Congestive Heart Failure (CHF) Overview (cont.)

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What causes congestive heart failure?

There may be many potential reasons for a patient to develop heart failure. It may be due to structural damage to the heart, inability of the heart to squeeze properly, medications or drugs that affect heart function, lung disease, and other underlying medical diseases. More than one cause may be present at the same time.

Cardiac output = stroke volume X heart rate (beats per minute)

Cardiac output and ejection fraction are measurements of the heart's function and efficiency. Cardiac output is calculated by measuring the amount of blood pumped by each heartbeat (stroke volume) multiplied by the pulse rate, the number of heart beats in a minute.

  • Normal for male is about 5.5 liters of blood pumped by the heart to the body every minute
  • Normal for female is about 5.0 liters per minute

Ejection fraction (%) = stroke volume / blood in left ventricle at beginning of heartbeat (end diastolic volume) X 100

A normal heart is able to pump out approximately 55% to 70% of the blood that fills it at the beginning of its contraction. The ejection fracture is the percentage of blood is pumped out of the heart with each heartbeat and is a measure of the pumping strength and efficiency of the left ventricle.

Anything that may affect the heart rate, stroke volume, and ejection fraction, may lead to the heart pumping less efficiently. This can cause blood to back up into the veins leading to the heart, increasing pressure within the capillaries, the smallest of blood vessels in the body and in turn cause water (fluid) to leak into the interstitial space (the space between cells that make up the tissue and organs of the body).

Consequently, ↓cardiac output results in → ↑pressure in capillary blood vessels→water leaking→heart failure symptoms

Heart failure most commonly is due to weakness of the muscle of the left ventricle resulting in decreasing stroke volume and ejection fraction; the following are some reasons why the heart muscle weakens:

  • Atherosclerotic heart disease (ASHD) describes narrowing of the coronary arteries that supply the heart muscle with oxygen that can lead to myocardial infarction (heart attack) and replacing some muscle with scar tissue.
  • When heart valves become diseased, either with stenosis (narrowing) or insufficiency (leaking, regurgitation), blood flow in and out of the heart is compromised. Aortic stenosis, narrowing of the valve that leads from the left ventricle to the aorta, makes the left ventricle struggle to push blood out of the narrowed opening. Mitral insufficiency describes leakage in the valve that connects the left atrium to the left ventricle. When the heart contracts, blood should go out the aortic valve to the body but in this situation, blood can also leak backwards, decreasing ejection fraction and stroke volume.
  • Poorly controlled hypertension (high blood pressure) and diabetes may lead to left ventricular failure.
  • Myocarditis describes inflammation of the heart muscle and may be due to a variety of reasons including infection. Like any other muscle that is inflamed or irritated, the ability to squeeze and pump may be limited.
  • Cardiomyopathies (cardio=heart + myo=muscle = path=abnormality) is a term used to describe heart muscle that loses its ability to squeeze efficiently. Ischemic cardiomyopathy describes a heart that is damaged because of atherosclerotic heart disease. Dilated cardiomyopathy describes an enlarged heart where heart muscle fibers are damaged and stretched and cannot contract efficiently. The heart, in effect, becomes floppy and the ejection fraction decreases. Hypertrophic cardiomyopathy describes abnormally thick heart muscle that cannot squeeze effectively. Amyloidosis and sarcoidosis can also affect the heart. Some cardiomyopathies are due to alcohol and drug (especially cocaine) abuse. Idiopathic cardiomyopathy describes heart disease where the cause is unknown.
  • Heart rhythm abnormalities can decrease ejection fraction and cause heart failure. If the heart beats too slowly, cardiac output may be decreased. If the heart beats too quickly, stroke volume may decrease because there is not enough time for the heart to fill between beats.

Right heart failure may occur when the heart has to pump against increased resistance in the blood vessels leading to the lungs. As pressure rises in the pulmonary arteries and veins, the right ventricle has to pump harder and may not be able to overcome this higher pressure. Some causes of right heart failure include the following:

  • Pulmonary embolus (blood clot to the lung)
  • Pulmonary hypertension (increased blood pressure within the lung's blood vessels)
  • Chronic obstructive pulmonary disease (COPD)
  • Pulmonary valve stenosis or narrowing of the valve that connects the right ventricle to the pulmonary artery

Diseases that affect other systems of the body can cause heart failure by influencing heart function directly or by altering the way the body delivers oxygen or controls the water balance in the body. Examples include the following:

  • Patients with profound anemia (low red blood cell count) may not be able to deliver enough oxygen to heart muscle to allow it to function appropriately. Patients with too many red blood cells (polycythemia rubra vera) may have blood that sludges and is too thick to pump efficiently.
  • The heart function is affected by extremes of thyroid disease (too high = thyrotoxic; too low = myxedema)
  • The kidneys, brain, and hormones control the water content of the body. Diseases that alter this control mechanism can lead to heart failure.
Medically Reviewed by a Doctor on 10/16/2013

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