ECG Changes in a Case of Posterior Myocardial Infarction in the Presence of Right Bundle Branch Block

A 70-year-old male with hypertension and diabetes presented to the emergency department with a 1-hour history of chest pain. Initial 12-lead ECG revealed a right bundle branch block (RBBB) and ST depression (STD) in V2-V4. The anterior STD prompted a 15-lead ECG in which there was no evidence of ST elevation (STE). With a positive troponin, cardiology was consulted and the patient was admitted as a high-risk non-ST-elevation myocardial infarction (NSTEMI). Subsequently, his chest pain returned without further ST changes, regardless the patient went for emergency coronary angiography, which found a complete occlusion of the left circumflex artery. Anterior STD is a normal finding in RBBB and posterior STEs in the posterior leads are not always present making the recognition of posterior STEMI difficult. This case highlights three findings in leads V1-V3 that are concerning for posterior ischemia in the context of chest pain and an RBBB: tall R waves, upright T waves, and marked STD > 2 mm. This should prompt serial 15-lead ECGs and prompt cardiology consultation.