Question: I have been diagnosed with severe aortic stenosis in a heart valve. I am now having more symptoms, such as chest pains and shortness of breath. I’ve heard about a minimally-invasive procedure called TAVI. How does it compare to heart surgery to replace the valve.
Answer: The TAVI (Transcatheter Aortic Valve Implantation) procedure is currently being performed on only those patients who are not suitable for open-heart surgery. Of course, you could be one of those people. So it’s worthwhile exploring this option.
Let’s start with an explanation of the aortic valve, which is the source of your medical problem.
The aortic valve regulates the flow of oxygen-rich blood from the heart into the main blood vessel leading to the rest of the body. It is composed of three triangular-shaped flaps that fit neatly together.
As the main chamber of the heart contracts, the flaps open up and allow blood to enter into the artery. They then slap shut to prevent blood from flowing back into the heart. As with other parts of the body, over a long period of time this valve can wear out and become dysfunctional.
“Aortic-stenosis is, for the most part, a chronic degenerative process of aging.” says Dr. Sam Radhakrishnan, Director of the Cardiac Cath Labs and Physician Lead of the TAVI program at Sunnybrook Health Sciences Centre.
About 7 per cent of people over the age of 65 develop aortic stenosis.
Typically, the valve becomes caked in calcium deposits that narrow the opening and prevent it from operating properly. As a result, the heart has to work harder to pump blood around the body. Patients may experience chest pains, become quickly out of breath if they exert themselves and may suffer fainting spells as well as other symptoms. Eventually, they develop more serious complications including heart failure.
There is no medication that can reverse the damage.
“It requires a mechanical solution – the replacement of the valve,” explains Dr. Radhakrishnan.
This means patients have had to undergo open-heart surgery. The chest is cut open to expose the heart. The patient is placed on a heart-lung bypass machine while the heart is stopped. The surgeon cuts into the organ and removes the decrepit valve and then inserts a new one – either a mechanical device or one made partly with animal tissue.
This has been the standard treatment for several decades. But not all patients can withstand the rigors of open-heart surgery. They are too old and frail, or suffer from too many other health problems, to survive the operation. Roughly one-third of all patients with severe aortic stenosis are considered too high risk for open-heart surgery. Without treatment, their condition only gets worse. About 50 per cent of them die within one to two years without corrective therapies.
However, about 15 years ago doctors began to make significant progress on an alternative therapy known as Transcatheter Aortic Valve Implantation, or TAVI for short. (In the United States, it’s called Transcatheter Aortic Valve Replacement or TAVR.)
TAVI represents a Canadian-research success story. Much of the pioneering work was carried out by Dr. John Webb and his team at St. Paul’s Hospital in Vancouver.
Rather than cutting open the chest, TAVI accesses the heart through the circulatory system.
A catheter – a flexible hollow tube – containing a tightly-compacted replacement valve is inserted into an artery and carefully threaded to the heart. The most common route is through a leg artery, which can be accessed through a small incision in the groin.
Once the catheter is in the correct position – literally inside the old aortic valve – the new valve is released from the catheter and expands to its full size. The diseased flaps of the old valve are not removed, but flattened back and serve to anchor the new valve device in place. The new valve immediately takes over the job of regulating blood flow.
As an added bonus, the recovery time is much faster for TAVI patients who are typically out of hospital within three to five days. Open-heart surgery patients spend about 10 days in hospital and it takes a long time for their chest incision to heal.
TAVI is part of a growing trend in the field of minimally-invasive surgeries. For instance, stents – which prop-open clogged blood vessels – are also delivered to the right spot in the body by way of a catheter.
TAVI is not without risks, however. Threading the catheter – about the thickness of a pen – through the blood vessels can cause damage and dislodge plaque deposits. If pieces of that plaque travel to the brain they can block blood flow and trigger a stroke.
Furthermore, doctors don’t yet know how long the TAVI valves will last. “We don’t have definitive long-term – more than ten years – data for these patients yet,” says Dr. Radhakrishnan. By contrast, the durability of the valves used for the traditional open-heart surgery has been well documented.
Because TAVI is still relatively new and there are uncertainties surrounding the procedure, it should not be considered a patient’s first choice, says Dr. Radhakrishnan.
“If you’re deemed to be a good candidate for open-heart surgery, you should go for open-heart surgery. ”
So that mean TAVI is restricted to those patients who can’t tolerate the traditional approach or they are deemed to be at high risk of suffering serious complications from open-heart surgery.
TAVI patients must undergo a series of screening tests before being eligible for the procedure. High-resolution CT imaging machines are used to determine a number of important anatomical considerations to increase the chances for a successful TAVI procedure. For example, CT imaging helps to pick the best entry point for the catheter. If the leg artery poses a risk for complications, the doctors can use an artery under the collarbone or one in the chest wall.
This pre-operative investigation also enables the doctors to select the correct size of the replacement valve. (All of these valves are made of animal tissue, attached to a stainless-steel mesh.)
During the actual operation, high-resolution X-ray imaging is used to help guide the catheter through an artery to the exact spot in the heart where the new valve will be placed. A team of nurses and doctors from different disciplines– including an interventional cardiologist, cardiac surgeon and cardiac anesthetist – take part in the procedure.
Dr. Radhakrishnan believes TAVI will eventually be used in a broader range of patients.
“It is still an evolving technique and procedure,” he says. The equipment is changing, too. The catheters are becoming less bulky and newer valves are emerging made by different manufacturers.
“We are already seeing a lowering of the complications in terms of vascular complications, strokes and mortality,” says Dr. Radhakrishnan
“For the first generation devices, the incidence of stroke was close to 5 per cent in the first 30 days after the operation. Now we are seeing stroke rates of 2 to 3 per cent – which are very much in keeping with the stroke rates for traditional open-heart surgery.”
Sunnybrook, he notes, is involved in an international clinical trial that is evaluating a broader range of patients as potential TAVI candidates including those who are considered to be at intermediate risk of suffering complications from open-heart surgery.
And at a conference of the American College of Cardiology held in Washington, D.C. in April, a series of promising TAVI studies were made public.
“It is fair to say that as the technique gets better, some of the procedural risks will diminish and we will see it move into a larger population of patients,” predicts Dr. Radhakrishnan.
But, right now, one the biggest obstacle to its wider use is financial. “The TAVI procedure is more expensive than open-heart surgery because of the extra cost of these specialized valves,” explains Dr. Radhakrishnan. The TAVI valves cost around $20,000 apiece, while the open-heart valves are under $5,000.
In Ontario, the provincial government has provided six hospitals with funds allocated for the procedure. (In Toronto, the medical centres include Sunnybrook, St. Michael’s Hospital and the University Health Network.)
“We are funded to do 90 TAVI procedures in the coming year,” says Dr. Radhakrishnan, adding that the hospital has the capacity to do more but is limited by its budget.
He expects “market economies will undoubtedly bring down the cost of these devices” if research can show that TAVI really is a suitable option for many more patients.
I just have to mention that TAVI was first invented by Alain Cribier in 2002 in at the University Hospital of Rouen, France. Webb has pioneered some of the early evaluations of TAVI no doubt, and was the first to perform TAVI through the trans-apical approach.