A modified ajmaline test for prediction of the effective refractory period of the accessory pathway in the wolff-parkinson-white syndrome

Abstract

Patients with the Wolff-Parkinson-White syndrome in whom the atrioventricular accessory pathway has a short anterograde effective refractory period (ERP) are considered at risk of sudden death if atrial fibrillation occurs. 1 Administration of ajmaline during sinus rhythm (50-mg intravenous bolus over 3 minutes) has been suggested as a test for identifying patients with an accessory pathway ERP shorter than 270 ms; in such patients the drug usually does not block anterograde conduction over the accessory pathway. 2 This study evaluates (1) the relation between dose of ajmaline, injected at a constant rate of 10 mg/min, blocking conduction over the accessory pathway, and duration of the accessory pathway ERP; (2) the reproducibility of the test, so modified; and (3) the possibility of predicting accessory pathway ERP on the basis of the dose of ajmaline blocking conduction over the accessory pathway. Thirty-two consecutive patients (21 men, 11 women), mean age 34 4- 15 years, with Wolff-ParkinsonWhite syndrome were studied. During continuous 6lead (I, II, III, V1,V~ and V6) electrocardiographic recording, ajmaline was administered intravenously at a constant rate of 10 mg,/min up to conduction block of the accessory pathway or a maximum total dose of 100 mg. The next day, after the patient gave informed written consent, electrophysiologic study was performed; the anterograde accessory pathway ERP was determined as the longest atrial premature beat interval not followed by anterograde conduction over the accessory pathway, at a driven rate 10 beats/rain faster than sinus rate. In 15 patients the ajmaline test was repeated after 24 to 72 hours. In 6 of the first 22 patients treated, ajmaline did not block conduction aver the accessory pathway: in 2 of them the accessory pathway ERP could not be determined because it was less than atrial refractoriness (250 and 200 ms, respectively) and in 4 the mean acces