Prevalence of acute myocardial infarction in patients with presumably new left bundle-branch block

Abstract Objectives We assessed the prevalence of true acute myocardial infarction and the need for emergent revascularization among patients with new or presumably new left bundle branch block (nLBBB) for whom the primary percutaneous coronary intervention protocol was activated. Methods and Results Among 802 patients, 69 (8.6%) had nLBBB. The chief presenting symptom was chest pain or cardiac arrest in 36 patients (52.2%) and shortness of breath in 15 (21.7%). Less than 30% of the patients had elevated cardiac troponin-I, and less than 10% had elevated creatine kinase–MB. Only 11.6% of the patients underwent emergent revascularization; the rate was higher for patients who presented with chest pain or cardiac arrest or shortness of breath than for patients who presented with other symptoms. Conclusions Acute myocardial infarction and the need for emergent revascularization are relatively uncommon among patients who present with nLBBB, especially when symptoms are atypical. Current guidelines for primary percutaneous coronary intervention protocol activation for nLBBB should be reconsidered.