Implantable cardioverter defibrillator therapy for patients with less severe left ventricular dysfunction

The implantable cardioverter defibrillator (ICD) is an effective therapy for sudden cardiac death (SCD). Identifying patients who will benefit from an ICD is key. Most SCD events occur in patients with less severe left ventricular (LV) dysfunction, yet past trials and guidelines focus on those with severe LV dysfunction. Given the large pool of patients with less severe LV dysfunction and a modest risk of SCD, methods to identify those who might benefit from an ICD are required.

Observational studies indicate that abnormal cardiac repolarization and impaired autonomic function, particularly in combination, appear to identify patients with less severe LV dysfunction at risk of SCD. Extensive scarring also appears to identify patients at risk. Ongoing and planned studies will better define the role of using noninvasive tests to select patients for ICD therapy.

Noninvasive measures of cardiac structure, autonomic function and myocardial substrate appear to be promising in identifying patients with less severe LV dysfunction at risk of SCD. However, it is not clear that ICD therapy will improve survival in these patients. Until definitive data from prospective randomized trials are available it is premature to recommend use of these tools to guide ICD therapy.