Cath Lab Digest

Introduction

Transcatheter aortic valve implantation (TAVI) was first performed by Alain Cribier in 2002¹ using the balloon-expandable Cribier-Edwards valve. Soon after, the self-expandable CoreValve ReValving system (Medtronic, Inc., Minneapolis, Minnesota) was introduced based on a completely different design concept.² Initial reports on safety and technical feasibility of these two new technologies raised expectations among interventional cardiologists,^3–5 and both prostheses have undergone rapid development and implementation thanks to the information generated from these initial experiences. Following market approval in Europe, the number of patients treated with both technologies has exponentially increased, with more than 8,000 implants to date.

Technical aspects and clinical outcomes related to the Edwards-SAPIEN aortic valve (Edwards Lifesciences, Irvine, Calif.) have been summarized in a similar review in this journal. Therefore, this review will discuss the CoreValve transfemoral experience.

Valve Design

The CoreValve ReValving system includes a biological bioprosthesis made of self-expandable nitinol and porcine pericardium and a dedicated delivery system (Figures 1 and 2). The current-generation nitinol frame is 50 mm in length and is hour-glass shaped. The lower (inner) portion of the frame is designed to seat on the left ventricular outflow tract (LVOT), but care must be taken not to impinge the anterior mitral leaflet. This is the part that affixes the valve to its position and thus has the greatest radial strength. The mid-portion of the prosthesis corresponds to the area of the sinuses of Valsalva and the coronary ostia, and it is not attached to the aortic wall so as not to jeopardize coronary flow. Finally, the upper section (outflow) has the lowest radial force and is designed to fix and stabilize the prosthesis in the ascending aorta (Figures 3 and 4).

The valve itself consists of three leaflets of porcine pericardium sutured to the frame. Once deployed, the point of coaptation of these leaflets is supra-annular. Hence, the functional diameter of the valve is fixed at 22 mm for the smallest device and 24 mm for the largest one.⁶
The ascending aorta and LVOT dimensions (measured in a parasternal long-axis view just below the point of insertion of the valves, incorrectly described as the “aortic annulus”) are therefore important to select the most appropriate valve size. Two sizes are currently available commercially. The smallest one has a 26 mm inflow diameter and is dedicated for patients with aortic annuli measuring in the range of 20–23 mm; the largest one has a 29 mm inflow diameter and is suitable for patients with 24–27 mm aortic annuli.

The CoreValve ReValving system rapidly evolved from the initial 25 Fr delivery system to the current 18 Fr device, which allows for a completely percutaneous arterial access (with the help of closure devices positioned preprocedure). This empowered the transition to a truly percutaneous procedure, avoiding general anesthesia and orotracheal intubation.⁵

Patient Selection

The gold standard for the treatment of severe aortic stenosis is surgical valve replacement⁷ and therefore, initial transcatheter aortic valve implantation (TAVI) studies restricted patient inclusion to those for whom surgery was not an option (patients either already rejected for surgery or at very high surgical risk). Market approval opened the way to more flexible indications, thereby broadening the spectrum of patients treated, although most of them are still high risk.

Ascending aorta and LVOT dimensions have already been mentioned as important factors for patient selection, but there are several other issues to be taken into consideration in order to select the most appropriate candidates and anticipate potential difficulties and complications. Vascular complications, although less frequent with the CoreValve than with the Edwards-SAPIEN valve due to the former’s lower profile, do warrant attention and careful planning based on accurate imaging assessment of the vasculature. Therefore, ileo-femoral diameter, tortuosity and calcification must be carefully evaluated before the procedure. Attention should also be paid to the anatomy of the aortic root, as the position of the coronary ostia too low in the sinuses of Valsalva, a short sinus height in relation to the length of the native leaflet, or a narrow diameter at the sinuses level may cause coronary obstruction. A very horizontally positioned aortic root may also cause difficulty in valve crossing and device placement.

Piazza et al postulated 15 anatomic criteria that, in their experience, seem to be related to procedural and clinical outcomes.⁸ According to these criteria, patients who are not good candidates for TAVI procedures have one or more of the following:
• left ventricular (LV) thrombus;
• subaortic stenosis;
• aortic annulus < 20 mm or > 27 mm;
• aortic regurgitation grade > II/IV;
• LV ejection fraction < 20%;
• LV wall thickness > 17 mm;
• annulus-to-aorta angle > 45º;
• sinuses of Valsalva height < 10 mm;
• aortic root diameter < 27 mm (if sinuses diameter is
< 15 mm);
• low coronary ostia position;
• severe proximal coronary stenosis;
• ascending aorta width > 43 mm;
• significant angulation of the aortic arch;
• ileofemoral diameter < 6 mm
• moderate-to-severe arterial access disease.