title: Human ventricular action potential duration during short and long cycles. Rapid modulation by ischemia.
abstract: BACKGROUND
  Mechanisms underlying the initiation of ventricular arrhythmias in ischemia by a premature beat or after a pause remain unclear. The kinetics of electrical restitution, which is the modulation of action potential duration (APD) by an abrupt alteration in cycle length, may be important.
  
  
  RESULTS
  We recorded one or two simultaneous monophasic action potentials (MAPs) from the right ventricular septum during balloon occlusion of the left anterior descending coronary artery (LAD) (14 patients), which is expected to induce ischemia at the recording site, and during occlusion of the right coronary artery (RCA) (7 patients), which is not expected to induce ischemia at the recording area. The latter acted as a control. A test pulse sequence was incorporated whereby during steady-state pacing, test beats of altered cycle length were interpose. During LAD occlusion, APD for basic beats shortened from 260 +/- 4 to 236 +/- 4 ms (P < .0001), whereas the control group (RCA occlusion) showed no significant change (251 +/- 7 to 249 +/- 9 ms; P = NS). LAD occlusion resulted in flattening of the slope relating APD of test beats to diastolic interval (P = .001), whereas in the control group (RCA occlusion) the slope remained unchanged. Similar results were obtained during a second occlusion.
  
  
  CONCLUSIONS
  LAD occlusion in patients during balloon angioplasty shortened MAP duration of basic beats and minimized, abolished, or reversed the normal APD/diastolic-interval relation of test beats of altered cycle length at sites served by the occluded vessel. The results suggest that ischemia flattens the electrical restitution curve in the human endocardium. These findings may have important implications in arrhythmogenesis.
authors.affiliation: Department of Cardiology, Middlesex Hospital, London, UK.
authors.forename: P
authors.initials: P
authors.lastname: Taggart
authors.forename: P M
authors.initials: PM
authors.lastname: Sutton
authors.forename: M R
authors.initials: MR
authors.lastname: Boyett
authors.forename: M
authors.initials: M
authors.lastname: Lab
authors.forename: H
authors.initials: H
authors.lastname: Swanton
mesh_terms: D000200:Action Potentials; D000368:Aged; D002304:Cardiac Pacing, Artificial; D002404:Catheterization; D003331:Coronary Vessels / Q000503:physiopathology; D004594:Electrophysiology; D005260:Female; D006706:Homeostasis; D006801:Humans; D008297:Male; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000503:physiopathology*; D011930:Reaction Time; D016276:Ventricular Function