Thursday, March 27, 2014

AV block occurring when it shouldn't: the paradoxical critical rate phenomenon

When we think of rate related AV block we almost always assume it occurs at faster supraventricular rates, especially type 2 AV block and bundle branch block. Occasionally, rarely in fact, it's the reverse: block occurs only during bradycardia or following a longer RR interval. If a vagal mechanism is excluded (which can usually be done by careful examination of the strips and clinical circumstances) the best known mechanism is phase 4 block which is the topic of the linked article.

Other causes of related electrocardiographic curiosities are supernormal conduction and the Wedensky effect.

1 comment:

Vince DiGiulio said...

Since you mention supernormal conduction, a topic few folks are aware of, I can't help but plug my own case of a patient in subtle high-grade AV-block with the added bonus of what I (and others) believe to be evidence of supernormal conduction:
http://ecgguru.com/blog/featured-case-study-guru-member-vince-digiulio-emt-cc