About AVR Surgery and Mechanical Heart Valves

What is AVR surgery?

Aortic valve replacement (AVR) surgery is exactly what the name says it is: a surgical procedure in which a faulty aortic valve is replaced with a new one.

Shopping time! Except in cases where immediate surgery is required, patients usually take time before the operation to browse through a couple of different options to decide what exact valve they would like to receive. There are two basic types of replacement valves: organic ones (often porcine in origin) and mechanical valves. Those who are deemed eligible for the Ross Procedure may choose a very special type of organic valve: their own pulmonary valve. In this procedure, the patient’s pulmonary valve is used to replace the damaged aortic valve, and then the pulmonary valve of a cadaver is used to replace the original pulmonary valve of the patient.

Image from onxlti.com, (c) On-X Life Technologies, Inc.

Tissue valve vs. mechanical valve. Image from onxlti.com, (c) On-X Life Technologies, Inc.

The pros and cons of organic vs mechanical valves are, of course, nuanced and will vary somewhat from case to case. One main difference lies in how long they last. Organic valves tend to last ten to fifteen years (though Ross Procedure valves may last much longer) before more surgery is required, whereas mechanical valves, like parrots, often outlive their owners. On the other hand, mechanical valves also require their owners to take certain medications for the rest of their lives, while the prescriptions for organic valves are almost always finite, finishing in a matter of months.

In some cases a minimally invasive procedure involving relatively small incisions and reduced recovery time (both in the hospital and at home) is possible. Less fortunate patients with more severe symptoms or heart damage usually require traditional open-heart surgery, which involves a much larger incision as well as opening up the breastbone, not to mention a longer recovery time (and larger scars).

In my case, the damage in my heart was too extensive to allow for a minimally invasive procedure, and for reasons which will be covered in a later post (I promise!), I chose a mechanical valve.

So how do mechanical aortic valves work?

As I mentioned above, mechanical valves, unlike their organic counterparts, require lifelong medication — specifically, anticoagulants (blood thinners). This is because the inorganic materials used for mechanical hearts can cause blood clots around the new valve, which can have potentially fatal consequences.

Anticoagulants are a tricky business, and the exact dosage required varies from person to person and can change over time as well. Too low a dose compromises their effectiveness; too high a dose can make them work a little too well. As such, they require regular check-ups in the form of PT-INR tests.  A blood sample is taken, and a machine measures how long it takes that sample to coagulate. The blood sample may be drawn with a syringe, but typically a simpler (and less painful) fingertip pinprick test is used instead. PT stands for prothrombin time — that is, the amount of time it takes your blood to clot. INR stands for International Normalized Ratio — basically, the INR is a standardized number which is used to represent the results of the test.

Photo courtesy of pexels.com

Too low an INR reading indicates the current dose is too low; the patient is at risk for blood clots. Too high an INR reading indicates the current dose is too high; the patient is at risk for bleeding problems. Owners of mechanical heart valves are given target INR ranges to aim for in order to avoid both extremes. This usually falls somewhere around 2.5 to 3.5. In my case, because of the specific valve I chose — the On-X valve — my range is not only lower but also tighter, 2.0 to 2.5, making it more difficult to hit the bulls-eye.

But wait, there’s more! Coumadin (or its generic version, Warfarin) is almost always the anticoagulant prescribed for lifelong use. This is because it has been used for the longest out of all the currently available anticoagulants, and has, in many ways, stood the test of time. However, it can also be an extremely touchy drug. For instance, vitamin K, mostly found in dark, leafy greens, works against the drug and lowers INR readings. At the same time, some vitamin K intake is a necessary part of a healthy diet. Therefore, in order to keep your INR steady, you’ve got to keep your diet consistent as well, taking care to consume the same amount of vitamin K every day. This is to say nothing of other factors which can affect INR, including alcohol, herbal supplements, weight gain or loss, changes in sleep patterns, and even stress. (Who wouldn’t be stressed out when taking such a temperamental drug?)

Then there’s the ticking. Because mechanical valves are, well, mechanical, they tend to produce a ticking sound not unlike a timer or a clock. When they were first invented, this noise was ridiculously loud — some people reported being able to hear it from several rooms away. Thankfully as technology has improved over the years the valves have gotten quieter; some say they can barely even hear their own tickers. I can hear mine loud and clear, though others only seem to be able to pick up the sound in a fairly quiet environment. It is strange and a bit disquieting at first, but you learn to get used to it, as you learn to get used to so many other things that come with the territory.



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