Distinguishing STEMI from LVH on the ECG

I've started saying really something annoying at work.

When a resident starts interpreting an ECG, listing off features that either suggest or weigh against active ischemia, they will invariably (and properly) mention the deviation in millimeters of ST segments. I will then sanctamoniously intone

"Amateurs measure millimeters, professionals interpret the whole ECG."

If you think I'm smug about ECGs, ask about my thoughts on Huey Lewis.

Despite the my pretentiousness, there is an important element of truth there. (Dr Smith makes this point without smugness, but that's no fun. For me.) If you slavishly follow the standard criteria for STEMI diagnosis on the ECG (with so-and-so number of millimeters in this lead, so many leads with such elevation, etc.), you're going to make a lot of mistakes. 

One example is LBBB, a very common etiology of STE on the ECG. Usually, of course, the LBBB is immediately identified, owing to its characteristic appearance, and discussion switches to old vs new, and a review of Sgarbossa vs Smith criteria (peer-reviewed video lecture!).

The Problem with Left Ventricular Hypertrophy

Left ventricular hypertrophy (LVH), however, may not be as obvious, and ED physicians may mistakenly activate the cath lab based on the degree of ST segment elevation. Now, mistakes happen, and we want to have a certain "over-triage" rate, just like surgeons (before the use of CT scanners) had to have a certain "false appendectomy" rate. 

LVH, however, is very common, especially in the ED patient population. In fact, LVH is found in about a quarter of the ECGs in the ED that show STE, and is the most common cause.

Brady 2001

And it looks like emergency physicians get fooled by LVH fairly often. In one study of cath lab activations, it was found that LVH predicted a "false-postive" result, with an odds ration of 3.1.

How do we keep from getting fooled by this harmless (in the short-term) mimic of STEMI? It isn't simple. Indeed, one recent article suggested that "novice interpreters" of ECGs avoid diagnosing a STEMI in any patient with deep R- or S-waves.

Don't do it!

Well, I hope you are aspiring to more than "novice" status. I also hope that I can provide you some guidance beyond my usual semi-mystical injunctions and platitudes. 

"Be the ECG, Danny"

The Article

"Electrocardiographic Criteria for ST-Elevation Myocardial Infarction in Patients With Left Ventricular Hypertrophy"

Fortunately, there are non-novice ECG interpreters out there who want to share their secrets, like this group out of UC-Davis. The authors used  a database ("ACTIVATE-SF) of all the emergency physician-initiated cath lab activations over a period of 3 years in the San Francisco area. This gave a denominator of 411 activations.

Applying any of 3 different scoring systems (Cornell, Sokolow-Lyon, or aVR > 11mm), they found that 79 of these patients met ECG criteria for LVH. Now, some of these patients with LVH ended up having culprit arteries identified at angiography, but most didn't. 

They went further, and analyzed this select group of patients who had LVH and a positive cath. They found a few predictors on the ECG.

Certain locations of STE, the degree of STE, and the number of leads with STE all increased the odds of a true STEMI. So did the presence of Q-waves or reciprocal ST depression.

Now, LVH usually only gives you a pseudo-STEMI appearance in the anterior leads, so elevations in the inferior leads, for example, won't cause much confusion. You can see from the table above that STE in the inferior or lateral leads, or a true posterior STEMI, will be easy to distinguish. But what we really care about is trying to distinguish an anterior MI from LVH, and the data above confirms the difficulty; STE in V1-V3 was more often found to not have a culprit artery.

ST Elevation: Absolute and Relative
 Rather than just measuring the absolute amount of STE, however, the authors also analyzed the relative amount of STE, normalized against the difference of the preceding R- and S-waves. 

% STE = (Height T-P segment to J-point) / (Height of R-wave minus depth of S-wave)

Here is an illustration of applying this, using an example of LVH without STEMI from the paper:

True STEMIs, overall, had a higher percent STE (25%) versus "false" STEMI (9%).  More importantly, if the percent STE < 25%, STEMI was essentially ruled out. If the percent STE > 25%, a STEMI was predicted with a sensitivity of 77%, and 91% specificity. 


When they compared this rule, using relative STE, versus the conventional criteria for STEMI that use absolute STE, they found it to be more sensitive and far more specific (73% and 58%, respectively).

Examples
For example this patient has LVH, and STE in V1-V3:

But they also have a ratio of STE/(R - S) = 45% STE

Indicating that it's a true STEMI.

Contrast this ECG with this patient with LVH:

They have STE, just like the preceding patient, but a closer look at the anterior leads shows...

 

... a fairly insignificant STE/R-S ratio, suggesting no active ischemia.

Putting it all together...

For practical use, the authors summarized, in an algorithm, the practical use of their findings, when interpreting an ECG with ST segment elevations.

The Bottom Line

Even if you don't crunch the numbers, try to appreciate the pattern, the proportionality, of the elevations and deviations. You need to look beyond the numbers, feel the waveforms, you need to...

Ah heck, I did it again.