What is Prinzmetal’s angina?
Prinzmetal’s angina is cardiac pain caused by an inadequate blood supply (ischemia) as a result spasm of the coronary artery. It is just one type of angina pectoris – heart pain caused by the inadequate flow of blood to the heart muscle. The coronary arteries carry oxygen-rich blood to the heart and a constant supply is necessary on an ongoing basis to the heart wall that is always contracting and relaxing. When the muscles in the arterial walls go into spasm (vasospasm), the artery lumen is narrowed and less blood flows through it. The condition was named after Dr. Myron Prinzmetal and is also known as variant angina or angina inversa.
How common is Prinzmetal’s angina?
Angina pectoris affects almost 10 million Americans and there is about half a million new cases reported annually. It is the most significant cardiac symptoms indicating a potentially fatal coronary event. The most common type is typical angina which is narrowing of the coronary arteries due to the build up fatty plaques in the arterial walls (atherosclerosis). Prinzmetal’s angina is very uncommon comparatively, account for only 2 out every 100 cases of angina pectoris.
Meaning of Coronary Artery Vasospasm
The cardiac wall is mainly composed of a thick muscle layer known as the myocardium. It is this muscle layer that contracts and relaxes to pump blood through the heart. This ensures that the heart can distribute oxygenated blood throughout the body in order to maintain life. The myocardium is always in need of a good supply of oxygen-rich blood which it derives from the coronary arteries. When the heart is beating less frequently or less hard like when a person is very relaxed or sleeping peacefully, then the need for oxygenated blood is less. However, when the heart is beating faster and harder like when a person is exercising or very stress then the need is greater. This need for blood is referred to as the myocardial demand – sometimes it is less and sometimes it is more.
Picture of the coronary arteries from Wikimedia Commons
The coronary artery, like any other artery in the body, has smooth muscle fibers which can constrict and relax in order to narrow and widen the lumen respectively. These smooth muscles maintain a normal tone that allows for an adequate blood supply even with increased myocardial demand. However, it has the potential to relax thereby widening the artery lumen and allowing for a greater blood flow to the heart if it is needed. Sometimes these smooth muscle fibers in the coronary artery wall go into spasm thereby narrowing the artery and reducing the blood supply to the heart wall. Since the blood supply is not in line with the myocardial demand, the heart wall is “starved” of oxygen and nutrients leading to tissue injury known as ischemia.
Angina and Coronary Artery Vasopasm
Pain is a consequence of myocardial ischemia – injury to the myocardium due to interrupted blood supply. This pain is known as angina pectoris. It can be reversed with resting and the use of certain drugs like nitrates which relaxes the smooth muscle fibers in the coronary artery. However, there is an added risk of myocardial infarction – death of a portion of the myocardium due to inadequate blood supply which is commonly known as a heart attack. The severity of the tissue injury to the myocardium depends on the myocardial demand at the time. It also depends on the extent of vasoconstriction of the coronary artery which can be a slight constriction not producing any symptoms, or in severe instances even a complete obstruction of blood flow.
Signs and Symptoms
Prinzmetal angina presents in similar manner to typical angina. The difference however, lies in the modalities associated with these attacks. Whereas typical angina symptoms arise with physical exertion, psychological stress and sometimes after heavy meals, Prinzmetal angina appears to arise spontaneously, even when a person is at rest and tends to be more frequent at certain times of he day, particularly between midnight and 08h00.
Prinzmetal’s Angina Pain
A person usually complains of :
- Centralized chest pain lying behind the breastbone (retrosternal pain)
- Pain radiating to the left shoulder and arm, neck or jaw.
- A crushing or squeezing chest pain that is more of a tightness in very mild cases.
- Pain that last for between 5 to 30 minutes and is quickly relived with nitrates.
- Chest pain associated with dizziness and sometimes fainting.
Causes of Prinzmetal’s Angina
Prinzmetal’s angina is a consequence of coronary artery vasospasm. Although it is classified as a non-exertional chest pain, there are instances where increased physical activity may elicit an attack. Most people with Prinzmetal’s angina do have underlying coronary artery disease (CAD). This means that the coronary artery is narrowed to some extent due to the build up of fatty plaques in the artery wall (atherosclerosis). However, the atherosclerosis may be minor in comparison to patients with typical angina.
Coronary artery disease affects the normal physiology of smooth muscles in the artery walls thereby increasing the chances of vasospasm by affecting the release of nitric oxide, a chemical secreted by the inner lining of the coronary artery and responsible for vasodilation (widening of the artery). However, not every person with Prinzmetal’s angina has underlying coronary artery disease. Several genetic factors associated with nitric oxide production has also been identified as possible causes of coronary vasospasm. Cigarette smoking remains one of the major risk factors for the development of Prinzmetal’s angina.
Although the cause of coronary artery vasospasm cannot always be clearly identified, there are certain known trigger factors of Prinzmetal’s angina. This includes :
- Cocaine use
- Cold exposure
- Medication or other substances containing acetylcholine, ergonovine, histamine, or serotonin.
- Tobacco use
Tests and Diagnosis
There are various tests that may be considered in the course of diagnosing and assessing Prinzmetal’s angina. Most of these tests are conducted for all types of angina and is also a useful tool to identify a heart attack (myocardial infarction). It involves :
- Blood tests to assess the lipid levels, cardiac enzymes and troponin levels. Other blood tests are also conducted.
- ECG (electrocardiogram) to assess the electrical activity of the heart.
- Echocardiography is an ultrasound scan of the heart.
- Coronary angiography visualizes the blood flow through the coronary arteries.
Since coronary artery vasospasm is episodic, sometimes it may not be discernible during these tests. In order to elicit the vasospasm in a controlled environment, the physician may introduce a known trigger like ergonovine into the bloodstream. The trigger substance is administered in incremental doses until the desired effect (vasospasm) is elicited. This type of testing is known as a provocative test but is not frequently conducted.
Prinzmetal’s Angina Treatment
The aim of treatment for Prinzmetal’s angina is to dilate the coronary arteries during an attack and reduce the frequency of episodes.
The medication used to achieve these goals include :
- Nitroglycerin to treat episodes of angina.
- Long-acting nitrates and calcium channel blockers prevent coronary artery vasospasm.
Beta-blockers that are commonly used for coronary artery disease can worsen vasospasm and it is therefore important that the exact type of angina is diagnosed.
About 20% of patients with coronary artery vasospasm may not respond to drugs during an attack. Surgical measures may be necessary in these cases to restore normal blood flow. This may involve balloon angioplasty and sometimes even stenting of the coronary arteries. A coronary artery bypass graft is very rarely considered for Prinzmetal’s angina.