571-8. Bardy GH, Poole JE, Kudenchuk PJ, Dolack GL, Kelso D, Mitchell R. A prospective randomized repeat-crossover cornI-__parison of antitachycardia pacing with low-energy cardioversion. Circulation 1993:87:1889-96. Waspe LE, Kim SG, Matos JA, Fisher JD. Role of a catheter lead system for transvenous countershock and pacing during electrophysiologic tests: an assessment of the usefulness of catheter shocks for terminating tachyarrhythmias. Am J Cardiol 1983;52:477-84. Calvo RA, Saksena S, Pantopoulos D. Sequential transvenous pacing and shock therapy for termination of sustained ventriculartachycardia. AM HEART J 1988;115:569-75. Escher DJ. The treatment of tachyarrhythmias by artificial cardiac uacinn. AM HEART J 1969:78:829-32. Lew HT, March HW. Control of recurrent ventricular fibrillation by transvenous pacing in the absence of heart block. AM

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AG. Treatment of ventricular arrhythmias by permanent atrial pacemaker and cardiac sympathectomy. Ann Intern Med 1968;68:591-7. DeSanctis RW, Kastor JA. Rapid intracardiac pacing for treatment of recurrent ventricular tachyarrhythmias in the absence of heart block. AM HEART J 1968;76:i68-72. "--Hamer AW, Zaher CA, Rubin SA, Peter T, Mandel WJ. Hemodynamic benefits of synchronized 1:l atria1 pacing during

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sustained ventricular tachycardia with severely depressed ventricular function in coronary heart disease. Am J Cardiol 1985;55:990-4. 53. Walso LA, Krongrad E, Kupersmith J, Levine OR, Bowman FO Jr, Hoffman BF. Ventricular paired pacing to control rapid ventricular heart rate following open heart surgery: observations on ectopic automaticity. Report of a case in a fourmonth-old patient. Circulation 1976;53:176-81. 54. Fisher JD, Ostrow E, Kim SG, Matos JA. Ultrarapid singlecapture train stimulation for termination of ventricular tachycardia. Am J Cardiol 1983;51:1334-8. 55. Greve H, Koch T, Gulker H, Heuer H. Termination of malignant ventricular tachycardias by use of an automatic defibril-

American

April 1994 Heart Journal

lator (AICD) in combination with an antitachycardia pacemaker. PACE 1988;11:2040-4. 56. Newman DM, Lee MA, Herre JM, Langberg JJ, Scheinman MM, Griffin JC. Permanent antitachycardia pacemaker therapy for ventricular tachycardia. PACE 1989;12:1387-95. 57. Bonnet CA, Fogoros RN, Elson JJ, Fiedler SB, Burkholder JA. Longterm efficacy of an antitachycardia pacemaker and implantable defibrillator combination. PACE 1991:14:814-22. 58. Saksena S, Pantopoulous D, Hussian SM, Gielchinsky I. Mechanism of ventricular tachycardia termination and acceleration during transvenous cardioversion is determined by cardiac mapping in man. AM HEART J 1987;113:1495-506.

The role of cardioversion therapy in patients with implanted cardioverter defibrillators Stable ventricular tachycardias can be treated with pacing or electrical countershock. Use of pacing includes several advantages, but it is not always effective; when pacing is not effective, shocks can be used for cardioversion of the arrhythmia. Use of such shocks includes advantages and disadvantages, but generally they are well tolerated and form an important part of the treatment of patients with sustained ventricular arrhythmias. (AM HEART J 1@94;127:1046-51.)

Anthony

Wayne Nathan, MD London, England

Modern implanted cardioverter defibrillators (ICDs) can treat bradycardias with pacing and tachyarrhythmias with either pacing or direct current countershock. The concept of countershock is often divided into defibrillation and cardioversion, but these terms are used differently by different authors and in different contexts according to use of different devices. To further complicate matters, the terms low energy and high energy are sometimes used. A countershock is a direct current shock used to treat arrhythmias. The terms low energy and high energy are arbitrary and variable, and as systems are developed that are effective with use of less energy,

From the Department of Cardiology, St. Bartholomew’s Hospital. Reprint requests: Anthony Wayne Nathan, MD, Department of Cardiology, St. Bartholomew’s Hospital, West Smithfield, London, EClA 7BE, England. Copyright @ 1994 by Mosby-Year Book, Inc. M)oZ-8703/941$3.00+0 4/O/63022

the meanings of these terms are likely to change. Most authors use the term cardiouersion to describe a shock used to treat ventricular tachycardia (VT) and defibrillation to describe a shock used to treat ventricular fibrillation (VF). However, a myriad of definitions exist, and some are tailored to fit the device they describe. Thus Fromer et a1.r rather confusingly defined cardiouersion as synchronized uncommitted countershock therapy and defibrillation as nonsynchronized, committed therapy, because these definitions fit the different zonal therapies for the device they described in their article. This article will discuss the practical use of cardioversion therapy for VT with use of ICDs. As will be seen, energy requirements depend on arrhythmia type; the cycle length of the arrhythmia; electrode types, size, and position; the type of waveform used; elapsed time before delivery of the shock; and a host of other factors, including any antiarrhythmic drugs that may be taken by the patient, the effect of pre-