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(Circulation. 1997;96:1525-1531.)
© 1997 American Heart Association, Inc.
Articles |
A Prospective Evaluation of Catheter Ablation of Ventricular Tachycardia as Adjuvant Therapy in Patients With Coronary Artery Disease and an Implantable Cardioverter-Defibrillator
From the Division of Cardiology, Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor.
Correspondence to S. Adam Strickberger, MD, University of Michigan Medical Center, 1500 E Medical Center Dr, Box 0022, Ann Arbor, MI 48109-0022.
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Abstract |
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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.
Key Words: implantable cardioverter-defibrillator • catheter ablation • coronary artery disease • tachycardia
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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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.
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Methods |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Patients
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.
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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.
Catheter Ablation
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-
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.
Follow-up
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
2 analysis. A probability value <.05 was
considered statistically significant.
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Results |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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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.
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Mapping Techniques
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.
Ablation Results
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).
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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).
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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).
Quality-of-Life Results
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).
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Major Findings
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.
Defibrillator Therapies
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.
Previous Studies
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.
Limitations
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 ß 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.
Clinical Implications
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.
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Acknowledgments |
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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.
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