title: Evidence for a reexcitability gap in man after treatment with type I antiarrhythmic drugs.
abstract: The intention of this study was to determine whether type IA antiarrhythmic drugs cause a disparity between refractoriness and repolarization, and if so, its magnitude. We simultaneously measured monophasic action potential duration (MAPD) and effective refractory period (ERP) at a right ventricular site in 11 patients without overt right ventricular disease. The pacing protocol, which included sinus rhythm and a 600 and 400 msec cycle length of ventricular drive, was performed at baseline and after the intravenous administration of 15 mg/kg of procainamide in nine patients, and of 10 mg/kg of quinidine in two patients. Despite trivial changes in sinus rates, drug therapy caused a 10% to 17% increase in MAPD and ERP that shortened with decreasing drive cycle lengths. At baseline there was a small gap (10 to 13 msec) between MAPD and ERP in sinus rhythm and with a 600 or 400 msec drive. However, the type IA drug caused a significant widening of this gap that was most profound in sinus rhythm (45 msec) and that shortened but was not abolished with a 600 and 400 msec drive (28 and 29 msec, respectively). The disparity was caused in one third of cases by postrepolarization refractoriness. Type I drugs increase the difference between repolarization and refractoriness, and this effect is partially reversed with increases in heart rate. The clinical implications of these findings are discussed.
authors.affiliation: Lankenau Hospital and Medical Research Center, Wynnewood, PA 19096.
authors.forename: R J
authors.initials: RJ
authors.lastname: Haberman
authors.forename: S J
authors.initials: SJ
authors.lastname: Rials
authors.forename: J L
authors.initials: JL
authors.lastname: Stohler
authors.forename: R A
authors.initials: RA
authors.lastname: Marinchak
authors.forename: P R
authors.initials: PR
authors.lastname: Kowey
mesh_terms: D000200:Action Potentials / Q000187:drug effects*; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004562:Electrocardiography / Q000187:drug effects; D005260:Female; D006321:Heart / Q000187:drug effects* / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D011342:Procainamide / Q000494:pharmacology* / Q000627:therapeutic use; D011802:Quinidine / Q000494:pharmacology* / Q000627:therapeutic use; D012032:Refractory Period, Electrophysiological / Q000187:drug effects*
chemical_list: D011802:Quinidine; D011342:Procainamide