In asymptomatic individuals, left bundle branch block (LBBB) is associated with an increased risk of cardiovascular events, but its impact on maximal functional capacity remains unclear. This study aimed to evaluate maximal aerobic capacity (peakVO2) in asymptomatic adults with LBBB without structural heart disease and compare it to an age-, physical activity-, and sex-matched control population.

This prospective case-control study included asymptomatic adults with isolated LBBB and matched controls. All participants underwent maximal cardiopulmonary exercise testing and echocardiography. The primary outcome was to compare peakVO2 and percent predicted peakVO2 (pp-peakVO2) between LBBB and matched controls. Secondary outcomes included differences in left ventricular indexed end-diastolic volumes (iLVEDV) and left ventricular ejection fraction (LVEF). Multivariate linear mixed models were used to analyze primary and secondary outcomes.

A total of 162 participants (81 with LBBB and 81 controls) were included. The mean age was 65.7±10.2 years, and 106 participants (65.4%) were women. The mean pp-peakVO2 and peakVO2 were 93.6±16.9% and 19.9±6.4mL/kg/min, respectively. There were no significant differences in cardiovascular risk factors, NT-proBNP, or hemoglobin values between groups. Multivariate analysis showed that the presence of LBBB was associated with lower peakVO2 (−3.3mL/kg/min, 95%CI,−4.6 to−2.1; P <.001) and pp-peakVO2 (−17.2%; 95%CI, −22.1 to −11.9; P <.001). Regarding secondary endpoints, individuals with LBBB showed higher iLVEDV (+4.4mL/m2, 95%CI, 1.3 to 7.6; P=.006) and lower LVEF (−2.8%, 95%CI, −4.3 to −1.2; P <.001) compared with controls.

In this study, adults with isolated LBBB showed reduced maximal functional capacity compared with controls.

Registered at ClinicalTrials.gov (NCT05643404).