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Transcatheter aortic valve implantation (TAVI) appears feasible and safe even in patients with an annulus notably smaller than the smallest available bioprosthesis, according to results from a small single-center series published in the August 30, 2011, issue of the Journal of the American College of Cardiology. 

Investigators led by Eric Dumont, MD, of Laval University (Quebec City, Canada), analyzed data on prosthetic valve hemodynamics and early and midterm outcomes for 35 inoperable patients with severe symptomatic aortic stenosis who underwent TAVI via the transfemoral (n = 11) or transapical (n = 24) route at their institution between April 2007 and July 2010. All patients had a small annulus (< 20 mm; mean 18.5 ± 0.9 mm) and received a 23-mm Edwards Sapien bioprosthetic valve (Edwards Lifesciences, Irvine, CA).

Implantation Successful, Effective in Most

Procedural success was achieved in all but 1 patient, a 96-year-old female with a severely calcified valve who died following complications requiring surgical repair and who was excluded from subsequent analyses.

Major procedural and 30-day complications included:

• 1 case of severe paravalvular regurgitation requiring a second prosthesis
• 2 cases of third-degree atrioventricular block requiring a permanent pacemaker
• 3 instances of acute renal failure

In addition, 3 patients experienced access-site complications. No annular ruptures, acute aortic dissections, coronary occlusions, or conversions to sternotomy occurred, and cardiopulmonary bypass or extracorporeal circulation was not needed in any case.

Postprocedure, peak and mean transaortic gradients declined from baseline, while mean effective orifice area (EOA) increased (table 1).

Table 1. Echocardiographic Outcomes

Mean indexed EOA measured 0.90 ± 0.18 cm²/m². Severe mismatch between patient and prosthesis (indexed EOA < 0.65 cm²/m²) was observed in 5.9% of patients, while moderate mismatch (indexed EOA 0.65 cm²/m²-0.85 cm²/m²) occurred in 32.4%. Overall, 71.4% of patients had aortic insufficiency, although most cases were categorized as trace. Six patients had mild insufficiency; the 1 patient who showed moderate insufficiency died on day 3 after experiencing an MI. Insufficiency was paravalvular in 16 patients, transvalvular in 8, and mixed in 1 patient.

Midterm Clinical Outcomes

Over a mean follow-up of 14.4 ± 11.1 months, 35.3% of patients were readmitted to the hospital for conditions ranging from bronchopleural pneumonia (n = 3) to congestive heart failure (n = 3), GI bleeding (n = 3), MI (n = 2), and symptomatic atrial fibrillation (n = 1). Three deaths occurred, at 1 month, 16 months, and 24 months postprocedure. All survivors were in NYHA functional class I or II except for 1 patient, who had severe preexisting pulmonary disease.

Transthoracic echocardiography performed at 6, 12, and 24 months revealed persistently low transaortic gradients and durable stenotic relief. The prevalence of aortic insufficiency was lower at 6 months than immediately postprocedure (40.7% vs. 71.4%; P = 0.013); thereafter, the level of aortic regurgitation remained stable with respect to severity and type.

The authors conclude, “[O]ur results suggest that the hemodynamic advantage of the Edwards Sapien prosthesis is maintained in small and very small (< 19 mm) annuli, and there appears to be no deleterious effect on both clinical and hemodynamic outcomes following the deployment of a fixed-sized 23-mm prosthesis within a small, calcified aortic annulus.”

The investigators suggest that “smaller annuli may minimize prosthesis-annulus incongruity and may allow for a better ‘fit’ and more complete apposition of the balloon-expandable prosthesis against the aortic annulus.”

The authors acknowledge that the small size of the study and its relatively short follow-up preclude drawing any firm conclusions about the safety and efficacy of TAVI in small-annulus cases. However, they add, these results compare favorably with surgical options in operable patients with similarly small annuli.

Patients with Small Annuli May Actually Benefit

Certain aspects of the construction of stented bioprostheses, such as the absence of a sewing ring, makes them more attractive for use in smaller annuli compared with surgical valves, Peter C. Block, MD, of Emory University Hospital (Atlanta, GA), told TCTMD in a telephone interview.

“The bad news is that currently the smallest available transcatheter valve is 23 mm,” he said, “although I understand that both Edwards and Medtronic are looking forward to providing smaller sizes. But the good news is that the 23 mm valve, by expanding a small annulus, will actually produce a somewhat larger orifice. And it’s always better to stretch the annulus a little because you get less leak.”

The absence of annular ruptures in these 35 patients “is a good sign,” Dr. Block said. Nonetheless, “rupture is always an issue, particularly in extremely calcified and rigid annuli, which are difficult to predict,” he added.

Calling the small study “a good first step,” Dr. Block said paravalvular leakage, which occurred in about 70%, remains an ongoing concern, although it is a common finding in TAVI, and so far has relatively few clinical consequences, particularly in elderly patients.

“All of these outcomes are as good as one would expect from TAVI with standard annuli,” Dr. Block commented. “The valve variants are good and the gradients are decent—although interestingly they seem to be a little bit higher than you see with large annuli.”

Younger Patients May Want to Stick With Surgery

“For me, though, the bottom line is: If you’re a 55- or 60-year-old patient with a small annulus, it seems unlikely you are going to want a transcatheter valve anyway,” Dr. Block said. “You’re probably going to want a good long-term surgical placement with an aortic root enlargement. Even though that is more of an operation, the outcomes are excellent and more durable. But for an elderly patient who isn’t concerned about longer-term outcome, I think this is a good option.

“The important thing this paper tells us is that we should not exclude patients with an 18 mm or 19 mm annulus just because currently the smallest transcatheter valve we have is 23 mm,” he concluded.

For the time being, however, this reassurance may be moot for some US patients, Dr. Block commented, since US TAVI trial protocols typically exclude annulus sizes at both extremes (in fact, PARTNER excludes annuli < 16 mm and > 24 mm). But with the anticipated approval of TAVI in this country, more patients with borderline-small annuli likely will receive the procedure, he predicted, and these results suggest they will do well.

Dr. Block added that it would be interesting to see data on how small annuli do over time with CoreValve prostheses, which unlike the Edwards device, continue to expand after implantation.

Study Details

Patients with failed bioprosthetic aortic prostheses were excluded.

Aortic annulus diameter was measured preoperatively using transesophageal echocardiography in the long axis, mid-esophageal view, and from leaflet insertion to leaflet insertion in mid-systole.

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