While the gold standard for severe aortic stenosis remains open aortic valve replacement (AVR), the surgery is not an option for many very ill, elderly patients. For these individuals, a new, less-invasive treatment known as transcatheter aortic valve replacement, or TAVR, received Food and Drug Administration approval last November and has been shown to reduce mortality by 20 percent over medical therapy alone at one year.
TAVR provides a treatment option for relieving aortic stenosis in very high-risk patients who were previously deemed inoperable. A team of Stanford cardiologists and cardiovascular surgeons have collaborated on and performed nearly 200 TAVR surgeries over the past four years as part of the PARTNER Trial, a randomized, multi-center clinical trial. The Stanford team consists of two cardiovascular surgeons — Craig Miller, MD and Michael Fischbein, MD — and two interventional cardiologists — William Fearon, MD and Alan Yeung, MD — who work as part of an integrated team that includes echocardiographers, cardiovascular radiologists and cardiovascular anesthesiologists. The team has begun performing TAVR on a commercial basis in patients with symptomatic, critical aortic stenosis who are deemed inoperable for open surgical aortic valve replacement. TAVR is now covered by Medicare following a CMS National Coverage Decision (NCD) issued in May 2012.
"Many of these patients were too sick or too old to even consider a surgical option, but now we can offer them something with reasonable risk, which extends life and improves their sense of well-being and functional capacity," said Miller, Stanford's principal investigator in the PARTNER I and PARTNER II trials. "It is a major paradigm shift, a major step forward. The only thing that rivals this in terms of its powerful impact on clinical practice is heart transplantation in 1968."
Less invasive repair
TAVR enables a multidisciplinary heart team to replace a patient's obstructed aortic valve without traditional open surgery while the heart continues to beat, avoiding the need for cardiopulmonary bypass.
When performing TAVR, the valve is crimped down onto a catheter-based delivery system and then inserted it into the body transfemorally or transapically. Once delivered to the site of the patient's obstructed valve, the new valve is expanded with a balloon and immediately functions in place of the patient's native valve, allowing relief of the obstruction and symptomatic improvement.
"The main advantage of TAVR is the fact that it's less invasive," said Fearon, associate professor of cardiovascular medicine. "We avoid the sternotomy and cardiopulmonary bypass, which allows for a quicker recovery." But there are risks. Patients undergoing TAVR suffered a major stroke rate of 3.8 percent, compared to 2.3 percent for those undergoing the open surgery. They also had more vascular complications, but significantly less bleeding. Miller attributes the added stroke risk in part to the calcium fragments that dislodge when the balloon in the valve is inflated.
Continued research required
Stanford's TAVR team is currently participating in the PARTNER II Trial to evaluate the role of TAVR in moderate-risk patients, those with a 4 to 8 percent chance of death from open surgery. Stanford is one of 21 institutions nationwide testing this new treatment option in this trial where 2,000 patients are being randomized to undergo open surgical AVR or TAVR, and then followed for two years. The risk of stroke and the unknown durability of the percutaneous valve are the two main concerns with using TAVR routinely in younger, less sick patients who have much longer life expectancies.
Subsequent to approval by a FDA Panel in June, the Stanford TAVR team is awaiting FDA approval to use the transcatheter approach in high-risk (defined as >8-10%), but operable patients, a population that was randomized between open AVR and TAVR as part of the PARTNER IA Trial. "While we see a real role for TAVR in highly selected high-risk operable patients, many referred by surgeons, these patients must be aware of the higher neurological complication risk with the catheter valve and its unknown durability," Miller said.
Is TAVR for everybody?
There is a large pool of patients with severe aortic stenosis, but not every patient will be eligible for TAVR. The Multidisciplinary Valve Team will need to consider the patient's overall risk profile and age to decide when it is reasonable to do TAVR, when it makes sense to perform open AVR and when doing either would be futile therapy.
"We must apply this new, expensive technology intelligently," said Miller, the Thelma and Henry Doelger Professor of Cardiovascular Surgery at Stanford, "understanding that it really complements, rather than competes with, traditional open surgical AVR."
Two-year data are now available for TAVR in inoperable patients with aortic stenosis from the PARTNER IB Trial. Forty-four percent of inoperable patients who underwent the TAVR procedure as part of the PARTNER IB Trial died within two years, and another 20 to 30 percent did not sustain any symptomatic benefit. It is the nature of this very sick, elderly population rather than the device that portends this sobering outcome, Miller said.
"The ultimate value of TAVR in inoperable patients will depend on carefully selecting patients who do not have extreme co-morbidities that overwhelm the potential benefits of TAVR and render the intervention futile," he added.
The CMS National Coverage Determination (NCD) mandates that all patients in the U.S. undergoing commercial TAVR be followed in the national ACC-STS TVT Registry, which is unprecedented for medical devices; patient outcomes will be watched carefully by all concerned stakeholders, said Miller, including CMS with respect to decisions concerning ongoing hospital and physician reimbursement.
TAVR is a team sport
"Transcatheter valve replacement is a very complicated procedure and requires expertise from a number of different groups," Fearon said. "It is very important to have a team approach, because we all bring certain skills to the table that help benefit the patient."
At Stanford, the TAVR program is a 50-50 collaborative effort between cardiac surgeons and interventional cardiologists working closely with dedicated team members David Liang and Rajesh Dash (echocardiography); Dominik Fleischman (Radiology), Charles Hill, Pieter van der Staare, P. David Soran and Jim Wong (CV Anesthesia); and nurses Martina Speight, Cheryl McWard and Leigh Trautman. From the beginning, the team sees patients together, makes treatment decisions together, performs procedures together and conducts follow-up care together. It is a true multidisciplinary team approach, Miller said.
"It has been the most refreshing thing I've seen in our field in 35 years," he added. "We are working together for the patient's welfare."
By Grace Hammerstrom