Trans-catheter aortic valve implantation (TAVI) is a very promising new treatment for native aortic stenosis or failed bioprostheses [1]. Glutaraldehyde xenograft tissue is employed because of its pliability for folding during implantation and minimizing its size in order to reach its final position in the aortic root. In the CoreValve system, the stent is self-expanding, whereas in the Edwards Sapien, the valve has to be dilated by balloon inflation to approximate the stent to the aortic annulus without suturing, so as to prevent escape of the prosthesis and paravalvular leakage. In the latter procedure the pericardium is crushed against the stent. Since the operation is relatively easily accomplished with early success, the question arises of whether it might also be indicated in low-risk patients, thus avoiding sternotomy, general anaesthesia, cardio-pulmonary bypass and cardiac arrest. However, in contrast to the traditional surgical implant, TAVI requires cusp crimping and, in the case of the Edwards Sapien, balloon inflation. Both manoeuvres may be responsible for tissue injury. Previous observations by Zegdi et al. have shown evidence of cusp injury following percutaneous aortic valve deployment of the Edwards Sapien [2]. To confirm these preliminary findings, the same group made an experimental study, comparing the severity of traumatic cusp injury in home-made balloonvs self-expanding valved stents (VS); a non-crimped pericardium was used as a control [3]. According to the authors’ findings, all deployed valves were associated with microscopic lesions, in keeping with traumatic disruption, both in terms of transverse fractures and longitudinal cleavages. Transverse fractures were seen both in balloonand in self-expanding VS, whereas longitudinal cleavages were more frequently observed in balloon-expanded VS. Crushing and shearing of the pericardium during crimping and deployment are the most plausible causes. They may facilitate plasma and lipid insudation with tearing in the long term, thus affecting durability. These data support and expand the preliminary observations of the same authors [2]. An editorial comment by our group expressed some concern in interpreting these data, due to the limitations of technology used in pathological investigations [4]. However, the new data provided herein by Amahzoune et al. [3] seem to be convincing, even in the absence of macroscopic evidence of lacerations, commissural dehiscences or tears. They support the occurrence of some iatrogenic damage, particularly in balloon-expandable VS. However, in our opinion, the experiment should be repeated in a core lab employing special histological staining, such as picrosirius red, and scanning electron microscopy, to assess collagen waviness and to exclude the artifacts arising from manipulation at histology. If confirmed, these observations may cast a shadow on the safety of the TAVI procedure in terms of tissue integrity and biological compatibility, although crimping was proven not to influence propensity to cusp calcification in the long term [5]. Glutaraldehyde-fixed pericardium is the best available tissue because of its strength (thick fibrosa) and pliability (elasticity of wavy collagen bundles). If handled gently, as in the current secondand third-generation stented or stentless pericardial valve prostheses, it is not at risk of mechanical failure. Whether this is the case with TAVI—in which the pericardium is exposed to crimping or even crushing, with a potential traumatic injury— is a matter of concern. According to the findings by Amahzoune et al. [3], the following considerations may be put forward:
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Apr 1, 2015
Steffen Pfeiffer + 2
Open Access