Impaired Recovery of Left Ventricular Function in Patients With Cardiomyopathy and Left Bundle Branch Block

Background: Patients with left bundle branch block (LBBB) often respond to cardiac resynchronization therapy (CRT) with left ventricular ejection fraction (LVEF) improvement. Guideline directed medical therapy (GDMT) not CRT is first line therapy for patients with reduced LVEF with LBBB. However, there is little data on how patients with reduced LVEF and LBBB respond to GDMT. Methods: Using data from the Duke Echocardiography Laboratory Database, we identified patients with a baseline ECG and LVEF≤35% who had a follow-up LVEF 3–6 months later. We excluded patients with severe valve disease, a cardiac device, LVAD, or heart transplant. QRS morphology was classified as: LBBB, QRS<120msec (NQRS), or a wide QRS≥120msec but not LBBB (WQRS). ANOVA testing compared mean change in LVEF between the three groups with adjustment for significant comorbidities and GDMT. Results: 659 patients met the above criteria: 111 LBBB (17%), 59 WQRS (9%) and 489 NQRS (74%). Adjusted mean increase in LVEF over 3–6 months in the 3 groups was 2.03, 5.28, and 8.00 respectively (p<0.0001). Results were similar when adjusted for interim revascularization and myocardial infarction. Comparison of mean LVEF improvement between patients with LBBB on GDMT and those not on GDMT showed virtually no difference (3.50 vs. 3.44%). The combined end point of heart-failure hospitalization or mortality was highest for patients with LBBB. Conclusions: LBBB is associated with a smaller degree of LVEF improvement compared to other QRS morphologies, even with GDMT. Some patients with LBBB may benefit from CRT earlier than guidelines currently recommend.