Time-dependence of appropriate implantable defibrillator therapy in patients with ischemic cardiomyopathy

Introduction: Little is known about the risk of appropriate implantable cardioverter-defibrillator (ICD) therapy outside the context of controlled clinical trials where routine practice patients are followed for longer durations and questions of device replacement frequently arise. We assessed the incidence and time-dependence of appropriate ICD therapy in a routine clinical practice primary prevention population with prior myocardial infarction (MI) and reduced left ventricular ejection fraction (LVEF).
Methods and Results: Patients with prior MI and LVEF ≤35%, who received an ICD at our institution (1995–2005) for primary prevention, were identified. Incidence and time-dependence of first appropriate ICD therapy for ventricular arrhythmia (VA) and rapid VA (cycle length ≤260 ms) were determined. Of 525 ICD recipients for primary prevention, 115 (22%) had appropriate ICD therapy. Incidence of first appropriate ICD therapy was highest in the first year postimplant (20%), decreased to 12% in year 2, and remained at 6–11% yearly thereafter. A similar trend was observed with rapid VA, a higher risk in the first year (6%), and a lower but persistent risk thereafter (3.8% in year 7).
Conclusion: In a routine clinical practice primary prevention population with prior MI and LVEF ≤35%, the incidence of first ICD therapy for VA, including potentially life-threatening VA, is highest in the first year postimplant, and persists for up to seven years thereafter. Risk of first appropriate ICD therapy persists over time, and thus replacement of ICDs appears to be indicated for all patients.