title: Postpacing tachycardia: autonomic involvement.
abstract: The cessation of pacing from the sinus node region is followed by a transient sinus tachycardia or postpacing tachycardia (PPT). We sought to characterize autonomic involvement in PPT. We used alpha-chloralose-anesthetized dogs and recorded electrocardiograms, blood pressure, and electrograms from the sinus node, right atrium, right ventricle, and His bundle. Both vagi and both stellate ganglia were transected. PPT developed immediately after either linear or stepped heart rate changes. PPT followed pacing from the rostral but not the caudal region of the sulcus terminalis. Independent manipulation of absolute level of heart rate (+33, +66, and +100 beats/min above control) and duration of atrial pacing (10, 20, and 30 s) revealed that PPT is dependent predominantly on the duration of pacing and less on level of heart rate. During pacing in the control state, a 1:1 atrial capture was maintained. After atropine administration (0.2 mg/kg iv), PPT increased significantly in magnitude, time to peak PPT was shortened significantly, and loss of 1:1 atrial capture during pacing was evident at pacing rates of from 10 to 60 beats above control. In contrast, propranolol significantly attenuated PPT. We conclude that acetylcholine, released during pacing from the sinus node region, suppresses inherent sinus node acceleration induced by the concurrent release of intramural catecholamines. During pacing, acetylcholine release is essential for the maintenance of 1:1 atrial capture and significantly modulates both the latency and magnitude of PPT.
mesh_terms: D000818:Animals; D001341:Autonomic Nervous System / Q000502:physiology*; D002304:Cardiac Pacing, Artificial; D004285:Dogs; D006339:Heart Rate; D011433:Propranolol; D013564:Sympathetic Nervous System / Q000502:physiology; D013997:Time Factors
chemical_list: D011433:Propranolol