title: Repolarisation and refractoriness during early ischaemia in humans.
abstract: OBJECTIVE
  To determine whether effective refractory period (ERP) shortens or lengthens in the first minutes of ischaemia in humans, and the relation between ERP changes and action potential duration (APD).
  
  
  METHODS
  ERP and monophasic action potential duration (MAPD) were measured from a single left ventricular epicardial site in 26 patients undergoing coronary artery surgery. Cardiopulmonary bypass was instituted and normothermia maintained. Refractory period was determined by the extrastimulus technique at a basic cycle length of 500 ms, at four times (group 1, 15 patients) or two times (group 2, 11 patients) the preischaemic diastolic threshold. A three minute period of ischaemia was instituted by aortic cross clamping between the input from the pump oxygenator and the heart.
  
  
  RESULTS
  After three minutes of ischaemia, mean (SEM) ERP lengthened from 232 (5) ms (control) to 246 (7) ms (p < 0.005) in group 1, and from 256 (10) ms (control) to 348 (25) ms (p < 0.005) in group 2. In the same time MAPD shortened from 256 (5) ms (control) to 189 (9) ms (p < 0.001) with no difference between groups. Thus postrepolarisation refractoriness developed during ischaemia. Before ischaemia, ERP showed a good correlation with APD (R(2) = 0.64) but by one minute of ischaemia the correlation was poor (R(2) = 0.29).
  
  
  CONCLUSIONS
  These results show that during the first three minutes of global ischaemia in patients with coronary artery disease: (1) ERP lengthened in response to both a low and a high stimulus strength; and (2) there was a good correlation between ERP and APD before ischaemia, which was lost by one minute as APD decreased and ERP increased. These findings may have important implications in arrhythmogenesis.
authors.affiliation: The Hatter Institute, Department of Cardiology, University College London Hospitals, Grafton Way, London WC1E 6DB, UK. peter.sutton@ucl.ac.uk
authors.forename: P M
authors.initials: PM
authors.lastname: Sutton
authors.forename: P
authors.initials: P
authors.lastname: Taggart
authors.forename: T
authors.initials: T
authors.lastname: Opthof
authors.forename: R
authors.initials: R
authors.lastname: Coronel
authors.forename: R
authors.initials: R
authors.lastname: Trimlett
authors.forename: W
authors.initials: W
authors.lastname: Pugsley
authors.forename: P
authors.initials: P
authors.lastname: Kallis
mesh_terms: D000200:Action Potentials; D000328:Adult; D000368:Aged; D002304:Cardiac Pacing, Artificial; D002315:Cardiopulmonary Bypass; D003327:Coronary Disease / Q000601:surgery; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000503:physiopathology* / Q000628:therapy; D013997:Time Factors; D018487:Ventricular Dysfunction, Left / Q000503:physiopathology* / Q000628:therapy