Aims: Atrial fibrillation (AFib) with a rapid ventricular response may adversely impact cardiac performance, especially in patients with heart failure. However, it remains uncertain whether rhythm irregularity per se has unfavourable effects apart from tachycardia, and whether rate regularization alone can improve heart function.
Methods and results: Nine subjects with chronic AFib, atrioventricular nodal block, and symptomatic heart failure (ejection fraction 14-30%) were studied using a pressure-volume catheter. Ventricles were biventricularly paced (RV-apex, LV-lateral wall) at 80 or 120 min(-1) mean rate, using regular or irregular, Poisson-distributed stimulation. At 80 min(-1), ventricular function was similar between the two pacing modes. However, at 120 min(-1), irregular pacing impaired systolic (dP/dt(max): -8.2%, P<0.001) and diastolic function (dP/dt(min): +21%, P<0.001, LV end-diastolic pressure: +26%, P=0.007) compared with regular rate pacing. Contractile function during irregular pacing varied with the ratio of preceding/pre-preceding intercycle (RR) interval (dP/dt(max): 80 b.p.m.: r=0.69; 120 b.p.m.: r=0.74), whereas pre-load had little effect on instantaneous contractility.
Conclusion: In heart failure subjects with AFib, RR-interval irregularity worsens cardiac function at elevated but not at normal range heart rate. Overall rate control is most important in these patients while rate regularization of rapid AFib may impart additional benefits.