Which of the following conditions is the predominant cause of angina?
A. Increased preload
B. Decreased afterload
C. Coronary artery spasm
D. Inadequate oxygen supply to the myocardium.
Correct Answer: D. Inadequate oxygen supply to the myocardium.
Inadequate oxygen supply to the myocardium is responsible for the pain accompanying angina. The heart is dependent on adequate oxygen supply for energy production to support contractility. At the cellular level, ischemia causes an increase in anaerobic glycolysis. This increases the levels of hydrogen, potassium, and lactate in the venous return of the ischemic or affected area of the myocardium.
Option A: Increased preload would be responsible for right-sided heart failure. Increases in preload, as demonstrated through an elevated PCW, are seen in several conditions such as heart failure, mitral stenosis, and mitral regurgitation. At higher preloads, the heart also has an increased oxygen demand, further debilitating the already diseased heart. In cases of heart failure, eventually, the heart cannot keep up with the increased load, and deleterious ventricular remodeling and loss of function ensue.
Option B: Decreased afterload causes increased cardiac output. Afterload is the force against which the ventricles must act in order to eject blood, and is largely dependent on the arterial blood pressure and vascular tone. Similarly, reducing afterload can increase cardiac output, especially in conditions where contractility is impaired.
Option C: Coronary artery spasm is responsible for variant angina. Coronary artery vasospasm (CAVS) is a constriction of the coronary arteries that can cause complete or near-complete occlusion of the vessel. In 1959, Dr. Myron Prinzmetal described a different entity of angina than the classic Heberden’s angina which was originally described in 1772. This vasospastic disease can cause acute ischemia and present anywhere along the spectrum of angina from stable angina to acute coronary syndrome.
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