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

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.