What lurks in a (not-so-forgotten) interval

~40 y.o. woman with chest pain associated with cough

Welcome back.  After last week’s EKG quiz proved harder than I expected I decided to change gears and go with one that I hoped would be more straight-forward (though something that I feel I’m more guilty than I should be of being prompted by the computer read to note.)  Not so for most of you; in this quiz everyone at minimum commented on the most positive finding.

So as usual, let’s follow our system and assess the rate.  In this case it’s 3-4 big boxes wide, I would estimate this to be in the high 80’s.  Next up is rhythm.  There appears to be a P before every QRS and no dropped beats.  We see no sign of extra P waves hidden in the T waves.

It’s easy to skip at this point on to the QRS, but first we need to look at the PR interval.  Recognition of PR depression can aid in recognizing pericarditis (though there’s a lot of more important things to look at for that) as well as determining whether ST segments are truly elevated or not.  Many patients can have some PR depression that will cause the ST to look falsely elevated.  We’ll look at cases of each in the future.  The other aspect of any interval is the length.  Let’s zoom in on V4 and V5:


Here, magnified many times we can easily see the up-slurred QRS (delta wave) that indicates an accessory pathway, the most common of which is Wolf-Parkinson-White.

Looking at the rest of the EKG, the QRS is (aside from the delta wave) otherwise fairly normal in appearance.  ST waves abnormalities (with repolarization opposite the delta wave) are fairly common (though not always present) in WPW patients, in this EKG there is some mild indication of this in aVL:


Given that the bulk of the QRS can appear narrow to the naked eye and that the repolarization changes aren’t always present (or can be subtle), if a person doesn’t look specifically for delta waves (especially in the anterior chest leads), this can be missed.  You also need to be aware that in many patients (up to half of some series of WPW patients), the delta wave will NOT be present on every beat.  If it happens to not be present while the computer is recording the lateral chest leads it’s even easier to miss.  Per Chou’s Electrocardiography in Clinical Practice, WPW is more common in hyperthyroidism, pregnancy, various congenital heart diseases, and dilated cardiomyopathy, but most of the time does not indicate other associated heart disease.



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