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- Oxygenated blood is normally delivered to the heart muscle by arteries to the heart (coronary arteries).
- Inadequate oxygenation of heart muscle (ischemia) can occur because of either narrowing or spasm of the coronary arteries.
- Narrowing of the coronary arteries (coronary artery disease or CAD) is usually caused byarteriosclerosis (cholesterol deposits on the inner wall of the arteries).
- In patients with narrowed coronary arteries, factors that increase work demand and oxygen consumption of the heart (such as exercise, excitement, increased blood pressure and heart rate) can precipitate heart muscle ischemia and angina.
Patients who develop angina only during stress or physical exertion have stable, exertional angina. When a coronary artery becomes critically narrowed, heart muscle ischemia or angina can occur with minimal or no exertion. These patients have unstable angina, and are at imminent risk of heart attack (myocardial infarction). A heart attack occurs when a diseased coronary artery becomes completely obstructed by a blood clot, leading to irreversible death of heart muscle. During the early hours of a heart attack, irregular heart rhythms can occur which commonly cause sudden cardiac death.
Heart ischemia resulting in angina can be caused by spasm of the coronary arteries. This is a rare condition called vasospastic angina (also known as Prinzmetal's angina) and is not associated with exertion.
It has been known for some time that the symptoms of ischemic heart disease are more common in the morning hours than at any other time of day.
- Patients experience episodes of stable angina with lower levels of exertion in the morning than in the afternoon.
- The occurrence of episodes of vasospastic angina is higher in the morning than in the afternoons.
- In patients with CAD, electrocardiogram (ECG) changes indicative of heart muscle ischemia are seen more frequently in the morning than in the afternoon.