Intermittent Atrioventricular Block: Procainamide Administration as a Provocative Test*

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Abstract
Patients (12) with clinical features suggesting possible intermittent high degree atrioventricular block were studied. All 12 patients had basic 1:1 atrioventricular [AV] conduction but 9 had an ECG pattern of bifascicular distal conduction disease (right bundle branch block with left anterior or posterior hemiblock, or left bundle branch block). Intracardiac conduction was assessed by recording the His bundle ECG and atrial pacing techniques before and 20 min after i.v. administration of procainamide, in a dose of up to 10 mg/kg. Before procainamide administration, 7 of the 12 patients had a prolonged H-V [His-Purkinje] interval (> 55 ms). Procainamide administration lengthened the H-V interval in all 12 patients by 5-40 ms. In 5 patients, procainamide induced 2nd or 3rd degree AV block below the level of the bundle of His. Procainamide administration may be a useful provocative test of distal conduction in patients with possible intermittent AV block.