Blood Flows and Heart Valves

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Today I would like to tell you about advances in heart valve replacement techniques. But first, allow me to review how blood flows through the human heart. The main vein that returns unoxygenated blood to the heart is the vena cava. The superior vena cava drains the upper body, arms, and head while the inferior vena cava drains the lower body and legs. Blood flows from the vena cava into the right atrium, then through the tricuspid valve into the right ventricle. When the right ventricle contracts, it pushes the blood through the pulmonary valve into the pulmonary arteries, then into the lungs where the blood is reoxygenated and carbon dioxide is released. The reoxygenated blood returns to the heart via the pulmonary veins, where it enters the left atrium. The blood then moves through the mitral valve, into the left ventricle which, when it contracts, pushes the blood through the aortic valve into the aorta and out to the body.

As an aside, the pulmonary arteries are the only arteries that carry unoxygenated blood, and the reverse is true of the pulmonary veins. The purpose of the heart valves is to act as check valves and prevent the backflow of blood when the ventricles contract.

All four valves have a similar design in that each valve has three leaflets that open and close as needed. The leaflets are anchored to the heart wall to prevent prolapse, or over extension. Over time, heart valves may become tight or may leak. Sometimes a leak is caused by a flail leaflet, which occurs when the leaflet’s anchor snaps. A fairly common congenital abnormality is a bicuspid valve, where the valve has two leaflets instead of three. A valve that either cannot fully open or close will, over time, cause heart failure. This is overwhelmingly true of the aortic and mitral valves. The two right heart valves, the tricuspid and pulmonary, rarely fail because the pressure in the right heart is considerably lower than the left side. For example, each year in the U.S. about 180,000 heart valve replacements are performed. Of these, about 250 are for the tricuspid valve.

Traditionally, heart valve replacement involved opening the chest wall and replacing the damaged valve, a very complicated and high-risk procedure. Early in this century, a new procedure was developed which used catheters inserted into a large vein or artery, usually the femoral vessels in the groin, to replace the damaged valve. This is called transcatheter valve replacement and is rapidly becoming the procedure of choice. As of 2019, the number of transcatheter aortic valve insertions (TAVI) exceeded the number of surgical aortic valve replacements (SAVR) by 77,991 to 57,626, and the number of TAVIs is expected to exceed 130,000 by 2026.

There are two main types of replacement valves. There are mechanical valves which have a fabric ring and leaflets made of titanium or carbon fiber and there are bioprosthetic valves which use pig or cow tissue for leaflets. Only bioprosthetic valves may be inserted using the transcatheter method. Mechanical valves are more durable but come with a risk of blood clots, so lifetime anticoagulation (blood thinners) is needed. They tend to be used in younger patients with longer life expectancy. Bioprosthetic valves are less durable, do not require blood thinners, but are subject to deterioration and may need to be replaced. They are usually used in older patients with shorter life expectancies.

For more information go to:

www.ctsurgerypatients.org/deciding-between-a-tissue-and-a-mechanical-valve 

Questions and comments may be sent to This email address is being protected from spambots. You need JavaScript enabled to view it..">This email address is being protected from spambots. You need JavaScript enabled to view it. 

 By Peter Galvin, MD

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