Improvement in left ventricular intrinsic dyssynchrony with cardiac resynchronization therapy

OBJECTIVE Cardiac resynchronization therapy (CRT) has been shown to induce a structural and electrical remodeling; the data on whether left ventricle (LV) reverse remodeling is associated with restitution of intrinsic contraction pattern are unknown. In this study, we investigated the presence of improvement in left ventricular intrinsic dyssynchrony in patients with CRT. METHODS A total of 45 CRT recipients were prospectively studied. Dyssynchrony indexes including interventricular mechanical delay (IVMD) and tissue Doppler velocity opposing-wall delay (OWD) as well as QRS duration on 12-lead surface electrocardiogram were recorded before CRT device implantation. After 1 year, patients with chronic biventricular pacing were reprogramed to VVI 40 to allow the resumption of native conduction and contraction pattern. After 4-6 h of intrinsic rhythm, QRS duration and all echocardiographic measurements were recorded. Dyssynchrony was defined as IVMD >40 ms and OWD >65 ms. CRT response was defined by a ≥15% reduction in left ventricular end-systolic volume (LVESV) at a 12-month follow-up. RESULTS Thirty-two patients (71%) showed response to CRT. The native QRS duration reduced significantly from 150±12 ms to 138±14 ms (p<0.001), and dyssynchrony indexes showed a significant improvement only in responders. The mean OWD reduced from 86±37 ms to 50±29 ms (p<0.001), and the mean IVMD decreased from 55±22 ms to 28±22 ms (p<0.001) in responders. The reduction in LVESV was significantly correlated with ΔOWD (r=0.47, p=0.001), ΔIVMD (r=0.45, p=0.001), and ΔQRS (r=0.34, p=0.022). CONCLUSION Chronic CRT significantly improves LV native contraction pattern and causes reverse remodeling in dyssynchrony.