title: Rate dependence of mechanically induced electrophysiological changes in right ventricle of anaesthetized lambs during pulmonary artery occlusion.
abstract: OBJECTIVE
  Mechanically induced early afterdepolarization (EAD) is morphologically similar but different in the mechanisms with drug-induced EAD, which lead to arrhythmia. Pacing suppresses the drug-induced EAD and arrhythmia, however the effect of pacing on mechanically induced EAD and arrhythmia is not clear. This study addressed this issue in right ventricle (RV) of anaesthetized lambs.
  
  
  METHODS
  Six lambs were anaesthetized, and their hearts exposed. Nine monophasic action potential (MAP) electrodes were placed on RV apex, outflow and inflow regions, and recorded before, during, and after a 10 s occlusion of pulmonary artery at a number of pacing rates.
  
  
  RESULTS
  Pacing significantly reduced the baseline MAP duration at 90% repolarization (MAPD90), decreased the reduction of MAPD at early repolarization at the peak of occlusion. Nonetheless, the percentage of reduction was not significantly different among them. Pacing was able to reduce the frequencies, size of mechanically induced EADs. MAPD90 at the peak of occlusion was all shortened during pacing rather than some lengthened at intrinsic rate. Therefore, the dispersion of MAPD90 at the peak of occlusion reduced from 86 +/- 6 ms at intrinsic rate to 42 +/- 4 ms at 120 beats min-1, 38 +/- 3 ms at 150 beats min-1 and 26 +/- 3 ms at 170 beats min-1. Ultimately, pacing reduced/suppressed mechanically induced premature ventricular beats. These alterations were inversely related to heart rates.
  
  
  CONCLUSIONS
  Pacing reduces/suppresses both stretch-induced EADs and arrhythmia. These modulations are remarkably similar to those on other EADs by the pacing.
authors.affiliation: National Heart and Lung Institute, Imperial College of Science, Technology and Medicine, London, UK.
authors.forename: R
authors.initials: R
authors.lastname: Chen
authors.forename: D J
authors.initials: DJ
authors.lastname: Penny
authors.forename: G
authors.initials: G
authors.lastname: Greve
authors.forename: M J
authors.initials: MJ
authors.lastname: Lab
mesh_terms: D000200:Action Potentials; D000758:Anesthesia; D000818:Animals; D001145:Arrhythmias, Cardiac / Q000503:physiopathology; D001794:Blood Pressure / Q000502:physiology; D003250:Constriction; D006339:Heart Rate / Q000502:physiology; D011651:Pulmonary Artery / Q000502:physiology*; D012756:Sheep; D016278:Ventricular Function, Right / Q000502:physiology*