INTRAINDIVIDUAL COMPARISON OF DILTIAZEM AND VERAPAMIL ON INDUCTION OFPAROXYSMAL SUPRAVENTRICULAR TACHYCARDIA

The effects of i.v. diltiazem (0.25 mg/kg) and i.v. verapamil (0.15 mg /kg) were studied in 18 patients with recurrent paroxysmal supraventri cular tachycardia (SVT) who underwent serial electrophysiological stud ies. In 10 of 18 patients with extranodal accessory pathways the effec ts of diltiazem and verapamil were similar in comparable plasma concen trations. SVT was prevented in 10/10 cases after diltiazem and 9/10 ca ses after verapamil, furthermore there as an increase in antegrade ref ractoriness of the normal AV nodal pathway of 22 and 27%, respectively ; accessory pathway refractoriness and conduction remained unchanged i n both drugs. In 8 of 18 patients with dual AV nodal pathways diltiaze m was significantly less effective as compared to verapamil (p < 0.02) regarding prevention ov SVT (3/8 vs. 8/8 cases) and increase in the a ntegrade refractoriness of the slow AV nodal pathway (+21 vs. +34%). H owever, both drugs produced equivalent slowing of antegrade AV nodal c onduction and a similar increase in antegrade refractoriness of the fa st AV nodal pathway. In all 18 patients, the site of action of both dr ugs was the antegrade limb, regardless of SVT mechanism. The data sugg est that the two calcium antagonists are equipotent in AV reentrance b ut verapamil may offer greater benefit in AV nodal reentrance than dil tiazem.