QRS morphology, left ventricular lead location, and clinical outcome in patients receiving cardiac resynchronization therapy

Several studies have reported a poor outcome with cardiac resynchronization therapy (CRT) in non-left bundle branch block (LBBB) patients. Although the left ventricular (LV) lead location is an important determinant of the clinical outcome, there is scant information regarding its role in non-LBBB patients. This study sought to examine the impact of electrical and anatomical location of the LV lead in relation to baseline QRS morphology on the CRT outcome. A left ventricular lead electrical delay (LVLED) was measured intra-procedurally as an interval between QRS onset on the surface electrocardiogram (ECG) to the peak of sensed electrogram on LV lead and corrected for QRS width. The impact of the LVLED on time to first heart failure hospitalization (HFH), and composite outcome of all-cause mortality, HFH, LVAD implantation, and cardiac transplantation at 3 years was assessed. Among 144 patients (age 67 12 years, QRS duration 156 28 ms, non-LBBB 43), HFH was higher in non-LBBB compared with LBBB (43.5 vs. 24, P 0.015). Within LBBB, patients with the long LVLED (50) had 17 HFH vs. 53 in the short LVLED (50), P 0.002. Likewise in non-LBBB, patients with the long LVLED compared with the short LVLED had a lower HFH (36 vs. 61, P 0.026). In adjusted Cox proportional hazards model, the long LVLED in LBBB and non-LBBB was associated with an improved outcome. Specifically, in non-LBBB, LVLED 50 was associated with improved event-free survival with respect to time to first HFH (HR: 0.34; P 0.011) and composite outcome (HR: 0.41; P 0.019). Cardiac resynchronization therapy delivered from an LV pacing site characterized by the long LVLED was associated with the favourable outcome in LBBB and non-LBBB patients.