[Comparison of the effects of ajmaline and procainamide in the diagnosis of paroxysmal atrioventricular block].

14 suspected of having a paroxystic atrio-ventricular block underwent a complete electrophysiological exploration including an ajmaline test. It was administered at the standard dose of 1 mg/kg at the rate of 1 mg/s. In order to evaluate a replacement test, an equivalent dose of procainamide was injected at the same rate (10 mg/kg, 10 mg/s) a few hours later. In 4 out of 14 cases the ajmaline test was positive. In only one patient, procainamide was able to demonstrate a sub-nodal block. The maximal lengthening of HV occurred at an earlier time after ajmaline than after procainamide (2.2 +/- 0.75 min. versus 4.1 +/- 1.59 min, p less than 0.02) and certainly more clear-cut (MaxHV = 73.5 +/- 12.9 ms versus 59.5 +/- 12.1 ms, p less than 0.01). The lengthening of HV after administration of these two products was significantly correlated but always markedly lesser with procainamide. In conclusion, the procainamide is less sensitive than the ajmaline test in the positive diagnosis of paroxystic atrio-ventricular blocks concerning absolute criteria in the positive diagnosis as well as relative criteria such as a definite lengthening of HV with ajmaline.