Overview of Transcatheter Aortic Valve Replacement
Aortic stenosis (AS) is a condition where the heart’s aortic valve narrows due to buildup of calcium, making it harder for the heart to pump blood to the rest of the body. This is the most common reason for blockage in the pathway that blood uses to leave the heart (left ventricular outflow tract). If someone has moderate AS, the condition is likely to get worse and become severe over time.
In the past, the usual treatment for severe AS was to replace the faulty aortic valve with a new one through surgery. High-risk patients who couldn’t undergo surgery were given medications or a procedure known as balloon valvuloplasty. The latter would temporarily open up the narrowed valve, but neither of these options improved long-term survival rates.
However, a new treatment called transcatheter aortic valve replacement (TAVR) has shown promise for patients who can’t go through surgery. TAVR not only improves the symptoms of AS but it also significantly increases survival rates. This procedure was first attempted in the 1980s by a Danish researcher named H. R. Anderson using a balloon to expand the valves.
The first successful aortic valve replacement using this method on a patient who couldn’t have surgery was performed by Dr. Alain Cribier in 2002. The TAVR method received approval for use on patients with severe AS who were at high risk for surgery in 2011. Over the years, approval has been granted for its use in other patient groups, including those at intermediate risk in 2016, and even low-risk patients in 2019, thanks to successful clinical trials like the PARTNER-3 trial.
Anatomy and Physiology of Transcatheter Aortic Valve Replacement
The aortic valve is a key part of your heart, functioning like a gate between the left section of your heart and your body’s largest artery, the aorta. Imagine it as a door that has three flaps, which open and close to let blood flow through. This valve should typically open to about 3-5 square cm. Your physician can look at your aortic valve using various imaging tests including an ultrasound of your heart.
If this valve becomes narrower, it is considered severely narrowed when it opens to a size of only 1.0 square cm or less. One common form of this condition, referred to as severe aortic stenosis, is characterized by a high pressure difference, or gradient, of 40 mmHg or more across the valve as well as a fast blood flow speed of more than 4 meters per second.
There’s also a less common form of this condition where the flow of blood is low along with a low pressure across the valve which sometimes happens because either the heart muscle is weaker and is not pumping well or because the heart is thicker than usual, causing less blood volumes in the left section of your heart. For people who have normal heart pumping function (known as LVEF), the term “low flow” is used when the blood volume per heartbeat is less than or equal to 35 mL/ m² body size.
If this is the case, and if the heart pumping function is lower than usual, a specialty ultrasound test at rest and during stress (called a dobutamine stress echocardiogram) is done. This helps the doctor tell the difference between a truly narrowed aortic valve and what’s known as a pseudostenosis, where the valve appears narrowed not because of an actual blockage but because of a low blood flow rate making the valve leaflets appear to not open fully.
Why do People Need Transcatheter Aortic Valve Replacement
Medical professionals recommend replacing the aortic valve (via surgery or a procedure known as transcatheter aortic valve replacement, or TAVR) in several situations, and these are generally categorized as follows:
1. If a person has severe aortic stenosis (AS)- which is a rare condition where the heart’s aortic valve narrows and doesn’t open fully- accompanied by symptoms. This condition affects the blood flow from your heart into your aorta, the main blood vessel in our bodies.
2. People who have severe AS, but show no symptoms and have a Left Ventricular Ejection Fraction (LVEF) – a term medical professionals use to describe how much blood the left heart chamber is pumping out – less than 50%.
3. Cases of severe AS in individuals who are also undergoing other types of heart surgery.
4. People without symptoms but have severe AS and are at low risk for surgery.
5. Individuals with symptoms and a condition where they have severe AS but a lower than normal flow of blood out of the heart (a ‘low-flow/low-gradient’ situation).
6. And finally, those with moderate AS who are also undergoing other heart surgeries.
Transcatheter aortic valve replacement, which is a less invasive procedure where a new valve is inserted within the old, damaged one, is approved for individuals who have the following conditions:
1. People with severe AS who are at a low to high risk for undergoing surgery.
2. Additionally, TAVR can also be used when a previously inserted valve replacement (bioprosthetic valve) has failed and needs a new replacement. These are known as valve-in-valve procedures.
When a Person Should Avoid Transcatheter Aortic Valve Replacement
There may be several reasons why a person wouldn’t live for more than a year due to diseases not related to the heart. They might have had a heart attack recently, within the last month, or were born with a condition where their heart valves have either one, two, or no hardened parts. Other reasons include a certain type of heart disease that causes the heart muscles to thicken (hypertrophic cardiomyopathy), or if the distance between the ring-like part of the heart (annulus) and the opening of a heart artery (coronary ostium) is too short.
Emergency surgery requirement, when your heart pump’s efficiency is less than 20% (left ventricular ejection fraction), or severe high blood pressure in the lungs with related issues in the right side of your heart can also limit your life expectancy. Presence of any mass, clot, or build-up inside the heart (evidence from an echo test of the heart), small or larger size of the native aortic annulus (less than 18mm or larger than 25mm), severe leakage through the valve at the left side of the heart are some other reasons.
If MRI confirmed you have had stroke or a mini-stroke (TIA) within the last six months, end-stage kidney disease, or mixed aortic valve disease (simultaneous aortic regurgitation, where blood leaks back into your heart after being pumped out) or significant aortic disease (problems with the main blood vessel carrying blood from your heart to the rest of your body), it might limit how long you can expect to live.
Who is needed to perform Transcatheter Aortic Valve Replacement?
The procedure of TAVR (transcatheter aortic valve replacement), which is a type of heart operation, needs a team of various expert medical professionals. This team is responsible not just for the operation, but also for taking care of you after the surgery. The team is usually made up of:
- An interventional cardiologist: A doctor who specializes in heart-related operations like TAVR
- A cardiac surgeon: A heart operation specialist
- An echocardiographic imaging specialist: A professional who uses special images to look at your heart
- Skilled nurses: Health professionals who give treatment and care before, during, and after the operation
- A cardiac anesthesiologist: A doctor who makes sure you stay unaware and don’t feel any pain during the operation, if it’s needed
If there are complications during the procedure, other specialists like heart electric activity doctors (cardiac electrophysiologists), brain specialists (neurologists), kidney experts (nephrologists), and blood vessel operation specialists (vascular surgeons) should be quickly available.
Preparing for Transcatheter Aortic Valve Replacement
Before undergoing a procedure called Transcatheter Aortic Valve Replacement (TAVR), patients undergo a detailed evaluation and testing process. This process is overseen by a heart team made up of heart specialists, heart surgeons, and doctors who specialize in anesthesia. They use different types of imaging techniques to study the heart’s structure and function.
They typically use a heart imaging test called transthoracic echocardiography. Sometimes, they also use a procedure called transesophageal echocardiography to get a better view of the heart’s aortic valve, which is the valve that controls the blood flow from the heart to the rest of the body.
In addition, a type of imaging test called Computed Tomography Angiography (CTA) is done. This test is used to measure the size of the aortic valve and to visualize the blood vessels. It helps the doctors plan the best approach for the TAVR procedure.
Finally, a procedure called left heart catheterization is commonly done. This procedure provides detailed information about the pressures in the different chambers of the heart and helps rule out other conditions like coronary artery disease (CAD), which is a disease of the blood vessels that supply the heart.
These tests help the heart team decide whether a surgical or a non-surgical (TAVR) approach is best. One of the factors that might influence this decision is if the patient needs an additional procedure called coronary artery bypass grafting, which is a surgery to improve blood flow to the heart.
Previously, there was a debate about whether treating stable CAD before or during TAVR offered any advantage. However, studies done in 2019 showed that treating CAD at the same time as TAVR didn’t provide any additional benefits and didn’t improve key outcomes like the risk of heart attack, stroke or death within 30 days.
How is Transcatheter Aortic Valve Replacement performed
There are many kinds of artificial aortic valves, which are devices used to replace a faulty heart valve. However, in the USA, there are only two kinds that have been approved by the FDA for use. One type is the SAPIEN valves, made by Edwards Lifesciences. These valves are made from the tissue of a cow’s heart sac (bovine pericardial tissue) and framed with a chromium cobalt alloy. To insert the SAPIEN valves, doctors use a balloon to expand them.
The second type is the CORE valves by Medtronic. Their latest model is called the EVOLUT-R. This valve is made from pig tissue (porcine tissue) and fortified with a nitinol frame. What sets the EVOLUT-R valve apart is that it can expand on its own without a balloon. Plus, if needed, it can be repositioned after it’s been placed. So far, there haven’t been any direct comparisons in studies between these two types of valves.
The procedure to insert these valves is usually performed in a special room that has the facilities of both an operating room and a cath lab (a room with special imaging equipment to visualise the arteries and chambers of the heart). The medical team typically includes an interventional cardiologist, a cardiac surgeon, and an anesthesiologist. The procedure is carried out while being watched with a fluoroscope (a tool that gives live X-ray images), and sometimes with the guidance of a transesophageal echocardiogram (TEE), which is an imaging test that uses sound waves to create detailed images of the heart.
The most common and least invasive way to insert these valves is to go through the large artery in your leg, which is called the transfemoral approach. However, if this isn’t possible, a different and usually more invasive method may need to be used, such as going through the artery in your shoulder (subclavian), the tip of your heart (apical), or straight into your aorta (trans-aortic).
Possible Complications of Transcatheter Aortic Valve Replacement
There are several risks that come with the TAVR procedure, short for Transcatheter Aortic Valve Replacement. These could include issues with the heart’s electrical system which might require a permanent pacemaker, a stroke, leakage around the valve that’s replaced, complications at the place where the doctor made the cut, bleeding, rupture of the aortic ring surrounding the heart’s valve, puncture of the heart’s left ventricle, sudden fluid build-up in the heart leading to impaired heart function, need for immediate surgery, heart attack, sudden damage to kidneys, infection, low blood pressure, and in extreme cases, death.
However, recent analyses have shown some benefits of TAVR over another procedure called SAVR (Surgical Aortic Valve Replacement). TAVR has lower rates of sudden kidney damage and significant bleeding problems, and there’s a possible positive trend in terms of lower deaths and strokes. Moreover, patients who have TAVR procedure usually stay in the hospital for a shorter period.
On the other hand, TAVR has some downsides too. There are higher chances of damage to blood vessels, leakage around the valve, and requiring a permanent pacemaker. Also, it’s critical to note that in a medical study known as the PARTNER 1-A trial, patients at high risk who had the TAVR procedure had more strokes.
What Else Should I Know About Transcatheter Aortic Valve Replacement?
Transcatheter aortic valve replacement is a well-known treatment for a severe medical condition called aortic stenosis. Aortic stenosis is when the heart’s aortic valve narrows and doesn’t open fully which can make your heart work harder. This treatment is particularly suitable for individuals who are at a high risk if they undergo surgery. It’s also a good alternative for patients who are at a low to medium risk for surgery.
