Defibrillation thresholds in hypertrophic cardiomyopathy.

BACKGROUND: Defibrillation threshold (DFT) testing is performed in part to ensure an adequate safety margin for the termination of spontaneous ventricular arrhythmias. Left ventricular mass is a predictor of high DFTs, so patients with hypertrophic cardiomyopathy (HCM) are often considered to be at risk for increased defibrillation energy requirements. However, there are little prospective data addressing this issue. OBJECTIVE: To assess DFTs in patients with HCM and evaluate the clinical predictors of elevated DFTs. METHODS: Eighty-nine consecutive patients with HCM and 600 control patients with ischemic or nonischemic cardiomyopathy underwent a uniform modified step-down DFT testing protocol. DFT was compared between the control and HCM populations. Predictors of elevated DFT were evaluated in the HCM group. RESULTS: There was no difference in DFT between HCM and control groups (10.4 ± 5.8 J vs 11.2 ± 5.6 J, respectively). Among patients with HCM, clinical parameters such as left ventricular ejection fraction, interventricular septal thickness, left ventricular mass, and QRS duration were not predictive of an elevated DFT. Only 3 patients (3.4%) with HCM had a DFT >20 J. CONCLUSION: Patients with HCM do not have elevated DFTs as compared to more typical populations undergoing implantable cardioverter-defibrillator implant; high-energy devices or complex lead systems are not needed routinely in this population.

Role of cardiac resynchronization therapy in asymptomatic and mildly symptomatic heart failure.

Cardiac resynchronization therapy (CRT) improves quality of life, left ventricular (LV) size and function, and mortality among moderate to severe symptomatic congestive heart failure (CHF) patients with decreased LV ejection fraction and QRS prolongation. Whether these benefits extend to similar groups with minimal or mild CHF is an area of ongoing investigation. Two small studies with limited follow-up demonstrated reverse remodeling but no symptomatic improvement. A recent, larger study in a population of asymptomatic or mildly symptomatic CHF patients with longer follow-up confirmed the beneficial effect of CRT on LV size and function; furthermore, it was the first study to show that CRT improves clinical outcome with delayed time to heart failure hospitalization. Ongoing trials of CRT in such patients will soon provide further data on morbidity and mortality.

Cardiac arrest survival after implementation of automated external defibrillator technology in the in-hospital setting.

BACKGROUND: Survival from ventricular tachycardia (VT) or ventricular fibrillation (VF) arrest is inversely related to delay to defibrillation. The automated external defibrillator (AED) has improved survival after out-of-hospital VT/VF arrest by decreasing time to defibrillation. The purpose of this study was to determine whether survival to discharge after in-hospital cardiac arrest caused by VT/VF could be improved via an institution-wide change from a standard monophasic defibrillator to a biphasic defibrillator with AED capability. METHODS AND RESULTS: After extensive staff education, all standard defibrillators were replaced by AEDs at a single institution. Outcomes were analyzed for 1 year before the change and 1 year after the change using a prospective database. In patients whose initial rhythm was VT/VF, AEDs were not associated with improvement in time to first shock (median 1 minute for both cohorts, p = 0.79) or survival to discharge (31% vs. 29%, p = 0.8) compared with standard defibrillators. In patients whose initial rhythm was asystole or pulseless electrical activity, AEDs were associated with a significant decrease in survival (15%) compared with standard defibrillators (23%, p = 0.04). The overall AED cohort showed no difference in survival to discharge compared with the standard cohort (18% vs. 23%, p = 0.09). CONCLUSIONS: Replacement of standard monophasic defibrillators with biphasic AEDs was associated with unchanged survival after in-hospital VT/VF arrest and decreased survival after in-hospital asystole or pulseless electrical activity arrest.