Havoc from an single PVC
Recently I saw beautiful strip posted on Linked In by Jean-Pierre Geuskens.
Jean-Pierre Geuskens eloquently presented the events on the tracing on the following ladder diagram as well.
I wanted to add my interpretation of the tracing to the ladder diagram.
The PVC conducts retrograde into the atrium and collides with the antegrade sinus impulse. The post-collision P-wave (P-wave #4) occurs essentially on time, thus representing ‘Non-reset’ of the sinus node. I was bothered by the relatively short V-A conduction time of this PVC (only 200 ms V-A while the antegrade fast pathway is conducting at 240 ms) but based on the ‘Non-reset’ I still feel that this is the likeliest scenario. The coincident echo beat conducts down the slow pathway and then conceals retrograde into the fast limb of the AV node while the infra-Hisian conduction of this echo beat likely conducts with left anterior hemiblock. The retrograde fast pathway concealment results in complete refractoriness in the fast pathway to the next conducted sinus impulse. This pattern repeats itself while shortening of the PR intervals are noted due to ‘warmup’ in slow pathway conduction; I can only explain the shortening of the PR intervals due to ‘warmup’ as the P-P intervals remain constant. Since the antegrade slow pathway conduction is accelerating due to the ‘warmup’, the ability of these impulses to conceal retrograde into the fast limb of the circuit is progressively diminished. Ultimately, the slow pathway conducts so rapidly antegrade, during the eighth beat, that there is no concealment retrograde into the fast pathway and the ninth beat of the tracing demonstrates return of the baseline PR interval due to unencumbered antegrade fast pathway conduction.
I did debate whether the 8th beat, or perhaps any of beats 4-8, could have been representative of delayed antegrade fast pathway conduction due to retrograde concealment into the fast pathway from the preceding slow pathway’s antegrade conduction. I felt however that the abrupt drop in PR interval from 360 ms to 240 ms between beats 8 to 9 was most consistent with a change in antegrade conduction from the slow to fast pathway given the constant P-P interval.
Happy to hear any critique of my interpretation.