Congestive Heart Failure
DescriptionAn in-depth report on the causes, diagnosis, treatment, and prevention of CHF.
Alternative NamesCardiomyopathy; Heart Failure
Heart failure has many causes and can evolve in different ways:
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, or hypertension, can cause a heart attack, but it is also a major cause of heart failure even in the absence of an attack. In fact, about 75% of cases of heart failure start with hypertension. It generally develops in the following way:
[For more information, see the Well-Connected report #14, High Blood Pressure.]
Coronary Artery Disease
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 on the arteries, with inflammation and injury in the cells of the blood vessels. The arteries narrow and become brittle and subject to damage. Heart failure in such cases most often results from a localized pumping defect in the left side of the heart. [For detailed information, see other Well-Connected reports, including #3, Coronary Artery Disease and Angina and #23, Cholesterol, Lipoproteins, and Other Lipids.]
Damage after a Heart Attack
People now often survive heart attacks, but eventually many develop heart failure from the physical damage done to the heart muscles by the attack. So ironically, heart attack recovery is probably one of the major factors in the dramatic increase in heart failure cases over the past decade. On an encouraging note, however, new therapies that are reducing the severity of heart attacks may help stabilize the heart failure rates. [For more information, see the Well-Connected report #12, Heart Attack.]
Valvular Heart Disease
The valves of the heart control the flow of blood leaving and entering the heart. Abnormalities can lead to failure:
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.
Cardiomyopathies are diseases that damage the heart muscles and lead to heart failure. Injury to the heart muscles may cause them to thin out (dilate) or become too thick (become hypertrophic). In either case, the pumping action is disrupted.
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 (in which case it 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. Experts posit that an autoimmune response occurs in which infection-fighting antibodies attack a person's own proteins in the heart, mistaking them for foreign agents.
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, diminished 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.
Corrective Mechanisms, Remodeling, and the Failing Heart
High blood pressure, heart attacks, or other initial processes that impair the pumping actions of the heart trigger a number of hormonal and neurochemical mechanisms to correct imbalances in pressure and blood flow. Unfortunately, while these corrective responses help in the short term, they increase the work of the heart. The mechanisms, then, are now viewed as major contributors to the end stages of heart failure. Some are described briefly in the following sections.
Remodeling. The heart responds to high blood pressure and overload by enlarging in order to increase blood input. This leads to structural damage called remodeling:
Activation of the Sympathetic Nervous System. The sympathetic nervous system consists of the nerve cells that automatically govern and regulate the beating heart.
The Renin-Angiotensin-Aldosterone System (RAAS). The renin-angiotensin-aldosterone system (RAAS) is a group of hormones that are responsible for the opening and narrowing of blood vessels and retention of fluids. They also affect cell development in the heart.
Immune System Response. The immune system may also compound the damage:
In response to injury in the heart muscle cells or in other parts of the body that occurs as the heart fails, the immune system releases factors intended to protect these areas.
In excess, however, they can cause inflammation and damage.
Other Players. Other molecules or compounds have been identified that might play a positive or negative role in the process of the failing heart: