Conduction of wave of depolarization in left ventricle is altered proceeding from the anterior septum through left myocardium to the inferior and lateral left ventricular walls.
Results in left ventricular contracture dyssynchrony with the interventricular septum contracting before the left ventricular free wall.
Left ventricular dyssynchrony results in mechanical inefficiency and decreased the left ventricular ejection fraction and cardiac output.
One quarter to one third of patients with congestive heart failure have left bundle branch block.
Approximately 6.7% of patients with an acute MI present with LBBB, which could interfere with EKG interpretation and diagnosis when the age of the LBBB is unknown.
Chest pain may not be present in up to half of patients with LBBB and acute MI (Shipak MG).