Prolonged PR Interval due to Concealed Ventriculoatrial (VA) Conduction

An adult with h/o of HTN came in due to mechanical fall. 

 
Figure 1 - Lead II

Why is the PR interval longer on the left than on the right?

  
Complex-looking arrhythmias are better interpreted when viewed in full disclosure and numbered.

 
Figure 2 - Full disclosure

There are bigeminal premature ventricular complexes (PVC) . QRS complexes 1,3,5,7,9,11 are conducted with prolonged PRI's (~280 ms or 0.28 sec). The PRI's of complexes 13 and 14 are shorter (~160 ms or 0.16 sec). The P wave after QRS complex # 12 is not conducted.

The possible explanation as shown in the ladder diagram is PVC with concealed retrograde conduction. 


Figure 3 - Ladder diagram

Prolonged PRI

The sinus P wave following the interpolated PVC reaches the AV node during it relative refractory period (induced by concealed retrograde conduction of the PVC) and is conducted with prolonged PRI.

Blocked P  wave

The P wave (after complex # 12) reached the AV node during its absolute refractory period (induced by concealed retrograde conduction of the PVC) and failed to conduct.

Reference: Fisch C and Knoebel, 2000, Electrocardiography of Clinical Arrhythmias, Futura Publishing Company Inc, NY

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