Heart Attack
(Myocardial Infarction · MI)
In this condition factsheet:
The Facts on Heart Attack
The heart is one of the largest muscles in the body. The wall of the heart is the muscle that does the pumping, and it is called the myocardium. In a heart attack, this muscle tissue is denied oxygen-carrying blood due to a blocked artery. When the shortage of oxygen gets so bad that many cells die, it's called infarction. The medical name for a heart attack is an acute myocardial infarction (MI).
Heart attack is directly responsible for about 10% of all deaths in Canada every year. This represents half of all deaths due to coronary artery disease. Although having a heart attack is very serious, the chances of survival are greatly increased if you are able to get to a hospital right away.
Causes of Heart Attack
Every organ needs oxygen-carrying blood to stay alive, and the myocardium (the muscle that forms the wall of the heart) is no exception. It has its own oxygen supply, via the coronary arteries. In coronary artery disease, fatty deposits (plaques) form in the inner walls of the coronary arteries, narrowing them and reducing blood flow to the heart. This process is called atherosclerosis.
Most heart attacks occur when the atherosclerotic plaque lining an artery ruptures. Blood then forms a clot on the damaged artery, which may partially or completely obstruct blood flow. If the blockage gets severe enough, heart attack symptoms appear, and heart muscle cells may start to die. This is now considered a heart attack.
Rarely, a coronary artery spasm stops blood flow through an apparently healthy coronary artery, causing a heart attack. In most of these cases there's no identifiable cause.
Symptoms and Complications of Heart Attack
Most heart attack victims feel some symptoms in the days leading up to the attack. The most common symptom is angina (chest pain). Chest pain results when the heart muscle is not getting enough oxygen, a condition called ischemia. Angina is likely to get worse or more frequent as the heart attack approaches. Other possible symptoms are extreme fatigue and shortness of breath.
If someone has angina, they may have difficulty distinguishing angina symptoms from heart attack pain. Heart attack symptoms are usually much more severe and longer-lasting (more than 20 minutes) than angina. Heart attack symptoms are relieved only slightly or temporarily by rest or medications used to relieve angina.
Many people report feeling a sense of warning as a heart attack approaches. There can be tightness, pressure, pain, and a "squeezing" feeling in the chest. The pain may also be felt in the back, jaw, shoulder, or arm (especially the left arm). The heart may speed up and beat irregularly. Although chest pain is usually the first symptom, up to 20% of people having a heart attack do not experience chest pain.
These other symptoms may or may not develop:
- shortness of breath
- anxiety
- sweating
- confusion
- nausea and vomiting
- temporary changes in vision
- lightheadedness
Almost everyone who suffers a heart attack experiences arrhythmias (irregular heartbeats). Some of these irregular heartbeats are harmless, while other types can cause serious problems, even death. One type, ventricular fibrillation (VF), can lead to death in about 5 minutes. The left ventricle, the main pumping chamber of the heart, quivers uselessly instead of delivering blood to the body. The heart does this because of the lack of oxygen delivery.
Not all heart attacks are this severe. In fact, some heart attacks go unnoticed or are shrugged off as heartburn or angina. Distinguishing a heart attack from heartburn is not as easy as you might think - antacids and belching can actually relieve heart attack pain, though it usually returns quickly. Nitroglycerin sprays or pills, often carried by people with angina, may also relieve pain temporarily. However, chest discomfort caused by most heart attacks is not relieved by nitroglycerin. It is important to use your discretion and common sense: if the discomfort feels worse or different than usual, consult your doctor.
