Implantable Cardioverter Defibrillator for Hypertrophic Cardiomyopathy
ABSTRACT & COMMENTARY
Synopsis: Ventricular arrhythmias may be sporadic and unpredictable in patients with hypertrophic cardiomyopathy, even if they have survived an initial episode of aborted sudden death. This limits the ability of implantable cardioverter defibrillator therapy to change prognosis.
Source: Primo J, et al. J Am Coll Cardiol 1998;31: 1081-1085.
Since sudden death is a well-recognized complication of hypertrophic cardiomyopathy (HCM), there has been considerable interest in prophylactic implantable cardioverter defibrillator (ICD) placement. Thus, Primo and associates retrospectively analyzed the prevalence of ICD shocks documented to be appropriate in 13 patients with obstructive or nonobstructive HCM. The indication for ICD implant was cardiac arrest with documented ventricular fibrillation (VF) in 10 patients, recurrent syncope with inducible polymorphic ventricular tachycardia (VT), or VF in two patients and recurrent sustained monomorphic VT in one patient. Seven of 13 patients had inducible ventricular arrhythmias in response to programmed ventricular stimulation. ICD use in these patients with HCM were compared to use in two control groups. The first control group consisted of 196 patients with ischemic heart disease or nonischemic dilated cardiomyopathy with similar clinical indications for ICD implant. A second control group consisted of 19 patients who had idiopathic ventricular fibrillation and received an ICD. Most HCM patients received some form of anti-arrhythmic therapy after implant. Data about drug therapy in the other two groups are not provided.
During a follow-up period of 26 ± 18 months, only two of 13 patients in the HCM group received appropriate ICD shocks. The actuarial occurrence was 21% at 47 months. This was significantly different from a recurrence rate of 65% at 47 months in the ischemic and dilated cardiomyopathy group and 68% in the idiopathic ventricular fibrillation group. Three additional HCM patients had ICD shocks for rapid supraventricular arrhythmias that potentially could have been hemodynamically significant. There were no deaths in the HCM or the idiopathic ventricular fibrillation groups. Twenty-six patients (4%) died in the ischemic and dilated cardiomyopathy group.
Primo et al conclude that ventricular arrhythmias may be sporadic and unpredictable in patients with HCM, even if they have survived an initial episode of aborted sudden death. This limits the ability of ICD therapy to change prognosis.
COMMENT BY JOHN DiMARCO, MD, PhD
This paper illustrates some of the problems encountered in managing and advising patients with hypertrophic cardiomyopathy. Sudden death and syncope are well-described parts of the natural history of this condition, but the pathogenesis of any individual episode is often uncertain. In the two control groups, recurrent arrhythmias were highly likely since a structural or electrical abnormality, which forms all arrhythmia propagation, had become established. In HCM patients, the pathophysiology of ventricular fibrillation appears to be more related to dynamic variables rather than to a stable abnormality. Presumably, a combination of a number of hemodynamic, ischemic, and electrical triggers must occur. As yet, we have no reliable method for predicting how frequently such deadly interactions will take place in any individual patient.
Primo et al recognize that conclusions about their data are limited because of the small number of subjects. Two or three additional appropriate ICD shocks in the HCM group would markedly change their conclusions. A change in the use of agents with negative inotropic properties after the initial arrest may also have favorably influenced prognoses. Finally, it should be noted that most of the patients in the HCM group were older than 35 years. The most malignant patterns of sudden death in the inherited forms of HCM usually present earlier in life, and the observations here should not be generalized to teenagers and young adults.
Each patient with HCM and aborted sudden death requires a careful evaluation. Treatment of all potential causes should be addressed. Unless a clearly reversible and nonrecurrent factor is identified, the ICD will continue to be an important part of a comprehensive management strategy.
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