[Bundle-branch block in the course of myocardial infarction. Recent advances].

In case of acute myocardial infarction and a bundle-branch block (BBB) major diagnostic and prognostic issues should be addressed with different considerations, depending on the presence of a left BBB (LBBB) or a right BBB (RBBB), distinguishing new or presumably new BBB, considering the possibility that the BBB masks electrocardiographic features of MI with ST-segment elevation. In this paper we briefly discuss the results of published trials that assessed the prognostic difference between different types of BBB during the early phase of acute myocardial infarction. The Wong et al. analysis of HERO-2 trial demonstrates that in the setting of an anterior STEMI, the presence of an RBBB, whatever its onset, is associated with a higher risk of death. The same analysis shows as RBBB associated with an inferior infarction does not portend a worse prognosis independently of its onset. Patients with LBBB already present at randomization were found to have worse pre-infarction characteristics, responsible, by itself, for the worst prognosis. However, the occurrence of an LBBB after randomization indicates a 'true' ischaemic conduction damage, thus carrying an independent negative prognostic value due to the large percentage of myocardium involved. HERO-2 trial, showing prognostic differences between different clinical presentations, underlines the importance to be familiar with the mechanisms related to BBBs and with the prognostic implications of BBBs in the setting of an acute myocardial infarction.