What is Ischemic Heart Disease?

Posted by Dr.Ghafoor October 4, 2009

Ischemic heart disease is caused by an imbalance between the myocardial blood flow and the metabolic demand of the myocardium. Reduction in coronary blood flow is related to progressive atherosclerosis with increasing occlusion of coronary arteries. Blood flow can be further decreased by superimposed events such as vasospasm, thrombosis, or circulatory changes leading to hypoperfusion.

Coronary artery perfusion depends upon the pressure differential between the ostia (aortic diastolic pressure) and coronary sinus (right atrial pressure). Coronary blood flow is reduced during systole because of Venturi effects at the coronary orifices and compression of intramuscular arteries during ventricular contraction.

Factors reducing coronary blood flow include:

  1. Decreased aortic diastolic pressure

  2. Increased intraventricular pressure and myocardial contraction

  3. Coronary artery stenosis, which can be further subdivided into the following etiologies:

    • Fixed coronary stenosis

    • Acute plaque change (rupture, hemorrhage)

    • Coronary artery thrombosis

    • Vasoconstriction

  4. Aortic valve stenosis and regurgitation

  5. Increased right atrial pressure

40 micron collateral vessels are present in all hearts with pressure gradients permitting flow, despite occlusion of major vessels. In general, the cross-sectional area of the coronary artery lumen must be reduced by more than 75% to significantly affect perfusion. Coronary atherosclerosis is diffuse (involving more than one major arterial branch) but is often segmental, and typically involves the proximal 2 cm of arteries (epicardial).

"Thrombolytic therapy" with agents such as streptokinase or tissue plasminogen activator (TPA) is often used to try and lyse a recently formed thrombus. Such therapy with lysis of the thrombus can re-establish blood flow in a majority of cases. This helps to prevent significant myocardial injury, if early (less than an hour or so) in the course of events, and can at least help to reduce further damage.


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