Simple in structure but complex in its functions, the heart is the hardest working organ in the human body. In a single day, it pumps about 2,000 gallons of blood through an adult body. In healthy adults, its steady beat repeats itself about 37 million times a year. Complex chemical changes within the heart’s own cells create electrical impulses that initiate and pace its forceful contractions. When the heart fails, death usually follows. In normal circumstances a person can survive only a few minutes after the heart has stopped performing its critical task of delivering life-sustaining, oxygen-filled blood to the body’s billions of cells.
The structure of the human heart is relatively uncomplicated. About the size of a fist, it is a hollow, four-chambered muscle located between the lungs and slightly towards the left side of the chest. Deoxygenated blood, high in carbon dioxide waste from its voyage through the body, is drawn into the right atrium of the heart through two large veins, the inferior and superior venae cavae. The blood is drawn through a valve into the right ventricle, which in turn pumps it to the lungs to be cleansed of carbon dioxide and enriched with oxygen. The pulmonary veins return the freshened blood to the heart’s two left chambers, which pump it out through the aorta, the large trunk artery that carries blood back to the body. The heart gets its own blood supply from the coronary arteries, which quickly branch off from the aorta.
Although the heart is susceptible to many ailments, including damage from infections such as rheumatic fever and genetic disorders such as Down’s syndrome, by far the most common causes of heart disease are conditions resulting from atherosclerosis. Often referred to as hardening of the arteries, atherosclerosis results from the buildup of cholesterol and other fatty deposits, called plaque, in the lining of the arteries. The plaque can hamper blood flow and damage the muscle fibres in the artery wall.
Fatal: While nearly all adults in industrialized countries have plaque deposits, some people experience an excessive buildup that eventually leads to serious—and often fatal—forms of heart disease. Said Anthony Graham, a Toronto cardiologist who is president of the Heart and Stroke Foundation of Canada: “We understand a lot more than we did 10 years ago about risk factors. But how they all fit together is what we need to know.”
Among people who die of heart problems, 80 per cent are victims of coronary heart disease. That is a dangerous, self-perpetuating condition in which plaque buildup progressively narrows the coronary arteries, reducing the flow of blood to the heart. To counteract the blockage, the heart has to pump harder. As its work load increases, the heart’s need for oxygen grows—but it cannot be satisfied because the coronary arteries are also clogged.
An early warning sign that such a condition exists may be an attack of angina, a sharp pain in the centre of the chest following some form of stimulus, such as exercise, anger or sexual intercourse. Heavy smoking or a large meal may also trigger an episode. Doctors usually advise people with angina to make changes in their lives—giving up smoking or reducing stress— that will place them at lower risk. During the past decade, drugs designed to lower blood cholesterol have come on the market. Dr. Wilbert Keon, director-general of the University of Ottawa Heart Institute, said that the drugs are “tremendously beneficial” for people with significantly elevated cholesterol levels. But he added that it was not clear whether they were useful in treating people whose cholesterol levels were only slightly elevated.
Other signs that the heart may be in trouble include the diagnosis of hypertension, or high blood pressure. A condition that afflicts about 1.5 million Canadians, hypertension results when nerves that control the arteries cause them to contract, increasing pressure in the circulatory system. Often, hypertension may not produce any warning symptoms—until a life-threatening heart attack or stroke occurs. Although the causes of hypertension are unclear, many medical experts say that heredity, diet and stress all appear to be involved.
Pain: For many people, one of the most feared consequences of heart disease is a heart attack. Although smokers, the overweight and men are at higher risk, heart attacks theoretically can fell anyone at any time. Usually, an attack occurs when a major blood vessel serving the heart becomes blocked, often by a blood clot (also called a thrombus) that reduces the flow of blood to the heart. The result can be a possibly fatal heart attack. Although the blockage may occur suddenly, it is usually the result of atherosclerosis in the coronary arteries. A victim experiences an intense, squeezing pain in the chest, sometimes radiating down the left arm.
Most victims survive their first heart attack. Treatment may include drugs and other procedures that dissolve clots, or bypass surgery that grafts sections of blood vessels from other parts of the body to create a new, unblocked route for the blood. Most doctors say that longterm survival for many patients is closely linked to changes in lifestyle, including quitting smoking, eating more sensibly—and perhaps taking steps to reduce iron in the blood.
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