The aim of the study was to provide comparative analysis of the zones with maximum intraventricular myocardial dyssynchrony (IVD) and the localizations of ventricular electrodes in patients with differential responses to cardiac resynchronization therapy (CRT). Materials and Methods: Retrospective study comprised patients (n=40) who had sinus rhythm, complete left bundle branch block (LBBB), left ventricular (LV) ejection fraction (EF) 15%, relative increase of LV eF ≥10%), and group 2 (n=20) with insufficient response to CRT (the absence of dynamics in the sizes, volumes, and LV EF). For topical evaluation of the zone of stimulation with ventricular electrode, a vector analysis of ECG was performed in the beginning and the end of the follow up period (VL was divided in 12 segments, RV was divided in 3 segments). Intraventricular and interventricular dyssynchrony of the myocardium was detected by echocardiography with tissue Doppler sonography. Results: initially, the groups did not differ in regard to gender, age, and parameters of echocardiography with tissue Doppler sonography. The absence of initial IVD was observed in 7 patients of group 1 and in 8 patients of group 2, p = 0.503, cardiomyopathy of ischemic genesis significantly prevailed in group 2 (75%, n=15, р=0.014). Dislocation of the leads was not documented for the entire period of the study, displacement of LV electrodes within the vein of the coronary sinus occurred in three cases. The final sizes, volumes, and LV EF values differed between the groups (р < 0.001), mean LV EF was 44.9±5.9% in group 1 and 26.9±6.4% in group 2. Overlapping of maximum IVD zone with the site of LV electrode implantation was more significant in group 1, р = 0.028. Final values of IVD were within normal ranges in both groups, the absence of IVD was observed in 95% and 80% of patients in group 1 and group 2, respectively, р = 0.493. Conclusions: correspondence of the myocardial zone with maximum dyssynchrony to the site of the Lv lead implantation was associated with a high response to CRT in the long term. Insufficient response can be caused by a non-optimal positioning of the LV electrode, lack of agreement between implantation site and IVD zone, and by positions of the ventricular electrodes close to each other.
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