VEBs in Quadrigeminy

Report:

Sinus rhythm 98/min

VEBs, one couplet and three triplets (runs of VT)

Left atrial abnormality (LAA)

Possible old inferior infarction

Comment:

The VEBs are undoubtedly what they look like, with taller left rabbit ear in an R wave in V1. They greatly outnumber the sinus beats and occur at a rate over 200/min; one would expect some hæmodynamic compromise. The triplets are, technically, runs of non-sustained VT19.

The first couplet replaces two sinus cycles, as a single VEB would. Two for the price of one! This crowding of the compensatory pause is reflected in the prolongation of the subsequent PR interval, through concealed retrograde conduction of the second VEB in the couplet. The triplets replace three sinus cycles each.

More of the same can be seen in the leads 1-2-3 strip below (Fig 136a). Idem, sed aliter: the first two sinus beats reveal prolongation of the PR interval – a Wenckebach conduction. What follows is Wenckebach compounded by concealed retrograde conduction. Every second P wave is blocked, and every second P wave is conducted with longer PR interval, until a triplet puts a stop to all conduction. Wenckebach conduction superimposed on 2:1 block is common in atrial tachyarrhythmias, especially flutter, but remains quite rare in normal (well, 90/min) sinus rhythm116. This is analogous to the reported cases of alternating Wenckebach periods terminating in two blocked P waves117. The uniqueness of this case lies in the fact that alternate P waves are not blocked at a different level of nodal-His system, but by the VEBs.

In Fig 136b the patient shows escape capture bigeminy or alternating 2:1 and 3:1 AV block. In the latter case, the PR intervals of conducted P waves show nice R-P – P-r elasticity. 136a. From the third cycle onwards, the conducted P waves have progressively longer PR intervals. The VEB triplets stops the sequence. 136b. Escape-capture bigeminy or alternating 2:1 and 3:1 AVB? 137. 49 year old man with primary congestive cardiomyopathy (COCM).