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What Is a Heart Attack?

In order to keep pumping, day in and day out, the heart requires its own constant supply of oxygen and nutrients. Two large, branching coronary arteries deliver oxygenated blood to the heart muscle. Should one of these arteries or branches shut down, a portion of the heart is starved of oxygen and fuel, a condition called "cardiac ischemia."

If cardiac ischemia lasts too long, the starved heart tissue dies. This event defines a heart attack, otherwise known as myocardial infarction — literally, "death of heart muscle."

Most heart attacks last for several hours. (Never wait to seek help if you think an attack is beginning.) The signs of a heart attack may be no more than shortness of breath, dizziness, faintness, or nausea. In some cases there are no symptoms, but most heart attacks produce some chest pain. The pain of a severe 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.

Angina

The majority of heart attack victims are warned of trouble well in advance by episodes of angina — chest pain that, like a heart attack, is provoked by ischemia. The difference is mainly one of degree: With angina, blood flow is quickly restored, pain recedes within minutes, and the heart is not permanently damaged. With heart attack, blood flow is critically reduced or fully blocked, pain lasts and heart tissue dies without prompt treatment.

About a quarter 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 gradually damage the heart tissue. The condition can be detected by ECG (electrocardiogram) testing. People with diabetes often have silent ischemia.

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 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 attack weakens the heart to some degree. But generally, a normal life can be resumed within three months. Depending on the severity of the attach and of the subsequent scarring of the heart and how fast a person gets treatment for the attack, a heart attach can lead to:

• Heart failure, where the heart doesn't pump well enough to meet the body's needs.
• Arrythmias or abnormal heart rythms.
• Cardiac arrest or sudden cardiac death in which the heart stops beating.
• Cardiogenic shock, where the heart is so damages from the heart attack they go into shock.
• Death.

Most heart attacks are the end result of coronary heart disease, a condition that clogs coronary arteries with fatty, calcified plaques over time. The typical trigger is often a blood clot that blocks the flow of blood through a coronary artery.

In the early 1980s, researchers confirmed that the precipitating cause of nearly all heart attacks is not the obstructive plaque itself, but the sudden formation of a blood clot on top of plaque that cuts off blood flow in an already narrowed vessel. This is called "plaque rupture."

Heart attacks may also be caused by coronary artery spasm, where a heart artery undergoes temporary constriction.

New research shows that inflammation also plays a role in the evolution of heart attacks. It appears that the coronary artery walls become inflammed over time, further increasing the buildup of fatty plaques.

While the step-by-step process leading to heart attack is not fully understood, major risk factors for coronary artery disease are well-established. Some can be controlled. Of these, the main ones are high blood pressure, high cholesterol, obesity, smoking and a sedentary lifestyle. Stress is also believed to raise the risk, and exertion and excitement can act as triggers for an attack.

Other risk factors include being a man over 50, being a postmenopausal woman, having diabetes, and a family history of heart disease.

Reviewed by Charlotte E. Grayson, MD, July 2005.

Sources: Heartcenteronline.com

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