Angina pathophysiology
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Angina Pathophysiology: Oxygen Supply-Demand Imbalance and Ischemia
Angina is primarily caused by an imbalance between the heart muscle's need for oxygen and the supply it receives. This mismatch leads to myocardial ischemia, which is the underlying mechanism for angina symptoms. The classic trigger is increased demand (such as during exercise or stress) in the presence of limited blood flow due to narrowed or dysfunctional coronary arteries 810.
Atherosclerosis and Plaque Complications in Angina
In stable angina, the most common cause is atherosclerosis, where fatty plaques build up in the coronary arteries, narrowing them and restricting blood flow. When these plaques remain smooth and unbroken, they cause predictable, exertion-related symptoms. However, if a plaque develops fissures, ruptures, or ulcerations, it can lead to thrombus (clot) formation, resulting in unstable angina. This can rapidly worsen symptoms and increase the risk of heart attack .
Variant Angina and Coronary Artery Spasm
Variant (Prinzmetal’s) angina is different from classic angina. It is caused by transient spasms of the coronary arteries, which temporarily reduce blood flow. These spasms often occur at rest, especially at night or early morning, and can cause severe chest pain and even dangerous heart rhythms. The underlying mechanisms include endothelial dysfunction (reduced nitric oxide release), increased smooth muscle contractility, autonomic nervous system imbalance, oxidative stress, inflammation, magnesium deficiency, and genetic factors. Notably, coronary artery spasm can occur even in arteries that appear normal on angiography .
Angina with Non-Obstructed Coronary Arteries (ANOCA/INOCA)
A significant number of patients experience angina despite having no significant blockages in their coronary arteries. This condition, known as angina with non-obstructed coronary arteries (ANOCA) or ischemia with no obstructive coronary artery disease (INOCA), is increasingly recognized. The pathophysiology involves:
- Microvascular Dysfunction: Abnormalities in the small vessels of the heart (microvasculature) can impair blood flow and oxygen delivery, even when larger arteries are clear. This can be due to structural changes (like capillary rarefaction) or functional issues (like abnormal vasomotor tone) 36910.
- Vasospastic Angina: Spasms in either the small or large coronary arteries can cause transient reductions in blood flow 69.
- Endothelial Dysfunction: The inner lining of the blood vessels (endothelium) may not function properly, leading to impaired dilation and increased risk of spasm or clot formation. This dysfunction is a key factor in both obstructive and non-obstructive forms of angina and can persist even after interventions like stenting .
Role of Plaque Characteristics in Non-Obstructive Angina
Even in the absence of significant blockages, the presence of non-calcified, low-attenuation plaques in the coronary arteries is associated with more frequent angina symptoms, especially in women. These plaques may not cause major narrowing but can still contribute to symptoms and future risk .
Refractory Angina and Heart-Brain Interactions
Some patients continue to experience angina despite optimal medical therapy and revascularization. This "refractory angina" involves complex interactions between the heart and the brain, affecting how symptoms are perceived and experienced. Understanding these pathways is important for developing new treatment approaches beyond traditional revascularization .
Conclusion
Angina is a complex condition with multiple underlying mechanisms. While classic angina is often due to atherosclerotic blockages, many patients have symptoms due to microvascular dysfunction, coronary artery spasm, or endothelial dysfunction, even when major arteries are clear. Recognizing the diverse pathophysiology of angina is essential for accurate diagnosis and effective treatment.
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