Heart Attack - How exactly does it happen ?

Dateline: 05/04/99

Have you read the earlier article on Heart Attack ? This week's article deals with a basic explanation about the evolution of a heart attack.

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Dynamics of a Heart Attack

A heart attack is caused essentially by a mis-match between the energy demands of the heart and it's blood supply. Whenever blood flow is too low to supply the nutrients and oxygen demands of the heart, the risk of heart muscle death increases.

The commonest mechanism of this situation is a narrowing of the coronary arteries by disease. Atherosclerosis is the disease responsible for narrow coronary arteries in the majority of patients. Rarely other diseases like arteritis (inflammation of the artery wall) can produce similar obstruction. The narrowed coronary artery might suddenly become completely blocked. This happens by an interesting sequence of events.

Atherosclerotic plaque rupture

The "atherosclerotic plaque" inside the coronary artery is inherently unstable. It might "burst" unexpectedly. The exact mechanism of this is uncertain. As a result of the plaque rupture, its uneven and rough interior is exposed to blood circulating inside the coronary artery. Special blood cells called "platelets" are conditioned to stick to "rough" surfaces in the blood stream. These platelets then produce a variety of chemicals that attract still more platelets, until a plug of these cells is formed. In addition, these chemicals stimulate the formation of a blood clot inside the coronary artery - a process called THROMBOSIS. The combined effect of the platelet plug and blood clot totally occludes the coronary artery and stops blood flow to the heart muscle.

Bleeding into the plaque

Another sequence involves sudden bleeding (the cause of which is also uncertain) inside the atherosclerotic plaque inside the coronary artery. Because of this bleeding, the plaque swells and increases in size, and blocks the coronary artery fully. No blood can now flow beyond it to the heart muscle.

A situation is now created where the heart muscle cannot receive blood carrying nutrients and oxygen. If this situation is left uncorrected for long, the heart muscle will die, leading to a heart attack.

Coronary artery spasm

The chain of events described above account for most heart attacks. But uncommonly some patients with unobstructed coronary arteries also suffer heart attacks. The mechanism is slightly different in these cases. In response to some unknown stimuli, the coronary arteries might "shrink" in size due to a sudden and sustained contraction of muscle in their walls (spasm). The consequence of this spasm is similar to plaque rupture and thrombosis - blood flow inside the coronary artery is brought to a halt. The stage is set again for a heart attack.

Recommended Reading:

• The Heart Attack Handbook by Joseph S. Alpert
  The Commonsense Guide for Patients and Their Families. Paperback; A useful resource for the family of a victim of heart attack.
• 8 Steps to a Healthy Heart by Robert E. Kowalski
  The Complete Guide to Heart Disease Prevention and Recovery from Heart Attack and Bypass Surgery.
• Guide to Heart Attack Treatment, Recovery, and Prevention by American Heart Association
  The official recommendations of the American Heart Association for treatment and management of a heart attack.

For more resources on smoking and heart disease, visit the resource library.

Read another article on Heart Disease and Smoking.

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You can also review articles in the following interest areas dealing with heart disease:

• Minimally Invasive Heart Surgery
• MICAS website
• Fetal Heart Surgery
• Congenital Heart Disease
• Heart Disease in Women
• Post operative care after heart surgery
• Pregnancy and Heart Disease

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