ECG Case 179: Acute Inferior and Posterior STEMI

This article is an answer to the ECG Case 179

There is a regular rhythm at a rate of 100 bpm, with a P wave (*) before each QRS complex and a stable PR interval (0.16 sec). The P wave is upright in leads II, aVF, and V4-V6 and negative in lead aVR. This is a sinus tachycardia.

Acute Inferior and Posterior STEMI
Acute Inferior and Posterior STEMI

The QRS complex duration (0.08 sec) and morphology are normal. The QRS axis is not able to be determined accurately because of very significant ST-segment elevation (↓) in leads II, III, and aVF. ST-segment elevation (↓) can also be seen in lead V6. The ST segments are convex and are merged with the T waves.

There is also ST-segment depression (^) in leads I, aVL, and V2-V4. The ECG is typical for an acute inferior wall ST-segment elevation myocardial infarction (STEMI), and the ST-segment depressions are reciprocal changes, although in leads V2-V3 the depressions represent involvement of the posterior wall of the left ventricle.

Interestingly, there is evidence of ST-segment alternans (ie, beat-to-beat changes in the height of the ST segment), best seen in leads aVL and aVF. This has primarily been described with coronary artery vasospasm and transient occlusion of a coronary artery during angioplasty. It is a marker of more severe transmural ischemia.