Abstract â–¡ 99

Abnormal cardiac autonomic innervation may be a mechanism leading to sudden death in infants. We have developed an animal model in neonatal swine for the study of the possible role of abnormal cardiac innervation in the pathogenesis of SIDS (Gootman et al. J.SIDS Infant Mortal. 1996, 1:169; Tong et al. Lab. Animal Sci. 1995,45:398). In brief, piglets were separated into four groups: sham-operated control (C), left stellate ganglionectomy (LSG), right stellate ganglionectomy (RSG) or right cardiac vagotomy (RCV). Evaluation of the effects of denervation on ECG and heart rate (HR) were carried out in conscious piglets followed up to 3 months of age. Recordings of ECG were obtained during 1-2 hr intervals under resting conditions. Analysis of the ECG included: 1) measurements of QT interval and calculated QTc (Tong et al. J. Auton. Ner. Syst. 1997, 64:162) and Poincare plots to display differences in R-R and QT interval variability The results of these analyses revealed that HR decreased earliest in the RSG group and latest in the RCV group while the Poincare plots showed no differences between C and LSG & RSG groups until 1 wk post-surgery. On the other hand, within 24 hours HR changed following RCV. At the end of the chronic recording period we evaluated cardiovascular (CV) responses (HR, left ventricular [LV] and/or aortic [Ao] pressure [P]) to chemical stimulation of cardiopulmonary receptors and high pressure baroreceptors. Under Saffan anesthesia, we tested cardiopulmonary reflexes with phenyl biguanide (PBG), ventricular chemoreflexes (Bezold-Jarisch reflex) with veratrum alkaloids (VVA) and arterial baroreceptors with phenylephrine (PE). Postnatal maturation of responses to PBG were observed in C (Tong et al. "Advances in Swine in Biomedical Research", Tumbleson and Shook (eds.), Plenum Press, NY, 1996, pp. 123-130); following RSG or bilateral SG, responses reverted to the immature pattern (hypotension, bradycardia and A-V conduction block, (Schleman et al. Ped. Res. 1979, 13:1271; Tong et al. Ped. Res. 1997, 41:72)). The maximum decrease in LVP was reduced to LV injection of VVA following LSG but not following RSG. HR was reduced after RSG but not after LSG. Following equivalent AoP elevation elicited with PE, cardiac dysrhythmias occurred in the cardiac denervated groups but were not observed in the C group. Our results suggest that stimulation of these receptors in the presence of cardiac autonomic imbalance could alter cardiac function such that a catastrophic event occurs leading to SIDS. (Supported by NIH grants HD-28931 and HL-20864).