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

- The increase in heart rate is followed by a shortening of the intrinsic QRS duration only in patients with normal ejection fraction.
- The increased heart rate prolongs the ventricular-paced QRS duration particularly in patients with reduced ejection fraction.
- Following heart rate increase, the ventricular-paced QRS duration increases in patients with normal or reduced ejection fraction irrespective of the baseline intrinsic narrow or wide QRS complex as well as of the right ventricular apical or septal pacing site.
- The extent of the intrinsic and the ventricular-paced ΔQRS following heart rate increase may be useful in identifying patients with reduced ejection fraction.

BackgroundWe 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).MethodsWe 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.ResultsThe 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).ConclusionHeart rate increase is associated with further QRS prolongation in patients with reduced EF, regardless of RVA or RVS pacing site.