Effect of heart rate on the intrinsic and the ventricular-paced QRS duration

Abstract Background We evaluated the effect of heart rate on the intrinsic and the ventricular-paced QRS duration in implanted device recipients with normal or reduced left ventricular ejection fraction (EF). Methods We studied 239 outpatients with preserved intrinsic ventricular activation and normal (n = 92) or reduced (n = 147) EF who had apical (RVA) or mid-septal (RVS) right ventricular lead position. The QRS duration was measured at baseline and during atrial-based pacing at increased heart rate to ensure intrinsic or ventricular-paced QRS activation. Results The heart rate increase shortened the intrinsic QRS only in patients with normal EF, and further prolonged the ventricular-paced QRS in patients with reduced EF and either narrow or wide QRS (p < 0.001), irrespective of RVA or RVS pacing (p < 0.01). Conclusion Heart rate increase is associated with further QRS prolongation in patients with reduced EF, regardless of RVA or RVS pacing site.