In a previous post, we discussed the problem of ST segment elevation.
Because acute myocardial infarction (STEMI) is not the most common cause of ST segment elevation in chest pain patients, we need to consider other factors like reciprocal changes to shore up the diagnosis.
It’s also a good idea to be well versed in the typical appearance of the STE-mimics (paced rhythms, left ventricular hypertrophy, benign early depolarization, pericarditis, left ventricular hypertrophy, hyperkalemia, and so on).
Another factor that can assist you is an analysis of the morphology of the ST segment.
The normal ST segment should not be flat. It should have an upward concavity sometimes referred to as a “take-off”.
When an ST segment loses its concavity and becomes straight or upwardly convex, it can indicate acute myocardial infarction.
Consider this image from WJ Brady, SA Syverud, C Beagle et al. Electrocardiographic ST-segment Elevation: The Diagnosis of Acute Myocardial Infarction by Morphologic Analysis of the ST Segment Acad Emerg Med 2001; 8(10):961-967
You can draw an imaginary line between the J point and the apex of the T wave. If the ST segment is below that line, then it’s upwardly concave. If it’s even with or above that line, then it’s “non-concave” (straight or upwardly convex) which is suspicious for acute myocardial infarction.
(Note: As I learned on Facebook on 12/22/2010 this phenomenon was described in Pardee HEB. An electrocardiographic sign of coronary artery obstruction. Arch Intern Med 1920; 26: 244– 257 and referred to as “coving” of the ST-segment.)
If it helps you to remember, an upwardly concave ST segment makes a “smiley face” (good) and an upwardly convex ST segment makes a “frowny face” (bad).
Not at all! This finding is not particularly sensitive. It is, however, fairly specific. When non-concave ST segments are present, it’s another piece of the puzzle.
The STE-mimics almost always present with upwardly concave ST segments and an absence of reciprocal changes.
*** NOTE: Dr. Smith from Dr. Smith’s ECG Blog disputes this claim and has shown me a couple of cases of left ventricular hypertrophy with upwardly convex ST-segments in the right precordial leads that were not experiencing STEMI. ***
You might have noticed that I used the phrase “upwardly concave” as opposed to simply “concave”.
That’s because “concave” is “convex” depending on your perspective. That’s why I always mention the direction of the concavity or convexity.
Sometimes this can get confusing! Consider this image from the AHA’s new STEMI book.
The caption says “concave down” even though it’s referring to an ST segment that is upwardly concave. This may have been a typo, but I think it’s always helpful to use standardized definitions/language when it comes to medicine (or incident command)!
Regardless, if you look at this image from the STEMI book, the second window shows ST segments with a loss of upward concavity (ST segment straightening) and hyperacute T waves.
After PCI, you can see the development of Q waves and terminal T wave inversion (which usually indicates a STEMI that’s been around for a while).
It’s tough when a chest pain patient presents with an ECG with ST segments like we see in the third window. It’s often difficult to determine the age of an ECG abnormality like that.
ECG Challenges from AACN Advanced Critical Care (links to article about STEMI mimics)
Mimics of acute STEMI (left ventricular aneurysm)