Factors influencing appropriate firing of the implanted defibrillator for ventricular tachycardia/fibrillation

OBJECTIVES The purpose of this study was to prospectively examine the role of clinical, laboratory, echocardiographic, and electrophysiological variables as predictors of appropriate initial implantable cardioverter-defibrillator (ICD) therapy for ventricular tachycardia (VT) or ventricular fibrillation (VF) or death in the Multicenter Automatic Defibrillator Implantation Trial II (MADIT-II) population. BACKGROUND There is limited information regarding the determinants of appropriate ICD therapy in patients with reduced ventricular function after a myocardial infarction. METHODS We used secondary analysis in one arm of a multicenter randomized clinical trial in patients with a previous myocardial infarction and reduced left ventricular function. RESULTS We analyzed baseline and follow-up data on 719 patients enrolled in the ICD arm of the MADIT-II study. Appropriate ICD therapy was observed in 169 subjects. Clinical, laboratory, echocardiographic, and electrophysiological variables, along with measures of clinical instability such as interim hospitalization for congestive heart failure (IH-CHF) and interim hospitalization for coronary events (IH-CE), were examined with proportional hazards models and Kaplan-Meier time-to-event curves before and after first interim hospitalization. Interim hospitalization-CHF, IH-CE, no beta-blockers, digitalis use, blood urea nitrogen (BUN) > 25, body mass index (BMI) >= 30 kg/mz, and New York Heart Association functional class > 11 were associated with increased risk for appropriate ICD therapy for VT, VF, or death. In a multivariate (stepwise selection) analysis, IH-CHF was associated with an increased risk for the end point of either VT or VF (hazard ratio [HR] 2.52, 95% confidence interval [CI] 1.69 to 3.74, p < 0.001) and for the combined end point of VT, VF, or death (HR 2.97, 95% CI 2.15 to 4.09, p < 0.001). Interim hospitalization-CE was associated with an increased risk for VT, VF, or death (HR 1.66, 95% CI 1.09 to 2.52, p = 0.02). CONCLUSIONS These results provide important mechanistic information, suggesting that worsening clinical condition and cardiac instability, as reflected by an IH-CHF or IH-CE, are subsequently associated with a significant increase in the risk for appropriate ICD therapy (for VT/VF) and death.