Retrograde First Degree Ventriculoatrial Block

Report:

Junctional rhythm 37/min

Retrograde 1o ventriculoatrial (VA) block

VA interval 0.28”

Right bundle branch block

QRS 0.14”

Probable old inferoposterolateral infarction

Nonspecific ST/T changes

Comment:

There is a 1:1 retrograde conduction; its duration should be below 0.20”, same as for antegrade conduction. The VA interval includes the QRS broadened by the RBBB but this does not matter for the purpose of conventional reporting.

The retrograde P waves are small and narrow (as they sometimes are) but their direction is unmistakably retrograde: inverted in the inferior leads and upright in the remaining three frontal leads. Their place in the conduction sequences also leaves no doubt that they are retrograde.

Conduction sequences?

The Q waves in the anterolateral leads and L2 are pathological, with a borderline Q in aVF and upright T (despite RBBB) in V1. This supports the history of myocardial infarction and its topography may explain the difficulties in impulse generation and conduction in this patient (he was later paced).

Below (Fig 1a) is another trace taken a little earlier, showing allorhythmic junctional trigeminy in which the second beat of each sequence is almost certainly a reentry (echo) beat. The retrograde P waves (arrows) are midway between the first and the second complex in each group, attesting to the usual equivalence of antegrade and retrograde conduction times.

The patient’s sinus P waves are shown in Fig 1b, for comparison. The native PR interval is shorter than the programmed AV interval, a fact revealed by the failure of the slow-rising QRS to inhibit, in most cases, the barren pacing spike.

Fig 1a. Same patient, in junctional trigeminy.

Fig 1b. Same patient a few hours later, following the insetion of a permanent pacemaker. The sinus rhythm is conducted with RBBB distorted by pacemaker spikes (pseudofusion beats). Shorter-paced AV interval vould have resulted in haemodynamically less favourable LBBB-like ventricular pacing or true fusion sinus-pacemaker QRS complexes.

Fig 2. 50 year old woman with aortic endocarditis. Why is there no bradycardia in the presence of an advanced AV block? When is a block advanced? Is this one Möbitz 1 or Möbitz II block?