Systolic heart failure: should we care about electrical, mechanical or electromechanical dyssynchrony?

Prolonged QRS duration is electrocardiographic evidence of electrical dyssynchrony and is associated with a higher incidence of cardiac events and mortality. The study by Cho et al. (167 patients were followed up for 33.4 +/- 19.9 months) shows that mechanical dyssynchrony has an additional value over QRS duration in predicting cardiac events in patients with systolic heart failure. The dyssynchrony was assessed through tissue Doppler imaging - a temporal difference between the septal to lateral wall (Ts-1) of 65 ms or more defined the mechanical dyssynchrony. In multivariate Cox proportional hazard analysis, both QRS duration (hazard ratio [HR]: 1.85; p = 0.032) and Ts-1 (HR: 2.35; p = 0.002) were independent predictors of cardiac events. Those with both electrical and mechanical dyssynchrony had a HR of 3.98 (95% CI: 2.02-7.86; p < 0.001) when compared with those with a normal QRS duration and absence of mechanical dyssynchrony. Combining the information provided by QRS duration with mechanical dyssynchrony through Ts-1 is clinically relevant to stratifying the risk of hospitalization or death in systolic heart failure patients. However, these data do not support the use of mechanical dyssynchrony to select patients for cardiac resynchronization therapy, nor to predict response to this therapy. This was not assessed by the study.