title: Characterization of sinoatrial parasympathetic innervation in humans.
abstract: BACKGROUND
  The response to sinoatrial parasympathetic nerve stimulation (shortened atrial refractoriness) was used to determine the atrial distribution of these nerve fibers in humans. We hypothesized that, in humans, parasympathetic nerves that innervate the sinoatrial node also innervate the right atrium and that the greatest density of innervation is near the sinoatrial nodal fat pad.
  
  
  RESULTS
  Temporary epicardial wire electrodes were sutured in pairs in the sinoatrial nodal fat pad, high right atrium, and right ventricle by direct visualization during coronary artery bypass surgery in nine patients. Appropriate electrode placement was confirmed by electrically stimulating the fat pad in the operating room to prolong sinus cycle length by 50%. Experiments were performed in the electrophysiology laboratory 1 to 5 days after surgery. Programmed atrial stimulation was performed via an endocardial electrode catheter advanced to the right atrium. The catheter tip electrode was moved in 1-cm concentric zones around the epicardial wires by fluoroscopic guidance. Atrial refractoriness was determined in the presence and absence of sinoatrial parasympathetic nerve stimulation at each catheter site. In 8 of 9 patients, parasympathetic nerve stimulation reproducibly prolonged sinus cycle length by 50%. There was no effect on AV nodal conduction (no prolongation of PR interval) and no change in AV nodal refractoriness. Atrial effective refractory periods reproducibly shortened in response to parasympathetic nerve stimulation in 1-cm zones up to 3 cm surrounding the fat pad, by a mean (+/- SEM) of 26.6+/-4.3 msec (zone 1), 11.4+/-1.8 msec (zone 2), and 10.0+/-2.5 msec (zone 3), respectively (P = 0.0001). At distances > 3 cm from the fat pad, the effective refractory period did not shorten.
  
  
  CONCLUSIONS
  Stimulation of parasympathetic nerves that innervate the sinoatrial node shortened atrial refractoriness in humans.
authors.affiliation: Division of Cardiology, MetroHealth Medical Center, Case Western Reserve University School of Medicine, Cleveland, Ohio 44109, USA.
authors.forename: K J
authors.initials: KJ
authors.lastname: Quan
authors.forename: J H
authors.initials: JH
authors.lastname: Lee
authors.forename: A S
authors.initials: AS
authors.lastname: Geha
authors.forename: L A
authors.initials: LA
authors.lastname: Biblo
authors.forename: G F
authors.initials: GF
authors.lastname: Van Hare
authors.forename: J A
authors.initials: JA
authors.lastname: Mackall
authors.forename: M D
authors.initials: MD
authors.lastname: Carlson
mesh_terms: D000328:Adult; D000368:Aged; D001285:Atropine / Q000008:administration & dosage; D006328:Cardiac Catheterization; D001026:Coronary Artery Bypass; D003327:Coronary Disease / Q000503:physiopathology / Q000601:surgery; D004558:Electric Stimulation; D004562:Electrocardiography; D005260:Female; D006325:Heart Atria / Q000294:innervation* / Q000503:physiopathology; D006339:Heart Rate; D006801:Humans; D007275:Injections, Intravenous; D008297:Male; D010275:Parasympathetic Nervous System / Q000187:drug effects / Q000503:physiopathology; D010276:Parasympatholytics / Q000008:administration & dosage; D015203:Reproducibility of Results; D012849:Sinoatrial Node / Q000187:drug effects / Q000294:innervation* / Q000503:physiopathology; D013268:Stimulation, Chemical
chemical_list: D010276:Parasympatholytics; D001285:Atropine