Efficacy of ICDs in Patients with Hypertrophic Cardiomyopathy
abstract & commentary
Synopsis: ICDs are effective in terminating arrhythmias in high-risk patients with hypertrophic myopathy and ICD implantation may have a role in the primary and secondary prevention of sudden death in this syndrome.
Source: Maron BJ, et al. N Engl J Med 2000;342: 365-373.
This study reports experience with implantable cardioverter defibrillator (ICD) insertion in patients with hypertrophic cardiomyopathy from 19 centers in the United States and Italy. The study group included 128 patients who ranged in age from 8 to 82 years. Defibrillators in this study were used for both primary and secondary prevention. In 43 patients, the ICD was implanted after resuscitation from either cardiac arrest or sustained ventricular tachycardia. In the remaining 85 patients, the ICD was used for primary prophylaxis. The indication for implantation in this latter group was the presence of one or more of the following risk factors: syncope, a strong family history of sudden death due to hypertrophic cardiomyopathy, nonsustained ventricular tachycardia on ambulatory ECG monitoring, or massive left ventricular hypertrophy with a wall thickness of at least 30 mm.
The ICDs were implanted between December 1984 and June 1998. Transvenous systems were used for the initial implant in 83% of the patients. Ninety-five of the devices implanted had electrogram storage permitting review and classification of discharges during follow-up. A total of 126 patients survived to the end of the follow-up period, with a mean follow-up for the entire group of 3.1 years.
Twenty-nine of 128 patients (23%) had one or more appropriate ICD discharges. Nineteen of 43 patients who received the ICD for secondary prevention had discharges, while only 10 of 85 (12%) in the primary prevention group had defibrillator discharges. The overall rate for appropriate discharges in the entire study group was 7% per year. The rate was 11% per year in the secondary prevention group and 5% per year in the primary prevention group. Analysis of stored electrograms showed that ventricular tachycardia and ventricular fibrillation were the arrhythmias treated by appropriate ICD shocks. At least one inappropriate discharge occurred in 32 of 128 patients (25%). These discharges were due to either sinus tachycardia, atrial fibrillation with a rapid ventricular rate, or lead malfunction.
Eighteen patients experienced complications of defibrillator therapy. These included lead malfunctions (12 patients), infection (2 patients), subclavian vein thrombosis, hemorrhage at the time of insertion, hematoma, and depression.
Maron and associates conclude that ICDs are highly effective in terminating arrhythmias in high-risk patients with hypertrophic myopathy and feel that ICD implantation has an important role in the primary and secondary prevention of sudden death in this syndrome.
Comment by John P. DiMarco, MD, PhD
Prevention of sudden death in patients with hypertrophic cardiomyopathy has long been a vexing problem. The risk for sudden death has a poor correlation with the hemodynamic findings in this disease. Moderate cardiac hypertrophy and the severity of the outflow tract gradient are not good predictors of the risk of sudden death. Risk factors that have been shown to be helpful have been a family history of sudden death, the presence of a history of recurrent syncope, spontaneous nonsustained ventricular tachycardia, abnormal blood pressure responses to exercise, massive left ventricular hypertrophy, and particular genetic mutations, especially those for cardiac troponin T. Patients with one or more of these risk factors may have sudden death rates of between 5% and 10% per year. The role of drug therapy is not certain. Studies with low-dose amiodarone and high-dose beta adrenergic blockers suggest these drugs offer some protection but that this protection is incomplete.
In this paper, Maron et al report on the empiric use of implantable cardioverter defibrillators in patients with hypertrophic cardiomyopathy. It should be no surprise that the ICD was highly effective in terminating episodes of ventricular tachycardia or ventricular fibrillation in this study. It is surprising that there were only two deaths in the entire series, with both of these deaths due to progressive congestive heart failure.
Certainly, no one would argue with the use of ICDs for the purpose of secondary prevention in cardiac arrest survivors. In this study, the approximate rate of appropriate discharges in the secondary prevention group was 11% per year, and more than two-thirds of the patients had had an appropriate discharge by seven years after implantation. These data are similar to those for other groups of cardiac arrest patients treated with ICD therapy. The use of the ICD for primary prevention is more controversial. Here, the risk-benefit ratio and the issue of cost-effectiveness must be considered. Certainly, when ICD implantation required thoracotomy, the risk-benefit ratio for a prophylactic implant would be unfavorable, except in those patients with the highest predicted risk. However, ICD implantation is now safe and can be accomplished with little morbidity. Although there are long-term complications due to inappropriate discharges and components, especially lead malfunction, these issues have become less important with improvements in ICD technology and design. However, the cost-effectiveness of therapy must be considered. In this paper, which included a highly select group of individuals, the discharge rate in the primary prevention group was only 5% per year. At what level of estimated annual risk will prophylactic insertion of the device in any individual patient be justified is a difficult clinical decision.
Clinical experience has shown that the ICD is effective in preventing sudden death in populations where paroxysmal ventricular arrhythmias occur with appreciable frequency and are a major cause of death. At the present time, decisions about implanting an ICD will continue to be difficult. From a clinical standpoint, the safety and reliability of ICD therapy have now improved to the point that we can consider offering it to more groups of patients. Further studies to evaluate the cost-effectiveness, however, are indicated as this dramatic, yet expensive, therapy becomes more readily available.
The use of ICDs as primary prevention for sudden death in hypertrophic cardiomyopathy patients is impeded by:
a. high cost of the devices.
b. inappropriate discharges.
c. complications of device placement.
d. All of the above
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