title: Effects of hypoxia on atrioventricular node of adult and neonatal rabbit hearts.
abstract: We used an isolated perfused heart model to assess the effects of graded hypoxia (95, 45, 20, 10, or 0% O2, exposure for 5 min) on the adult and neonatal (0-3 days) rabbit atrioventricular (AV) node. The AV nodal function was assessed by measuring the A-H interval at a constant atrial pacing cycle length, the longest pacing cycle length resulting in Wenckebach periodicity [Wenckebach cycle length (WCL)] and the AV nodal effective refractory period (AVNERP). The A-H intervals remained stable in neonatal hearts until O2 saturation was decreased to 10%. On the other hand, the A-H intervals began to increase in adult rabbit hearts at 20% O2. In 95% O2, the AV nodal WCL was longer in adult hearts than in the neonatal hearts (165 +/- 8 ms vs. 142 +/- 7 ms). The effect of hypoxia on the AV nodal WCL was significantly greater in adult hearts than in neonatal hearts when the O2 saturation was decreased to 20% (a 54% increase in adults vs. a 14% increase in neonates, P = 0.02). The difference was greater at lower levels of O2. In 95% O2 at comparable basis driving cycle length (240 ms), the A-H intervals were equal in neonatal and adult hearts (43 +/- 3 vs. 43 +/- 7 ms), but the AVNERP of the neonates was significantly longer than that of the adults (133 +/- 21 vs. 97 +/- 19 ms, P = 0.007).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Pediatrics, University of Iowa Hospital and Clinics, Iowa City.
authors.forename: M L
authors.initials: ML
authors.lastname: Young
authors.forename: R C
authors.initials: RC
authors.lastname: Tan
authors.forename: B M
authors.initials: BM
authors.lastname: Ramza
authors.forename: R W
authors.initials: RW
authors.lastname: Joyner
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001283:Atrioventricular Node / Q000503:physiopathology*; D002304:Cardiac Pacing, Artificial; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D009431:Neural Conduction; D011817:Rabbits; D012032:Refractory Period, Electrophysiological; D013997:Time Factors