You’ve just started your shift in your regional ED when one of the staff members asks you to review a routine ECG of a 19yo female with cellulitis of the right leg.
What do you think of this ECG?
You kindly ask the staff member to perform another, with the amplitude doubled…
“Bulldust!” I hear you say; “There’s no delta wave!”
Well, not all that is pre-excitation is Wolff-Parkinson-White (WPW). WPW is the classic example of pre-excitation that is taught in medical school, pops up from time to time in practice and frequently trotted out (zebra trotting of course) as a random answer to a straightforward question during rounds.
Cardiac pre excitation describes the premature activation of the ventricles; the classic form being WPW, characterised by a short PR interval and a slurring of the QRS (the delta wave). This premature activation in WPW is caused by a band of myocytes bridging the atrioventricular junction (the bundle of Kent). This band inserts into the ventricular myocardium which conducts slower than the bundle of His and Purkinje fibres, hence the characteristic delta wave.
Looking at this ECG, you can see that there is a short PR interval (<0.12s) but no delta wave.
There are other pre-excitation syndromes that have been described, including the Lown-Ganong-Levine (LGL) syndrome, Enhanced Atroventricular Nodal Conduction (EAVNC) and Mahaim Fibre Tachycardia. Unlike WPW, the postulated pathways for these pre-excitation syndromes terminate into or near the conducting system, hence no delta waves. To make things even more complicated, pre-excitation syndromes can have a completely normal looking ECG too..
“Chris, I’m silently aspirating with boredom here, just tell me, what does this mean for the patient?”
Well, like WPW, these patients can suffer from a number of supraventricular tachycardias, such as atrioventricular nodal reentry (AVNRT) and orthodromic atrioventricular rentry (AVRT). They can also experience a rapid ventricular response from AF or atrial flutter.
Remember that not all pre-excitation is WPW, don’t just look for the delta wave, remember the PR interval – in the first timer SVT you might see something that will prompt an early referral to a cardiac electrophysiologist.
P.S. I don’t know yet which pre-excitation syndrome this is, when I hear back from the electrophysiologist I will update the post.
P.P.S. I will get some better images of the ECGs soon! I seem to have issues with the degradation of image quality from my camera to my mac.
- Podrid, PJ. Lown-Ganong-Levine syndrome and enhanced atrioventricular nodal conduction. In: UpToDate, Basow, DS (Ed), UpToDate, Waltham, MA, 2013.
- Podrid, PJ. Mahaim fiber tachycardias. In: UpToDate, Basow, DS (Ed), UpToDate, Waltham, MA, 2013.