Clinical efficacy of cardiac resynchronization therapy using left ventricular pacing in heart failure patients stratified by severity of ventricular conduction delay.

Objectives: We assessed the clinical efficacy of single-site left ventricular (LV) pacing and determined the impact of baseline conduction delay severity on the magnitude of benefit.

Background: Multisite biventricular pacing can improve heart failure (HF) symptoms in patients with an intraventricular conduction delay by resynchronizing abnormal ventricular contractions and improving LV systolic function.

Methods: Eighty-six patients with at least New York Heart Association functional class II HF, chronic LV systolic dysfunction, normal sinus rhythm, and a QRS interval over 120 ms were implanted for atrial-synchronized LV pacing. The single-blinded, randomized, controlled, crossover study stratified patients 1:1 by the baseline QRS interval into long (QRS >150 ms) and short (QRS 120 to 150 ms) groups, which were compared during a three-month period of active (univentricular) pacing and a three-month period of inactive (ventricular inhibited) pacing. The primary end point was peak oxygen consumption (VO(2)) followed by anaerobic threshold, distance walked in 6 min, and quality-of-life questionnaire score.

Patients: Twelve patients were withdrawn before randomization and 17 could not complete both study periods. The short QRS group did not improve in any end point with active pacing. For the long QRS group, peak VO(2) increased 2.46 ml/min/kg (p < 0.001), the anaerobic threshold increased 1.55 ml/min/kg (p < 0.001), the distance walked in 6 min increased 47 m (p = 0.024), and the quality-of-life score improved 8.1 points (p = 0.004).

Conclusions: Left ventricular pacing significantly improves exercise tolerance and quality of life in patients with chronic HF, LV systolic dysfunction, and a QRS interval over 150 ms.