Electrophysiologic properties of diphenylhydantoin.

The electrophysiologic properties of diphenylhydantoin (DPH) (5-10 mg/kg) intravenously was studied in 14 subjects using His bundle recordings and correlated with blood levels. Conduction through the A-V conducting system (AVCS) was studied at various paced atrial rates and refractory periods determined using programmed atrial premature depolarization within 10 min of drug administration. In 11 of 14 subjects the sinus cycle length was shortened by an average of 110 msec, lengthened in three (average 116 msec). Conduction through the A-V node (AVN) was shortened in seven subjects (average 10 msec), lengthened in one (5 msec), and unchanged in the remaining six. Conductinged by 5 msec). Prior to DPH, the longest mained constant in all but two subjects (proloengthened in four, and was unchanged in the rerefractory period of the AVCS was in the AVN in nine subjects, the atrium in four and the HPS in one. After DPH, the following effects were noted: (1) the effective refractory period (ERP) of the atria shortened in four subjects, lengthened in four, and was unchanged in the remaining six; (2) the ERP of the AVN shortened in 6/9 subjects, lengthened in 3/9; (3) functional refractory period of AVN shortened in si, prolonged in three subjects, and remained unchanged in five subjects; (4) the relative refractory period (RRP) of the HPS shortened in 7/7 subjects; (5) ERP of HPS in 1/1 subject shortened. Thus, DPH showed varied effects on A-V nodal conduction, inconsistent effect in the atrium, and consistent shortening of the refractorv period of the HPS. The data suggest DPH differs from other antiarrhythmic drugs such as quinidine and procaine amide.