Author + information
- Peter Wenaweser, MD and
- Stephan Windecker, MD⁎ ()
- ↵⁎Reprint requests and correspondence:
Dr. Stephan Windecker, Professor and Head of Cardiology, Department of Cardiology, Bern University Hospital, 3010 Bern, Switzerland
The study of Jilaihawi et al. (1) investigates the anatomic suitability of present- and future-generation transcatheter aortic valve prostheses. The principal finding is that 97% of patients screened for transcatheter aortic valve implantation (TAVI) are eligible for treatment with either the Edwards Sapien valve (ESV) (Edwards Lifesciences, Irvine, California) or the Medtronic CoreValve Revalving System (MCRS) (Minneapolis, Minnesota) with evidence of complementary utility. The investigators screened 100 patients with angiography, transthoracic or transesophageal echocardiography, as well as computed tomography with 3-dimensional reconstruction for technical feasibility. The focus of the assessment was on: 1) diameter of the common femoral artery; 2) diameter of the native valve annulus; and 3) dimension of the ascending aorta.
Transcatheter aortic valve implantation for the treatment of severe aortic stenosis in patients at high risk for surgery has already been performed in more than 20,000 patients worldwide since its first clinical application in 2004 (2). With growing experience, it has become evident that the screening process represents an integral component for the successful implementation of TAVI. However, evaluation of technical feasibility is only but 1 important consideration during the screening process. Careful assessment of risk for conventional surgical aortic valve replacement, identification of comorbidities, geriatric assessment, evaluation of frailty, and an interdisciplinary discussion of various therapeutic options should precede evaluation of technical feasibility (3).
A technical limitation of the current CE-approved devices for the transfemoral approach is the diameter of the common femoral artery (CFA). At least 6 mm for the MCRS and 7 to 8 mm for the ESV are required for the introduction of an 18-F or 22-/24-F sheath, respectively. The diameter of the CFA depends on age, sex, and body surface area and ranges between 6 and 10 mm in healthy subjects (4). Typically, female patients of small stature with severe aortic stenosis have small CFA not exceeding 6 mm in diameter. Of note, the minimal required diameter is feasible for patients with only mild tortuosity and absence of calcification of the iliofemoral axis. For patients with either peripheral vascular disease, which is present to some degree in most patients cases screened for TAVI (5), or renal insufficiency, at least 7 mm for the MCRS or 8 to 9 mm for the ESV system are required in order to overcome the friction imposed by the calcified and stiff vasculature. Peripheral vascular disease substantially influences the technical feasibility of the transfemoral approach as calcified parts of the CFA increase the risk of access site complications including dissections and perforations, especially if choosing a pure percutaneous approach with a closure device. Early experience shows that vascular access site complications and associated bleeding events are the most frequently encountered problems during TAVI (6–10). As bleeding is associated with adverse clinical outcome, meticulous screening of the intended access site remains of paramount importance. As bailout or alternative option, a surgical cutdown of the external iliac artery, a transapical approach, or a trans-subclavian access have to be considered.
Along with the diameter of the CFA goes the diameter of the native aortic valve. Anatomic studies highlight that the range of the aortic annulus diameter lies between 18 and 29 mm. Whereas the MCRS currently covers the range of 20 to 27 mm, the ESV can be used for a range between 18 and 25 mm. Accordingly, only a minority of patients with very small or exceedingly large anatomy are not amenable to treatment with either of the 2 devices as highlighted by Jilaihawi et al. (1). These net figures, however, obscure the fact that the aortic valve annulus has an elliptical rather than round shape and that the optimal tool for measuring the dimensions of the valve for the clinical setting of TAVI remain to be determined. Computed tomography scan measurements in the coronal view tend to overestimate the diameter, whereas reconstruction in the sagittal view often underestimates the diameter due to the septal muscular bulge. Transthoracic echocardiography can reliably exclude a too small annulus, whereas transesophageal echocardiography, which is frequently used due to its superior image quality, exposes only 1 dimension in the long-axis view. Measurements of invasive aortography correlate well with the coronal view of the computed tomography scan and therefore tend to overestimate the true annular dimensions. Finally, direct measurement of the valve plane during balloon dilation with simultaneous dye injection into the aortic root can be considered for cases with borderline dimensions. The pros and cons of the different measurement tools are summarized in Tables 1 and 2.⇓ The role of magnetic resonance imaging for measurement of the aortic dimensions remains to be elucidated (Fig. 1). Magnetic resonance imaging may provide complete assessment of other valvular pathologies than aortic stenosis, provides additional information in terms of left and right ventricular function as well as myocardial viability, and is able to assess hemodynamic parameters. The lack of visualization of calcified structures and the need of electrocardiogram triggering remain, however, unresolved issues.
Beyond the annular dimensions, the distance of the takeoff of the coronary arteries, the amount of calcification, and the diameter of the sinus portion are equally important considerations when choosing between the 2 currently available devices. Although coronary occlusion or myocardial infarction is a rare complication, acute myocardial ischemia can be deleterious in this setting. For the ESV, a minimal distance of 10 mm from the annular level to the takeoff of the coronary arteries is recommended as the height of the valve amounts to 14 to 17 mm with the lower half being circumferentially covered to avoid paravalvular leaks. Conversely, the frame of the MCRS circumvents the risk of coronary occlusion as the mid-portion is constrained and leaves more space between the frame and the takeoff of the coronary arteries. In case of a small sinus portion (<30 mm) of the aorta, however, occlusion of the coronary arteries is still possible especially in case of a too high implantation of the MCRS prosthesis.
As the ascending aorta is usually not dilated in patients with degenerative aortic valve stenosis, the size of the ascending aorta usually does not exceed 45 mm. Dimensions beyond 45 mm are formally considered to be an indication for replacement of the ascending aorta and represent a relative contraindication for the use of the MCRS as the upper part of the frame helps to orient the valve plane.
The 2 currently available devices have important differences in design. The ESV is a balloon-expandable system based on a cobalt-chromium stent that uses bovine pericardial tissue specifically treated using an anticalcification process. The valve requires correct deployment upon balloon inflation, as there is no possibility to reposition or retrieve the device once expanded. Coronary occlusion might occur due to shift of calcified material toward the left main ostium. Notwithstanding, these complications are exceedingly rare in experienced hands. As the stent is small in height, no interference with the left ventricular outflow tract and the superficially located left bundle is to be expected. Therefore, the rate of complete atrioventricular-block or atrioventricular-conduction disorders is low and comparable to conventional surgical aortic valve replacement. So far, a 22-/24-F sheath was used for the transfemoral approach. More recently, the NovaFlex system (Edwards Lifesciences) has been introduced with further downsizing of the sheath to 18-/19-F. This change in design has considerably reduced the proportion of patients ineligible for the transfemoral ESV system from 72% to 22% as mentioned by Jilaihawi et al. (1), challenging the previous advantage of the MCRS device in terms of vascular access and limiting the eligibility differences between the 2 devices to patients with large annuli (>25 mm) and coronary ostia in very close proximity to the valve plane.
The MCRS device is based on a Nitinol frame and uses porcine pericardium. This self-expanding system measures 5.5 cm in height, provides strong radial force in the distal third of the frame, which serves to anchor the device and is designed to avoid contact of the frame with the coronary ostia. The device typically extends to the subvalvular septum with the incumbent risk of interference with the left bundle branch (5). Consequently, a higher rate of atrioventricular-conduction disturbances is noted (11). Conversely, the self-expanding frame allows interventional cardiologists to correct the position of the valve during deployment and even offers the possibility of complete retrieval as long as it is attached to the proximal catheter tip. With respect to paravalvular leakage, no data have directly compared the 2 devices at this time. In light of the elliptical shape of the native annulus, mild paravalvular regurgitation is accepted but a potential impact on long-term clinical outcome needs to be determined.
Although the current CE-approved devices cover up to 97% with respect to the anatomic measurements, future devices will attempt to address the shortcomings of these systems. The following modifications will further expand the anatomic suitability for transfemoral TAVI while reducing the risk of periprocedural complications: 1) downsizing of the introducer sheath in order to further reduce the risk of vascular access complications; 2) development of a simplified and reproducible evaluation technique for the measurement of the anatomic valve dimensions, the aortic root, and the peripheral arteries; 3) development of completely repositionable and retrievable devices in order to immediately correct malpositioning and reduce paravalvular regurgitation; 4) percutaneous closure systems with reliable performance and ability to introduce a new device in case of insufficient access site closure.
In summary, the 2 current CE-approved devices are complementary and already cover a wide array of anatomic dimensions using various access routes today. The vast majority of TAVI procedures can be performed using the transfemoral approach, a trend that will be further enhanced by continued efforts to downsize future devices. Under ideal circumstances, centers are in the position to choose between the 2 currently approved devices according to the anatomic considerations discussed herein to fully exploit the advantages of TAVI in any given patient.
Drs. Wenaweser and Windecker receive honoraria and lecture fees from Medtronic CoreValve and Edwards Lifesciences.
↵⁎ Editorials published in JACC: Cardiovascular Interventions reflect the views of the authors and do not necessarily represent the views of JACC: Cardiovascular Interventions or the American College of Cardiology.
- American College of Cardiology Foundation
- Jilaihawi H.,
- Bonan R.,
- Asgar A.,
- et al.
- Cribier A.,
- Eltchaninoff H.,
- Bash A.,
- et al.
- Vahanian A.,
- Alfieri O.,
- Al-Attar N.,
- et al.
- Grube E.,
- Schuler G.,
- Buellesfeld L.,
- et al.
- Webb J.G.,
- Chandavimol M.,
- Thompson C.R.,
- et al.
- Webb J.G.,
- Pasupati S.,
- Humphries K.,
- et al.
- Roten L.,
- et al.