Beyond Mechanical Dyssynchrony: From the Perspective of Residual Myocardial Contractility

Cardiac resynchronization therapy (CRT) improves symptoms and outcomes in patients with advanced heart failure through the improvement of left ventricular (LV) systolic function, which is brought by the correction of the dyssynchronous LV contraction. Therefore, the response to CRT depends on the degree of mechanical dyssynchrony. Nevertheless, some patients with advanced heart failure does not respond to CRT despite the presence of mechanical dyssynchrony, which could be partly because that not only the mechanical dyssynchrony but also residual myocardial contractility would determine the improvement of LV systolic function after CRT. From the standpoint of this consideration, several studies have reported that the LV contractility or myocardial scar burden assessed by speckle-tracking echocardiography, myocardial perfusion SPECT, and cardiac MRI were associated with the improvement of LV systolic dysfunction or symptoms after CRT. Furthermore, a parameter which takes account for the LV contractility together with dyssynchrony could be a useful marker to predict the response. We thus have proposed an index of LV contractility loss due to dyssynchrony, strain rate dispersion index (SRDI), and reported that SRDI could better predict the response to CRT than the dyssynchrony indices. In this presentation, we will summarize the determinants of CRT response other than the mechanical dyssynchrony.