Chronic stable angina pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor-In-Chief: Cafer Zorkun, M.D., Ph.D. [2]

Overview

The primary causes of myocardial ischemia in chronic stable angina are: fixed epicardial stenosis, spasm of the epicardial artery and/or microvascualar disease. The causation of angina is not mutually exclusive. Two or more causes may coexist in the same patient.

Pathophysiology

The primary causes of myocardial ischemia in chronic stable angina are explained below:

1. Fixed epicardial stenosis: Most commonly, chronic stable angina is the result of fixed obstructive disease or atherosclerosis that causes narrowing of the coronary arteries.

  • This results in inadequate supply of blood and oxygen to meet the demands of myocardial metabolism. This supply/demand mismatch activates a molecular cascade of events that causes the release of molecules, such as bradykinin and adenosine, which in turn stimulate the sympathetic and vagal afferent fibers, causing the anginal pain.
  • Certain conditions can increase the myocardial oxygen demand secondary to an increase in cardiac output and can exacerbate chronic stable angina. These conditions include, but are not limited to:
The increase in cardiac demand is often treated with beta blockers as a method to treat the underlying condition.

2. Spasm of the epicardial artery: While fixed obstructive epicardial disease is the most common cause of chronic stable angina, vasospasm of the epicardial artery can also cause angina. Angina due to spasm of an epicardial artery is known as prinzmetal's angina or variant angina. Prinzmetal's angina or variant angina is often treated with calcium channel blockers to relieve the spasm.

3. Microvascular disease: Chronic stable angina can also result from microvascular disease as well. This is known as microvascular angina or syndrome X. Microvascular angina is often treated with calcium channel blockers to relieve the spasm.

Angina Due to Increased Myocardial Oxygen Requirements: Demand Angina

Angina that is precipitated by an increased myocardial oxygen requirement is sometimes referred to as demand angina or fixed threshold angina. In demand angina, evidence of increased cardiac oxygen requirements can be suspected in the following situations:

  • The factors mentioned below may trigger the release of norepinephrine, which increases myocardial oxygen requirements:

Demand angina has few dynamic (i.e. vasoconstrictor effect) components, and the amount of physical activity required to precipitate angina remains relatively constant.

Angina Due to Decreased Myocardial Oxygen Supply: Supply Angina

  • Angina that occurs secondary to a decrease in oxygen supply is sometimes referred to as supply angina or variable threshold angina.
  • Major determinants of myocardial oxygen consumption are:
  • Ventricular wall tension: intraventricular systolic pressure, ventricular volume, and ventricular wall thickness are the major determinants of left ventricular wall tension.
  • Heart rate: Various forms of tachycardias and tachyarryhthmias may also increase myocardial oxygen consumption and reduce myocardial perfusion by decreasing the duration of diastole. Therefore, reduction of heart rate is associated with a decrease in myocardial oxygen demand and improved left ventricular perfusion.
  • Myocardial contractility: adrenergic stimulation of the heart and tachycardia serve as major determinants of contractility.
  • Myocardial oxygen extraction is almost at maximal level at rest and arterial oxygen content is usually stable. However, anemic or marked hypoxic states are an exception. Therefore, myocardial oxygen supply is mainly determined by coronary blood flow.
  • Coronary blood flow is a function of myocardial perfusion pressure (the difference between the diastolic pressure in aortic root and the right atrium). The duration of diastole has an inverse relation with the coronary vascular resistance. Coronary vascular resistance, in turn, is determined by:
  • The severity of epicardial coronary artery stenosis
  • The changes in epicardial coronary artery tone
  • Coronary arteriolar resistance, which is regulated by metabolic, neural, humoral, and autonomic activity.
  • Myocardial demand for oxygen increases during exertion. In physiologically normal persons, increased myocardial oxygen demand during exercise reduces coronary arteriolar resistance, resulting in an increase in coronary blood flow (called an autoregulatory reserve). This autoregulatory reserve progressively diminishes with an increased severity of epicardial coronary artery stenosis. When coronary artery stenosis reaches 90% of the luminal diameter, dilatation in coronary arteriolar bed approaches its maximum level and coronary blood flow becomes more dependent on perfusion pressure. Under these conditions, reduction of arterial pressure may increase in myocardial oxygen demand and induce myocardial ischemia.

References


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