Prevalence of mechanical dyssynchrony in heart failure patients with different QRS durations

Cardiac resynchronization therapy (CRT) has emerged as an established therapy for congestive heart failure. However, up to 30% of patients fail to respond to CRT despite prolonged QRS.

This study aimed at defining the prevalence of interventricular and intraventricular dyssynchrony in heart failure patients with different QRS durations.

A total of 123 consecutive patients with severe heart failure (LVEF < 35% and NYHA class III-IV) were prospectively evaluated using 12-lead electrocardiogram and complete echocardiographic examination including tissue Doppler imaging.

According to the QRS duration, 56 patients had a QRS duration < or = 120 ms (Group 1), 33 patients had a QRS duration between 120 and 150 ms (Group 2), and 34 patients had a QRS duration > or = 150 ms (Group 3). Intraventricular dyssynchrony was present in 36% of Group 1 patients, in 58% of Group 2 patients, and in 79% of Group 3 patients (P < 0.000). Linear regression demonstrated a weak relation between QRS and intraventricular dyssynchrony. A greater proportion of patients with interventricular dyssynchrony was observed in Group 3 or Group 2 compared to patients with normal QRS duration (32% in Group 1 vs. 51.5% in Group 2 vs. 76.5% in Group 3, P < 0.000). Linear regression demonstrated a significant relation between QRS duration and interventricular mechanical delay.

Although both interventricular and intraventricular dyssynchrony increased with the increasing QRS duration, the correlation between intraventricular mechanical and electrical dyssynchrony was weak. The lack of intraventricular dyssynchrony in a fraction of patients with standard CRT indication by QRS duration may provide us insight into the nonresponders rates.