title: Reduced intrinsic heart rate is associated with reduced arrhythmic susceptibility in guinea-pig heart.
abstract: OBJECTIVE
  In the clinical setting, patients with slower resting heart rate are less prone to cardiovascular death compared with those with elevated heart rate. However, electrophysiological adaptations associated with reduced cardiac rhythm have not been thoroughly explored. In this study, relationships between intrinsic heart rate and arrhythmic susceptibility were examined by assessments of action potential duration (APD) rate adaptation and inducibility of repolarization alternans in sinoatrial node (SAN)-driven and atrioventricular (AV)-blocked guinea-pig hearts perfused with Langendorff apparatus.
  
  
  METHODS
  Electrocardiograms, epicardial monophasic action potentials, and effective refractory periods (ERP) were assessed in normokalemic and hypokalemic conditions.
  
  
  RESULTS
  Slower basal heart rate in AV-blocked hearts was associated with prolonged ventricular repolarization during spontaneous beating, and with attenuated APD shortening at increased cardiac activation rates during dynamic pacing, when compared with SAN-driven hearts. During hypokalemic perfusion, the inducibility of repolarization alternans and tachyarrhythmia by rapid pacing was found to be lower in AV-blocked hearts. This difference was ascribed to prolonged ERP in the setting of reduced basal heart rate, which prevented ventricular capture at critically short pacing intervals required to induce arrhythmia.
  
  
  CONCLUSIONS
  Reduced basal heart rate is associated with electrophysiological changes that prevent electrical instability upon an abrupt cardiac acceleration.
authors.affiliation: Department of Biomedical Sciences, University of Copenhagen, Copenhagen N, Denmark and Department of Health Science and Technology, University of Aalborg , Aalborg , Denmark.
authors.forename: Oleg E
authors.initials: OE
authors.lastname: Osadchii
mesh_terms: D000200:Action Potentials; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000209:etiology / Q000503:physiopathology; D006168:Guinea Pigs; D006321:Heart / Q000503:physiopathology; D006329:Heart Conduction System / Q000503:physiopathology*; D006339:Heart Rate / Q000502:physiology*; D012032:Refractory Period, Electrophysiological
keywords: arrhythmia; electrical restitution; refractoriness; repolarization; resting heart rate