Definitions

ischemic heart disease due to narrowing or blockage of coronary arteries, most commonly due to atherosclerosis, resulting in a mismatch between myocardial oxygen supply and demand

A form of CAD, in which patients are either asymptomatic or have stable or low-risk unstable angina; also used for patients with a history of MI whose symptoms are controlled with treatment.

• Cardiac chest pain: likely associated with cardiac ischemia based on symptoms (e.g., central, retrosternal, squeezing, exertional).

• Possible cardiac chest pain: may be associated with cardiac ischemia based on symptoms (e.g., stabbing, tearing, ripping, burning).

• Noncardiac chest pain: unlikely associated with cardiac ischemia based on symptoms (e.g., positional, fleeting).

The following terms are no longer recommended for use in the 2021 AHA/ACC chest pain guidelines. [1][2][3]

• Typical angina fulfills all of the following criteria:

  • Retrosternal chest pain of characteristic nature and duration (e.g., transient retrosternal pressure)

  • Provoked by exertion or emotional stress

  • Relieved by rest and/or nitroglycerin

• Atypical angina: fulfills only two of the aforementioned criteria

• Nonanginal chest pain: fulfills one or none of the aforementioned criteria

• CAD is the leading cause of death in the US and worldwide. [4]

• The lifetime risk of coronary artery disease at age 50 is approx. 50% for men and 40% for women.

Atherosclerosis is the most common cause

• For plaque formation, see “Pathogenesis of atherosclerosis.”

• Stable atherosclerotic plaque → vascular stenosis → increased resistance to blood flow in the coronary arteries → decreased myocardial blood flow → oxygen supply-demand mismatch → myocardial ischemia

• The extent of coronary stenosis determines the severity of the oxygen supply-demand mismatch and, thus, the severity of myocardial ischemia.

• Severe ischemia results in myocardial infarction (see “Acute coronary syndrome”).

• Coronary flow reserve (CFR): the difference between maximum coronary blood flow and coronary flow at rest (a measure of the ability of the coronary capillaries to dilate and increase blood flow to the myocardium).

  • In healthy individuals, the CFR can be up to 4 times higher on exertion than at rest.

  • CFR is reduced in individuals with CAD due to vascular stenosis and reduced vascular compliance.

• Definition: mismatch between the amount of oxygen the myocardium receives and the amount it requires

• Factors reducing oxygen supply

  • Coronary atherosclerosis and sequelae, including:

    • Rupture of an unstable atherosclerotic plaque (most common cause)

    • Thrombosis

    • Stenosis

  • Vasospasms

  • ↑ Heart rate

  • Anemia

• Factors increasing oxygen demand

  • ↑ Heart rate

  • ↑ Afterload

  • Anemia

• The resistance to blood flow within the coronary arteries is calculated using the Poiseuille equation: R = 8Lη/(πr4), where R = resistance to flow, L = length of the vessel, η = viscosity of blood, and r = radius of the vessel.

• Provided the length of the vessel and viscosity of blood remain constant, the degree of resistance can be calculated using the simplified formula: R ≈ 1/r4

Vascular stenosis increases vascular resistance significantly. For example, a 50% reduction in radius results in a 16-fold increase in resistance: R ≈ 1/(0.5 x r)4 = [1/(0.5 x r)]4 = (2/r)4 = 16/r4.

• Reversible ischemia: Tissue is ischemic but not irreversibly dead and, therefore, still potentially salvageable.

  • Myocardial stunning: acutely ischemic myocardial segments with transiently impaired but completely reversible contractility

  • Hibernating myocardium: a state in which myocardial tissue has persistently impaired contractility due to repetitive or persistent ischemia

    • Partially or completely reversible when adequate oxygen supply is restored (e.g., after angioplasty or coronary artery bypass grafting)

    • Seen in angina pectoris, left ventricular dysfunction, and/or heart failure

• Irreversible ischemia: tissue necrosis (myocardial scars)

• Definition: a phenomenon of vasodilator-induced alteration of coronary blood flow in patients with coronary atherosclerosis resulting in myocardial ischemia and symptoms of angina

• Pathomechanism

  • Long-standing CAD requires maximal coronary arterial dilation distal to the stenosis to maintain normal myocardial function.

  • In CAD, the affected coronary artery is maximally dilated distal to the stenosis to compensate for the reduced blood flow .

  • If a vasodilator (e.g., dipyridamole) is administered, the subsequent vasodilation of healthy vessels causes these to “steal” blood from the stenotic blood vessels, resulting in poststenotic myocardial ischemia.

• Clinical relevance

  • Coronary steal is the underlying mechanism of pharmacological stress testing.

  • Administration of vasodilators (e.g., dipyridamole) → coronary vasodilation → decreased hydrostatic pressure in the normal coronary arteries → blood shunting back to well-perfused myocardium → decreased flow to the ischemic myocardium → myocardial ischemia downstream to the pathologically dilated vessels → angina pectoris and/or ECG changes

progressive heart failure that occurs after many years of chronic ischemic damage to the myocardium