ECG Review-Nonhyperkalemic T Waves
Clinical Scenario: The ECG shown in the Figure was obtained from a previously healthy 69-year-old woman who presented with chest tightness of a few hours duration. She was hemodynamically stable at the time this ECG was recorded. Serum potassium was normal. No prior tracing was available. What do you suspect was going on? Clinically, what would you do?
Interpretation: The rhythm is sinus at a rate of 100/minute. The mean QRS axis and all intervals are normal. There is no sign of chamber enlargement. There are no Q waves, R wave progression is normal, and nondiagnostic ST-T wave flattening is seen in the inferior leads. However, the appearance of the ST segments and T waves in the precordial leads is exceedingly worrisome. Specifically, T waves are peaked in leads V1 through V4 and there is definite ST depression in leads V2 through V5. In view of the history (new chest tightness in an older adult), the combination of these findings should strongly suggest the possibility of true posterior infarction that may be in active evolution. If more than 20-30 minutes had passed, a new ECG should have been requested in the hope of clarifying the clinical picture. This patient was catheterized acutely—and severe 3-vessel disease with a 99% occlusion of the left main coronary artery was found. Unfortunately, the patient coded shortly thereafter, and could not be resuscitated.
Although acute posterior infarction most often occurs in association with acute inferior infarction (since both areas of the heart are usually supplied by the same right coronary artery)—true posterior infarction may sometimes occur in isolation, as it does here. Anterior precordial leads demonstrate the "mirror image" view of electrical activity in the posterior wall (instead of coded ST elevation and T wave inversion, there is ST depression and T wave peaking as seen here in leads V1 through V4).
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