Successful Reduction of Intraventricular Asynchrony is Associated with Superior Response to Cardiac Resynchronization Therapy

Background: Cardiac resynchronization therapy (CRT) is generally associated with a low to moderate increase of the left ventricular ejection fraction (LVEF). In some patients, however, LVEF improves remarkably and reaches near-normal values. The aim of the present study was to further characterize these so called 'super-responders' with a special focus on the extent of intra- and interventricular asynchrony before and after device implantation compared to average responders.

Methods: 37 consecutive patients who underwent CRT device implantation according to current guidelines were included in the study. Patients were examined by echocardiography before, one day after and six months after device implantation. Pre-defined criterion for superior response to CRT was an LVEF increase > 15% after six months.

Results: At follow-up, eight patients (21.6%) were identified as super-responders. There were no significant differences regarding age, gender, prevalence of ischemic heart disease and LVEF between average and super-responders at baseline. After six months, LVEF had significantly increased from 26.7% ± 5.7% to 33.1% ± 7.9% (p < 0.001) in average and from 24.0% ± 6.7% to 50.3% ± 7.4% (p < 0.001) in super-responders. Both groups showed a significant reduction of QRS duration as well as LV end-diastolic and -systolic volumes under CRT. At baseline, the interventricular mechanical delay (IVMD) was 53.7 ± 20.9 ms in average and 56.9 ± 22.4 ms in super-responders - representing a similar extent of interventricular asynchrony in both groups (p = 0.713). CRT significantly reduced the IVMD to 20.3 ± 15.7 (p < 0.001) in average and to 19.8 ± 15.9 ms (p = 0.013) in super-responders with no difference between both groups (p = 0.858). As a marker for intraventricular asynchrony, we assessed the longest intraventricular delay between six basal LV segments. At baseline, there was no difference between average (86.2 ± 30.5 ms) and super-responders (78.8 ± 23.6 ms, p = 0.528). CRT significantly reduced the longest intraventricular delay in both groups--with a significant difference between average (66.2 ± 36.2 ms) and super-responders (32.5 ± 18.3 ms, p = 0.022). Multivariate logistic regression analysis identified the longest intraventricular delay one day after device implantation as an independent predictor of superior response to CRT (p = 0.038).

Conclusions: A significant reduction of the longest intraventricular delay correlates with superior response to CRT.