The heart is one of the most efficient and durable organs in the human body. Each day, it beats 100,000 times to pump more than 2,000 gallons of blood through the body, never resting for longer than a second, for an average lifetime of 75 years! Unfortunately, disease, genetics, or a host of environmental factors can conspire to make the heart less efficient or even cause it to break down completely.
Diseases of the heart and blood vessels, collectively known as cardiovascular diseases, are the most common disorders in Western societies. Fully 20 percent of Americans are afflicted with one or more forms. And these diseases—mainly heart disease—kill one American every 33 seconds; they account for about 40 percent of all deaths in the United States.
Despite these statistics, advances in diagnosis and treatment have caused a decline in death rates from heart attacks, strokes, and other cardiovascular diseases. The death rate from cardiovascular diseases actually declined between the years 1990 and 2000 by 17.0 percent. But there is still a long way to go before heart disease ceases to be a serious threat to health.
The physician can use any number of tests to study the function of the heart's arteries, muscle, valves, and electrical system, as well as the structure of cardiac chambers and layers. One of the most common tests is called an electrocardiogram (ECG), in which the electrical activity of the whole heart is recorded by electrodes on the skin. Another procedure, the echocardiogram, is a radarlike technique in which sound waves emitted by a handheld crystal bounce off the heart and back to the crystal, producing an image of the beating heart muscle, the four chambers, thevalves, and the pericardial covering as the heart beats. One evaluation technique is the treadmill, or exercise stress test, in which the patient performs various types of exercise to produce "stress" on a heart that may have blockages in its coronary arteries. The resultant decrease in blood supply to the working heart muscle can then be detected by an ECG, echocardiogram, or through imaging techniques such as thallium scans or PET scans.
Another important diagnostic test is the angiogram, or cardiac catheterization. In this procedure, plastic tubes called catheters are passed through the skin into an artery or vein of the leg or arm, and advanced into the chambers or coronary arteries of the heart. Once installed, the catheter permits pressures in different locations to be measured, and contrast dye is then injected into the heart. The dye is illuminated using X rays, causing the heart chambers and arteries to appear white on a black background. This allows doctors to clearly see any blockages in the arteries, to determine damaged areas in the heart, and to assess myocardial pumping function.
In the late 1990s, doctors began to use magnetic resonance imaging (MRI) techniques to reveal the structure of a diseased heart and determine the location and extent of any damage. Scientists also discovered that damage to the heart is associated with a drop in the level of a chemical substance called creatine, which can be measured using MRI technology.
The most common cause of death in the United States is myocardial infarction (MI), commonly known as heart attack. MI literally means the death of the myocardium, or heart muscle; it is usually due to blockages in the coronary arteries that feed blood to the myocardium. Of the approximately 1 million MIs annually in the United States, about 460,000 are fatal. Of these deaths, about 220,000 occur within one hour of the onset of symptoms and before the victim can reach a hospital.
Blockages in the coronary arteries are due to atherosclerosis, or hardening of the arteries, a condition characterized by fatty, sticky buildups, or plaques, in the inner wall of the coronary arteries and in other arteries throughout the body.
Coronary plaques impair blood flow to the myocardium, leading to reduced pumping force and lowered cardiac output of blood to the body. If plaques are severe but stable, they usually cause angina pectoris—a chest pain or pressure usually triggered by exercise or emotional stress.
Plaques have rough surfaces and are prone to rupturing into the blood, which results in the release of tissue substances that cause blood clots to form at the site of the plaque. These clots may block off the artery completely and suddenly, causing most MIs and sudden death.
Treatments for coronary plaques include medications that reduce the workload on the heart or dilate the arteries to increase blood flow past the narrowed areas. Aspirin and other drugs help thin the blood and prevent clotting if the plaques rupture. In more-serious cases, balloon-angioplasty catheters, which can reach the blockages and dilate them open, have been successful. In some cases, doctors perform bypass surgery, in which surgeons take a patient's vein or artery from elsewhere in the body and transplant it around the blockages to restore blood flow.
Congestive heart failure (CHF) is a serious condition affecting nearly 5 million Americans and causing or contributing to some 250,000 deaths annually. It is marked by a progressive decline in the heart's pumping function. The heart chambers usually dilate in a vain effort to compensate for declining contraction. As the forward flow of blood declines, blood backs up in the heart. This leads to fluid leaking out of the blood vessels and into the tissues. The patient becomes fatigued, swollen, and short of breath. Death occurs from slow progression of pump failure or suddenly from rapid, abnormal heart rhythms.
There are many possible causes for CHF. Among the most common are severe coronary-artery blockages (which starve the muscle of blood); serious valve malfunctions (which prevent efficient forward flow of blood); damage to the heart muscle by high blood pressure; infections of the heart; and inflammation of the heart, or myocarditis, due to the body's immune system attacking its own tissue. Certain medications, alcohol, heavy metals, and other toxins can also cause CHF.
Treatment for CHF includes medications that improve cardiac contraction or reduce fluid retention. In extreme cases, transplantation of a normal heart is undertaken.
A number of diseases can affect the heart's four valves. Some occur from birth, while others occur as a result of wear and tear or specific injuries to the valves. There are two types of valvular diseases. Leaking, or regurgitation, of the valves leads to the backward flow of blood through the heart's chambers and the buildup of blood into the lungs and body, fluid retention, and reduced forward flow. Narrowing, or stenosis, of the valves also leads to reduced forward flow, increased backward flow, and congestive heart failure. Reduced forward flow may also cause fainting and chest pains.
Valve diseases are accompanied by either thickening, calcification, infection, inflammation, or rupture of the valve leaflets, and may be due to various causes. The abnormal structures distort blood flow, producing sounds called heart murmurs that can be heard by a stethoscope and detected by an echocardiogram.
Treatment includes medications to increase forward flow (for regurgitant types only); balloon valvuloplasty, in which balloons on catheters crack open stenotic valves; surgical valve repair (for regurgitant valves) involving tightening up of loose, leaky valves; or replacement of the whole valve with an artificial valve (either a metal type or a pig's heart valve).
Abnormalities of the heart's rhythm, called arrhythmias, impair the efficiency of the heart, leading to reduced cardiac output, weakness, fainting, palpitations, fluid in the lungs, poor blood flow to the coronary blood vessels, and even death. Some arrhythmias are mild but annoying, while others are unpredictable and lethal. Millions suffer from various abnormal rhythms, and each year at least 40,000 U.S. deaths are attributed directly to these disorders.
Slow heartbeats may require a pacemaker, a wire electrode implanted through the skin, usually in the right chamber wall, into a large vein leading to the right ventricle. There it produces an electric current that stimulates the myocardium when the normal pacemaker doesn't fire properly. Fast heartbeats may require medications to suppress abnormal areas of electric activity. Catheter ablation or surgery to destroy areas of the heart causing arrhythmia are also common procedures. In some cases, implantable defibrillators are used. These implants recognize fast rhythms and deliver an electric shock to the heart to restore the normal rhythm.
Miscellaneous Heart Disorders
There are a number of rare but often deadly tumors that can affect the heart. A variety of blood clots, or thrombi, can arise in heart chambers or valves, break off, travel out of the heart to the body, and block off blood flow in various organs. Rheumatic fever is an inflammatory response to strep-throat infection in which heart tissue is attacked by the immune system. In endocarditis, bacteria and other organisms grow on the valves, erode through the leaflets, and impede valve functions. Pericardial diseases lead to tightening of the pericardium around the heart, causing strangulation; painful inflammation of the pericardial layers; or accumulation of fluid between the layers, which can dangerously compress the heart and prevent it from filling with blood.
The information provided should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies.
Copyright Information: Public domain information with acknowledgement given to the U.S. National Library of Medicine.