4:2 AV Block?

Report:

Supraventricular tachycardia, probably sinus, 132-150/min

First degree AV block (PR 0.22”)

Second degree AV block, Möbitz I

Concealed AV conduction - Wenckebach with two blocked P waves

4:2 overall conduction ratio

or,

2:1 AV block (unspecified)

Junctional premature beats

4:1 overall conduction ratio

Phasic aberrant conduction

Intraventricular conduction delay (QRS 0.12”), probably incomplete RBBB

or,

2o AV block (unspecified)

Junctional escape beats

Sinus captures with 1o AV block and phasic aberrant conduction

Escape-capture bigeminy

Comment:

The patient, not surprisingly, had a Mallory-Weiss tear.

It is difficult to assign the mechanism to this bigeminy with certainty. While Wenckebach AV nodal block can have more than one dropped P wave, this “multiple blockage”51,52,53 is commoner in Möbitz 2 blocks.

The simplest hypothesis, however, is that the early beats are junctional premature ectopics increasing the degree of AV block from basic 2:1 to 4:1, again with overall 4:2 ratio. They may have additional aberrancy superimposed on the pre-existing RBBB, or be different through non-phasic aberrancy characteristic of junctional beats. Again, the early beats may be sinus captures and the late ones junctional escapes.

Below are two strips taken previously, on a different lead, showing atrial flutter with 3:1 block (an unusual conduction ratio) and episodes of 2o AV block in sinus rhythm that look like Wenckebach, but start with junctional escape beats without any variation in the subsequent PR intervals. This patient obviously had complex conduction problems, perhaps modified by autonomic reflexes from vomiting and bleeding.

Fig 77a . Strips from old records. Not answers, but grounds for questions already raised.