title: Heterogeneous memory in restitution of action potential duration in pig ventricles.
abstract: BACKGROUND
  Restitution of action potential duration and memory importantly affect electrical stability in ventricles. Studies have reported heterogeneous restitution among different regions of the ventricles. However, existence of heterogeneity in memory is not as well investigated.
  
  
  METHODS
  Transmembrane potentials were recorded in endocardial and epicardial tissues from both ventricles of farm pigs. Pacing protocols with sinusoidally changing diastolic intervals were used to reveal hysteresis in restitution, from which quantitative measures of memory were calculated.
  
  
  RESULTS
  Larger measures of hysteresis were observed in the endocardium than the epicardium (P < .05): loop thickness (in milliseconds), 26.9 vs 16.2; overall tilt, 0.376 vs 0.249; and loop area (in square milliseconds), 7288 vs 4146. Except for overall tilt, no significant differences in these measures were observed between ventricles.
  
  
  CONCLUSIONS
  Heterogeneity in memory exists in pig ventricles. Because regions with the steepest restitution may also have the largest memory, our results suggest that heterogeneity in memory should also be factored in when predicting electrical stability.
authors.affiliation: Center for Biomedical Engineering, University Of Kentucky, KY 40506-0070, USA.
authors.forename: Linyuan
authors.initials: L
authors.lastname: Jing
authors.forename: Sonam
authors.initials: S
authors.lastname: Chourasia
authors.forename: Abhijit
authors.initials: A
authors.lastname: Patwardhan
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D002304:Cardiac Pacing, Artificial; D022062:Electrophysiologic Techniques, Cardiac; D004699:Endocardium / Q000502:physiology; D006329:Heart Conduction System / Q000502:physiology*; D006352:Heart Ventricles; D010496:Pericardium / Q000502:physiology; D013552:Swine