A Prospective Evaluation of Catheter Ablation of Ventricular Tachycardia as Adjuvant Therapy in Patients With Coronary Artery Disease and an Implantable Cardioverter-Defibrillator
Background Implantable cardioverter-defibrillator (ICD) therapy is integral to current therapy for ventricular tachycardia. Patients with an ICD frequently require concomitant antiarrhythmic drug therapy. Despite this, some patients still receive frequent ICD therapies for ventricular tachycardia. Therefore, the purpose of this prospective study was to determine the utility of ablation of ventricular tachycardia in patients with an ICD who experience frequent ICD therapies.
Methods and Results Twenty-one consecutive patients with frequent ICD therapies despite antiarrhythmic drug therapy were the subjects of this study. The mean age was 69±6 years, and 17 were men. The mean ejection fraction was 0.22±0.08, and all patients had coronary artery disease. During the 36±51 days (range, 4 days to 7 months) preceding the ablation procedures, the patients received 34±55 ICD therapies for the clinical ventricular tachycardia, or a mean of 25±88 ICD therapies per month. The patients underwent radiofrequency ablation of the presumed clinical ventricular tachycardia by inducing the tachycardia and mapping according to endocardial activation, continuous electrical activity, pace mapping, concealed entrainment, or mid-diastolic potentials. Ablation of the clinical arrhythmia was successful in 76% of patients during 1.4±0.6 (range, 1 to 3) ablation procedures and required 12.5±9.2 applications of energy. During 11.8±10.0 months of follow-up, the frequency of ICD therapies per month decreased from 60±80 before successful ablation to 0.1±0.3 ICD therapies per month after ablation (P=.01). A quality-of-life assessment demonstrated a significant improvement after successful (P=.02) but not unsuccessful ablation (P=.9).
Conclusions Radiofrequency ablation of ventricular tachycardia as adjuvant therapy in patients with coronary artery disease and an ICD has a reasonable success rate, significantly reduces ICD therapies, and appears to be associated with an improved quality of life.
Patients with an implantable cardioverter-defibrillator (ICD) often require concomitant therapy with antiarrhythmic agents to decrease the frequency of defibrillator therapies.1 2 3 4 5 Despite concomitant antiarrhythmic therapy, some patients still have frequent episodes of ventricular tachycardia, resulting in numerous shocks or antitachycardia pacing therapies, or may have sustained ventricular tachycardia below the ICD rate cutoff. Ventricular tachycardia can be ablated suc- cessfully in the setting of a previous myocardial infarction.6 7 8 9 10 Although the efficacy of radiofrequency ablation of ventricular tachycardia to decrease the frequency of ICD therapies has not been systematically evaluated in patients with frequent ICD therapies due to recurrent ventricular tachycardia, ablation is recommended as a class I indication in this setting by the American College of Cardiology/American Heart Association Task Force on Practice Guidelines.11 Therefore, the purpose of this prospective study was to determine the utility of catheter ablation for ventricular tachycardia in post-myocardial infarction patients with an ICD who experienced frequent ICD therapies.
The subjects of this prospective study were 21 consecutive patients with coronary artery disease and a previous myocardial infarction who were treated with radiofrequency catheter ablation for a ventricular tachycardia that was triggering multiple ICD shocks or antitachycardia pacing therapies, or who presented with sustained ventricular tachycardia at a rate below the ICD rate cutoff (Table 1⇓). The patients in this study included 17 men and 4 women, with a mean age of 69±6 years. All patients had coronary artery disease and the mean left ventricular ejection fraction was 0.22±0.08. The indication for ICD implantation was cardiac arrest in 6 patients and sustained ventricular tachycardia or syncope in 15 patients. An ICD had been implanted a mean of 11.3±13.6 months before ablation therapy. Among the 21 patients, 13 had been treated with an ICD that could provide the ventricular electrograms and/or the RR intervals of the treated tachycardia (5 Cardiac Pacemakers Inc, 2 Medtronic Inc, and 6 Ventritex Inc) and the remaining 7 patients had an ICD that only could log the number of delivered therapies (5 Cardiac Pacemakers Inc, 2 Medtronic Inc, and 1 Intermedics Inc). Attempts to treat the clinical ventricular tachycardia with a mean of 2.5±1.1 antiarrhythmic agents had been unsuccessful, including amiodarone therapy in 16 patients (Table 1⇓). At the time of the ablation procedure 16 patients were being treated with amiodarone, 18 were being treated with multiple antiarrhythmic agents, and 9 were being treated with 1.2±0.5 intravenous antiarrhythmic agents.
Clinical Ventricular Tachycardia
In 14 patients, the spontaneously occurring ventricular tachycardia was documented with a 12-lead ECG. In the remaining 7 patients, the cycle length of the clinical ventricular tachycardia was determined from monitor strips or from intracardiac electrograms stored in the ICD. A ventricular tachycardia induced by programmed stimulation that had a cycle length identical to that of the spontaneous ventricular tachycardia was presumed to be the clinical ventricular tachycardia.
Electrophysiological Testing Protocol
Each patient provided informed consent. Electrophysiological studies were performed with the patient in the postabsorptive state. A quadripolar electrode catheter (7F) was inserted into a femoral vein and positioned in the apex of the right ventricle. The surface ECG leads and intracardiac electrograms were recorded at a paper speed of 100 mm/s on a Siemens ELEMA Mingograph-7 Recorder. The filter settings for the intracardiac electrograms were 50 to 500 Hz. Pacing was performed with a programmable stimulator (Bloom Associates). Right ventricular pacing and programmed ventricular stimulation were performed at a current strength of twice diastolic threshold, which was always <0.8 mA. The inducibility of ventricular tachycardia was assessed by programmed ventricular stimulation with 1 to 4 extrastimuli at the right ventricular apex, using basic drive cycle lengths of 350, 400, and 600 ms. Mapping and ablation were performed with a 7F quadripolar electrode catheter with 2-5-2–mm interelectrode spacing (Mansfield EP or EP Technology Inc) inserted percutaneously into a femoral artery and positioned in the left ventricle. Each of these catheters was equipped with a deflectable shaft and a 4-mm distal electrode. One of these catheters (EP Technology, Inc) was equipped with a thermistor incorporated into the tip of the distal electrode. The thermistor bead was thermally insulated from the surrounding platinum electrode with a polyamide plastic sleeve. After the catheter was positioned in the left ventricle, 5000 units of heparin was administered intravenously. An additional 1000 units of heparin was administered every hour. In the left ventricle, local stimulation thresholds ranged from 0.5 to 10 mA, and current strengths of 1 to 20 mA were used for pacing. Pacing stimuli were 2 ms in duration for right ventricular pacing and ranged from 2 to 9 ms in duration for left ventricular pacing. Electrodes 1 (distal tip) and 3 were used for pacing and electrodes 2 and 4 were used for recording.
The criteria used to select a target site for ablation of ventricular tachycardia included concealed entrainment, identification of an isolated mid-diastolic potential, identification of the earliest presystolic endocardial activation during ventricular tachycardia, and pace mapping.6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Generally, concealed entrainment was the first mapping technique used. Potential target sites identified with other mapping techniques were usually also evaluated for concealed entrainment. Radiofrequency energy was applied at target sites meeting one or more of these criteria.
Radiofrequency energy was delivered by a generator that supplied a continuous unmodulated frequency of 500 kHz (EP Technologies, Inc). Radiofrequency energy was delivered between the 4-mm distal electrode of the ablation catheter and a large adhesive skin electrode that was placed over the posterior chest. Ventricular tachycardias were selected for ablation on the basis of a 12-lead ECG of the spontaneously occurring ventricular tachycardia or on the basis of the rate of the spontaneous ventricular tachycardia determined either from a monitor recording or from the ICD. Additionally, other hemodynamically stable ventricular tachycardias that occurred during the procedure were targeted for ablation. Whenever possible, power was delivered during ventricular tachycardia. Power was titrated to a target temperature of ≈60°C. This was achieved by titrating power to obtain a 5- to 10-Ω decrease in the measured impedance or to achieve a target temperature of 60°C.24 25 All applications were continued for at least 10 seconds after the target temperature or impedance was obtained. If the ventricular tachycardia terminated, then the application was continued for 60 seconds. After each application of radiofrequency energy the inducibility of ventricular tachycardia was assessed by programmed ventricular stimulation with 1 to 4 extrastimuli at the right ventricular apex using basic drive cycle lengths of 350, 400, and 600 ms.26
A successful ablation procedure was defined as one in which the ventricular tachycardia responsible for the excessive number of ICD therapies was terminated by an application of radiofrequency energy and was no longer inducible by programmed ventricular stimulation. The ablation procedure duration was defined as the time required to perform the procedure from the initiation of mapping until the final application of radiofrequency energy.
After the ablation procedure, patients were monitored in the hospital and the same oral antiarrhythmic drug therapy present at the time of the ablation was continued. After patients were discharged from the hospital, they were evaluated as outpatients every 3 to 4 months. Delivered ICD therapies were noted. When interrogation of the ICD allowed determination of the treated ventricular tachycardia cycle length, the treated ventricular tachycardia was considered consistent with the ablated ventricular tachycardia if the cycle length of the treated ventricular tachycardia was within 20 ms of the ablated ventricular tachycardia cycle length. If the ICD did not provide information regarding the tachycardia cycle length, the ventricular tachycardia was considered consistent with the ablated ventricular tachycardia.
Quality of Life
Within 1 month of the last follow-up visit, an assessment of quality of life was performed. Each patient was surveyed by telephone with a quality-of-life instrument consisting of 23 questions.27 Each patient was first asked to respond to the questionnaire with respect to how they felt during the month preceding the ablation procedure(s). The questionnaire was then administered a second time with the patients queried as to how they felt during the most recent month. Patient responses were given on a scale of 1 to 5, with 5 indicating the highest level of concern for a specific item and 1 indicating the least concern. The total score for each patient, before and after ablation, was determined and the mean scores were compared.
The questions in this instrument address approximately five general areas of potential concern for patients with an ICD. The areas of concern include incision pain or pain caused by defibrillator shocks, anxiety relating to ICD therapies, the implications of an electronic implant and the potential for interaction with environmental energy sources, implications for insurance and insurability, the ability to obtain appropriate medical care while traveling or from a rescue squad, and the implications for employment.27 “I worry about the ICD firing and creating a scene”; “The sensation I feel when the ICD fires bothers me”; “I worry that my insurance is not going to cover all my medical bills”; “It bothers me not knowing when the ICD will fire”; and “I worry about being denied a job in the future because of the ICD” are five specific questions from this questionnaire.27
Analysis of Data
The continuous variables are expressed as mean±SD and were compared by use of a paired or unpaired t test when appropriate. Nominal variables were compared by χ2 analysis. A probability value <.05 was considered statistically significant.
Characteristics of the Clinical Ventricular Tachycardias
Among the 21 patients included in this prospective study, frequent ICD therapy was the presenting symptom in 9 patients, sustained ventricular tachycardia below the rate cutoff of the ICD was the presenting symptom in 3 patients, and 9 patients presented both with frequent ICD therapies and with sustained ventricular tachycardia below the rate cutoff (25±88 ICD therapies per month; Table 1⇑). The patients received 17±16 shocks and 18±57 antitachycardia pacing therapies from the onset of symptoms caused by ventricular tachycardia in the 36.8±51.7 days before ablation (Table 2⇓). During electrophysiological testing, 4.7±3.2 monomorphic ventricular tachycardias were inducible (range, 1 to 15) with programmed ventricular stimulation. The mean cycle length of these ventricular tachycardias was 430±102 ms.
Concealed entrainment, isolated mid-diastolic potentials, early ventricular activation, and pace mapping were used to identify successful target sites for ablation of 20, 7, 6, and 3 ventricular tachycardias, respectively. Pace mapping during sinus rhythm was the only technique used to map hemodynamically unstable ventricular tachycardias, and this technique was not successful in either of the two patients in whom it was used in this study.
Twenty-six ventricular tachycardias were responsible for the clinical symptoms in these 21 patients, although a total of 46 ventricular tachycardias were targeted for ablation and 36 were successfully ablated (78%) in 16 patients (76%). The likelihood of successful ablation if the ventricular tachycardia was hemodynamically well tolerated was 89%. The mean cycle length of the 46 ventricular tachycardias was 455±93 ms (Tables 2⇑ and 3⇓) and ranged from 270 to 670 ms, whereas the 36 successfully ablated ventricular tachycardias had a cycle length of 483±78 ms (range, 360 to 670 ms; Table 2⇑).
The number of radiofrequency energy applications was 12±9, and the number of procedures was 1.4±0.6 (range, 1 to 3). The duration of the ablation portion of the procedures in the 21 patients was 93±36 minutes, and the fluoroscopic time for the entire procedure in the 21 patients was 50±29 minutes.
In five patients, the clinical ventricular tachycardia was not successfully ablated. These ventricular tachycardias had a mean cycle length of 454±94 ms. Two of these five patients had hemodynamically unstable ventricular tachycardia, in two patients the ventricular tachycardia could not be adequately mapped with any of the available techniques, and in the remaining patient the clinical ventricular tachycardia could not be induced with programmed ventricular stimulation. In this latter patient, pace mapping during sinus rhythm was used to identify target sites.
Complete heart block was the only complication and occurred in one patient who then underwent implantation of a dual-chamber pacemaker. This patient had ventricular tachycardia arising from the high left ventricular septum.
ICD Therapies During Follow-up
The 21 patients were followed for 11.8±10.0 months after ablation (range, 1.3 to 32.0 months). Before ablation, the entire cohort of 21 patients received 134.1±338.1 ICD therapies per month for the clinical ventricular tachycardia and 0.5±1.1 ICD therapies per month during follow-up for the clinical ventricular tachycardia (P=.09). The frequency of ICD therapies per month for the clinical ventricular tachycardia decreased from 59.3±79.7 before successful ablation to 0.1±0.3 ICD therapies per month after successful ablation (P=.01, Figure⇓). The number of ICD therapies per month for the clinical ventricular tachycardia after unsuccessful ablation (1.5±1.9) was not statistically different than the number per month before ablation (358.4±660.9; P=.3). The number of ICD therapies per month for the clinical ventricular tachycardia before successful and unsuccessful ablation were statistically similar (P=.09). However the number of ICD therapies per month for the clinical ventricular tachycardia after successful ablation was significantly less than after unsuccessful ablation (P<.01). Likewise, the total number of ICD therapies for any ventricular tachycardia was 134.1±338.1 ICD therapies per month before ablation and was 0.8±1.4 therapies per month after ablation in the entire cohort of 21 patients (P=.09). The total number of ICD therapies per month before successful ablation for any ventricular tachycardia was 59.3±79.7 and decreased to 0.6±1.1 therapies per month after successful ablation (P=.01). After unsuccessful ablation, the total number of ICD therapies per month for any ventricular tachycardia was 1.5±2.0 and was 358.4±660.9 before unsuccessful ablation (P=.03).
Five patients underwent unsuccessful ablation of ventricular tachycardia. After the unsuccessful ablation procedure, all of these patients were treated with additional antiarrhythmic medications. Subsequently, in one of these patients, an effective ICD antitachycardia pacing therapy was identified after all antiarrhythmic therapy was discontinued, although an effective antitachycardia prescription could not be identified before discontinuation of antiarrhythmic therapy. One patient died 6 weeks later after an endocardial resection.
During 11.8±10.0 months of follow-up, two patients died. One patient died of progressive congestive heart failure, and one patient died after an endocardial resection.
Predictors of Ablation Results
Successful ablation did not correlate with age (P=.3), sex (P=1.0), left ventricular ejection fraction (P=.4), or the number of ICD therapies per month before ablation (P=.09). The correlation of unsuccessful ablation of hemodynamically unstable ventricular tachycardia trended toward statistical significance (P=.06). Successful ablation of the two targeted ventricular tachycardias that were hemodynamically unstable was not achieved in either instance, as opposed to successful ablation of 80% of the hemodynamically stable ventricular tachycardias that were targeted (P=.06).
The mean quality-of-life score for all patients before ablation was 2.1±0.8 compared with 1.4±0.1 after ablation (P=.02). There was a significant improvement in quality of life after successful ablation (1.4±0.5 versus 2.2±0.8 before ablation, P=.02), but there was no significant improvement after unsuccessful ablation (1.8±0.6 versus 1.7±0.1 before ablation, P=.9). The quality of life before ablation did not differ between patients who subsequently underwent successful or unsuccessful ablation (P=.5).
One finding of this prospective study is that patients with coronary artery disease, a history of ventricular tachycardia or ventricular fibrillation treated with an ICD and an antiarrhythmic drug(s), and who subsequently develop frequent defibrillator therapies typically have multiple inducible ventricular tachycardias, and the symptomatic arrhythmia is often hemodynamically stable. Radiofrequency ablation of sustained ventricular tachycardia or the ventricular tachycardia responsible for frequent ICD therapies has a success rate of ≈75% and results in a 99.8% reduction in defibrillator therapies. When the clinical ventricular tachycardia is hemodynamically unstable, successful ablation is unlikely.
Patients who receive frequent ICD therapies usually have multiple morphologies of ventricular tachycardia. When ablation of the clinical ventricular tachycardia was successful, the frequency of ICD therapies decreased by 99.8%, and 50% of these patients did not receive additional ICD therapies. However, because these patients usually have multiple ventricular tachycardias, about half of these patients still receive ICD therapies for other ventricular tachycardias.
Mapping Techniques and Successful Ablation
A variety of techniques to map ventricular tachycardia, including concealed entrainment, identification of an isolated diastolic potential, identification of the earliest presystolic endocardial activation during ventricular tachycardia, and pace mapping during sinus rhythm, were used in this study.6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 This study was not designed to determine the superiority of one or another of these techniques. In fact, all of these techniques were used to identify potential target sites for ablation. All of these techniques except pace mapping require that the patient’s rhythm be ventricular tachycardia during mapping. Therefore, if the ventricular tachycardia is not tolerated hemodynamically, then the only mapping technique available is pace mapping during sinus rhythm to identify concordance with the 12-lead ECG during ventricular tachycardia. However, the clinical ventricular tachycardia for two of the patients in this study was hemodynamically unstable and the only possible mapping tool available was pace mapping. Ablation was unsuccessful in each of these instances. This finding highlights the major problem with mapping and ablation of ventricular tachycardia in the setting of coronary artery disease: That is, usually the ventricular tachycardia must be hemodynamically stable to be successfully mapped. In fact, no previous study has reported a series of patients who have undergone successful ablation of hemodynamically unstable ventricular tachycardia.
Several previous studies have demonstrated the feasibility of ablating hemodynamically tolerated ventricular tachycardia in patients with a previous myocardial infarction.6 7 8 9 10 These studies have reported success rates of 56% to 100%.6 7 8 9 10 The success rate in the present study, 76%, is similar. Additionally, the success rate of radiofrequency catheter ablation for hemodynamically tolerated and inducible ventricular tachycardia was 89% in the present study. Only one of these studies, a small study with five patients having ventricular tachycardia arising out of a scar from a previous myocardial infarction, used catheter ablation of ventricular tachycardia as adjunct therapy in patients with an ICD.9 In this study, the ventricular tachycardia in all five patients was successfully ablated.9 While these authors found that ablation reduced ICD therapies in this small number of patients, two of the five patients still received ≈30 ICD therapies after ablation, and information to determine concordance of the treated arrhythmia with the ablated arrhythmia was not provided.9
Quality of Life
These results suggest that improvement in quality of life occurs after successful ablation of ventricular tachycardia in patients receiving frequent ICD therapies but not in patients with an unsuccessful ablation procedure. Alterations in quality of life after ablation of ventricular tachycardia in the setting of coronary artery disease have not been reported previously, although quality of life appears to improve after successful ablation of supraventricular tachycardia and idiopathic ventricular tachycardia.28 The tool used in the present study to assess quality of life was designed to be used prospectively in patients with an ICD.27 In the present study, the preablation quality-of-life assessment was performed retrospectively at the conclusion of the study. The retrospective nature of the baseline quality-of-life assessment is a limitation.
The ICD cutoff rate in 50% of the patients who underwent a successful ablation procedure was higher than the rate of the ablated ventricular tachycardia. Therefore, an asymptomatic recurrence of the ablated ventricular tachycardia in these patients would not have been identified. Second, ICD therapies did not decrease significantly after unsuccessful ablation, although the absolute number of therapies decreased by >99%. The lack of statistical significance in this instance may be due to small numbers or to a β error. Third, this study was not designed with a control group. Therefore, one could argue that the decreases in ICD therapy observed after successful ablation were due to spontaneous variation in the frequency of ventricular tachycardia. However, clinically and ethically it is difficult to assign a patient to a control treatment group when the patient is receiving frequent ICD therapies despite multiple intravenous and oral antiarrhythmic medications. Finally, after a successful ablation procedure, patients were systematically maintained on the same oral antiarrhythmic regimen as before ablation; however, all intravenous medications were discontinued. The discontinuation of some antiarrhythmic medications would most likely increase the number of ventricular tachycardia episodes, although it is possible that the drugs could have been proarrhythmic and hence discontinuation would have decreased the number of ventricular tachycardia episodes.
These results demonstrate that successful radiofrequency ablation of ventricular tachycardias can reduce the frequency of ICD therapy. While these patients will typically have many morphologically distinct ventricular tachycardias, the clinical arrhythmia is often hemodynamically stable and ablation is associated with a reasonable success rate and low complication rate. Ablation of hemodynamically stable ventricular tachycardia in patients with an ICD may be reasonable adjunctive therapy for patients on a multiple drug regimen. A ventricular tachycardia that is hemodynamically unstable is unlikely to be successfully ablated, and other therapeutic options should be considered. These other options should include discontinuation of antiarrthythmic drugs with the addition of antitachycardia pacing if an effective antitachycardia pacing regimen could not be identified during antiarrhythmic drug administration.
All of the patients in this study were being treated with antiarrhythmic drugs at the time of the ablation procedure. These drugs probably contribute to the slowing of the ventricular tachycardia and may render the ventricular tachycardia more amenable to mapping and ablation. Without the concomitant use of antiarrhythmia drugs, the success rate observed in the present study may have been lower. Hence, one can assume that ablation and drug therapy will remain important components in managing patients with frequent ICD therapies. Finally, shocks from an ICD are a therapy that most patients find unpleasant. A reduction in the number of shocks may improve patient acceptance of this therapeutic modality.
The authors would like to thank Allyson Navyac for her secretarial support and Seema Sonnad, PhD, from the Consortium for Health Outcomes, Innovations and Cost Effectiveness Studies, at the University of Michigan Medical Center.
- Received February 10, 1997.
- Revision received April 25, 1997.
- Accepted May 1, 1997.
- Copyright © 1997 by American Heart Association
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