heart attack
What causes most heart attacks?
What are the risk factors for a heart attack?
Why do most heart attacks occur in the morning?
What are the common symptoms of a heart attack?
How is a heart attack treated?
heart attack, the sudden interruption of blood flow to a portion of the heart muscle. Most heart attacks stem from coronary artery disease, which develops through atherosclerosis—a process in which cholesterol-rich plaques build up in the coronary arteries. A heart attack typically occurs when one of these plaques ruptures, triggering the formation of a blood clot that abruptly blocks blood flow to part of the heart muscle.
Risk factors
Several factors increase the likelihood of developing atherosclerosis and experiencing a heart attack, including high blood pressure (hypertension), diabetes mellitus, increased blood levels of low-density lipoprotein (LDL) cholesterol, smoking, and a family history of cardiovascular disease. Middle-aged men and individuals with inherited conditions such as familial hypercholesterolemia are at particularly high risk. In the early 21st century, heart attacks were becoming increasingly common among women under age 55. Although the reason for this increase was unclear, increased rates of diabetes, hypertension, and obesity in women likely played a role.
Most heart attacks occur in the morning, a phenomenon that researchers have linked to circadian rhythm. In the morning hours, increasing circadian-driven secretion of certain hormones, particularly epinephrine, norepinephrine, and cortisol, triggers subsequent increases in oxygen demand and blood pressure. These factors in turn increase circulatory activity. In addition, the production of endothelial progenitor cells, which appear to play a crucial role in repairing the lining of blood vessels, also follows a circadian pattern, with fewer cells present in the circulation in the early morning. Decreased levels of these cells results in depressed endothelial maintenance, which scientists suspect may facilitate the onset of a heart attack upon waking.
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Symptoms
A heart attack most often announces itself with intense chest discomfort—commonly described as a crushing, squeezing, or heavy feeling—that persists for 30 minutes or longer. The pain often radiates to the arms, neck, and back and is similar to that of angina pectoris, though it typically lasts longer and does not ease with rest.
Other common symptoms include shortness of breath, sweating, nausea, a rapid or irregular heartbeat (arrhythmia), and reduced blood pressure. Symptom severity varies depending on how much heart muscle is affected. In a small number of cases, particularly among older adults or people with diabetes, little or no chest pain occurs, and the event may be detected only through an electrocardiogram (ECG).
Treatment and prognosis
After a heart attack begins, heart muscle continues to be injured with every passing minute that blood flow remains blocked. For that reason, treatment is aimed at restoring circulation as quickly as possible to limit the amount of permanent damage. This typically involves continuous monitoring of heart rhythm and vital signs, along with the administration of medications and procedures designed to reopen the blocked artery and improve oxygen delivery to the heart..
Aspirin is usually given immediately because it helps prevent further clot formation and may improve blood flow through the blocked artery. Additional medications often include anticoagulants such as heparin to reduce clotting, fibrinolytic (clot-dissolving) drugs such as tissue plasminogen activator (tPA) to break up existing clots, and nitroglycerin to ease chest pain and improve circulation to the heart. In some cases, mechanical procedures are required, including angioplasty to reopen the artery or coronary artery bypass surgery to reroute blood flow around the blockage. Pain relief, often with medications such as morphine, along with rest and careful monitoring, is an important part of early care. Beta-blockers may also be administered to reduce the heart’s workload and limit further damage.
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Outcomes after a heart attack depend largely on how much of the heart muscle was damaged and how well the heart can continue to pump blood. When injured tissue heals, it is replaced by scar tissue, which does not function as well as healthy muscle and can disrupt the heart’s electrical signaling. Over time, this may reduce pumping strength and increase the risk of heart failure. To address this problem, researchers are exploring regenerative approaches, including stem cell-based therapies designed to repair or replace damaged heart tissue with functional muscle cells.