Friday, 15 January 2010

Wolff-Parkinson-White (WPW) - STEMI Mimics

A really interesting 12-Lead ECG was posted to the Cardiology & Electrocardiography (ECG, EKG) Experts group on Facebook the other day.

If you're not familiar, this is one of the groups / fan pages on Facebook I help moderate with Jason Winter who also started the Cardiology & Electrocardiography Experts blog.

What's so interesting about this ECG is that it shows a relatively infrequent STEMI mimic. In addition, it helps demonstrate a point I've been pondering about several of the STEMI mimics in general.

Let's take a look.



The patient was a 29 year old male with no complaints. The ECG was captured during a routine workup according to the contributor Chris de Beer (thanks again for the interesting ECG, Chris).

The ECG shows a WPW pattern as evidenced by a short PR interval and delta waves. The delta waves create a pseudo-infarct pattern (Q-waves) in the septal leads.

You might recall from my previous post about left ventricular hypertrophy (LVH) that I think recognizing the so-called "strain pattern" is actually more important than knowing the "voltage criteria" for LVH.

I'm sure some of you are waiting for "Part II" of the left ventricular hypertrophy series, but I'm still waiting for inspiration! :)

What does this ECG have in common with a strain pattern from left ventricular hypertrophy (LVH)? What does it have in common with left bundle branch block (LBBB)? What does it have in common with ventricular rhythms? Including paced rhythms?

The answer is, it has a widened QRS-T angle! To put it another way, the T-waves and ST-segments are deflected opposite the main deflection of the QRS complex, and (this point is the most critical) the degree of the ST-T abnormality is proportional to the size of the QRS complex.

Think of this as a supplement to Sgarbossa's criteria and the "rule of appropriate T-wave (and ST-segment) discordance".

Here's a graphic to help illustrate the point.



When you see a pattern like this, regardless of cause, it should set off alarm bells that you are dealing with a STE-mimic and not acute STEMI!

Note that the S-wave in lead V3 is cut off by the bottom of the ECG paper. This is a common problem with prehospital 12-lead ECGs! We must presume that the S-wave would be the deepest in lead V3 if we were able to view the entire QRS complex.

That doesn't mean the patient isn't experiencing acute myocardial infarction (although this patient is asymptomatic so let's pretend he was over the age of 30 and complaining of chest discomfort).

It just means you should wait before pulling the trigger on the cardiac cath lab.

Look for changes on serially obtained ECGs instead!

See also:

Left ventricular hypertrophy

Identifying AMI in the presence of LBBB

Sgarbossa's criteria - new graphic

ECG mimics of acute STEMI