99 EFFECTS OF CHRONIC HYPOXIA ON CARDIAC ELECTROPHYSICLOGICAL FUNCTION

Abstract

Because of arrhythmias seen in children with cyanotic congenital cardiac disease, we compared electrophysiological (EP) function in normoxically raised rabbits (N) with EP function in rabbits raised in an hypoxic environment (H, ambient pO2=60 torr). Twelve week-old rabbits (N, H) were anesthetized with pentobarbital sodium and alpha-chloralose. Insulated stainless steel wires were sutured directly to the right atrium for pacing. Surface ECG and arterial blood pressure (EP) were recorded. An intra-cardiac electrogram was recorded from a bipolar catheter inserted via the left superior vena cava into the coronary sinus. Data are presented in milliseconds and are compared as irean ± standard error of the mean. Significance was set at p<0.02. The control cycle length in H (330±9.9) was significantly longer than in N (231±16.2). Rapid atrial pacing resulted in a corrected pacemaker recovery time (CPRT) that was not significantly different between the two groups. Single programed extra stimuli ware used to evaluate atrial and AV nodal effective (AERP, AVNERP) and functional refractory periods (AFRP, AVNFRP). Statistically significant differences were found in AFRP, AVNFRP, and in AERP when results of N were compared to H. AVNERP was not significantly different. BP did not differ between H and N prior to or during the pacing protocol. We conclude that, in this model, chronic hypoxia during maturation alters control cycle length and influences cardiac EP function. This information may be important in evaluating arrhythmias in children with cyanotic congenital cardiac disease.