Effect of Hypoxia on Antegrade and Retrograde Atrioventricular Conduction in Isolated Perfused Heart

ABSTRACT

PURPOSE: Cyanotic congenital heart diseases patients are in a state of hypoxia since birth. In general, hypoxia delays atrioventricular conduction. The atrioventricular node in such a hypoxic condition would have a different function, and some possibility for arrhythmia. The authors studied atrioventricular nodal function during hypoxia to elucidate the relationship between hypoxia and arrhythmia, including atrioventricular node in terms of cardiac tissue level. METHODS: After extraction of an adult rabbit heart under pentobarbital anesthesia, the heart was retrogradely perfused through the aorta with graded hypoxic Krebs' solution(100, 70, and 50% oxygen). The intracardiac electrocardiograms were obtained by a custom-made programmed stimulation at basic cyde length 40ms antegradely and retrogradely. All the data was analysed at His-electrogram and conduction time. Refractory periods and Wenckebach cycling length were determined. RESULTS: During antegrade conduction, the fast AV nodal conduction was prolonged and the slow conduction shortened, resulting in decreased compliance of the AV nodal conduction with graded hypoxia. The His-Purkinje system also showed a similar result. Among the refractory periods, only the AV nodal effective refractory period was prolonged with hypoxia. Wenckebach cycle length was sensitive to hypoxia, especially for retrograde conduction. CONCLUSION: Because the AV conduction during hypoxia was characterized by decreased AV conduction compliance, prolonged AV nodal effective refractory period, and sensitive Wenckebach cyding length, hypoxia would not seem to be a special risk for arrhythmia, including AV node.