DISCUSSION:  
As the indications for TAVR are expanding, operators are faced with more complex and challenging anatomy. In the present case, we demonstrated that TAVR is feasible by over-expansion of 29 mm SAPIEN 3 THV in a tricuspid AS patient with an annulus area exceeding 800 mm2. Shivaraju et al (6) first described the over-expansion technique in an AS patient with annulus area of 742 mm2, with 4 mL of additional volume in the delivery balloon. Mathur et al (7) and Barr et al (8) then reported the results of TAVR in 8 patients, with aortic annulus area ranging from 691.0 mm2 to 800.0 mm2, using the same technique. To our best knowledge, there has been only 1 reported TAVR case with annulus area exceeding 800 mm, but in a bicuspid aortic valve (10). In contrast, our case valve was tricuspid configuration and the implant depth was at the annulus, thus resulting in the largest over-expansion of SAPIEN S3 THV ever reported.
Nominal volume 29 mm SAPIEN 3 THV deployment will definitely result in significant valve under-sizing in our patient. Additional 4 mL volume expansion on THV deployment, according to calculation, will still result in -9.8% undersize. In our pre-TAVR planning, 5 mL additional volume post-dilatation will be performed if significant paravalvular leakage (PVL) was noted after deployment. This will reduce the estimated undersize to -6.7%. With the new frame geometry and outer skirt design of the SAPIEN 3 THV, however, even this maneuver was unnecessary. In recent analysis of SAPIEN 3 study (11), rate of PVL was low even with SAPIEN 3 THV undersized up to -5%.
The actual safe limit of over-expansion for SAPEIN 3 THV, however, are still unknown. Over-expansion may prohibit proper leaflet coaptation, increase the risk of valve dislodgement, and incur positioning challenges due to excessive frame shortening. The design of longer leaflets might allow the SAPIEN 3 THV to be more tolerant to over-expansion, and accommodate larger annulus sizes without resulting in significant central aortic regurgitation. Sengupta et al (12) reported 105 large annulus AS patients, with mean annulus area of 721.3±36.1 mm2, implanted with SAPIEN 3 THV. The rate of ≧moderate transvalvular aortic regurgitation and PVL were 0% and 4.3% respectively at 1 year. Miyasaka et al (9) also demonstrated the feasibility of SAPIEN 3 THV in 30 patients with large annulus (mean annulus area 737.3±54.7 mm2), with similar procedural outcomes and 1-year mortality compared to those with regular annulus (area < 683.0 mm2). These results, along with the present case experience, may provide evidence for the use of over-expanded 29mm SAPIEN 3 THV in patients with extremely large annulus. Longer term follow-up in a larger patient population is mandatory to determine its durability.
Conclusion:
We demonstrate that TAVR using over-expanded 29 mm SAPIEN 3 THV in a patient with annuls areas of 831.8 mm2 is safe and feasible.