What causes angina?
The heart gets its blood supply from coronary arteries that branch off the aorta just as it leaves the heart. The coronary arteries run along the surface of the heart, branching into smaller and smaller blood vessels as they supple each muscle cell of the heart. The most common reason a patient complains of angina is because of narrowed coronary arteries caused by atherosclerotic heart disease (ASHD).
Cholesterol plaque gradually builds on the inner lining of a coronary artery, narrowing its diameter and decreasing the amount of blood that can flow past the blockage. If the heart is asked to do more work and pump harder and faster, enough oxygen may not be able to be delivered beyond the blockage to meet the energy demand of the myocardium and this can cause the symptoms of angina to occur.
If a plaque ruptures, a blood clot may form that completely occludes the coronary artery and prevents any blood flow to the section of the heart muscle that the artery supplies. This is called a heart attack or myocardial infarction and is a medical emergency. Heart muscle that loses its blood supply will die and be replaced with scar tissue that is unable to contract. This may decrease the heart's ability to pump as strongly as before. As well, heart muscle that loses its blood supply can become irritable and result in heart rhythm disturbances like ventricular fibrillation or ventricular flutter that can result in sudden cardiac death.
Because each beat of the heart not only sends blood to the body, but also to itself, there are a variety of systems in the body and within the heart that have to function normally to deliver oxygen to the heart muscle. Should any of them, either individually or in combination, fail to perform adequately, angina may occur. Examples include the following:
- The electrical system of the heart needs to be able to generate a heartbeat that is neither too slow (bradycardia) nor too fast (tachycardia). There may be an intrinsic problem with the heart's electrical conducting system. Atrial fibrillation with rapid ventricular response, atrial flutter, and ventricular tachycardia are too fast rates that can be associated with chest pain, shortness of breath, and other angina symptoms. Complete heart block can make the heart beat too slowly. The abnormal heart rhythm may be due to electrolyte or hormone abnormalities, medications, or toxic ingestions (for example cocaine overdose).
- Heart valves need to allow blood to flow between heart chambers and to the body and lungs in the right direction and at the right speed. This is especially true of the aortic valve that controls blood leaving the heart into the aorta. Severe aortic stenosis or narrowing of the aortic valve, may not allow enough blood to leave the heart with each heartbeat to provide blood flow into the coronary arteries.
- The heart muscle has to be able to have an adequate squeeze or strength to pump blood. The lack of this ability may be due to cardiomyopathy (damaged heart muscle).
- There needs to be enough red blood cells in the bloodstream to carry oxygen. Patients who have anemia can develop shortness of breath, fatigue, and chest pain with activity.
- The lungs need to work so that they deliver enough oxygen to the body. Patients with COPD or emphysema may not be able to extract enough oxygen from the air to supply the body's needs. Most often these patients have shortness of breath but they may also develop angina.
- Certain poisonings including carbon monoxide can prevent oxygen from attaching to red blood cells and cause shortness of breath and chest pain.
If any of these steps fail, the heart muscle may not get enough oxygen and the patient may feel pain or discomfort called angina.