What Causes Myocardial Ischemia?

Myocardial ischemia occurs when the blood flow from the coronary arteries to the heart muscle is insufficient to meet the oxygen demands of the heart. This condition can be caused by either a reduction in blood supply or an increase in oxygen demand by the heart muscle. In most cases, the primary issue is reduced blood flow. Common underlying conditions include coronary artery disease, cardiac syndrome X, coronary artery spasm, myocardial bridging, and certain types of arrhythmias. Below is a detailed overview of these contributing factors:

1. Coronary Artery Disease (CAD)

Coronary artery disease is the most common cause of myocardial ischemia. The coronary arteries are responsible for supplying oxygen-rich blood to the heart muscle. Normally, these arteries can dilate to increase blood flow when the heart requires more oxygen, such as during physical activity. However, when plaque builds up inside the arteries—a process known as atherosclerosis—the arteries may narrow or become completely blocked. This restricts blood flow and leads to chest pain or angina. CAD impairs the natural compensatory mechanisms of the coronary arteries, making the heart more vulnerable to oxygen deprivation.

2. Cardiac Syndrome X

Cardiac syndrome X is another condition that can lead to symptoms of myocardial ischemia. Patients may experience chest pain and show signs of ischemia on an electrocardiogram (ECG), yet coronary angiography reveals no significant blockages in the major coronary arteries. The exact cause of this syndrome is not fully understood, but it is thought to involve dysfunction in the small coronary arteries, which can impair blood flow to the heart muscle.

3. Vasospastic Angina (Prinzmetal's Angina)

Vasospastic angina, also known as variant angina or Prinzmetal's angina, is characterized by episodes of chest pain caused by temporary spasms in the coronary arteries. Unlike syndrome X, this condition can be identified during coronary angiography, where transient narrowing of the artery is observed during an angina attack. The spasms are often linked to abnormalities in vascular tone regulation rather than structural coronary artery disease. This condition tends to affect younger individuals who may smoke but otherwise lack traditional risk factors for coronary artery disease.

4. Myocardial Bridging

Myocardial bridging is an anatomical variation where a segment of a coronary artery runs through the heart muscle instead of lying on the surface. During heart contractions, this segment can become compressed, reducing blood flow to the heart muscle and potentially causing ischemia. Tachycardia (rapid heart rate) can exacerbate this condition by shortening the time available for blood to flow through the affected artery, further increasing the risk of ischemic symptoms.