DIAGNOSIS: Sinus arrhythmia with acute inferior myocardial infarction [MI]

EXPLANATION: P waves with normal morphology and constant PR intervals are evident at a rate varying between 55 and 80.
The subtle ST segment elevations [of <1 mm] in leads II, III, aVF are suggestive of acute current of injury. A bit more obvious are the reciprocal changes in leads I and aVL. In lead I, the ST segment is noted to be flat and prolonged [>200 msec] with a sharp well demarcated take-off to the T wave. This has been termed plane ST depression. Lead aVL shows the more typical ST segment depression of ischemia. Frequently these are the first changes noted early in the course of inferior myocardial infarction and may be easily overlooked with potentially disastrous consequences for the patient and a lawsuit for the unhappy physician. [Of note, the precordial leads, taken of the right chest to evaluate the possibility of a right ventricular infarct, are normal.]
In this 43 year old man with atypical chest pain, intravenous nitroglycerin resolved his symptoms but not the ECG changes. Thrombolytic agents were not given. He did meet enzymatic criteria for acute infarction and at cardiac catheterization was noted to have a high-grade obstruction of the right coronary artery which was opened and a stented.

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

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