QRS prolongation induced by cardiac resynchronization therapy correlates with deterioration in left ventricular function

Background: The benefits of cardiac resynchronization in inducing reverse ventricular remodeling in patients with left ventricular (LV) systolic dysfunction have been well established. Still, up to 30% of the patients fail to derive significant improvement from this therapy. A subset of "nonresponders" experience deterioration in LV function following cardiac resynchronization therapy (CRT). Characteristics of this patient population, however, have not been studied. Objective: To determine characteristics of patients who experience deterioration in LV function following CRT. Methods: Clinical, electrocardiographic, and echocardiographic data were collected in 856 consecutive patients presenting for a new CRT device. For inclusion, all patients had an LV ejection fraction '40%, a QRS duration '120 ms, and available baseline and follow-up echocardiograms and electrocardiograms. Deterioration in LV function was defined as an absolute decrease of 5% or greater in ejection fraction from baseline. Multivariate models were constructed to identify variables significantly associated with deterioration. Results: A total of 507 patients met inclusion criteria, of which 60 (11.8%) met criteria for deterioration. Patients with deterioration were more likely to be men (86.7% vs 66.9%; P =.002), have a non-left bundle branch block morphology (41.7% vs 23.7%; P =.001), and a history of atrial fibrillation (66.7% vs 51.7%; P =.03). On comparing the pre-CRT QRS duration with the first biventricular-paced QRS duration post-CRT implant, it was found that patients with LV deterioration had significant QRS widening than did those without deterioration (ms) (+3.9 ± 34.1 vs -9.0 ± 27.4, P =.007, respectively). In multivariate analysis, QRS widening indexed to the baseline QRS duration was significantly associated with LV deterioration (odds ratio 1.14 [1.06-1.23]; P =.001). Conclusion: QRS widening is associated with deterioration in LV function following CRT.