Implantable Cardioverter-Defibrillator Shocks ; A Marker of Poor Prognosis but Themselves Do Not Affect Mortality

Abstract

Implantable cardioverter-defibrillator (ICD) therapy has been proven to reduce mortality in patient with high risk for sudden cardiac death. However, recent studies suggest that ICD shocks, even inappropriate shocks, are associated with an increased risk of mortality. To clarify the prognostic implication of ICD shocks, consecutive 253 patients with ICD (79% men, 63±11 years, 36% primary prevention, left ventricular ejection fraction [LVEF]38±14%) were analyzed with respect to ICD shocks and death. During a median follow up period of 1428 days, appropriate and inappropriate shocks occurred in 62 (24.5%) patients each. A total of 55 patients (31 cardiac deaths) among the 253 patients died. In a Cox proportional-hazards model adjusted for baseline prognostic factors, age (HR : 1.044, p=0.007), LVEF (HR : 0.969, p=0.011), serum creatinine (HR : 1.867, p<0.001), a history of atrial fibrillation or atrial tachycardia (HR : 2.093, p=0.012), and appropriate shocks (HR : 2.777, 95%CI : 1.514-5.096, p=0.001) were associated with all-cause mortality. However, inappropriate shocks did not affect the mortality.
ICD shocks themselves do not contribute to the increased risk of mortality. Appropriate shocks are adverse prognostic marker indicating recurrence or new onset of ventricular tachyarrhythmia.