Myocardial Stretch in Early Systole is a Key Determinant of the Synchrony of Left Ventricular Mechanical Activity in Vivo

Background: Recent in-vitro observations suggest that left ventricular (LV) contraction is powered by 'stretch activation', an intrinsic mechanism by which the stretching of an activated cardiomyocyte causes delayed force redevelopment. We hypothesized that mechanical dyssynchrony is related to prolonged early systolic stretch that delays the timing of peak segmental shortening. Methods and Results: The time intervals from R wave to segmental longitudinal stretch in early systole (T-stretch) and peak shortening (T-peak) and the respective standard deviations (sigma T-stretch and sigma T-peak) were measured by speckle-tracking echocardiography in 57 patients undergoing cardiac resynchronization therapy (CRT). The percentage of time spent in shortening, normalized to T-peak duration [corrected Delta T=(T-peak-T-stretch)/T-peak] correlated with LV reverse remodeling (reduction in end-systolic volume >= 15%). Of the 57 patients, 40 (70.2%) demonstrated LV reverse remodeling at an average follow-up of 263 125 days after CRT. At baseline, T-stretch and sigma T-stretch correlated with T-peak and sigma T-peak, respectively. Though there was no difference in T-stretch, T-peak, sigma T-stretch and sigma T-peak between responders and non-responders, corrected Delta T in the mid-lateral and mid-septal segments was shorter in the responders (P < 0.05 for both) and the average of the 2 independently predicted LV reverse remodeling (area under the curve: 0.77, P=0.001). Conclusions: Mapping LV segmental shortening in relation to early systolic stretch may aid dyssynchrony assessment in patients undergoing CRT.