Left ventricular pacing threshold and outcome in MADIT-CRT

Introduction: High left ventricular (LV) pacing threshold (PT) may in some cases indicate the presence of scarred myocardium, a predictor of poor outcome in cardiac resynchronization therapy (CRT) treated patients. We hypothesized that intraoperative LVPT can be used to determine echocardiographic and clinical responses to CRT.

Methods and results: The study comprised 975 patients enrolled in the CRT-D arm of the Multicenter Automatic Defibrillator Implantation Trial with Cardiac Resynchronization Therapy (MADIT-CRT). Multivariate regression analysis was performed to evaluate the relationship between LVPT and percent reduction in LV end-systolic volume (ESV) and left atrial volume (LAV) 1 year after CRT. Cox proportional hazards analysis was used to evaluate the relationship between LVPT and heart failure (HF) events or death (primary endpoint) and all-cause death (secondary endpoint). An increasing LVPT was inversely related to percent reduction in both LVESV (P = 0.02) and LAV (P<0.01). Patients with LVPT in the highest quartile (>1.8 V) were less likely to achieve reverse LV remodeling (≥15% LVESV reduction from baseline) than those with LVPT in the lower quartiles (hazard ratios [HR] OR 0.56, P = 0.02). Mean percent reduction in LAV and LVESV was also significantly greater among those with lowest quartile LVPT. Multivariate analysis showed borderline significant 13% (P = 0.06) and significant 22% (P = 0.03) increase in the risk of HF/death and death alone, respectively, per 1 volt increase in LVPT.

Conclusion: High intraoperative LVPT is associated with significantly lower echocardiographic and clinical response to CRT-D.