A reader of the Prehospital 12-Lead ECG blog asks, “How can you tell the difference (based on ECG criteria alone) between right ventricular hypertrophy and acute isolated posterior STEMI?”
Well, the good news is you don’t have to tell “based on ECG criteria alone” and I’m sure all of my regular readers know that I don’t advocate interpreting an ECG “in a vacuum”.
Having said that, it’s not that difficult to tell these conditions apart. But before we talk about that, let’s talk about what makes them similar.
You might recall from my previous post “Differential diagnosis of tall R-waves in lead V1” that both right ventricular hypertrophy and posterior MI can cause tall R-waves in lead V1. Sometimes this is referred to as the R/S ratio, and it should be less than 1 (although I always take a second look when the R/S ratio is greater than 1 in lead V2 as well).
Keep in mind that acute isolated posterior STEMI need not show tall R-waves in lead V1! That tends to be a “late” finding (since the tall R-waves are really reciprocal Q-waves from the posterior wall). In fact, most if not all of the acute isolated posterior STEMIs I’ve shown on this blog have not shown tall R-waves in lead V1.
But let’s say you have a patient who presents with chest pain and tall R-waves in lead V1, and it’s not a right bundle branch block.
Let’s say this ECG looks like this:
How would you know it’s right ventricular hypertrophy (with a right ventricular strain pattern) and not acute posterior STEMI or anterior ischemia?
The short answer is, because it shows a right axis deviation* as well as a “typical” looking right ventricular strain pattern in the right precordial leads (V1-V3).
What makes it “typical”?
The fact that the ST-depression and T-wave inversion is “pouty-lipped” (downwardly concave) and the degree of the secondary ST-T wave abnormality is proportional to the size of the R-wave!
In other words, the tallest R-waves are in lead V2 and lead V2 shows the most pronounced secondary ST-T wave abnormality in the opposite direction.
The bottom line is, when you see a right axis deviation (often with right atrial enlargement), and tall R-waves in the right precordial leads, take any ST-depression and T-wave inversion in the right precordial leads (V1-V3) with a grain of salt!
Perform serial ECGs and capture modified chest leads V7-V9 to help with the diagnosis of acute ischemia or acute isolated posterior STEMI!
* So yes, we can add this to the large list of reasons that axis determination is a critical skill for any serious student of electrocardiography to master.