Long-Term Impact of Left Bundle Branch Block on Cardiopulmonary Exercise Test Variables and Left Ventricular Systolic Function: A Two-Stage Observational Study

Introduction: Left bundle branch block (LBBB) disrupts the electrical activation of the left ventricle, potentially impairing its systolic function, leading to LBBB-induced cardiomyopathy. This study examined cardiopulmonary exercise test (CPET) variables in patients with and without LBBB and assessed the longitudinal development of left ventricular ejection fraction (LVEF).

Method: An observational, comparative clinical study was executed in two stages at a private hospital in Brazil. The sample consisted of 27 individuals: 11 with LBBB and 16 without LBBB, all with preserved LVEF (>50%) and without confirmed ischemia. CPET variables were assessed, and after 4 years, participants had a transthoracic echocardiogram for LVEF re-evaluation. Groups were compared using the t test or the χ2 test. Multivariate analysis of covariance determined effect magnitude.

Results: Patients with LBBB demonstrated significant differences in CPET variables, particularly in predicted peak <inline-formula><mml:math id="m1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mi mathvariant="normal">V</mml:mi><mml:mo>˙</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula>O2, predicted peak PO2, <inline-formula><mml:math id="m2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mi mathvariant="normal">V</mml:mi><mml:mo>˙</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula>E/<inline-formula><mml:math id="m3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mi mathvariant="normal">V</mml:mi><mml:mo>˙</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula>CO2 slope, and T ½ <inline-formula><mml:math id="m4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mi mathvariant="normal">V</mml:mi><mml:mo>˙</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula>O2. They also exhibited a more significant decline in LVEF over a 4-year span compared to the patients without LBBB. Although initial preservation of LVEF, changes in contractile patterns due to LBBB interfered with its systolic function, suggesting early ventricular dysfunction indicated by a reduction in LVEF and an increase in the <inline-formula><mml:math id="m5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mi mathvariant="normal">V</mml:mi><mml:mo>˙</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula>E/<inline-formula><mml:math id="m6" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover accent="true"><mml:mi mathvariant="normal">V</mml:mi><mml:mo>˙</mml:mo></mml:mover></mml:mrow></mml:math></inline-formula>CO2 slope. Despite differences in cardiopulmonary function and changes in LVEF over time between patients with and without LBBB, the effect size was considered mild to moderate.

Conclusions: LBBB patients with initially preserved LVEF displayed reduced exercise tolerance and a decrease in LVEF over time, emphasizing the need for vigilant monitoring and early intervention in these patients.