TABLE II Effect of Ouabain on Sinus Node and Atrial Conduction Intervals with Refractory Periods

formed in 16 patients before and 30 min after intravenous administration of ouabain (0.1 mg/kg). P-A interval (mean+SEM) was 40±2.1 ms before and 44± 1.5 ms after ouabain (P <0.001). Atrial effective and functional refractory periods (ERP and FRP) were measured in all patients during sinus rhythm and during driving at equivalent paced rates in 12 patients. The mean atrial ERP and FRP during sinus rhythm were, respectively, 244± 10.5 and 307± 11.0 ms before and 253±9.7 and 318±11.4 ms after infusion of ouabain (NS). Mean atrial ERP and FRP during driving were, respectively, 231±15.3 and 264±14.9 ms before and 266±+18.6 and 296±+19.7 ms after ouabain (P < 0.01 and P <0.01). Mean sinus cycle length and sinus recovery times were, respectively, 887±31.2 and 1,113-+38.7 ms before and 905+±38.2 and 1,008+30.7 ms after infusion of ouabain (NS and P < 0.005). Calculated sinoatrial conduction times before and after ouabain were 90±6.8 and 110±8.5 ms, respectively (P < 0.005). In summary, ouabain produced depression of intraatrial conduction as manifested by increase in P-A interval and atrial effective and functional refractory periods. Ouabain significantly increased calculated sinoatrial conduction time wtihout significant effect on spontaneous sinus cycle length.