Summary
Patient selection plays a crucial role in the success of transcatheter aortic valve implantation (TAVI). It requires meticulous attention to the smallest of details and needs to be performed in a systematic manner for every patient. In essence, the patient must be assessed from access to implantation site. Becoming over “complacent” and “routine” may lead to failure and impact patient safety. TAVI is indicated for high or prohibitive surgical risk patients with severe aortic stenosis. Some patients, however, are too high risk even for TAVI. In addition to patient risk evaluation, anatomical selection criteria need to be considered. Multimodality imaging, using a combination of angiography, echocardiography and multislice computed tomography, is necessary to determine the anatomical suitability for the procedure.
Résumé
La sélection des patients joue un rôle majeur dans le succès des implantations de valve aortique par voie percutanée. Elle nécessite de porter une attention méticuleuse au moindre détail et doit être réalisée de façon systématique chez chaque patient. Le patient doit être évalué du site d’abord à la valve aortique. Un bilan « complacent » ? (je ne sait pas le traduire) ou trop « routinier » peut conduire à l’échec du geste et entraîner des complications. Les valves aortiques percutanées sont indiquées chez les patients porteurs d’un rétrécissement aortique serré et considérés comme étant à risque chirurgical trop élevé, voire même contre-indiqués. Certains patients peuvent également être à risque trop élevé pour une valve percutanée. À l’évaluation du risque opératoire doit s’ajouter l’évaluation anatomique du patient. Diverses modalités d’imagerie telles que l’angiographie, l’échographie et le scanner, sont nécessaires pour évaluer la faisabilité technique du geste.
Background
Patient selection plays a crucial role in the success of transcatheter aortic valve implantation (TAVI). It requires meticulous attention to the smallest of details and needs to be performed in a systematic manner for every patient. In essence, the patient must be assessed from access to implantation site. Becoming over “complacent” and “routine” may lead to failure and impact patient safety.
In Europe, TAVI is indicated for high or prohibitive surgical risk patients with severe aortic stenosis. Some patients, however, are too high risk even for TAVI. In addition to patient risk evaluation, anatomical selection criteria need to be considered. Multimodality imaging, using a combination of angiography, echocardiography and multislice computed tomography (MSCT), is necessary to determine the anatomical suitability for the procedure. In particular, assessment of the peripheral vasculature and aortic valvar complex will allow selection of the access route and prosthesis type and size, respectively.
Patient risk evaluation
A number of cardiac surgical risk algorithms have been developed over the last 20 years. Despite their known limitations, the logistic EuroSCORE I and the STS (Society of Thoracic Surgeons) Predicted Risk of Mortality score have guided enrolment of “high surgical risk” patients into TAVI trials. Because low-to-intermediate surgical risk patients characterized the development of these risk models, their reliability when applied to high or prohibitive surgical risk patients has been rightfully questioned. Furthermore, models may not take into account important comorbidities (e.g. porcelain aorta, chest wall radiation, liver cirrhosis, pulmonary hypertension) and frailty variables that may impact clinical outcomes. The newly updated logistic EuroSCORE II and STS score, however, are expected to incorporate frailty variables.
In high surgical risk patients, the logistic EuroSCORE I tends to overestimate the observed mortality risk by a factor of 2 to 3; the new logistic EuroSCORE II appears to provide significantly lower mortality estimates than the logistic EuroSCORE I. The STS score has been found to be more reliable than the logistic EuroSCORE I or the Ambler Risk Score for the prediction of operative and long-term mortality in high-risk patients undergoing surgical aortic valve replacement.
Clinical judgment should supersede any surgical risk algorithm. Risk scores should guide but not dictate clinical decision-making.
A need for a transcatheter aortic valve implantation (TAVI) risk score?
A TAVI risk score for TAVI patients, akin to the logistic EuroSCORE or STS score for surgical patients, is currently not available. A TAVI risk score may provide additional information during the preprocedural screening process to better understand the potential outcomes of patients after TAVI.
Recent publications have identified a number of baseline variables to be independently associated with mortality or poor treatment response in patients undergoing TAVI: low body mass, functional status, left ventricular dysfunction, low gradient aortic stenosis, concentration of N-terminal prohormone of brain natriuretic peptide, diabetes, prior stroke, chronic obstructive pulmonary disease, chronic kidney disease, severe tricuspid and mitral regurgitation and baseline anaemia . In addition to baseline demographics, anatomical characteristics may also help to predict treatment response after TAVI.
Anatomical patient selection criteria
The most important aspect of anatomical screening involves assessment of the arterial vasculature and aortic valvar complex (left ventricular outflow tract, aortic annulus, sinus of Valsalva, sinutubular junction and ascending aorta) ( Fig. 1 ). This information will guide physicians to select the most appropriate access route (i.e. transfemoral, subclavian, apical or direct aortic) and transcatheter valve size. Furthermore, it will alert physicians to potential complications that may arise during the procedure. Information about specific anatomical criteria is provided in the paragraphs that follow.
Assessment of the arterial vasculature
The occurrence of vascular complications associated with TAVI is not surprising given the use of large bore catheters and imperfect vascular closure devices. Vascular complications have been reported in 2% to 30% of patients undergoing TAVI; the conflicting reports are due to heterogeneous end-point definitions .
Peripheral contrast angiography is practical and associated with relatively lower costs, lower contrast dye injection and lower radiation exposure compared with MSCT . MSCT, however, provides greater appreciation of vessel size, tortuosity and calcific burden .
A recent angiographical study identified an outer sheath diameter to femoral artery minimal luminal diameter (SFAR) ratio greater or equal to 1.05 as a predictor of Valve Academic Research Consortium (VARC) major vascular complications as well as 30-day mortality . The SFAR cut-off ratio increased to 1.10 in the absence of calcium and decreased to 1.00 in the presence of calcium. These results need to be confirmed in prospective studies and should also include MSCT.
The femoral artery is typically used as the default vascular access. Peripheral vascular disease is not an absolute contraindication to TAVI; it does, however, increase the risk of complications significantly. Physicians must be skilled or have the necessary resources to treat vascular injuries (percutaneously or surgically). Some physicians attempt to cautiously advance the vascular access sheath and catheter delivery system across the diseased vasculature, implant the valve and repair any complications such as dissections “on the way out” by percutaneous transluminal angioplasty/stent implantation. Alternatively, peripheral vascular interventions (percutaneous transluminal angioplasty or stent implantation) can be performed prior to valve implantation. While this latter approach has been performed successfully in experienced centres, the risk of dislodging the implanted stent during advancement of the vascular access sheath or delivery catheter needs to be considered.
Significant tortuosity alone of the iliofemoral vessels is not necessarily a contraindication to TAVI as long as the vessels are otherwise healthy and compliant — gentle advancement of the stiff guidewire or vascular access sheath will tend to straighten the vessel.
The Edwards eSheath features the innovative “dynamic expansion mechanism” (DEM) that allows for transient sheath expansion during valve delivery. Immediately after the Edwards SAPIEN XT prosthesis passes through the sheath, the DEM allows the sheath to return to a low profile diameter. This reduces the time the access vessel is expanded, thereby minimizing the risk of vascular trauma. The unexpanded eSheath has an inner diameter of 5.3 mm (16F) and an outer diameter of 6.7 mm (20F) for implantation of the 23 mm prosthesis; an inner diameter of 5.9 mm (18F) and an outer diameter of 7.2 mm (21–22F) for implantation of the 26 mm prosthesis; and an inner diameter of 6.7 mm (20F) and an outer diameter of 8 mm (24F) for implantation of the 29 mm prosthesis ( Table 1 ). Acceptable minimal iliofemoral diameters for implantation of the 23, 26 and 29 mm Edwards SAPIEN XT prostheses are 6.0, 6.5 and 7.0 mm, respectively.
