Etiology of atrioventricular-conduction abnormalities following cardiac surgery.

Atrioventricular-nodal-conduction abnormalities following cardiac surgery have been attributed to the potassium ion in cardioplegic solutions. To clarify the etiology of these rhythm problems, 15 dogs were subjected to (I) 60 min 4 degrees C potassium cardioplegic arrest; (II) 30 min normothermic ischemic arrest; or (III) cardiac hypothermia without ischemia. In sinus rhythm and during atrial pacing, A-H and H-V intervals, Wenckebach cycle length (WCL), atrial- and AV-nodal refractory periods (ARP and NRP) were measured at 37 degrees C before and 30 min after arrest (groups I and II) and at various myocardial temperatures (group III). Following cardioplegic arrest and reperfusion, all AV-nodal-conduction properties were unchanged from preischemic values. In contrast, unprotected ischemia significantly prolonged AV-nodal-conduction time (P less than 0.01) and myocardial hypothermia resulted in prolonged WCL (P less than 0.01), prolonged functional NRP (P less than 0.05), in addition to delayed A-H interval (P less than 0.05). The data suggest that properties of AV-nodal conduction are preserved following potassium cardioplegic arrest, but impaired by ischemic injury or persistent local cardiac hypothermia.