title: Early detection of abnormal left ventricular relaxation in acute myocardial ischemia with a quadratic model.
abstract: OBJECTIVE
  The time constant of left ventricular (LV) relaxation derived from a monoexponential model is widely used as an index of LV relaxation rate, although this model does not reflect the non-uniformity of ventricular relaxation. This study investigates whether the relaxation curve can be better fitted with a "quadratic" model than with the "conventional" monoexponential model and if changes in the LV relaxation waveform due to acute myocardial ischemia could be better detected with the quadratic model.
  
  
  RESULTS
  Isovolumic relaxation was assessed with quadratic and conventional models during acute myocardial ischemia performed in 6 anesthetized pigs. Mathematical development indicates that one parameter (Tq) of the quadratic model reflects the rate of LV relaxation, while the second parameter (K) modifies the shape of the relaxation curve. Analysis of experimental data obtained in anesthetized pigs showed that the shape of LV relaxation consistently deviates from the conventional monoexponential decay. During the early phase of acute myocardial ischemia, the rate and non-uniformity of LV relaxation, assessed with the quadratic function, were significantly enhanced. Tq increased by 16% (p<0.001) and K increased by 12% (p<0.001) within 30 and 60 min, respectively, after left anterior descending (LAD) coronary artery occlusion. However, no significant changes were observed with the conventional monoexponential decay within 60 min of ischemia.
  
  
  CONCLUSIONS
  The quadratic model better fits LV isovolumic relaxation than the monoexponential model and can detect early changes in relaxation due to acute myocardial ischemia that are not detectable with conventional methods.
authors.affiliation: GIGA - Cardiovascular Sciences, Hemodynamics, University of Liège, Belgium; Medical Intensive Care Unit, University Hospital of Liège, Belgium. Electronic address: ph.morimont@chu.alg.ac.be.
authors.forename: Philippe
authors.initials: P
authors.lastname: Morimont
authors.affiliation: GIGA - Cardiovascular Sciences, Hemodynamics, University of Liège, Belgium; Faculty of Sciences, University Hospital of Liège, Belgium.
authors.forename: Antoine
authors.initials: A
authors.lastname: Pironet
authors.affiliation: GIGA - Cardiovascular Sciences, Hemodynamics, University of Liège, Belgium; Faculty of Sciences, University Hospital of Liège, Belgium.
authors.forename: Thomas
authors.initials: T
authors.lastname: Desaive
authors.affiliation: Mechanical Engineering Department, University of Canterbury, Christchurch, New Zealand.
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Chase
authors.affiliation: GIGA - Cardiovascular Sciences, Hemodynamics, University of Liège, Belgium; Medical Intensive Care Unit, University Hospital of Liège, Belgium.
authors.forename: Bernard
authors.initials: B
authors.lastname: Lambermont
mesh_terms: D000208:Acute Disease; D000465:Algorithms; D000758:Anesthesia; D000818:Animals; D003324:Coronary Artery Disease; D004195:Disease Models, Animal; D008955:Models, Cardiovascular; D017202:Myocardial Ischemia / Q000503:physiopathology*; D013552:Swine; D013997:Time Factors; D016277:Ventricular Function, Left / Q000502:physiology*
keywords: Hemodynamic models; Myocardial ischemia; Ventricular relaxation