title: Intrinsic sinus and atrioventricular node electrophysiologic adaptations in endurance athletes.
abstract: OBJECTIVE
  In the present study, we evaluated sinus and atrioventricular (AV) node electrophysiology of endurance athletes and untrained individuals before and after autonomic pharmacologic blockade.
  
  
  BACKGROUND
  Endurance athletes present a higher prevalence of sinus bradycardia and AV conduction abnormalities, as compared with untrained individuals. Previous data from our laboratory suggest that nonautonomic factors may be responsible for the longer AV node refractory period found in well-trained athletes.
  
  
  METHODS
  Six aerobically trained male athletes and six healthy male individuals with similar ages and normal rest electrocardiograms were studied. Maximal oxygen uptake (O(2)max) was measured by cardiopulmonary testing. The sinus cycle length (SCL), AV conduction intervals, sinus node recovery time (SNRT), Wenckebach cycle (WC) and anterograde effective refractory period (ERP) of the AV node were evaluated by invasive electrophysiologic studies at baseline, after intravenous atropine (0.04 mg/kg) and after addition of intravenous propranolol (0.2 mg/kg).
  
  
  RESULTS
  Athletes had a significantly higher O(2)max as compared with untrained individuals. The SCL was longer in athletes at baseline, after atropine and after the addition of propranolol for double-autonomic blockade. The mean maximal SNRT/SCL was longer in athletes after atropine and after propranolol. The WC and anterograde ERP of the AV node were longer in athletes at baseline, after atropine and after propranolol.
  
  
  CONCLUSIONS
  Under double-pharmacologic blockade, we demonstrated that sinus automaticity and AV node conduction changes of endurance athletes are related to intrinsic physiology and not to autonomic influences.
authors.affiliation: Cardiology Division, Hospital de Clínicas de Porto Alegre, and Department of Medicine, Faculty of Medicine, Federal University of Rio Grande do Sul, Porto Alegre, Brazil.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Stein
authors.forename: Claudio M
authors.initials: CM
authors.lastname: Medeiros
authors.forename: Guido A
authors.initials: GA
authors.lastname: Rosito
authors.forename: Leandro I
authors.initials: LI
authors.lastname: Zimerman
authors.forename: Jorge P
authors.initials: JP
authors.lastname: Ribeiro
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects / Q000502:physiology*; D000319:Adrenergic beta-Antagonists / Q000008:administration & dosage; D000328:Adult; D001283:Atrioventricular Node / Q000187:drug effects / Q000502:physiology*; D001285:Atropine / Q000008:administration & dosage; D004562:Electrocardiography; D022062:Electrophysiologic Techniques, Cardiac; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006801:Humans; D008297:Male; D010276:Parasympatholytics / Q000008:administration & dosage; D010807:Physical Endurance / Q000187:drug effects / Q000502:physiology*; D011433:Propranolol / Q000008:administration & dosage; D012016:Reference Values; D012804:Sick Sinus Syndrome / Q000188:drug therapy / Q000503:physiopathology*; D013177:Sports; D013997:Time Factors
chemical_list: D000319:Adrenergic beta-Antagonists; D010276:Parasympatholytics; D001285:Atropine; D011433:Propranolol