Dual Conduction

Report:

Sinus rhythm

First degree AV block (PR intervals 0.24" and 0.40")

SVEB (atrial premature beat, with P’R = 0.48”

(?? blocked SVEB, with junctional escape)

VEB

Dual AV conduction (pathway)

Comment:

Manifest dual conduction13 in the same recording is rare; this is one of the two examples I have seen in 30years.

In both records, the change is effected by a premature beat: atrial in the top strip and ventricular in the bottom one (each is a simultaneous 2-channel Holter). The VEB comes after a P wave, but there is no question of fusion, since the basic PR intervals are so much longer.

The P’R interval is so long that the premature atrial beat causes a late QRS complex! Another example is shown below (Fig 19a), this time with less change in the PR interval, but with a marked post-ectopic sino-atrial depression. Here, one could postulate a blocked SVEB followed by a junctional escape beat - a much commoner situation. There are, however, problems with this: (i) the escape interval is relatively short, implying an accelerated junctional rhythm and (ii) the escape cycle is not followed by other junctional beats of same or similar cycle length, despite ample opportunity. Also (iii), in the original strip, the presumed junctional escape beat would have to be retrogradely blocked, as the sinus P wave follows at its heels.