Heart Disease | The Canadian Encyclopedia


Heart Disease

In industrial countries more people die from diseases of the heart and blood vessels than from any other single cause.

In industrial countries more people die from diseases of the heart and blood vessels than from any other single cause. Over the last 30 years, extensive cardiovascular research has resulted in such revolutionary techniques as cardiac catheterization, heart-lung machines, artificial valves, cardiac pacemakers, echocardiography (a machine that uses ultrasound to produce a picture of the heart) and nuclear diagnostic technology. In addition, the management of heart disease by drugs has also improved with the discovery of new agents capable of controlling the force of cardiac contraction. These drugs include inotropic agents, beta blockers (which reduce the amount of work the heart must do) and calcium antagonists.

Cardiovascular disease remains one of the leading causes of death for Canadians. It does not discriminate and affects both genders and all ethnicities. One-third of Canadians die every year from cardiovascular disease, which includes heart disease and stroke.

Heart disease causes not only an increased risk of death, but also a reduced quality of life. Almost one-quarter of Canadians over age 70 report heart problems and must deal with the decline in health, restriction of activity and requirement for assistance with the daily necessities of life that often accompany cardiovascular disease.

The provinces and territories have different rates of the population affected by cardiovascular disease. Newfoundland's population consistently has a higher risk of mortality than the rest of Canada. It also has a higher number of modifiable risk factors, such as diabetes and high blood pressure, than the overall Canadian population. The Canadian north has lower rates of death from cardiovascular disease, except for congestive heart failure, than the rest of the country.

Cardiovascular disease tends to affect men and women differently. It is more common for women than men to die as from congestive heart failure (impaired heart pumping functions) and cerebrovascular disease (stroke). In contrast, more men than women die from ischemic heart disease (coronary artery disease, such as atherosclerosis) and acute myocardial infarction (heart attack).

Coronary Artery Disease

Coronary artery disease, the most common type of heart disease and the leading cause of death in North America, is almost always the result of atherosclerosis, the clinical name for hardening of the coronary arteries. Atherosclerosis is characterized by the accumulation of fatty deposits and the formation of fibrous tissue in the walls of arteries that then become narrow, thus diminishing the flow of blood and oxygen to the heart muscle. Although atherosclerosis develops quite early in life as the result of a diet rich in animal fat, cigarette smoking and the leading of a sedentary life, symptoms usually develop in the fourth or fifth decade of life. The disease may result in a sudden death in approximately 50% of the patients who have coronary artery disease without knowing it.

The average age of death due to coronary artery disease is 52 years. In the remaining 50% of patients the disease may produce attacks of crushing pain (angina pectoris) in the central chest. The surgical management of coronary artery disease enjoys unprecedented popularity because of very low operative mortality (1% to 3%) and because relief of pain is obtained in about 90% of cases. More than 200 000 such operations are performed annually in North America.

Heart Valve Damage

Another form of heart disease is that associated with the heart valves. They can be damaged by rheumatic fever, bacterial infections or other disease processes. A defective valve fails to close completely or cannot open fully, thus disturbing the smooth unidirectional flow of blood required for normal functioning of the body. Some malfunctioning valves can be repaired through surgical techniques, but in some cases the valve is so severely damaged that it must be replaced with an artificial (prosthetic) one. The outlook for patients with valvular heart disease has changed dramatically with the development of prosthetic valves in the 1950 and 1960s.

Implantation of prosthetic valves to treat valvular disease has become increasingly common. Medication is the best alternative, but in some cases defective valves have to be replaced with a prosthetic one in order for a patient to live a normal life. Replacement of diseased valves reduces the morbidity and mortality associated with valvular disease but comes at the risk of complications unique to the implanted device.

The first mechanical prosthetic heart valve was implanted in 1952. Since then, 30 different mechanical designs have been developed worldwide. The two main prosthetic valve designs are mechanical and bioprosthetic (tissue) valves. The main problem with all types of mechanical valves is the increased risk of blood clotting, which is accompanied by a high probability of heart attack or stroke. To prevent blood clots, mechanical valve recipients must take anti-coagulant drugs chronically, which effectively makes them borderline hemophiliacs. The anti-coagulant used causes birth defects in the first trimester of fetal development, rendering mechanical valves unsuitable for women of child-bearing age. Mechanical valves are also subject to mechanical failure. They are suitable for people who do not want additional valve replacement surgery in the future.

Prosthetic tissue valves, also called bioprosthetic valves, can be made of either human or animal tissue. They have many advantages over mechanical valves. They are much closer natural valves and do not require long-term anticoagulants, do not cause blood cell damage, and do not experience many of the structural problems experienced by mechanical heart valves. The most common cause of bioprosthesis failure is stiffening due to calcification.

Artificial Support Devices

The heart is a pump made of special muscle whose contractions are triggered and synchronized by electrical impulses produced by its own natural pacemaker. When the natural pacemaker falters, an artificial pacemaker, using batteries and timers, can be used to produce electrical impulses transmitted along tiny wires secured to the heart. The pacemaker is a small battery-powered unit usually implanted under the skin and wired to the heart to control its rate and rhythm of contraction. These devices are now very small and durable.

Many patients with pacemakers experience anxiety after receiving a shock from the device. Although the shocks are not associated with an increased severity of disease, they do have strong psychological effects. New treatment methods to address the psychological needs of cardiac patients with pacemakers are being developed and implemented. Patients often benefit from psychological therapy to explore and help address the distress that can result from receiving a shock from a pacemaker.

Congenital Defects

One baby in about a hundred is born with an abnormality of the cardiovascular system. In general, such congenital defects include incorrectly formed valves, holes in the walls (septa) that separate the 2 sides of the heart, and abnormalities in the blood vessels leading in and out of the heart. These fall into 2 broad categories: conditions in which the baby is "blue" (cyanotic heart disease) and those in which the baby's colour is normal (acyanotic heart disease). Most congenital heart defects can be corrected surgically in infancy or early childhood. The surgical risk is relatively low (about 5%) and the long-term results are generally excellent.

The last 30 years have witnessed remarkable achievements in cardiovascular medicine and surgery. Some of these achievements have been made by Canadians. Dr W.G. Bigelow of Toronto and Dr J.C. Callaghan of Edmonton pioneered the work on total body hypothermia (cooling off the body to reduce oxygen requirements during surgery) and laid the foundations for modern cardiac pacemakers. Callaghan was also the first to successfully use the heart-lung machine for open-heart surgery in Canada (1956) and the first to insert an artificial valve and correct the tetralogy of Fallot. Dr W. Mustard of Toronto's Hospital for Sick Children pioneered techniques in pediatric cardiovascular surgery, and the "Mustard Repair" for transposition of the great vessels in children has gained international acceptance. Among pediatric cardiac care centres, Edmonton's Stollery Children's Hospital is among the best in North America. Dr. A.M. Vineberg of Montréal studied myocardial revascularization for many years and developed an implantation procedure that was widely used before the introduction of coronary artery bypass procedures and is still sometimes used.

Risk Factors

There are numerous risk factors for cardiovascular diseases. Smoking, high blood pressure, diabetes, physical inactivity and overeating are significant but modifiable risk factors. Cardiovascular disease is on the increase in Canada, and 80% of the population has at least one modifiable risk factor for the disease. Educating Canadians about modifying existing risk factors for heart disease has been shown to be an important aspect of prevention.

Research studies investigate the emotional factors involved in heart disease and stroke. Many patients experience depression, anxiety and stress due to the progress of the disease and its effect on the social support network. Living with a chronic disease is physically and emotionally challenging. Physicians have begun to address the full spectrum of factors associated with heart disease and stroke.

People with diabetes frequently have heart disease and stroke and tend to have the risk factors associated with cardiovascular and cerebrovascular disease such as high blood pressure, high blood cholesterol levels, smoking, obesity and a lack of exercise. Studies indicate that a frequent aspect of type II diabetes, insulin resistance, is a distinct risk factor for heart disease. Cardiovascular disease is the leading cause of diabetes-related death. People with diabetes can lower their risk of heart disease by managing blood sugar levels, quitting smoking if they smoke, exercising regularly and eating a healthy diet.

All over the world, including Canada, people are being encouraged to reduce their risk of cardiovascular disease. A balanced diet low in saturated and trans fats is vital and regular physical activity is beneficial. Quitting smoking is one of the most important changes a person can make to improve quality of life as well as reduce the risk of heart disease and many cancers.

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