Bundle branch blocks and/or hemiblocks complicating acute myocardial ischemia or infarction

Despite the bulk of anatomical and histologic evidence supporting the existence of three fascicules in the left branch of the His bundle, the concept of a bifascicular system proposed by Rosenbaum and his school has been adopted by the cardiological community as a practical teaching tool. Left anterior hemiblock (LAH) refers to block of the antero-superior branch of the left branch which is small and left posterior hemiblock (LPH) to block of the postero-inferior branch which is larger. The LAH is more common that the LPH and often associated with a complete right bundle branch block (RBBB). Coronary artery disease (CAD) is a major cause of hemiblocks. In this review article, we discuss various aspects of the relation of hemiblocks with CAD. We looked at the prevalence of LAH in consecutive patients undergoing coronary angiography and who had a significant coronary lesion in one vessel or more. In all patients with LAH, a significant lesion of the left anterior descending coronary artery was present, with in the majority of patients, an impairment of the left ventricular function. Bifascicular block (RBBB with LAH or LPH) can complicate acute myocardial infarction and is often associated with a poor prognosis and the presence of heart failure. Thrombolysis and or early angioplasty in acute myocardial infarction have significantly improved the prognosis and reduced the mortality associated with bifascicular block. Left anterior hemiblock pattern was also observed during angina pectoris occurring at rest or induced by exercise or atrial pacing. In these circumstances, LAH is transient and is likely to be due to ischemia in the anterolateral wall related to a lesion of the main trunk or the proximal left anterior descending coronary artery with the postero-inferior wall being first depolarized. The presence of bifascicular block in acute myocardial infarction still is associated with an unfavorable prognosis as compared to non-bundle branch block patients because of the common association with heart failure and other comorbidities.