Cardiac Muscle Intermittence

• Myocardium & Intermittence - cardiac muscle:

  • However, in coronary artery blood the a-vO2 difference is 65 – 70 % at rest
  • This wide a-vO2 difference of demonstrates how extremely efficient the heart muscle is at extracting and utilising O2
  • Even at rest the coronary venous blood is almost desaturated – and there is only a little O2 reserve that the myocardium could “tap into” if required
• Myocardium & Intermittence - cardiac muscle pt2:

  • Since cardiac muscle routinely extracts most of the oxygen available to it even at rest, there is little more for it to extract if it needs to
  • This means that when the heart needs greater O2 supplies (e.g. on exercise) the blood flow in the coronary system must be substantially increased
  • This increased blood flow is primarily achieved by vasodilation of the coronary arteries
• Myocardium & Intermittence - cardiac muscle pt3:

  • The trigger for coronary artery vasodilation is primarily an O2 deficiency and CO2 excess, i.e. when the activity of the heart increases there is a temporary oxygen lack in the myocardial tissues and an increase in metabolic waste products
  • This O2 lack plus a host of vasodilator substances (NO, H+, K+, adenosine and CO2 etc..) released by the myocardial and coronary artery endothelial cells cause coronary artery vasodilation and increased blood flow
• Myocardium & Intermittence - cardiac muscle pt4:

  • In health, coronary artery blood flow is matched to the metabolic needs of the heart i.e. supply = metabolic demand
  • This matching of O2 need and O2 supply is absolutely critical to cardiac function, because as an entirely aerobic organ, the heart depends entirely on oxidative processes to produce ATP
• Myocardium & Intermittence - cardiac muscle pt5:

  • A temporary inadequacy of blood (O2) supply quickly results in a loss of cardiac muscle function and dysfunction within the intrinsic conducting system
  • A more sustained decoupling of supply and demand can result in permanent cardiac tissue damage and a permanent loss of function
  • Certain pathologies e.g. atherosclerosis may impair the supply of blood to the myocardium