Myocardial Hypofunction Due to Ischemia and/or Hypoxia in Collateralized and Noncollateralized Hearts

The severity of coronary artery (CA) disease depends on the degree of CA stenosis possibly aggravated by an O₂ deficiency in the blood and the CA architecture. To analyze the functional response of the myocardium to hypoxia provoked by different methods, studies on dogs and domestic pigs were retrospectively evaluated. The left anterior descending coronary artery (LAD) was mechanically narrowed while the coronary blood flow (Q_LAD) and myocardial shortening fraction (MSF) of dependent left ventricular subendocardial wall segments were assessed. Myocardial oxygen delivery () was calculated from Q_LAD and O₂ content. In dogs, MSF decreased to half that in the control when was lowered by about 50% irrespective of the mode of hypoxia (i) CA narrowing: Q_LAD = –51%. (ii) Hypoxemia by pump-controlled CA perfusion with venous blood: Q_LAD = –29%. (iii) O₂-transport capacity lowered by hemodilution: Q_LAD = +47%). In pigs, mechanically impeding Q_LAD and by 47% diminished MSF by 82%. MSF of –50% was achieved at a Q_LAD of –31%, with Q_LCx unaffected. In dogs in contrast, MSF of –54% in the LAD region was obtained at a Q_LAD of –53% while the LC_x flow rose by 22%. Consequently, local MSF lessened by 50% in dogs as well as in pigs when the sum flow through the LCA (LAD + LC_x) was reduced by about 30%. This might indicate an onset of collateral blood flow, which occurs in dogs but not in swine.