One of the most confusing ST-elevation mimics for paramedics is the â€œstrain patternâ€ (or repolarization abnormality) occasionally found with left ventricular hypertrophy.
This is important because left ventricular hypertrophy is one of the most common causes of ST segment elevation in chest pain patients.
Many 12 lead ECG classes teach paramedics to recognize the voltage criteria for LVH (or at least one of the voltage criteria) but I donâ€™t think most 12 lead ECG classes do an adequate job explaining exactly what a â€œstrain patternâ€ looks like.
As a result, once the student identifies the voltage criteria for LVH, the interpretation stops. Similarly, once the student identifies the presence of â€œwideâ€ QRS complexes, the interpretation often stops.
Itâ€™s as if weâ€™re teaching students that itâ€™s impossible to identify STEMI in the presence of baseline abnormalities.
Itâ€™s more difficult, but itâ€™s certainly not impossible. The whole point is to know what a â€œnormalâ€ abnormality looks like. This is not an oxymoron! Itâ€™s the key to advanced 12 lead ECG interpretation.
In many cases, an ECG can meet the voltage criteria for LVH but show only minimal distortion of the ST segments and T waves. In other cases, the ECG will show the characteristic ST segment depression and T wave inversion in the lateral leads, but not the exaggerated ST segment elevation and T wave prominence in the right precordial leads.
Letâ€™s look at some examples. Let us assume that we are dealing with a patient complaining of chest discomfort.
Since this 12 lead ECG is not in the standard U.S. format, I used â€œcutâ€ and â€œpasteâ€ to structure it into a pattern more typical of prehospital 12 lead ECGs in the U.S.
In the first place, you will notice that the rhythm is sinus at about 75 beats per minute (using the large block method).
The frontal plane axis is probably around 30 degrees (40 degrees if you correct by 10 degrees due to the fact that lead III is slightly positive). This is important because a common misconception is that left axis deviation will be present with left ventricular hypertrophy. By no means is this always the case!
The QRS width is less than 120 ms, so we know that weâ€™re not dealing with a bundle branch block.
What about the ST segment elevation and huge T waves in the right precordial leads! Surely this patient is experiencing acute anterior STEMI!
Negative, ghostrider! (For my international friends, this is a reference to the movie Top Gun).
Letâ€™s look at the relationship between the QRS complex and the T waves in this ECG. The general pattern is one of discordance. In other words, When the QRS complex is positive (especially in the lateral leads I, aVL, V5 and V6) the T wave is negative. This is sometimes referred to as a widened QRS/T angle.
In addition, the ST segments are downwardly concave and the T waves are asymmetrical.
These are the cardinal findings with strain patterns (or repolarization abnormalities) secondary to left ventricular hypertrophy.
This ECG also shows ST segment elevation in the right precordial leads (V1, V2 and V3). You will note that the ST segments are upwardly concave and the severity of the ST segment elevation and T wave height is proportional to the depth of the S wave.
This is extremely important! With left ventricular hypertrophy, the deeper the QRS complex, the higher the ST segment and more pronounced the T wave abnormality.
This is also true of the ST segment depression and T wave inversion typically found in the lateral leads. The higher the R wave, the deeper the ST segment depression and more pronounced the inverted T wave.
Consider the following graphics to illustrate the point.
The most pronounced ST/T wave abnormality is found in lead V2. Itâ€™s difficult to tell because the QRS complexes run into one another, but the S wave is extremely deep in lead V2, possibly as deep as 35 mm (blue arrows). With LVH, you should expect the lead with the deepest S wave to show the most ST segment elevation and/or T wave height!
The red curve shows the upward concavity of the ST segment, which is another common finding with LVH. I have seen upwardly convex ST segments with LVH, but itâ€™s rare, and it always makes me suspicious of acute anterior STEMI!
Iâ€™ve outlined the shape of the T wave with orange lines. You can see that the T waves are asymmetrical, another finding consistent with a â€œstrain patternâ€ or depolarization abnormality with LVH.
In the left precordial leads, the most most pronounced ST/T wave abnormality is found in lead V5. Again, itâ€™s difficult to discern because the QRS complexes run into one another (as they often do with LVH) but the height of the R wave may be as high as 30 or even 40 mm (blue arrows).
The red curve shows the downwardly concave ST segment depression (exactly opposite the right precordial leads).
I have outlined the T wave inversion with orange lines to show the asymmetry. Again, a common finding with â€œstrain patternsâ€ or depolarization abnormalities with LVH.
In Part II, weâ€™ll review the voltage criteria for left ventricular hypertrophy.