Modification and abolition of re-entry within the His-Purkinje system in man by diphenylhydantoin

The phenomenon of macrore-entry (Re) within the His-Purkinje system (HPS) was consistently observed in 10 of 19 patients during retrograde refractory period studies. Effects of intravenous infusion of diphenylhydantoin (DPH) on Re were studied in these 10 patients 10 minutes after completion of infusion (mean plasma level equal to 17.0 ug/ml). Diphenylhydantoin modified determinants of Re in seven patients (group I) and abolished Re in the remaining three patients (group II). In group I, DPH shortened the critical V₁ V₂ from 310.0 ± 30.5 to 292.9 ± 25.6 msec (P < 0.025) and critical V₂ H₂ intervals for Re from 201.4 ± 18.4 to 185.0 ± 13.8 msec (P > 0.05). In group II, DPH abolished Re in two of three patients by precluding attainment of critical V₂ H₂ intervals whereas Re was abolished in the remaining one patient despite attainment of critical V₂ H₂ intervals (vs control). For both groups, DPH significantly shortened functional and effective refractory periods of the HPS (P < 0.001 and < 0.01, respectively) without significantly affecting the effective refractory period of the ventricular muscle. Diphenylhydantoin either completely abolished or significantly shortened the retrograde gap zones in the HPS. It is concluded that diphenylhydantoin significantly shortens His-Purkinje system refractoriness, abolishing Re in the patients with higher degree of improvement in refractoriness.