26 March, 2024

TAVR/TAVI (Transcatheter Aortic Valve Replacement/Implantation)

Introduction:
TAVR or TAVI refers to a minimally invasive procedure in which an artificial bioprosthetic valve is implanted into the human heart using a catheter in a suture-less fashion.

To read about heart valves, click here

Transcatheter Heart Valve (THV) is an artificial valve made from the outer covering of animal hearts (called pericardium). Such tissue is cut precisely to suit human heart needs, undergoes chemical treatment to make it more durable, and is stitched on a specialized metal alloy frame. A few of the THVs available in India are shown in the image below.

Valve names: (A) Sapien 3 (B) Sapien Ultra (C) Myval (D) Octacore (E) Evolut Pro+ (F) Hydra (G) Acurate Neo2 (H) Navitor

TAVR introduction:
TAVR (also known as TAVI) stands for Transcatheter Aortic Valve Replacement (in the term TAVI, ‘I’ stands for ‘implantation). TAVR is used to treat severe aortic stenosis. To read about Aortic Stenosis, click here. As the name implies, this procedure involves implanting a new valve in place of an old aortic valve using plastic tubes called catheters by a minimally invasive (suture-less) approach. TAVR is a revolutionary technique that replaces the need for open heart surgery in the treatment of Aortic Stenosis. Compared to surgery, TAVR is knife-less, suture-less, performed without the need for general anaesthesia, and has a short recovery time of 2-3 days.

What is a heart valve?
A valve is a “device that regulates, directs, or controls the passage of fluid or air by opening and closing”. We all have encountered valves in our daily lives. A tyre valve is one example that allows air to be injected into the tyre and doesn’t allow air to escape unless the valve is tampered with or leaky. The human heart has four such valves which allow unrestricted unidirectional blood flow from one chamber to another. When open, heart valves allow unrestricted blood flow and when closed, they prevent blood from leaking back into the previous chamber. When valves don’t open properly (a condition called ‘stenosis) they put undue stress on the heart by adding resistance to the blood flow. On the other hand, when valves don’t close properly, blood may leak back, making flow dynamics within the heart less efficient. This condition is called ‘regurgitation’.

The four heart valves are Aortic, Mitral, Tricuspid, and Pulmonic. The current discussion is related to the Aortic valve.

Aortic valve and Aortic Stenosis
The aortic valve (AV) can be regarded as the most important valve in the human heart. It is located between the main pumping chamber of the heart (called the Left Ventricle) and the main conduit that carries blood to the rest of the body (called the Aorta). The human heart beats about 1,00,000 (1 lakh) times a day and with each heartbeat, the Aortic valve opens to allow unrestricted blood flow from the Left Ventricle to the Aorta. The blood now travels to the rest of the body’s organs supplying necessary oxygen and nutrients. More than 7000 litres of blood flow across the Aortic valve per day. Heart valves get functional even before birth and, in most situations, can withstand this high demand for more than 50 years without any issues.

In certain situations, altered flow dynamics across the Aortic valve lead to micro-injury of the valve tissue. As with any injury, the body heals by forming scar tissue. Over time (usually years), continued micro-injury and healing lead to significant tissue/calcium deposition over the valve. This renders the valve stiffer, and less mobile, leading to a restricted opening, hence ‘stenosis’. This is more commonly seen in people with:

Increasing age
Diabetes or high cholesterol
Radiation treatment of the chest
Previous infection of the valve
Valve deformity by birth

Aortic Stenosis (AS) is a condition in which the Aortic valve narrows, making it difficult for blood to pass through it. The heart muscle has to work harder to overcome this resistance. The heart can compensate for this additional workload for many months to years, during which a person may not notice any symptoms. When the ‘stenosis’ gets severe, the heart eventually gives up by not generating enough force to overcome this resistance. This leads to heart failure and the eventual demise of the patient.

Symptoms of Aortic Stenosis
People with a mild or moderate degree of aortic stenosis typically don’t have any symptoms. Severe aortic stenosis may have the following symptoms:

Chest discomfort
Difficulty breathing, particularly during walking or while lying down
Dizziness/giddiness, or fainting
Decreased exercise capacity
Leg swelling

Many times, symptoms of severe aortic stenosis may not be obvious. Patients typically slow down in their life to adjust to the disease. They find themselves getting tired too early in activities which they were able to do a few months back. Such limitations are easily attributable to the normal ‘ageing’ process. For these reasons, symptoms largely go unnoticed or ignored.

Prevention and treatment of Aortic Stenosis
Unfortunately, most of the preventative strategies which work for coronary blockages (the one that causes a heart attack), like controlling diabetes, cholesterol, etc., don’t seem to work in the prevention of Aortic stenosis. Still, it is recommended that people should engage in a healthy lifestyle that includes:

* Balanced diet with fewer carbohydrates
* Control of Diabetes and Cholesterol
* Regular exercise and weight management
* Avoid Smoking

Aortic stenosis is a mechanical problem that needs a mechanical fix. Medications may improve symptoms by altering the body’s blood flow dynamics but have no effect on the degree of stenosis. Replacing the diseased valve with a new one is the best way to resolve this problem. The standard treatment for severe AS has been to replace the diseased valve with a new artificial valve via open heart surgery.

Heart surgery involves opening the chest, putting the patient on a heart-lung machine, removing the old valve, and stitching a new prosthetic valve in place. Patients typically spend 2-4 days in the intensive care unit and another 3-5 days in the general ward. There is a 6-week rehabilitation period post-surgery. Open heart surgery is highly effective in resolving most of the issues related to severe AS. However, as many as 40% of patients for whom surgery is indicated don’t go for surgery due to the increased risk associated with open heart surgery. A decade earlier, these patients were left with no viable alternative, until recently.

TAVR is an effective alternative to surgery for patients with severe AS. Using TAVR therapy, a cardiologist can implant a new valve in place of the old diseased aortic valve, all without major surgery.

Aortic stenosis can also be treated by balloon valvuloplasty, a procedure in which a balloon is inflated within the diseased Aortic valve. As the balloon inflates, it produces cracks and tears within the Aortic valve. While this procedure increases the valve opening, the benefit is short-lasting (usually 3-6 months) as the body heals from the injury, leading to restenosis.

Who should opt for TAVR?
While TAVR is an attractive minimally invasive alternative to open-heart surgery for the treatment of severe Aortic stenosis, patients should be selected based on certain criteria to ensure a good clinical outcome. Here is a simple checklist that one can follow to determine candidacy for TAVR. The list below is intended to provide basic guidance and by no means is complete. One should always seek the opinion of an expert before making a decision.

Diagnosis of severe aortic stenosis should be confirmed AND there should be evidence that severe aortic stenosis is affecting the patient in some form or the other, AND

There should be some reason to choose TAVR over open heart surgery: Patients who are either older than ~ 60 years of age or have other medical issues that put them at a higher risk for open heart surgery.

TAVR, pre-procedure
Patients with severe aortic stenosis are screened by the heart team to determine their candidacy for TAVR. This involves confirming the diagnosis of severe aortic stenosis, looking at other medical problems, and doing specific investigations to plan the procedure.

Necessary investigations are obtained beforehand to ensure appropriate therapy options are chosen. Such tests can be:

Routine blood and urine tests
ECG
Chest X-ray
Echocardiogram
CT scan of chest/abdomen
Dental Evaluation
Tests pertaining to lung function, as needed
Tests pertaining to brain function, as needed
Coronary angiography and angioplasty, as needed

TAVR, the procedure
TAVR is a minimally invasive procedure which means no major incision is required. The doctors’ team typically comprise an interventional cardiologist, cardiac anaesthetist, cardiac imaging expert, and a cardiac surgeon. The procedure is typically carried out in a Cardiac Catheterization Laboratory (the same laboratory where coronary angiography and angioplasty are done). The procedure is mostly done under local anaesthesia, but general anaesthesia can also be used based on the patient’s clinical profile. A small incision is made in the upper thigh (groin region) through which a plastic tube carrying an artificial heart valve is inserted. The valve is taken to its designated spot and implanted. TAVR obviates any need to open the chest, putting on a heart-lung machine, prolonged anaesthesia or intensive care etc. The procedure takes about 1 hour to perform and is done with x-ray and echocardiogram guidance. To some degree, the procedure is similar to getting a stent placed in the heart.
A brief animation of the TAVR procedure using the Evolut valve is shown here.

TAVR, post-procedure
A typical patient can talk immediately after the procedure, sit and eat within 4-6 hours, and walk that evening itself. The patient is typically observed in intensive care for 24 hours after which he/she is transferred to a regular room. Patients are typically discharged home within 2-3 days. They can resume their routine activities within a week and enjoy a scar-free life without major physical restrictions. Many patients are able to go shopping by the second week and travel abroad within a month. The majority of patients do not require blood thinners or any other special medicines after the procedure. In fact, they might be able to get off some of their previous heart medicines.

TAVR, the valve (THV)
The TAVR valve (or THV) is made from animal pericardial tissue that is laser-cut into small pieces and sewn together on a metal platform to take the shape of a valve. The metal platform helps the valve anchor at its designated place. The THV is pre-treated with chemicals to increase its longevity and withstand continuous blood flow across it. These valves undergo rigorous testing outside the human body before being bought into the market. Since they are tissue valves (as compared to metal valves that can only be placed by open heart surgery), they are expected to degenerate over time. Since TAVR is a new technique, studies are ongoing regarding their average lifespan. So far, these valves have been shown to function well 8 years after the implantation and are expected to last about 15 years.

TAVR, the science behind
TAVR has been extensively studied in over 10,000 patients to evaluate its efficacy and safety. In the majority of the studied population, TAVR has performed similar to or better than open heart surgery. TAVR offers the same benefits of implanting a new valve as open heart surgery minus the surgical risk.

TAVR, potential complications
While TAVR is a much safer alternative compared to open heart surgery in a patient with higher surgical risk, just like any other procedure TAVR is not free of complications. A few of the potential complications may include:

Bleeding
Infection
Peri-procedural stroke/paralysis
Peri-procedural death
Need for emergent open heart surgery
Blood vessel injury
Anaesthesia-related complications
Valve dysfunction
Kidney injury
Heart rhythm disturbances requiring pacemaker and others

TAVR, the bottom line
TAVR can easily be regarded as the most disruptive innovation in cardiovascular medicine in the past decade. The first TAVR was successfully performed in humans in the year 2002 in France. Since then, more than 3 lakh valves have been implanted across the world with excellent success. TAVR is not for everyone. A thorough discussion between the patient/family and the treating physician is necessary to understand a patient’s health condition and eligibility for TAVR. As it stands today, TAVR is a life-saving treatment alternative for many patients with severe AS who, till now, had no option other than to undergo open heart surgery.

I am sure I didn’t answer all your questions on this topic. Feel free to message me with your queries; I will happily answer them.

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