Congestive Heart Failure
Instructional Review
Congestive heart failure is a common condition that affects 5 million Americans every year. About 20% of hospitalized patients who are 65 or older have congestive heart failure. It is possible to control this disease of the heart. If not successfully controlled heart failure can cause serious disability or death.
The Heart
The heart is composed of two independent pumping systems, one on the left side, one on the right. The right atrium of the heart relaxes and expands to fill with blood that has returned from the body. This relaxed action causes diastolic pressure. The used blood is poor in oxygen and is rich in carbon dioxide. It enters the right ventricle which pumps the blood into the lungs were it exchanges the CO2 for oxygen. The blood now oxygen-rich, returns through the pulmonary veins to the left atrium were it is pumped back out to the body by the left ventricle. The left ventricle has thicker muscles than the right in order to perform contractions powerful enough to force the blood through the aorta to all parts of the body. This strong contraction produces systolic pressure.
What is CHF?
Congestive heart failure is not a disease but a condition that occurs when the heart is unable to pump enough blood to meet the needs of the body’s tissue. When the heart fails it is unable to pump out all of the blood that enters its chambers. To help determine its severity physicians use a calculation called an ejection fraction, which is the percent of blood, pumped out during each heartbeat. An ejection fraction between 50%-75% is normal. In most cases of heart failure the left side fails causing systolic dysfunction, in which fluid backs up and accumulates in the lungs. The ejection fraction in such cases drops below 40%. In severe failure it may drop as low as 5%. Right-sided failure, which is less common, causes diastolic dysfunction, in which fluid entering the heart backs up, causing the veins in the body and tissues surrounding them to swell. In these cases ejection fractions are paradoxically normal to high. Given the interconnected nature between the chambers of the heart left sided failure may ultimately precipitate failure in the right side of the heart.
Heart failure can occur in several ways. The ventricular muscles of the heart can become thin and weakened and dilate to the extent that they cannot pump the blood with enough force to reach all of the body’s tissues. In other cases the heart muscles stiffen or thicken so they lose their elasticity and cannot relax. Insufficient blood enters the chamber and the body does not get the blood it needs. Sometimes the valves in the heart may narrow causing a back up of blood. As a result of these changes, the body’s vital organs do not get enough oxygen and nutrients, and the body’s waste is removed more slowly and eventually vital systems break down.
What Causes CHF?
Congestive heart failure is usually the last stage of one or several heart or circulatory diseases. Heart failure can be a direct result of one of these diseases or it can occur over time as the heart tries to compensate for abnormalities caused be these conditions
- Coronary Artery Disease - CHF may develop slowly from heart damage due to arteriosclerosis, a build up of cholesterol on the walls of the arteries supplying the heart with oxygen. Heart failure in these cases often result from a localized pumping defect in the left side of the heart.
- Damage After AMI - The majority of infarcts involve the left ventricle. When about 25% of the left ventricular myocardium is involved, left heart failure usually develops. Onset of heart failure associated with AMI can be within 12 hours to 7 days
- High Blood Pressure - Hypertension is a major cause of heart failure even in the absence of an MI. In hypertension the heart muscles thicken to compensate for the increased blood pressure, and over time the force of the contractions weaken and they have difficulty in relaxing, thereby preventing normal filling of the heart.
- Diabetes - Diabetes contributes to heart failure not only because of its association with obesity, HTN, and coronary artery disease, but also because specific mechanisms that contribute to diabetes may also damage the heart.
- Cardiomyopathies - Cardiomyopathies are diseases that damage the heart muscles and lead to heart failure. Genetic factors or birth defects may also play a role in the development of these conditions.
- Dilated Cardiomyopathy. Involves an enlarged ventricle, in which the muscles thin out rather than becoming thick, causing reduced systolic blood pressure. Although this condition is associated with genetic factors, the cause is often not known (in which case it is called idiopathic dilated cardiomyopathy). Research is strongly indicating that the cases may be the result of an autoimmune response in which infection fighting antibodies attack a persons own protein in the heart, mistaking them for foreign agents.
- Hypertrophic Cardiomyopathy. This condition the heart muscles become thick and contract with difficulty. Some research indicates that this occurs because of a genetic defect that causes loss of power in the heart muscles cells and subsequently diminished pumping strength. To compensate for this power loss the heart muscles cells grow. This rare condition is the cause of many occurrences of sudden death in young athletes.
- Other Causes - Chronic alcohol abuse can cause damage to the heart muscle, cause hypertension, and studies show it to be the cause of idiopathic dilated cardiomyopathy. Severe emphysema is the major cause of right-sided congestive heart failure.
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