Although high defibrillation threshold (DFT) is a major and unavoidable clinical problem after implantation of an implantable cardioverter defibrillator (ICD), little is known about the cause and management of a high DFT in patients with hypertrophic cardiomyopathy (HCM). The purpose of this study was to assess the predictors of a high DFT in patients with HCM. Methods and Results: Twenty-three patients with non-dilated HCM who underwent ICD implantation were included. The DFT at the time of

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... device implantation was measured in all patients. The patients were divided into 2 groups, a high DFT group (DFT ≥15J, n=13) and a low DFT group (DFT <15J, n=10); and their baseline characteristics were compared. The QRS duration was longer in the high than in the low DFT group (128±31 vs 103±12 ms, respectively; P=0.02). QRS duration, left ventricular (LV) end-systolic diameter, and LV ejection fraction were significant predictors of DFT in univariate analysis. However, in multivariate analysis, the only factor significantly associated with DFT was QRS duration (P=0.002). Conclusions: QRS duration is the most consistent predictor of a high DFT in HCM patients undergoing ICD implantation. (Circ J 2009; 73: 1028 -1032