Myocardial infarction not so common in LBBB?

An observational cohort study of 7937 ED visits by patients presenting with chest pain or ‘ischemic equivalent’ (shortness of breath for which ACS was considered a possible cause) was done to examine the relationship between left bundle branch block (LBBB) on the ECG and the incidence of acute myocardial infarction (AMI). No difference was observed in the rates of AMI in patients with new or presumed new LBBB, old LBBB, and no LBBB. The authors suggest that this large cohort of undifferentiated ED patients may be more reflective of the true prevalence of AMI in LBBB (7.3% in this study) and question the appropriateness of a liberal fibrinolytic strategy for such patients. Another argument for primary PCI?

Lack of association between left bundle-branch block and acute myocardial infarction in symptomatic ED patients
Am J Emerg Med. 2009 Oct;27(8):916-21