What Is a Heart Attack?
The heart requires its own constant supply of oxygen and nutrients, like any muscle in the body. The heart has four main arteries, two of them large, branching arteries that deliver oxygenated blood to the heart muscle. If one of these arteries or branches becomes blocked suddenly, a portion of the heart is starved of oxygen, a condition called "cardiac ischemia."
If cardiac ischemia lasts too long, the starved heart tissue dies. This is a heart attack, otherwise known as a myocardial infarction -- literally, "death of heart muscle."
Most heart attacks occur during several hours -- so never wait to seek help if you think a heart attack is beginning. In some cases there are no symptoms at all, but most heart attacks produce some chest pain.
Other signs of a heart attack include shortness of breath, dizziness, faintness, or nausea. The pain of a severe heart attack has been likened to a giant fist enclosing and squeezing the heart. If the attack is mild, it may be mistaken for heartburn. The pain may be constant or intermittent. Also, women are less likely to experience the classic symptoms of chest pain; rather, they may feel a sense of fullness in their chest or pain in their arm, neck, back or jaw.
Angina: Early Warning Sign of a Heart Attack
Many heart attack victims are warned of trouble by episodes of angina, which is chest pain that, like a heart attack, is provoked by ischemia. The difference is mainly one of degree: With angina, blood flow is restored, pain recedes within minutes, and the heart is not permanently damaged. With a heart attack, blood flow is critically reduced or fully blocked, pain lasts longer, and heart muscle dies without prompt treatment.
About 25% of all heart attacks occur without any previous warning signs. They are sometimes associated with a phenomenon known as "silent ischemia" -- sporadic interruptions of blood flow to the heart that, for unknown reasons, are pain-free, although they may damage the heart tissue. The condition may be detected by ECG (electrocardiogram) testing. People with diabetes often have silent ischemia.
Other people mistake a heart attack for a symptom of the flu or reflux disease, which causes heartburn.
A quarter of all heart attack victims die before reaching a hospital; others suffer life-threatening complications while in the hospital. Serious complications include stroke, persistent heart arrhythmias (irregular heart beats), heart failure, formation of blood clots in the legs or heart, and aneurysm, or bulging, in a weakened heart chamber. But those who survive the initial heart attack and are free from major problems a few hours later stand a better chance of full recovery.
Recovery is always a delicate process, because any heart attack weakens the heart to some degree. But generally, a normal life can be resumed. Depending on the severity of a heart attack, a person may experience:
- Heart failure, where the heart doesn't pump well enough to meet the body's needs
- Arrhythmias or abnormal heart rhythms
- Cardiac arrest or sudden cardiac death, where the heart stops beating
- Cardiogenic shock, where the heart is so damaged from the heart attack that a person goes into shock, which may result in damage of other vital organs like the kidneys or liver
What Causes a Heart Attack?
Most heart attacks are the result of coronary artery disease, also known as atherosclerosis or "hardening of the arteries," a condition that clogs coronary arteries with fatty, calcified plaques over time. The typical trigger for a heart attack is often a blood clot that blocks the flow of blood through a coronary artery.
In the early 1980s, researchers confirmed that the trigger for nearly all heart attacks is not the obstructive plaque itself, but the sudden formation of a blood clot -- like a scab -- on top of plaque that cuts off blood flow in an already narrowed vessel. This is called "plaque rupture." Contrary to prior belief, doctors now recognize that the less severe plaques are the cause of most heart attacks: It's the milder blockages that rupture and then cause the blood clot to form.
Heart attacks may also be caused by coronary artery spasm, where a heart artery is temporarily constricted, although this is a fairly rare cause.
New research shows that inflammation also plays a role in the evolution of heart attacks. It appears that the coronary artery walls become inflamed over time, further increasing the buildup of fatty plaques.
While the step-by-step process leading to a heart attack is not fully understood, major risk factors for coronary artery disease are well-known. Some can be controlled, including high blood pressure, high cholesterol, obesity, smoking, and a sedentary lifestyle. Stress is also said to raise the risk, and exertion and excitement can act as triggers for a heart attack.