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There are a number of different ways that physicians and medical institutions classify and define heart failure. It may be classified by the portion of the heart that it affects or by its involvement with the heart rhythm. Alternatively, heart failure may be defined by the symptoms that are present or by the progressive stage of the condition.
Heart failure may be classified by which side of the heart it affects:
- Left-sided heart failure occurs when the left ventricle cannot adequately pump oxygen-rich blood from the heart to the rest of the body. The main symptoms include shortness of breath, fatigue and coughing, especially at night or while lying down. There may also be lung congestion (with both blood and fluid).
- Right-sided heart failure (cor pulmonale) takes place when the right ventricle is not pumping adequately, which tends to cause fluid build-up in the veins and swelling (edema) in the legs and ankles. Right-sided heart failure usually occurs as a direct result of left-sided heart failure. It can also be caused by severe lung disease (e.g., chronic obstructive pulmonary disease, pulmonary hypertension) in which the right side of the heart cannot generate enough force to pump blood through a diseased pair of lungs.
Heart failure is also commonly defined by which portion of the cardiac cycle is affected:
- Systolic heart failure means that the heart is unable to pump adequate amounts of blood during its contraction (systole). Lung congestion and swelling (edema) of the lower extremities are typical symptoms of systolic heart failure. This is most commonly caused by coronary artery disease, high blood pressure and heart valve disease.
- Diastolic heart failure refers to the heart’s inability to relax between contractions (diastole) and allow enough blood to enter the ventricles. Symptoms may be identical to systolic heart failure. Diastolic heart failure is often a precursor to systolic heart failure. Patients with diastolic heart failure may or may not have normal systolic function. Diastolic dysfunction causes about one-third of all heart failure in people over age 65 and occurs more often among women. This is most commonly caused by coronary artery disease, high blood pressure and cardiomyopathy.
To better understand the differences between systolic and diastolic heart failure, picture the heart as a balloon. Systolic heart failure is when the heart muscle is weak and flabby, like an old, worn-out balloon. Diastolic heart failure is when the heart muscle is stiff and hard, like a brand-new, never-inflated balloon. Neither extreme allows the heart to function properly, leading to a build up of blood in the lungs and shortness of breath (dyspnea).
In addition to these classifications, heart failure may be defined by how it affects patients. The New York Heart Association has developed a system that defines heart failure by the functional limitation it imposes on the patient. These levels are as follows (with approximate percentage of heart failure patients):
- Class I: No obvious symptoms, no limitations on patient physical activity (35 percent).
- Class II: Some symptoms during or after normal activity, mild physical activity limitations (35 percent).
- Class III: Symptoms with mild exertion, moderate to significant physical activity limitations (25 percent).
- Class IV: Significant symptoms at rest, severe to total physical activity limitations (5 percent).
The American Heart Association (AHA) and American College of Cardiology have developed a way to define heart failure that groups patients by their risk of developing heart failure. This system is useful because it helps physicians design a therapeutic approach to heart failure. The AHA/ACC stages are:
- Stage A: The patient at high risk for heart failure, but has no heart abnormalities.
- Stage B: The patient has structural abnormalities of the heart, particularly the left ventricle, but no symptoms.
- Stage C: The patient has past or present symptoms associated with heart failure.
- Stage D: The patient has end-stage heart disease, requiring specialized treatment (e.g., continuous intravenous [IV] drug therapy, left ventricular assist device, heart transplant) or severely symptomatic heart failure.
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