Causes:

Heart failure has many causes and can evolve in different ways.

• It can be a direct, last-stage result of heart damage from one or more of several heart or circulation diseases.
• It can occur over time as the heart tries to compensate for abnormalities caused by these conditions, a condition called remodeling.

In all cases, the weaker pumping action of the heart means that less blood is sent to the kidneys. The kidneys respond by retaining water and salt. This in turn increases edema (fluid buildup) in the body, which causes widespread damage.

High Blood Pressure

Uncontrolled high blood pressure (hypertension) is a major cause of heart failure even in the absence of a heart attack. In fact, about 75% of cases of heart failure start with hypertension. It generally develops as follows:

• The heart muscles thicken to make up for increased blood pressure.
• The force of the heart muscle contractions weaken over time, and the muscles have difficulty relaxing. This prevents the normal filling of the heart with blood.

[For more information, see In-Depth Report #14:High blood pressure.]

Hypertension is a disorder characterized by consistently high blood pressure. Generally, high blood pressure consists of systolic blood pressure (the "top" number, which represents the pressure generated when the heart beats) higher than 140, or diastolic blood pressure (the "bottom" number, which represents the pressure in the vessels when the heart is at rest) over 90.

Coronary Artery Disease and Heart Attack

Coronary artery disease is the end result of a complex process called atherosclerosis (commonly called "hardening of the arteries"). It is the most common cause of heart attack and involves the build-up of unhealthy cholesterol in the arteries, with inflammation and injury in the cells of the blood vessels. The arteries narrow and become brittle. Heart failure in such cases most often results from a pumping defect in the left side of the heart. [For more information, see In-Depth Report #3: Coronary artery disease and angina; and In-Depth Report #23: Cholesterol.]

People now often survive heart attacks, but eventually many develop heart failure from the physical damage the attack does to the heart muscles. Ironically, heart attack recovery is probably one of the major factors in the dramatic increase in heart failure cases over the past decade. [For more information, see In-Depth Report #12: Heart attack. ]

Valvular Heart Disease

The valves of the heart control the flow of blood leaving and entering the heart. Abnormalities can cause blood to back up or leak back into the heart.

In the past, rheumatic fever, which scars the heart valves and prevents them from closing, was a major cause of death from heart failure. Fortunately, antibiotics have relegated this disease to a minor cause of heart failure. Birth defects may also cause abnormal valvular development. Although more children born with heart defects are now living to adulthood, they still face a higher than average risk for heart failure as they age.

Cardiomyopathy

Cardiomyopathy is disease that damages the heart muscles and leads to heart failure. There are several different types. Injury to the heart muscles may cause the heart muscles to thin out (dilate) or become too thick (become hypertrophic). In either case, the heart doesn't pump correctly. Viral myocarditis is a rare viral infection that involves the heart muscle and can produce either temporary or permanent heart muscle damage.

Dilated Cardiomyopathy. Dilated cardiomyopathy involves an enlarged heart ventricle. The muscles thin out, reducing the pumping action, usually on the left side. Although this condition is associated with genetic factors, the direct cause often is not known. (This is called idiopathic dilated cardiomyopathy.) Research strongly indicates that viruses, such as Coxsackie virus, or other infections may be at the base of this condition. Researchers think that an autoimmune response occurs in which infection-fighting antibodies attack a person's own proteins in the heart, mistaking them for foreign substances.

Chronic alcohol abuse can damage the heart muscles, can cause hypertension, and may be one cause of idiopathic dilated cardiomyopathy. Moderate alcohol consumption, on the other hand (generally defined as 2 drinks a day for men and 1 drink for women), may protect against heart failure. Non-drinkers, though, are not advised to begin drinking.

Hypertrophic Cardiomyopathy. In hypertrophic cardiomyopathy, the heart muscles become thick and contract with difficulty. Some research indicates that this occurs because of a genetic defect that causes a loss of power in heart muscle cells and, subsequently, lower pumping strength. To compensate for this power loss, the heart muscle cells grow. This condition, rare in the general population, is often the cause of sudden death in young athletes.

Restrictive Cardiomyopathy. Restrictive cardiomyopathy refers to a group of disorders in which the heart chambers are unable to properly fill with blood because of stiffness in the heart. The heart is of normal size or only slightly enlarged. However, it cannot relax normally during the time between heartbeats when the blood returns from the body to the heart (diastole). The most common causes of restrictive cardiomyopathy are amyloidosis and scarring of the heart from an unknown cause (idiopathic myocardial fibrosis). It frequently occurs after a heart transplant.

Severe Lung Diseases

Chronic obstructive pulmonary disease (severe emphysema) and other major lung diseases are risk factors for right-side heart failure.

Pulmonary hypertension is increased pressure in the pulmonary arteries that carry blood from the heart to the lungs. The increased pressure makes the heart work harder to pump blood, which can cause heart failure. The development of right-sided heart failure in patients with pulmonary hypertension is a strong predictor of death within 6 - 12 months.

Thyroid Disorders

An overactive thyroid (hyperthyroidism) or underactive thyroid (hypothyroidism) can have severe effects on the heart and increase the risk for heart failure.