AUTONOMIC INFLUENCES IN ATRIAL ISCHEMIA - VAGALLY MEDIATED ATRIAL CONDUCTION IMPROVEMENT

To investigate the effects of autonomic nerve activation on electrophy siological properties of ischemic atrial myocardium, experiments were performed in 10 open chest adult dogs anesthetized with xylazine and a lpha-chloralose. Ischemia was created in the right atrial free wall by ligation of one or more branches of the right coronary artery. Bipola r electrograms were recorded from multiple sites in the ischemic and n on-ischemic zones. The atria were paced at 400 ms and 180 ms to assess conduction properties. One hour after ligation, delayed activation, e lectrogram fractionation, and electrogram alternans were observed in t he ischemic zone. All local conduction abnormalities were heart rate d ependent in that they were only observed at a pacing cycle length of 1 80 ms. The average duration of ischemic zone electrograms was signific antly prolonged from 17.7+/-1.6 ms to 26.4+/-1.6 ms (P<0.001). Right a nd left vagal stimulation significantly shortened the electrogram dura tion in the ischemic zone from 26.4+/-1.6 ms to 19.7+/-1.1 ms (P<0.01) and 20.0+/-1.1 ms (P<0.01), respectively. Ischemia-induced electrogra m alternans was eliminated completely. During right and left stellate stimulation, electrogram duration was not altered and alternans was st ill present. In conclusion, vagal stimulation in this canine model imp roves local conduction in ischemic myocardium in the right atrium. Thi s effect may be mediated by a reversal of the ischemia-induced membran e depolarization and a shortening of refractoriness in the atrium duri ng vagal activation. (C) 1997 Elsevier Science Ireland Ltd.