Alternate-Beat Wenckebach Caused by VEBs

Report:

Sinus rhythm 92/min

VEBs, couplets and triplets

R-on-T phenomenon

Wenckebach second degree AV block for alternate P waves

Acute or recent inferior infarction

Comment:

The first two consecutively conducted P waves show slight but definite PR interval prolongation, similar to the other pair of P waves, toward the end of the strip. The next P is blocked by a VEB couplet, but its successor is conducted, with further PR prolongation. The next one is again blocked by a VEB couplet, but the following one is conducted with even longer PR interval. Then another VEB couplet blocks the P wave, its successor being conducted with the longest interval in this strip. After that comes a triplet, blocking two P waves. Thus, every second P wave is conducted with a longer PR interval until two P waves get blocked. The term “blocked” is used here to illustrate the analogy with alternate-beat Wenckebaching discussed below; of course these two P waves had no opportunity of conduction in the first place.

Next, the second pair of consecutively conducted P waves shows the expected PR prolongation; the next P is blocked by a single VEB. Now the subsequent PR interval has recovered – there is no more Wenckebaching in the alternate beats.

Typically, in the reported cases of alternate-beat Wenckebach, the proximal block is Wenckebach in type and the distal is fixed 2:1 block (opposite of what commonly happens in atrial tachycardia or flutter); the pauses contain two blocked P waves. The situation here is analogous to such a bi-level AV block, the VEB couplets ant the triplet playing the role of the (obviously) distal block74. An experiment of nature.

Below (Fig 115a) is another interesting interaction – or, rather, lack thereof – between Wenckebach block and a VEB: the sequence continues regardless of the VEB and produces what might be called postponed compensatory pause, populated by a blocked P wave and a sterile pacing spike.

Fig 115a. Postponed compensatory pause. What precedes it is a combination of type 1 AVB and concealed retrograde conduction – doubly concealed, as it were, in this case. The lower strip shows simple Wenckebach sequences, with pauses decorated with non-capturing pacing spikes.

Fig 116. 32 year old man with history of unsuccessful radiofrequency ablation procedure for SVT. He stopped taking amiodarone one month prior to the recording shown below, taken in his GP’s surgery. He complained of palpitations even at the time of this recording.