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Despite the impressive results of cardiac resynchronization therapy (CRT) in major randomized studies, 20-30% of patients do not benefit from CRT when the established selection criteria were applied. We hypothesized that a combined assessment of mechanical dyssynchrony, myocardial deformation and diastolic function would identify patients who would benefit most from CRT.
In 36 CRT patients, clinical evaluation and echocardiography were performed before and after CRT. Clinical and echocardiographic response to CRT was defined as an improvement of ≥1 NYHA functional class and a reduction in left ventricular end-systolic volume (LVESV) of ≥15% at 1-year follow-up, respectively. Patients were classified into 3 subgroups according to their amount of response: echocardiographic responders, clinical responders, and nonresponders. Radial dyssynchrony and LV global longitudinal, radial, and circumferential peak strain (GLS, GRS, and GCS, respectively) was assessed by speckle tracking image. Diastolic function was quantified by conventional echocardiography.
Atrioventricular (AV) and intra-ventricular dyssynchrony was corrected in the echocardiographic response group. In addition to left bundle-branch block (LBBB), nonspecific intraventricular conduction disturbance (IVCD) with intra-ventricular dyssynchrony could also improve left ventricular remodeling. Echocardiographic responders had better GLS, GCS and GRS at baseline which significantly increased at 12-month follow up. An improvement in estimates of LV filling pressure and a decrease in mitral regurgitation and left atrial dimensions were observed only in echocardiographic responders to CRT. Patients with clinical but without echocardiographic response had greater LVESV and lower GCS at baseline. In this group, patients showed a significant improvement in AV synchrony and a nonsignificant improvement in other parameters. The nonresponder group did not improve the AV and intra-ventricular dyssynchrony. CRT could not improve restrictive filling pattern with normal filling time and showed a sustained restrictive filling pattern.
Overall, those patients with AV and intra-ventricular dyssynchrony and those with best contractile function and short diastolic filling time of restrictive filling pattern at baseline demonstrated the greatest benefit from CRT.
Mechanical dyssynchrony, contractile function and filling pattern are important determinants of the benefits in CRT.