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Who Should Receive a Percutaneous Aortic Valve and Who Should Not?
Introduction
Rising life expectancy results in an increase in degenerative and neoplastic diseases. Population-based observational studies revealed that 1–2% of patients > 65 years of age have moderate-to-severe aortic stenosis (AS).1 Surgical aortic valve replacement (AVR) dates back to 1960 and is currently the only treatment option for severe AS. It has been shown to improve survival, regardless of age.2 In the ideal candidate, surgical AVR has an estimated operative mortality rate of 4%. Unfortunately, up to one-third of patients with severe AS are ineligible for corrective valve surgery either because of advanced age or the presence of multiple comorbidities.3 Current treatment options for those patients not offered surgery include medical treatment or percutaneous balloon aortic valvuloplasty, though neither has been shown to reduce mortality. Medically treated patients with symptomatic AS have a 1- and 5-year survival rate of 60% and 32%, respectively.4 With the introduction of transcatheter aortic valve implantation (TAVI) in 2002, there seems to be an alternative for these patients.
Selection of Patients
Due to the existence of the tried-and-tested surgical valve replacement with good long-term results, the selection of patients for TAVI — which should be performed in a multidisciplinary consultation between cardiologists, surgeons, imaging specialists, and anesthesiologists — involves several critical steps.5 Candidates considered for TAVI must have severe symptomatic AS in addition to a formal contraindication to surgery or other characteristics that would limit their surgical candidacy because of excessive mortality or morbidity risks (Figure 1). The procedure should be offered to patients who have a potential for functional improvement after valve replacement. It is not recommended for patients who simply refuse surgery on the basis of personal preference.
Confirming the Severity of Aortic Stenosis
Different imaging modalities can assist in the selection process by providing important information about the aortic valve, coronary arteries, and vascular structures. First, the severity of AS should be assessed. Both transthoracic echocardiography (TTE) and transesophageal echocardiography (TEE) are the preferred tools to assess the severity of AS. In addition, the exact anatomy of the aortic valve should be assessed. Echocardiography, multislice computed tomography (MSCT), and magnetic resonance imaging (MRI) can all help to distinguish between a bicuspid and a tricuspid aortic valve. It is important to point out that the implantation of available percutaneous prostheses is contraindicated in the case of a unicuspid valve, and is not recommended in the case of a bicuspid aortic valve because of the risk of incomplete deployment, significant paravalvular regurgitation, and displacement of the prosthesis.5,6 Furthermore, the exact location and severity of aortic valve calcifications and the presence of bulky aortic valve leaflets should be assessed. Before the implantation procedure, MSCT may be the preferred tool to identify aortic valve calcifications. A severely calcified aortic valve may result in the inability to cross the native valve with the catheter. Bulky leaflets and calcifications on the free edge of the leaflets may increase the risk of occlusion of the coronary ostia during aortic valve implantation. Thus,the extent and exact location of calcifications should be carefully assessed before the implantation procedure. The assessment of coronary anatomy is also important in the selection process. Conventional coronary angiography, which remains the “gold standard,” should be performed to exclude the presence of significant coronary artery disease.
Analysis of Surgery Risk and Evaluation of Life Expectancy and Quality of Life
The precise evaluation of surgical risk in a specific patient is not easy and involves an attempt at individualization based on statistical data from databases containing a large number of procedures. The most accepted and validated algorithms that are widely available today are the EuroSCORE, the STS score and the Parsonnet score. These algorithms predict the surgical risk by assigning weight to various factors that affect the clinical result, but it is clear that they can underestimate or overestimate it in certain groups of patients who are not represented satisfactorily in the population used to generate the algorithm.7 There is some evidence in the literature of the incorrect prediction of aortic valve replacement outcome using the EuroSCORE model.8 Osswald et al report on the real risk of overestimation of death by EuroSCORE for patients undergoing isolated AVR, pointing to a possible incorrect assignment of high-risk patients to PAVI procedure.9 The key element to establishing whether patients are at high risk for surgery is multidisciplinary clinical judgement, which should be used in association with a more quantitative assessment based on the combination of several scores (for example, expected mortality > 20% with the EuroECORE and > 10% with the STS score). This approach allows the team to take into account risk factors that are not covered in scores, but often seen in practice such as chest radiation, previous aorto-coronary bypass with patent grafts, porcelain aorta or liver cirrhosis.
Assessment of Feasibility and Exclusion of Contraindications for TAVI
After the criteria of severe symptomatic aortic valve stenosis and high surgical risk are evaluated, a technical examination of the patient’s suitability for the percutaneous implantation technique begins (Table 1). The two most basic parameters are the suitability of the peripheral arteries and the size of the aortic valve annulus. Contrast angiography is needed to assess the former, while the latter requires an initial assessment of the diameter of the aortic annulus on a transthoracic echocardiography (TTE). In general terms, a large artery with dominant elastic elements should have a diameter up to 1 mm smaller than the external diameter of the sheath that has to be introduced for the valve implantation. Thus, current systems with an external sheath diameter of 28 Fr (SAPIEN 26 mm, Edwards Lifesciences, Inc., Irvine, California), 25 Fr (SAPIEN 23 mm, Edwards Lifesciences) and 18 Fr (CoreValve, Medtronic, Inc., Minneapolis, Minneosta) require minimum diameters in the order of 8, 7 and 6 mm, respectively. Apart from the minimum diameter, the existence of significant vessel tortuosity (> 90°), especially when combined with wall calcifications, makes advancing the large sheath problematic, with a high risk of vascular complications that could potentially affect the final outcome. In addition, the existence of extensive circumferential calcifications limits the elastic dilation of the artery; thus, the minimum diameters referred to above are underestimated. Patients who do not meet the criteria of suitable peripheral arterial access may still be candidates for subclavian or transapical implantation. For the assessment of aortic annulus diameter, we should keep in mind that TTE underestimates its size by a mean of 1.4 mm compared to the TEE,5,10 while the latter method also underestimates the size by 1.2 mm compared with intraoperative measurement.10 Therefore, in order to avoid undesirable and often catastrophic displacement of the prosthesis, there should be a margin of at least 1–2 mm between the diameter of the valve and the size of the aortic annulus estimated using TEE, so that the former may be successfully and safely anchored within the latter. Computed tomography (CT), aortography and angiography of the ascending aorta are the most appropriate examinations for investigating these aspects. Those examinations will also be used for the measurement of the dimensions of the ascending aorta and the aortic arch, which are essential for checking eligibility for the CoreValve (the most important being the diameter of the ascending aorta, which should be Transcatheter Aortic Valves On the basis of the first results from clinical trials, the CoreValve Revalving System and the Edwards Lifesciences System obtained CE mark approval in 2007, with the specification that these valves are intended for patients with a high or prohibitive risk for surgical valve replacement or those who cannot undergo AVR. The first generation balloon-expandable valve was called the Cribier-Edwards valve (Edwards Lifesciences), whereas at present, the Edwards SAPIEN valve (Edwards Lifesciences) is commercially available (Figure 2). The Edwards Lifesciences SAPIEN THV device is a balloon-expandable valve. It consists of bovine pericardium that is firmly mounted within a tubular, slotted, stainless steel balloon-expandable stent. Two valve sizes have been developed (23 mm and 26 mm). At present, available prosthesis sizes are 23 and 26 mm for aortic annulus diameters between 18–22 mm and 21–25 mm, respectively. The CoreValve Revalving device is a self-expanding frame-valve prosthesis (Figure 2). It consists of a porcine pericardial tissue valve that is mounted and sutured in a multilevel self-expanding nitinol frame, and is available in 26 mm and 29 mm sizes. The device has a broader upper segment (outflow aspect), which yields proper orientation to the blood flow. The first-generation valve used bovine pericardial tissue and was constrained within a 25 Fr delivery catheter. The second-generation valve was built with porcine pericardial tissue within a 21 Fr catheter to allow access through smaller-diameter vascular beds. The third generation of the device features a catheter with a valve delivery sheath size of 18 Fr and a follow-on shaft of 12 Fr. Newer devices that have first-in-man application include the Paniagua (Endoluminal Technology Research, Miami, Florida), the Enable (ATS, Minneapolis, Minnesota), the AoTx (Hansen Medical, Mountain View, California), the Perceval (Sorin Group, Arvada, Colorado), the Jena (JenaValve Technology, Wilmington, Delaware), the Lotus Valve (Sadra Medical, Campbell, California), and the Direct Flow percutaneous aortic valve (Direct Flow Medical, Inc., Santa Rosa, California). In the first cases, an antegrade implantation of the valve was performed using transseptal access to the left atrium and passage through the mitral valve to reach the aortic valve. However, at present, a retrograde approach through the femoral artery is used. During the procedure, balloon valvuloplasty is first performed to facilitate passage in the native aortic valve. During rapid right ventricular pacing, the prosthesis is positioned and deployed under fluoroscopic and echocardiographic guidance. Alternatively, in patients with difficult vascular access because of extensive calcifications or tortuosity of the femoral artery, a subclavian or transapical approach can be used. After a partial thoracotomy, direct puncture of the apical portion of the left ventricular free wall is performed to gain catheter access to the left ventricle and aortic valve. The prosthesis is subsequently positioned and deployed, similar to the antegrade approach.
Results from the Literature
Cribrier-Edwards Valve. Cribier et al performed the first human implantation in 2002.11 In the Initial Registry of EndoVascular Implantation of Valves in Europe (I-REVIVE) trial, followed by the Registry of Endovascular Critical Aortic Stenosis Treatment (RECAST) trial, a total of 36 patients (mean [SD] EuroSCORE 12 [2]) were included.12 Twenty-seven patients underwent successful percutaneous aortic valve implantation (23 antegrade, 4 retrograde). The 30-day mortality was 22% (6 of 27 patients), and the mean aortic valve area increased from 0.60 ± 0.11 cm2 to 1.70 ± 0.10 cm2 (p 13 After these first trials, the Cribier-Edwards prosthesis and the Edwards SAPIEN prosthesis have been used in numerous studies. Overall, acute procedural success is achieved in 75–100% of the procedures, and 30-day mortality ranges between 8–50% in the published studies. Using the transapical technique and the Sapien valve, Walther and colleagues reported their initial multicenter results of 59 consecutive patients, which is the largest feasibility study published on the Edwards SAPIEN thus far. Procedural success using the transapical technique was achieved in 53 patients. Thirty-day mortality was 13.6%, and none of these were thought to be valve-related, as there was good valve function at autopsy.14
CoreValve Revalving. Since the first implantation of the CoreValve prosthesis in a patient in 2005,15 a large number of patients have been treated with this device to date. The feasibility and safety of this valve were studied in a prospective, multicenter trial. A total of 25 symptomatic patients with an aortic valve area 2 were enrolled in the study. The device was successfully implanted using the retrograde technique in 22 of 25 patients. Procedural success and aortic mean pressure gradients were markedly improved immediately following implantations with preprocedure gradients 44.24 ± 10.79 mmHg to 12.38 ± 3.03 mmHg post procedure and were about the same at 30-day follow-up (11.82 ± 3.42 mmHg). New York Heart Association (NYHA) class improved by 1 to 2 grades in all patients. Major adverse cardiac events (MACE) defined as death from any cause, major arrhythmia, myocardial infarction, cardiac tamponade, stroke, urgent or emergent conversion to surgery or balloon valvuloplasty, emergent percutaneous coronary intervention, cardiogenic shock, endocarditis, or aortic dissection occurred in 8 of the 25 patients while in the hospital.16 Recently, Grube et al reported the results with the three different generations of the CoreValve Revalving system. In this nonrandomized, prospective study, a total of 136 patients were included.17 Ten patients were treated with first-generation devices, 24 patients with second-generation, and 102 patients with third-generation devices. At baseline, the mean aortic valve area was 0.67 cm2 and the mean logistic EuroSCORE was 23.1% in the overall study population. The overall procedural success rate increased significantly with the new-generation devices from 70.0% and 70.8% to 91.2% for the first-, second- and third-generation prostheses, respectively (p = 0.003). Interestingly, periprocedural mortality decreased using newer devices from 10% (first generation) to 8.3% (second generation) to 0% (third generation). Overall 30-day mortality for the three generations was 40%, 8.3%, and 10.8%, respectively. Pooled data demonstrated a significant improvement in mean NYHA functional class (from 3.3 to 1.7, p 18
Conclusion
Transcatheter valve implantation was developed in order to provide an alternative and less invasive method of treating aortic valve stenosis in high-risk patients. It has been proven that the method is feasible, with successful results that were reproduced by many physicians at many centers (approximately 8,000 implantations to date). Today at least 10 new percutaneous aortic valves have had their first implantation in humans, many more have reached the level of animal experiments, and even more are still in the initial design stage. As a new treatment tool, these valves must be evaluated in randomized, controlled trials with long-term follow-up in order to assess their safety and efficacy. Therefore, the performance of TAVI should be restricted to a limited number of high-volume centers that have both cardiology and cardiac surgery departments with expertise in structural heart disease intervention and high-risk valvular surgery. Due to the excellent results with surgical valve replacement, patient selection, which should involve multidisciplinary consensus, is of utmost importance. Like other interventional procedures, there is a learning curve that involves significant improvements in success rates and clinical results after the first 25 procedures, which implies that the TAVI procedure should initially be performed and thereafter supervised by a specially trained team.10,19 In addition to careful patient selection for TAVI intervention, close follow-up with assessment of clinical and objective parameters is mandatory in order to define the indications for this technique.
References
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20. Walther T, Dewey T, Borger MA, et al. Transapical aortic valve implantation: Stepp by Stepp. Ann Thorac Surg 2009;87:276–283.
From the Department of Medicine, Division of Cardiology at the University Hospital Rostock, Rostock School of Medicine, Rostock, Germany, and the *Department of Cardiothoracic Surgery, University Hospital of Rostock, Rostock School of Medicine, Rostock, Germany.
The authors report no conflicts of interest regarding the content herein.
Address for correspondence: Hüseyin Ince MD, PhD, Department of Medicine, Division of Cardiology, University Hospital Rostock, Rostock School of Medicinm, Ernst-Heydemann-Str. 6, 18057 Rostock, Germany. E-Mail: hueseyin.ince@med.uni-rostock.de
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VASCULAR DISEASE MANAGEMENT 2010;7(2):E41–E45
