Impact of Heart Rate on Mechanical Dyssynchrony and Left Ventricular Contractility in Patients with Heart Failure and Normal QRS Duration

AIMS: The quantification of mechanical dyssynchrony has important diagnostic value and may help to determine optimal therapy in heart failure (HF). We hypothesized that mechanical dyssynchrony may be augmented at increased heart rates in patients with HF and normal QRS duration. METHODS AND RESULTS: From online segmental conductance catheter signals, we derived indices to quantify temporal and spatial aspects of mechanical dyssynchrony during systole in 20 control subjects, 20 HF patients with normal QRS duration, and 12 HF patients with complete left bundle branch block (CLBBB). Data were collected at baseline, and then following a 40 bpm increase in heart rate induced by right atrial pacing. Mechanical dyssynchrony in HF patients with normal QRS duration or CLBBB was higher than that found in control subjects. In HF patients with normal QRS duration, mechanical dyssynchrony increased from 37.4+/-4.8% at baseline to 43.2+/-4.4% with increased heart rate (p<0.01), the resultant degree of mechanical dyssynchrony was similar to that at baseline in the HF patients with CLBBB. Increased heart rate did not affect dyssynchrony in the control patients. CONCLUSION: Mechanical dyssynchrony was augmented as heart rate increased by right atrial pacing in patients with HF and normal QRS duration.