Prognostic implications of nonsustained ventricular tachycardia in high-risk patients with hypertrophic cardiomyopathy

Background - The prognostic significance of nonsustained ventricular tachycardia (NSVT) in patients with hypertrophic cardiomyopathy is incompletely resolved. Methods and Results - The study group comprised 160 patients with implantable cardioverter defibrillators (ICDs), of whom 94 patients had 24- to 48-hour ambulatory monitoring preimplant. ICDs were interrogated and ambulatory ECGs monitored for NSVT episodes, with associations between NSVT- and ICD-treated ventricular arrhythmias examined. Eighty-six (54%) patients had runs of NSVT, including 17 before implant on ambulatory monitoring, 44 after ICD implantation, and 22 on both. Agreement between preimplant ambulatory monitoring and ICD interrogation for detecting NSVT was poor (κ=0.18). Eighteen of 86 patients (21%) with NSVT and 6 of 74 patients (8%) without NSVT experienced ICD-treated ventricular tachycardia (VT)/ventricular fibrillation (VF). NSVT was significantly associated with ICD-treated VT/VF (adjusted hazard ratio, 3.98; 95% confidence interval, 1.41-11.29; P=0.0093). ICD-treated VT/VF was associated with NSVT runs at a rate >200 beats per minute (adjusted hazard ratio, 15.63; 95% confidence interval, 4.01-60.89; P<0.0001) and >7 beats (adjusted hazard ratio, 6.26; 95% confidence interval, 2.02-19.41; P=0.0015). Repetitive runs of NSVT were also associated with ICD-treated VT/VF (adjusted hazard ratio, 9.22; 95% confidence interval, 2.53-33.60; P=0.0008). Slower (≤200 beats per minute), shorter (≤7), or a single run of NSVT were not associated with ICD-treated ventricular arrhythmias. Conclusions - On extended monitoring, NSVT was independently associated with ICD-treated ventricular arrhythmias, supporting the importance of NSVT in hypertrophic cardiomyopathy risk stratification. Faster rate (>200 beats per minutes), longer (>7 beats), and repetitive runs of NSVT were more highly predictive of ICD-treated VT/VF.