Invited Commentary

Abstract

The presence of bicuspid leaflet anatomy, in approximately 50% of patients in the surgical series of calcific aortic stenosis [1Roberts W.C. Ko J.M. Frequency by decades of unicuspid, bicuspid, and tricuspid aortic valves in adults having isolated aortic valve replacement for aortic stenosis, with or without associated aortic regurgitation.Circulation. 2005; 111: 920-925Crossref PubMed Scopus (642) Google Scholar], is currently considered a relative contraindication to transcatheter aortic valve implantation (TAVI). Presently it is understood that successful stent valve deployment in bicuspid anatomy often fails due to restricted excursion of one of the leaflets, usually the conjoined leaflet with the raphe. The end result is limited valve opening, valve-stent under-deployment, and frequently noncircular deployment; such distortion would likely result in significant valve-stent mismatch, aortic insufficiency, or premature failure, or a combination of these. One possible solution would be to use a stiffer stent with greater radial force. In their study, Zegdi and colleagues [2Zegdi R. Lecuyer L. Achouh P. et al.Increased radial force improves stent deployment in tricuspid but not in bicuspid stenotic native aortic valves.Ann Thorac Surg. 2010; 89: 768-772Abstract Full Text Full Text PDF PubMed Scopus (42) Google Scholar] deploy two types of braided nitinol self-expandable 26-mm stents with differing radial force (one stent significantly stiffer than the other) in 88 patients. These valve-stents were deployed under direct vision during surgical aortic valve replacement operations while the heart was arrested and the aorta was open. The adequacy of deployment was assessed, the valve-stent was removed, and the surgeon proceeded with conventional aortic valve replacement. Stent deployment was possible in 94% of patients. Thirty-six patients (41%) had bicuspid anatomy. The authors found that circular deployment, which is an important marker for adequate deployment, occurred in 77% of tricuspid valves, but only 19% of bicuspid valves; the latter group often appeared more elliptical. Although the use of the stiffer valve-stents improved circularity in the tricuspid valve patients (60% vs 93%) it had no significant effect on the bicuspid valves. Gaps between the valve-stent and the native valve were observed at the commissures in both tricuspid and bicuspid valves. However, use of the stiffer stent decreased these gaps in the tricuspid patients (64% vs 30%) but not in the bicuspid patients (55% overall). In effect, use of greater radial force to close the gaps at the commissures is essentially the rational behind the “over-sizing” technique now used clinically in patients with tricuspid aortic valves. However, the authors have now demonstrated increasing radial force does not overcome the mal-deployment problems seen in patients with bicuspid anatomy. Zegdi and colleagues [2Zegdi R. Lecuyer L. Achouh P. et al.Increased radial force improves stent deployment in tricuspid but not in bicuspid stenotic native aortic valves.Ann Thorac Surg. 2010; 89: 768-772Abstract Full Text Full Text PDF PubMed Scopus (42) Google Scholar] are to be congratulated on their ongoing commitment to understanding the bio-mechanisms at work during TAVI. Innovators must ponder the possible solutions to treating patients with bicuspid valve anatomy with TAVI. Does the solution lie with dividing the conjoined leaflet prior to valve-stent deployment or can an innovative new valve-stent design overcome the challenges of the bicuspid valve patient? Increased Radial Force Improves Stent Deployment in Tricuspid but Not in Bicuspid Stenotic Native Aortic ValvesThe Annals of Thoracic SurgeryVol. 89Issue 3PreviewStent deployment within stenotic native aortic valves has been shown to depend on valve anatomy (presence of bicuspid valve or not). This study investigated the influence of stent stiffness on stent expansion. Full-Text PDF