The effect of
procaine amide, 10 mg. per kilogram via
intravenous infusion, was studied in 13 patients with the
WPW syndrome. The delta wave was eliminated by
procaine amide in 10 and modified in three patients. This effect lasted between 30 minutes and 8 1/2 hours and was unrelated to the total dose administered. Anterograde A-V conduction was assessed by atrial pacing with increasing rates. More rapid atrial pacing rates with 1:1 A-V conduction were observed in patients who maintained rather than lost their delta wave during pacing. Ventriculoatrial conduction was assessed with ventricular pacing at increasing rates; ventricular conduction time was fixed regardless on the pacing rate.
Procaine amide significantly prolonged V-A conduction time in six and blocked V-A conduction in one patient. In addition, A-V and V-A refractory periods were measured by the extrastimulus technique. Two types of responses were observed: (1) Type I or (2) line of identity. A-V nodal refractoriness was observed to be within the normal range.
Procaine amide converted anterograde line of identity responses to Type I responses in all patients who had their delta waves eliminated. In this patient group, bypass refractoriness was shorter than A-V nodal refractoriness.
Procaine amide was not observed to alter significantly normal A-V conduction as assessed by atrial pacing or A-V refractory period measurements. Furthermore, a significant disparity between the effects of
procaine amide on anterograde and retrograde bypass refractoriness was observed.
Tachycardias could be induced in nine of the 13 patients with a mean rate of 167.2 +/- 7.9 beats per minute; delta waves were abent during all episodes of
tachycardia.
Procaine amide prevented
tachycardia induction in six of the none patients.
Procaine amide therefore demonstrates electrophysiologic effects which would be beneficial for prevention or treatment of
reciprocating tachycardias in the
WPW syndrome. Moreover,
procaine amide would be an ideal agent for the prevention of rapid ventricular rates in patients with the
WPW syndrome and
atrial fibrillation.