Relation of echocardiographic wall motion score index and response to dobutamine stress to defibrillation threshold at the time of implantation of a cardiac defibrillator.

Predictors of defibrillation threshold (DFT) at implantation remain poorly defined. It was hypothesized that a greater wall motion score index (WMSI) at rest on echocardiography and an ischemic or biphasic response on dobutamine stress echocardiography (DSE) would predict a greater DFT. Consecutive patients who underwent implantable cardiac-defibrillator implantation underwent echocardiography and DSE. DFT at implantation was assessed using the step-down method. Thirteen men aged 68 +/- 10 years with left ventricular ejection fractions of 28 +/- 10% participated in the study. DFTs ranged from 5 to 25 J (mean 14 +/- 8). A WMSI at rest of > or = 2.5 had a 71% positive predictive value and an 83% negative predictive value for a DFT > or = 15 J. An ischemic or biphasic response during DSE did not predict a greater DFT at implantation.

Biventricular pacing reduces the induction of monomorphic ventricular tachycardia: a potential mechanism for arrhythmia suppression.

OBJECTIVES: The aim of the present study was to evaluate in a prospective randomized fashion the electrophysiologic effects of acute biventricular (BV) pacing. We hypothesized that (1) the local coupling interval in the left ventricle in response to right-sided ventricular premature beats is prolonged when BV pacing is applied during the drive train compared with right ventricular (RV) pacing, and (2) BV programmed electrical stimulation (PES) decreases the induction of ventricular arrhythmias compared with standard RV-PES, regardless of the presence of intraventricular conduction delay. BACKGROUND: Previous studies have suggested that BV pacing might decrease the frequency of ventricular arrhythmias; however, the mechanism of arrhythmia suppression remains unclear. METHODS: Eighteen patients with coronary artery disease were randomized to RV-PES or BV-PES with a repeat study using the other pacing mode. The RV effective refractory periods were measured during RV-PES and BV-PES. In addition, the local LV S(1)-S(2) coupling interval was measured at 600/450 ms and 400/350 ms during RV-PES and BV-PES. RESULTS: BV-PES had no effect on RV effective refractory periods. On the other hand, the local LV S(1)-S(2) coupling intervals increased significantly during BV-PES compared with RV-PES (P < .0001). Ventricular tachycardia was induced in six patients using RV-PES but in only one patient with BV-PES (RR = 83%, P = .01). No difference was observed in the induction of ventricular fibrillation. CONCLUSIONS: BV-PES significantly reduced the induction of ventricular tachycardia compared to RV-PES, with no significant effect on ventricular fibrillation induction. Our findings may help explain the reduced incidence of ventricular arrhythmias noted with chronic BV pacing.