Predictors of response to cardiac resynchronization therapy in patients with a non-left bundle branch block morphology.

Patients with non-left bundle branch block (LBBB) morphologies are thought to derive less benefit from cardiac resynchronization therapy (CRT) than those with LBBB. However, some patients do exhibit improvement. The characteristics associated with a response to CRT in patients with non-LBBB morphologies are unknown. Clinical, electrocardiographic, and echocardiographic data were collected from 850 consecutive patients presenting for a new CRT device. For inclusion, all patients had a left ventricular ejection fraction of ≤35%, a QRS duration of ≥120 ms, and baseline and follow-up echocardiograms available. Patients with a paced rhythm or LBBB were excluded. The response was defined as an absolute decrease in left ventricular end-systolic volume of ≥10% from baseline. Multivariate models were constructed to identify variables significantly associated with the response and long-term outcomes. A total of 99 patients met the inclusion criteria. Of these 99 patients, 22 had right bundle branch block and 77 had nonspecific intraventricular conduction delay; 52.5% met the criteria for response. On multivariate analysis, the QRS duration was the only variable significantly associated with the response (odds ratio per 10-ms increase 1.23, 95% confidence interval 1.01 to 1.52, p = 0.048). During a mean follow-up of 5.4 ± 0.9 years, 65 patients died or underwent heart transplant or left ventricular assist device placement. On multivariate analysis, the QRS duration was inversely associated with poor long-term outcomes (hazard ratio per 10-ms increase 0.79, 95% confidence interval 0.66 to 0.94, p = 0.005). In patients with advanced heart failure and non-LBBB morphologies, a wider baseline QRS duration is an important determinant of enhanced reverse ventricular remodeling and improved long-term outcomes after CRT.