DIAGNOSIS: Sinus tachycardia, right bundle branch block, acute anterior myocardial infarction, occasional premature beats either ventricular or supraventricular with RBBB and LAHB aberration.

EXPLANATION: P waves with a normal PR interval are evident at a rate of 110 particularly in lead II. Morphology in V1 is qR with a duration of nearly 160 msec. This is diagnostic of RBBB [equally diagnostic would be rsR` morphology in V1 without infarction]. Q waves in V1 - V4 with ST segment elevations of 3-4 mm and primary T wave changes confirm the diagnosis of acute MI. [The T wave changes secondary to the BBB are expected to be opposite in direction to the QRS and here they are in the same direction; i.e. primary]. It's interesting that although BBB is traditionally reputed to mask ischemia, in showing this EKG around our department most everyone immediately saw the current of injury, but many attendings needed some prompting to diagnose the RBBB. But, you may be thinking, its really LBBB [not RBBB] that masks infarction. Stay tuned. LBBB may hide the Q waves but the current of injury is evident in the majority of cases, and with RBBB both the Q waves and the current of injury may be seen in the great majority of cases. The premature beats are probably PVCs, but one can't be sure. [Other EKGs in this same patient are suggestive of a supraventricular origin with RBBB and LAHB, and with this pattern the morphology in V1 is less helpful in differentiating. In the setting of an acute MI it's best to assume a ventricular source.]

Editor: Sol Nevins MD FACEP. Faculty, Emergency Medicine Residency, Morristown Memorial Hospital, Morristown, N.J.