2. Ischemic Heart Disease

3. DEFINITION
Ischemic heart disease (IHD), also known as coronary artery disease (CAD), is defined as a lack of oxygen and decreased or no blood flow to the myocardium resulting from coronary artery narrowing or obstruction.
IHD may present as an acute coronary syndrome (ACS), which includes unstable angina pectoris and acute myocardial infarction (AMI) associated with ECG changes of either ST-segment elevation (STEMI) or non-ST-segment elevation (NSTEMI).
IHD may also present as myocardial infarction (MI) diagnosed by biochemical markers only, chronic stable exertional angina, ischemia without symptoms, or ischemia due to coronary artery vasospasm (variant or Prinzmetal's angina).

4. Pathophysiology
Angina pectoris typically occurs when myocardial oxygen demand exceeds myocardial oxygen supply (perfusion). The underlying pathologic condition of this mismatch invariably is the presence of atherosclerosis in one or more of the epicardial coronary arteries (conductance vessels).
If the size of the atherosclerotic plaque obscures <50% of the diameter of the vessel, coronary blood flow can be augmented sufficiently during exertion by the intramyocardial arterioles (resistance vessels), and the patient is pain free.

5. Pathophysiology
In patients with chronic stable angina, most coronary artery stenoses are >70%.
A linear decrease in coronary blood flow occurs as the plaque occupies more of the arterial lumen until high-grade (>80%) obstruction develops.

6. Determinants of myocardial oxygen supply and demand