DIAGNOSIS: Sinus rhythm with right bundle branch block [RBBB], left anterior fascicular block [LAFB], a short run of atrial tachycardia, and most importantly, acute lateral wall myocardial infarction [MI].

EXPLANATION: P waves with a normal PR interval are evident at a rate of 65. Morphology in V1 is rsR' with a duration of at least 120 msec. This is diagnostic of RBBB. Small R waves in leads II, III, and aVF, with a leftward frontal plane axis of minus 60 degrees suggests LAFB.

ST segment elevations of 3 mm and primary T wave changes in leads I and aVL with reciprocal changes in the inferior leads confirm the diagnosis and location of the 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].

In this 86 year old woman who developed chest pain while visiting her granddaughter in the hospital [and was convinced to go to the ED because she "did not look good"], the ECG evidence of acute MI was strong enough for us to administer thrombolytic agents as soon as this tracing was obtained. The fact that the patient's blood pressure was 70 palpable [ultimately proved to be cardiogenic shock] only increased our certainty of the diagnosis.

The premature beats are almost certainly PACs since their morphology is identical to those of the normally conducted beats and there appear to be P waves preceding them of a different morphology than the sinus P waves. Since there are three in a row, an atrial tachycardia may be diagnosed.

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