ECG Challenge: What’s Happening?

K. Wang, MD


July 23, 2015


At quick glance, this looks like an electrical alternans. But careful examination, especially of V4, shows that every other beat has a shorter PR interval and a slurred upstroke (delta wave), indicating ventricular preexcitation of every other beat. Figure 2B, taken a moment later, shows that in addition to every beat being preexcited, more ventricular myocardium is preexcited, making the short PR interval and delta waves more easily recognizable (see V4 especially).

Figure 2.

Courtesy of Dr Wang.

Wolff-Parkinson-White (WPW) syndrome is well known to be intermittent. How intermittent? Sometimes only every other beat is preexcited; sometimes several beats are preexcited at a time or for several days at a time. The delta waves are isoelectric in some leads in this patient (especially in lead I), the PR interval is not short, and the delta wave is not seen even in the preexcited beats. The initial negative deflection of the QRS complexes in the inferior leads may be a combination of a Q wave of an old myocardial infarction and an inverted delta wave.

Electrical alternans would not have alternating PR intervals nor delta waves. The tracing does not show junctional or ventricular bigeminy because the R waves peak regularly (not prematurely).

We do not encounter ECG tracings of WPW syndrome frequently, but they can mislead us in so many different ways—this case being one such example.

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