Thursday, October 14, 2010

STEMI, NSTEMI or STEMI equivalent?

It doesn't matter much what you call this pattern so long as you know it indicates acute LAD occlusion. The author of the post calls it a STEMI. But it's a STEMI only in a sense—-in the sense that it represents acute LAD occlusion and should therefore be treated like a STEMI. But I would prefer to call this a STEMI equivalent because from a pure morphology standpoint it's a NSTEMI, there being no ST segment elevation, at least not in two contiguous leads (the minimal ST elevation in V1 could pass as normal variant ST elevation in that lead).

This is a good example of why, in the recent literature review published by Dr. Brendan Phibbs, the STEMI/NSTEMI distinction was meaningless in terms of pathologic correlation.

In the case under discussion here, the indicative STEMI equivalent changes are found mainly in V2 and V3. Note the high amplitude, broad based T waves (spread-eagle T waves as Barney Marriott affectionately called them). The pattern is typically seen in the very early “hyperacute” phase, so a repeat tracing minutes later often shows the typical ST segment elevations.

The blog author makes some important teaching points about this fascinating case:

Never trust the computer. Computerized ECG interpretation was introduced into clinical use in the early 80s. Although several generations of new machines have come out since then, almost three decades later they remain notoriously inaccurate. Most of the time you can trust them with the numeric data, which saves you some work with the calipers, but for analysis of rhythm, ischemia and infarction patterns all bets are off.

Be cautious in the interpretation of ST depressions. Contrary to what the computer may try to tell you, ST segment depressions do not localize ischemia (T wave inversions and ST elevations do, but ST depressions don't). However, ST depressions may indicate that ischemia is present and they may constitute reciprocal changes which sometimes offer the most important clues in the entire tracing. In this case, the author makes the point that when ST depressions are in the inferior leads only they likely represent reciprocal changes of anterior or high lateral STEMI equivalent and should be considered such in appropriate clinical circumstances, until proven otherwise.

The post also has some pearls on differentiating benign early repolarization from pathologic ST elevations, and is worth reading in its entirety.

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