Prolongation of the QTc Interval Predicts Appropriate Implantable Cardioverter-Defibrillator Therapies in Hypertrophic Cardiomyopathy

Objectives This study sought to determine factors predicting appropriate implantable cardioverter defibrillator (ICD) therapy in a large cohort of patients with hypertrophic cardiomyopathy (HCM). Background HCM is the leading cause of sudden cardiac death in those age <= 35 years. ICD therapy is offered to select patients at increased risk for sudden cardiac death. Currently, there are no clinical predictors of appropriate ICD therapy in HCM. Methods Patients attending the HCM clinic in Sydney, Australia, and who had undergone ICD insertion were included. Baseline data on clinical and ICD characteristics were collected. The primary endpoint was the proportion of patients who experienced at least 1 appropriate therapy from the ICD. Results Of 164 HCM patients included (62% male; mean follow-up, 6 +/- 4 years [range, 0 to 19 years]), 21 patients (13%) had at least 1 appropriate therapy. Corrected QT (QTc) interval was the strongest clinical predictor of appropriate ICD therapy (458 +/- 30 ms vs. 430 +/- 35 ms; p = 0.001). Multivariate logistic regression analysis demonstrated a 1.2-fold increased likelihood of appropriate therapy per 10-ms increase in QTc, independent of left ventricular wall thickness (LVWT) (odds ratio: 1.2; 95% confidence interval [CI]: 1.03 to 1.39; p = 0.02) and sex (odds ratio: 1.2; 95% CI: 1.07 to 1.42; p = 0.003). On analysis of cumulative event-free survival from appropriate ICD therapy, the risk for an appropriate ICD therapy in the subgroup with prolonged QT was >3-fold that in the subgroup without prolonged QT, after adjustment for LVWT (hazard ratio: 3.2; 95% CI: 1.02 to 9.88; p = 0.047) and sex (hazard ratio, 3.7; 95% CI, 1.22 to 11.41; p = 0.02). Conclusions The findings from this study suggest that QTc interval prolongation is a novel clinical predictor of appropriate ICD therapy in HCM. (C) 2013 by the American College of Cardiology Foundation