RESUMO
BACKGROUND: Cardiac resynchronization therapy (CRT) has proved to be very effective in improving morbidity and mortality in patients affected with severe congestive heart failure. Its efficacy has been shown to be greater in patients with left bundle branch block (LBBB). The aim of our study was to verify if newly proposed criteria for true LBBB identify patients with a better clinical and instrumental response to CRT. METHODS: Between May 2007 and April 2011, 111 patients with left ventricular ejection fraction (LVEF) ≤ 35% and LBBB morphology received a CRT device and were divided into two groups according to QRS morphology. Group 1 (61 patients) consisted of patients with "true" LBBB morphology; group 2 (50 patients) consisted of patients with "false" LBBB. The primary endpoint was the utility of criteria for true LBBB to predict a composite endpoint of all-cause mortality and hospital admission with heart failure. The secondary endpoint was the utility of the same criteria to predict an absolute increase in LVEF ≥ 10%. RESULTS: "False" LBBB morphology and a dose of bisoprolol <5 mg at last follow-up were the only parameters related to clinical outcome in multivariate analysis (respectively: hazard ratio [HR] 3.98, confidence interval [CI] 95% 1.51-10.48; HR 0.15, CI 95% 0.05-0.43). "True" LBBB morphology was the only variable significantly related to a greater increase in LVEF (HR 4.57, CI 95% 1.36-8.28). CONCLUSION: True LBBB morphology is related to a higher event-free survival rate in CRT patients and better echocardiographic response.