Left bundle branch block (LBBB) configuration has been described as a predictor of response to cardiac resynchronization therapy (CRT). We investigated whether different subtypes of true LBBB configuration could help select patients with better response and clinical outcome.

This retrospective study included 198 consecutive LBBB patients implanted with a CRT. True LBBB was defined using the Strauss and the Predict study criteria. Echocardiographic response was evaluated by the reduction in left ventricular end-systolic volume (LVESV) and the increase in left ventricular ejection fraction (LVEF). Clinical response was defined as an improvement in one category of the NYHA functional class.

Patients with true LBBB had a greater improvement in both LVESV reduction (median = − 27.6%, interquartile range = [− 4.9, − 50.1]) and LVEF increase (median 10.8 ± 10) than those with non-true LBBB (− 19.7%, [16.7, − 48.0]) p = 0.04 and 5.1 ± 10, p = 0.03, respectively. No differences were exhibited between true LBBB Strauss group (− 26.7%, [− 11.0, − 46.9]) and true LBBB Predict group (− 26.6%, [− 15.9, − 39.4]). There were no statistically significant differences in the percentage of patients with clinical response, assessed by NYHA improvement, among all groups. In the Cox model for death, age, ischemic etiology, and ΔLVESV were independent predictors of mortality. True LBBB (Strauss + Predict) patients had a trend towards lower mortality than non-true LBBB [HR = 0.55, 95% CI = (0.22–1.15)], p = 0.08. In the Cox model for HF hospitalization, age, sex male, prior LVEF, and ΔLVESV were independent predictors. True LBBB (Strauss + Predict) patients had a significantly lower risk of developing HF hospitalization than those with non-true LBBB [0.45 (0.21–0.90)], p = 0.029.

Patients with true LBBB, either Strauss or Predict criteria, had greater echocardiographic response and lower incidence of HF hospitalization than non-true LBBB when implanted with CRT.