Consultation: Sunil Sinha
Director, Arrhythmia Device Clinic, Johns Hopkins Heart Institute

What puts patients with hypertrophic cardiomyopathy at risk of sudden cardiac death?

The primary culprits are ventricular tachycardia and ventricular fibrillation.  Bradyarrhythmias are also on the list. Severe obstructive cardiogenic shock may occur in advanced cases.

We believe VT/VF is facilitated by the underlying substrate of disordered LV myocardial architecture that can trigger and maintain the arrhythmias. Some patients probably experience episodic myocardial ischemia, which results in necrosis and fibrosis and adds to the problem. Hypoxemia and catecholamine release during severe exertion can further increase risk.

Are there ways to stratify sudden cardiac death risk in HCM patients?

Yes, though it’s an inexact science. The most ominous sign, of course, is cardiac arrest or spontaneous sustained VT. But among patients who haven’t had a serious event, several major risk factors have been identified, including nonsustained ventricular tachycardia on ambulatory monitoring, a family history of SCD in close relatives, otherwise unexplained syncope, left ventricular wall thickness that measures 30 mm or more, and abnormal blood pressure response—blunting or a decrease—during a routine treadmill stress test.  LV outflow obstruction, an identified high-risk mutation or intense physical exertion represent significant risk factors in certain patients.

What’s the best way to minimize the risk of SCD in these otherwise healthy patients?

Patients who’ve had aborted sudden cardiac death or cardiac resuscitation are known to benefit from an implantable cardioverter defibrillator for secondary prevention. In those at high risk and already receiving optimal medical therapy, an ICD is indicated for primary prevention. We recommend routine follow-up every three months post-insertion. With newer devices equipped with a radiofrequency antenna, we can perform remote ICD analysis and download interrogation data from a secure Web site, reducing the frequency of in-clinic checks.

Can athletes with an ICD still participate in their sport?

HCM is believed to be the most common cause of sudden death in young competitive athletes. Many are extremely motivated, and it’s tough for them to accept that even with an ICD, they’re not immune to sudden death, as device malfunction or “refractory VT/VF” may uncommonly occur. So I’ll only clear them for moderate aerobic activities and workouts in an accompanied setting, but not to play collegiate sports.