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December 8, 2015

Aortic Valve Replacement

Valvular heart disease (VHD) refers to various conditions that affect the functioning of any of the four sets of valves in the heart. Of course, the heart is a muscular organ, located in the center of the chest. It contracts and relaxes rhythmically, about 100,000 times a day. Its sole function is to keep blood and nutrients circulating continuously, with a detour to the lungs for the exchange of gases.

Ultimately, oxygen-refreshed blood is sent under considerable pressure from the left ventricle of the heart, through the aortic valve, and into the aorta; the body’s largest blood vessel. From there, it travels to most of the body’s organs and tissues, before returning to repeat the cycle.

A Well-Designed Systemblog-post-image-1

Like any well-designed hydraulic system, the heart contains valves to prevent the back flow of blood during the pause between contractions. This greatly improves efficiency, but it also poses problems should anything go wrong with one of these valves. Defective valves may result from any number of causes. Inevitably, these defects allow blood to leak into the ventricle, reducing pumping efficiency. Such leakage is called aortic regurgitation. Another potential problem, in which the valve fails to open fully, is called aortic stenosis.

Aortic valve replacement is a surgical procedure to correct defects in the aortic valves. When successfully achieved, it allows the heart to resume normal function. It’s accomplished by inserting a replacement valve. Needless to say, this is a far more complex task than it sounds.

For starters, the heart contracts and relaxes (beats) about 70 times a minute. In the past, the typical replacement procedure involved open-heart surgery. The patient’s heart was temporarily stopped, while the patient’s circulation was shunted to a heart/lung machine. Recovery times were long and potential side effects were considerable. Materials traditionally used for replacement valves included tissues retrieved from pigs or cows. More recently, advances in technology have allowed the implantation of innovative artificial valve devices, constructed from metals or synthetic materials.

Open Heart vs. Minimally Invasive

Methods for defective valve removal, and new valve replacement, have undergone some dramatic changes in recent years. Minimally invasive techniques have been developed, which do not involve splitting open the sternum (sternotomy). Rather, small incisions are made in the thorax to facilitate access to the heart (minithoracotomyblog-post-image-3). Yet another procedure, called transcatheter aortic valve replacement (TAVR), is performed by threading a catheter into the heart from an incision in either the chest or groin.

The process of accessing the interior of the heart by threading catheters through the femoral vessels was pioneered in the 1940s. Since then, it has been the standard method used in the U. S. Recent innovative approaches have included access through the subclavian artery and jugular vein (in the neck), as well as less-obvious areas of ingress, such as through the heart’s apex (transapical). Access is gained through the chest, between the ribs. A further variation involves access through the upper chest (transaortic).

These less-invasive procedures are quickly becoming the norm, although classic sternotomy procedures are still considered “conventional.” Newer procedures tend to have better outcomes, in terms of patient survival, recovery times and cosmetic appearance, among other factors. Though some of these procedures require patients to be hooked up to a heart/lung machine longer. This discourages the use of newer procedures, especially among high-risk patients.blog-post-image-2

Nevertheless, innovations appear to be moving the technology toward these less-invasive procedures as the new norm. Minimally invasive aortic valve replacement involving sutureless valves, for example, are viewed by some experts as the superior alternative to transcatheter aortic valve implantation procedures in high-risk patients.

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