Novel Strain Rate Index of Contractility Loss Caused by Mechanical Dyssynchrony - A Predictor of Response to Cardiac Resynchronization Therapy -

Abstract

Time-delay indexes are limited in predicting the response to cardiac resynchronization therapy (CRT), partly because they do not reflect the residual left ventricular (LV) contractility. We computed a novel index of LV contractility loss due to dyssynchrony (the strain rate (SR) dispersion index: SRDI) by using the speckle-tracking SR and compared the efficacy of the SRDI, time-delay indexes, and strain delay index (SDI), the previously reported index of wasted energy due to dyssynchrony, for predicting the acute response to CRT. Echocardiography was performed in 19 heart failure patients (LV ejection fraction (EF) 25 ± 6%) before and 2 weeks after CRT. The standard deviation of time to peak velocity, or strain, was calculated as time-delay indexes. The SRDI was calculated as the average of segmental peak systolic SR minus global peak systolic SR. Longitudinal SDI (L-SDI), longitudinal SRDI (L-SRDI), and circumferential SRDI (C-SRDI) significantly correlated with the change in global longitudinal strain (Δglobal LSt), whereas the time-delay indexes did not. Although the time-delay indexes were comparable between responders (Δglobal LSt ≥ 0.3%) and nonresponders, the L-SDI, L-SRDI, and C-SRDI were greater in responders. The area under the receiver operating characteristic curve of the L-SRDI, L-SDI, and C-SRDI for predicting responders was 0.89, 0.81, and 0.78, respectively. The SRDI correlated fairly well with an improvement in global LV systolic function after CRT.