Heart failure develops when the pumping action of the heart is inadequate, typically because the heart muscle is weaker, stiffer, or both. What that means has been discussed before. This blog will address some of the reasons why this happens.
Causes
Systolic Dysfunction:
- Coronary artery disease is a common cause of systolic dysfunction. It can impair large areas of heart muscle because it reduces the flow of oxygen-rich blood to the heart muscle, which needs oxygen for normal contraction. Blockage of a coronary artery can cause a heart attack, which destroys an area of heart muscle. As a result, that area can no longer contract normally.
- Myocarditis (inflammation of heart muscle) caused by a bacterial, viral, or other infection can damage all or part of the heart muscle, impairing its pumping ability. Some drugs used to treat cancer and some toxins (such as alcohol) may also damage heart muscle. Some drugs, such as nonsteroidal anti-inflammatory drugs, may cause the body to retain fluid, which increases the workload of the heart and may precipitate heart failure.
- Heart valve disorders—narrowing (stenosis) of a valve, which hinders blood flow through the heart, or leakage of blood backward (regurgitation) through a valve—can cause heart failure. Both stenosis and regurgitation of a valve can severely stress the heart, so that over time, the heart enlarges and cannot pump adequately.
- An abnormal connection between the heart chambers can allow blood to recirculate within the heart, increasing the workload of the heart, and thus can cause heart failure.
- Disorders that affect the heart’s electrical conduction system and produce prolonged changes in heart rhythms (especially if these are fast or irregular) can cause heart failure. When the heart beats abnormally, it cannot pump blood efficiently.
- Some lung disorders, such as pulmonary hypertension may alter or damage blood vessels in the lungs (pulmonary arteries). As a result, the right side of the heart has to work harder to pump blood into the lungs. The person may then develop cor pulmonale, in which the right ventricle is enlarged and there is right-sided heart failure.
- Sudden, usually complete blockage of a pulmonary artery by several small blood clots or one very large clot (pulmonary embolism) also makes pumping blood into the pulmonary arteries difficult. A very large clot can be immediately life threatening. The increased effort required to pump blood into the blocked pulmonary arteries can cause the right side of the heart to enlarge and may cause the walls of the right ventricle to thicken, resulting in right-sided heart failure.
Diastolic Dysfunction:
- Inadequately treated high blood pressure is the most common cause of diastolic dysfunction. High blood pressure stresses the heart because the heart must pump blood more forcefully than normal to eject blood into the arteries against the higher pressure. Eventually, the heart’s walls thicker (hypertrophy), and stiffer. A stiff heart does not fill quickly or adequately, so that with each contraction, the heart pumps less blood than it normally does. Diabetes causes other changes that stiffen the walls of the ventricle.
- The combination of high blood pressure and diabetes, which are common among older people, and age-related stiffening makes heart failure particularly common among older people.
- Heart failure may result from other disorders that cause the heart’s walls to stiffen, such as infiltrations and infections. For example, in amyloidosis, amyloid, an unusual protein not normally present in the body, infiltrates many tissues in the body. If amyloid infiltrates the heart’s walls, they stiffen, and heart failure results. In tropical countries, infiltration by certain parasites into heart muscle can cause heart failure, even in young people. Some heart valve disorders, such as aortic valve stenosis, hinder blood flow out of the heart. As a result, the heart muscle thickens and has to work harder, and diastolic dysfunction develops. Eventually, systolic dysfunction also develops.
Hope this helps,
Dr T,
http://www.cardiac-risk-assessment.com/
(From: The Merck Manuals, Heart failure, by J. Malcolm O. Arnold, MD)