Ninety percent of myocardial oxygen demand is determined by myocardial contractile activity. In circumstances when the myocardium of the left ventricle must generate additional force to eject blood into the systemic circulation more oxygen will be required. This additional work can also be referred to as wall stress or wall tension. This increased myocardial oxygen demand, in the presence of coronary artery flow defect (such as atherosclerosis), can lead to ischemia and infarction of the myocardium and ultimately present as ACS.
The law of Laplace is used to identify factors that increase myocardial wall tension and oxygen demand. The formula states – p*r/2* wt; or the pressure times the radius divided by two times the wall thickness equals myocardial wall tension. By reducing the pressure or radius of the left ventricle or increasing the wall thickness ( as seen in chronic changes associated with CHF) the left ventricle can reduce its wall tension and its myocardial oxygen demand.
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