Shelley Wood

November 08, 2011

November 7, 2011 (San Francisco, California) — When Dr Renu Virmani (CVPath Institute, Gaithersburg, MD) looks to the past to make predictions about the future, people sit up and listen. Training her binoculars on the durability of transcatheter valves, Virmani made a prediction that was music to most of the ears in her audience here at TCT 2011.

"I think the differences [between surgical and transcatheter valves] will be very subtle. They will not be that dramatic," she said. "Overall, I actually think success with TAVI valves will be much better."

Virmani's presentation focused on the 26 autopsy cases of patients who'd received transcatheter valves--part of the CVPath transcatheter aortic-valve registry. The registry so far includes 15 Edwards Sapien/Cribier valves and 11 Medtronic CoreValves.

Virmani emphasized that surgical bioprosthetic heart-valve failure is typically gradual, progressive, and "time-dependent," and those will remain the key factors for transcatheter aortic-valve implantation (TAVI) devices, too, she predicted.

"Currently, fewer than 1% of porcine aortic valves implanted less than five years in adults suffer structural dysfunction, and I predict we'll be very close with our new TAVI procedure," she said. Twenty to thirty percent become dysfunctional within 10 years, and more than 50% fail due to tissue degeneration within 12 to 15 years postimplantation. "I predict we'll be very close to [these numbers], or perhaps just slightly early with our new TAVI procedures," Virmani said, "but it won't be that different."

So far, she notes, the forms of valve failure seen with TAVI have been "similar to those seen in surgical aortic bioprosthetic valves," namely tears, calcification, pannus formation, and endocarditis.

Patient Selection, Physician Technique

Some of the pathology samples Virmani showed should serve as a reminder to implanting physicians of the importance of good patient selection and impeccable technique.

One slide showed the heart of an 84-year-old man with severe aortic stenosis and other comorbidities who died postprocedure of annular rupture. But as Virmani pointed out, the short span between aorta to apex in this patient made it particularly difficult to navigate the bulky device. As a result, "unfortunately, this patient came to the autopsy table."

One case showed a patient with very heavy aortic-valve calcification, implanted with an Edwards device. Particularly in the early experience with this device, heavy calcification tended to lead to inadequate or nonuniform device expansion, resulting in paravalvular leak.

"You really must try to get as circular an orifice as possible," she said.

In another case, this time a CoreValve specimen, heavy calcification led to the device being deployed too low--another predictor of paravalvular leak.

"Positioning is all-important," she stressed.

Inflammation Present

Virmani also showed both Edwards and CoreValve specimens pointing to what she called "a fair amount of inflammation." But in both cases, the inflammation didn't seem to "translate into anything detrimental occurring around the implanted valves" or "into outcomes being poor," she said.

In fact, she said, showing two cases of patients who'd died of causes unrelated to their valves, the valve is looking surprisingly good several years out.

One case showed a CoreValve, two years post implantation, with "nice healing," minor inflammation, complete strut coverage, and normal valve function.

In another patient who died of nonvalve causes, an Edwards device four years postimplantation was functioning normally, and again despite evidence of inflammation, did not seem to have compromised device performance.

Other Issues

As with surgically implanted valves, TAVI recipients "are not immune" to infection, leading to heavy calcification and vegetations, as she showed in one of her cases--that of a patient who'd died 20 months after TAVI. In this case, however, Virmani believes the calcification was secondary to the infection and not degeneration of the TAVI device.

Only one of Virmani's cases showed clear calcification of the TAVI device--in this case, one of the earliest CoreValves ever implanted, with the sample obtained six years postimplantation. But at this time point, she says, "this is not surprising; we see this in surgical valves too."

Virmani's autopsy series contained one case of a patient who died of an aortic dissection two and a half years after TAVI implantation. But given the location of the dissection, Virmani and colleagues concluded that the dissection was unrelated to the valve itself or implantation procedure.

Focus on the Glaring Issues

For now, says Virmani, physicians should focus on the problems that need urgent attention, as confirmed by her pathology cases. The most pressing are transient ischemic attacks (TIAs) and stroke--something that Virmani believes could perhaps be better managed with improved anticoagulant control out to one week post-TAVI. Aortic incompetence post-TAVI is a second issue that should prompt physicians to improve their selection of patients. The third factor is left bundle branch block, highlighting the importance of optimizing valve positioning to avoid the need for pacemaker implantation.

But overall, says Virmani, "I'm more optimistic than I think other people will be."

She predicts the kinds of things she's seeing on autopsy will actually lessen as younger, healthier patients get TAVI. "When you go to younger patients, you will not have as much severe calcification, and there may be more evenly [distributed] calcification, and so our success rate may improve."

Speaking with heartwire after Virmani's presentation, Dr Friedrich Mohr (University of Leipzig, Germany), a surgeon, said neither he--nor Virmani for that matter--can make any pronouncements on valve durability. But he stressed that the tissue being used for transcatheter valves is much thinner than that used for surgical valves, since the TAVI valves need to be as low profile as possible for transcatheter delivery. "The wear-testing experimentally looks quite favorable, but we really need to see how this thinner tissue performs over time. It may have an implication on long-term durability, for sure."

Also speaking with heartwire , Virmani emphasized that they've only examined 25 to 30 cases so far.

"This is at an early phase, and it looks encouraging. That's all I can say, is that it looks encouraging."

Virmani and colleagues were expecting to see more calcification resulting from prosthetic degeneration, she said. "But so far, I don't think we're seeing that."