Ventriculophasic Sinus Arrhythmia

Report:

Sinus rhythm.

Second degree AV block, Möbitz 1

Ventriculophasic sinus arrhythmia.

Phasic aberrant conduction

Comment:

The “short” complexes are aberrantly conducted sinus beats. The promotion from 2:1 to 3:2 block has produced a long-short cycle sequence required for phasic aberrant conduction. The diminished S wave during aberrant conduction is the earliest sign of RBBB aberrancy in V119.

Another long-short event here is, of course, the transient switch to 3:2 conduction in the middle of the strip, producing two short QRS cycles.

The third long-short phenomenon here is seen in the P wave cycle alternation during 2:1 conduction - the ventriculophasic sinus arrhythmia. The P waves surrounding a QRS complex are closer together than those with an “empty” cycle. The alternation is broken by the two periods of 3:2 conduction, eliminating 3:2 sinoatrial Wenckebach exit block as the cause of P wave bigeminy.

The ventriculophasic sinus arrhythmia may coexist with respiratory or non-respiratory variety. Its mechanism is unknown and several theories have been proposed.20