Atrial Flutter with 1:1 Conduction

Report:

Atrial tachycardia (flutter) 202/min

2:1 block (top strip)

1:1 conduction (bottom strips)

Rate-dependent left bundle branch block

Comment:

Note the exact doubling of the ventricular rate in the lower strips.

From the rate alone, the rhythm would be diagnosed as probable atrial tachycardia rather than flutter. It is, however, the same rhythm as before (not shown), before quinidine was commenced. Unfortunately, the leads are unknown; the top one is probably L2, bottom ones V1 or MCL1. The patient had a nonspecific LBBB-like ventricular conduction delay from the time of aortic valve replacement a year previously; both quinidine and the fast rate appear to have combined to broaden it into a “real” LBBB.

Many years ago, quinidine therapy was considered “therapeutic” with QRS prolongation up to 25%. Over 50% it was deemed toxic. The main thing to remember was to always administer digitalis as well (which shortens atrial refractory period and increases atrial rate and AV nodal block). Quinidine monotherapy – as in this case – slows down atrial rate and may even increase AV nodal conductivity by a mild atropine-like action. Several protocols were in use.

This patient came to grief because those protocols were ignored or forgotten.

Below (Fig 45a) is another example of flutter with 1:1 conduction. It is distinguishable from VT by the fortuitously recorded atrial activity before the onset of 100% conduction and by the typical LBBB morphology. Again, quinidine alone is to blame. Alone in one sense, not alone in two others.

The rapid ventricular rate may cause syncope or worse, but this is not the mechanism of “quinidine syncope”. The latter is due to torsade de pointes46.