Retrograde Conduction of AIVR: From the Second Beat Onward

Report:

Sinus rhythm 75/min

PR interval 0.20”

Intraventricular conduction delay, probably LBBB

QRS 0.12”

Accelerated idioventricular rhythm (AIVR) 96/min

Retrograde VA conduction

RP interval 0.20”

Comment:

The retrograde and antegrade conduction times are usually identical or very similar. Note how the retrograde P wave appears following the second beat of the AIVR. This is because the blocked sinus beat renders the AV node refractory. The penultimate QRS in the top strip actually shows the blocked sinus P wave in its ST segment; the last QRS has retrograde conduction. While in some situations retrograde conduction starts after the onset of AIVR or VT because the faster rate favours conductivity, in most cases the delay is due to the last sinus P wave blocking the way.

Dyspnœa may have been due, at least in part, to the hæmodynamically unfortunate timing of the retrograde P waves.

174. 72 year old man with recurrent palpitations.

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