Statistics from Altmetric.com
Aortic stenosis (AS), which is now the most frequent native valve disease in Europe, has a predominantly degenerative origin and is mostly seen in elderly patients. Valve replacement is the definitive therapy1; however, the risk of surgery is high in elderly patients with significant comorbidities.2 In addition, several registries show that as many as one third of patients with severe valve disease and severe symptoms are not being considered for surgery.3 Thus, there is a role for less invasive alternatives. Balloon aortic valvuloplasty (BAV) is now rarely used in isolation, mainly due to its limited long term efficacy.
Seven years after its introduction in clinical practice by Alain Cribier,4 transcatheter aortic valve implantation (TAVI) currently represents a dynamic field of research and development.
Two devices are commercially available for TAVI (figure 1). One device is the Edwards-Sapien valve, which consists of three bovine pericardial leaflets, mounted within a tubular, slotted, stainless steel, balloon expandable stent. It is currently available in 23 and 26 mm sizes, necessitating, respectively, 22F and 24F introducer sheaths for the transfemoral approach and 26F for the transapical approach. The other device is the Medtronic CoreValve which has three porcine pericardial leaflets (initially bovine) mounted in a self expanding nitinol frame. It is available in 26 and 29 mm sizes, which go through an 18F introducer for transfemoral or transaxillary use.
The selection of candidates for TAVI and the performance of the procedure require the cooperation of a multidisciplinary team including cardiologists, surgeons, imaging specialists and anaesthetists, all with experience in the management of valve disease.5
This review will describe the main technical aspects and the steps to be taken for patient selection, summarise the current results of TAVI, and elaborate on future perspectives.
TAVI should be performed only in patients with severe signs and symptoms that can definitely be attributed to severe AS as assessed by echocardiography.5 This relationship could be difficult to establish in elderly patients—for example, in the two following situations:
In those patients with low left ventricular (LV) ejection fraction and low gradient, the evaluation of the degree of calcification and low dose dobutamine echocardiography are useful adjuncts to differentiate between severe and the rare ‘pseudo severe’ AS.
In patients with concomitant severe respiratory disease, the medical history, in particular the chronology of dyspnoea, as well as value of biomarkers such as B-type natriuretic peptide (BNP), are useful.
The next step is to carry out an analysis of the risks of surgery, which is also complex in these elderly patients who represent a heterogeneous population and require balanced and individualised analysis. Multivariate risk scores are increasingly used to estimate operative mortality. The EuroScore is user-friendly and widely used. However, it tends to overestimate operative mortality in high risk patients with valve disease. Other scores have been specifically developed for valvular diseases such as the STS PROM (Society of Thoracic Surgery Predicted Risk of Mortality) score which appears to be more reliable than the EuroScore in high risk patients.6 It is important, however, to realise that all scoring systems have limitations—in particular, they do not take into account the surgical results in the given institution.5
TAVI should currently be restricted to patients at high risk or with contraindications to surgery. The key element in establishing whether patients are at high risk for surgery is clinical judgement, which should be used in association with a more quantitative assessment, based on the combination of several scores (eg, expected mortality >20% with the Logistic EuroScore and >10% with the STS score). This approach allows risk factors that are not covered in scores but often seen in practice such as previous aorto-coronary bypass with patent grafts, chest radiation, porcelain aorta, liver cirrhosis, etc, to be taken into account.5
Life expectancy is most significantly influenced by comorbidities, which should be carefully looked for. In addition to clinical evaluation, semi-quantitative scoring systems such as those used in geriatric patients7 may be helpful for identifying those individuals whose life expectancy is compromised more by comorbidities than by the heart disease itself. TAVI should not be performed in patients whose life expectancy is very limited in terms of duration and quality of life (<1 year has been proposed as an acceptable threshold); these patients should be managed conservatively.5
When TAVI is envisaged the following steps should be taken to assess its feasibility:
Coronary angiography should be performed. If associated coronary artery disease requiring revascularisation is evident, the decision as to whether to proceed percutaneously as well as the chronology of intervention should be the subject of individualised discussions based on the patient's clinical condition and anatomy. In practice, without any robust evidence to support it, the trend is to use higher thresholds for combined revascularisation than in surgical candidates; revascularisation is performed only in cases with severe lesions of the left main coronary trunk or left anterior descending or dominant right coronary artery. In such cases percutaneous revascularisation is usually performed a few weeks before TAVI. Finally, the position of the coronary arteries relative to the aortic cusps is best assessed using multislice CT.
Correct sizing of the valve is critical to minimise the potential for paravalvular leakage and to avoid prosthesis migration after placement or annulus rupture. Several methods are available but today the most accurate remains to be determined (figure 2). Transthoracic echocardiography (TTE) is the most popular method while transoesophageal echocardiography (TOE), which has been found to show larger values than TTE, is advised if borderline values lead to doubt over the feasibility of the procedure.8 Multislice CT (MSCT) offers the opportunity to assess the complex three dimensional structure of the aortic annulus and confirms its oval shape.9 The measurements obtained by MSCT are somewhat larger than those shown by echocardiography.10 Finally, measurements on aortography performed during BAV are also advocated by a few teams.
Echocardiography and MSCT will also assess the morphology of the valve, the importance and location of calcification, and the dimensions of the aortic root, before the self expandable devices are implanted (figure 3).
Echocardiography will eliminate the presence of dynamic subvalvular LV obstruction and assess the mitral valve in quantifying the importance of regurgitation and establishing if mitral disease is organic or functional.
The choice of the approach, either retrograde or transapical, will depend on the size, tortuosity, and degree and location of calcification of peripheral arteries which will be evaluated by angiography and better MSCT (figure 4).
The contraindications for TAVI are shown in box 1.
Box 1 Contraindications for transcatheter aortic valve implantation
Aortic annulus <18 mm or >5 mm for balloon expandable devices and <20 mm or >27 mm for self expandable devices
Bicuspid valves (relative contraindication)
Presence of asymmetric heavy valvular calcification
Aortic root dimension >45 mm at the sino-tubular junction for self expandable prostheses
Low position of coronary ostia (<8 mm from the aortic annulus)
Dynamic subvalvular obstruction
Severe organic mitral regurgitation
Apical left ventricular thrombus
Specific contraindications for the transfemoral approach
Iliac arteries: severe calcification, tortuosity, small diameter (<6–9 mm depending on the device used), previous aorto-femoral bypass
Aorta: severe angulation, severe atheroma of the arch, coarctation, aneurysm of the abdominal aorta with protruding mural thrombus
The presence of bulky atherosclerosis of the ascending aorta and arch detected by transoesophageal echocardiography
Contraindications for the transapical approach
Severe respiratory insufficiency
Major chest deformity
Previous surgery of the left ventricle using a patch
A few specific issues are:
The presence of bicuspid valves, especially when severely calcified, is currently a relative contraindication because of the risk of asymmetric deployment of the prosthesis due to the calcification and the large size of the annulus.
Asymmetric heavy valvular calcification may compress the coronary arteries during TAVI and should be detected before TAVI on MSCT and also during BAV.
Dynamic subvalvular obstruction, which may lead to severe hypotension when the valvular obstacle is relieved, should also be carefully looked for, as well as the presence of severe septal hypertrophy localised in the close vicinity of the aortic cusps.
Severe organic mitral regurgitation is a contra-indication for TAVI but functional mitral regurgitation is not because it is likely to decrease if the procedure is successful.
Techniques of implantation
The performance of TAVI should be restricted to high volume centres, which have both cardiology and cardiac surgery departments, with expertise in structural heart disease intervention and high risk valvular surgery.
The optimal environment for TAVI should be spacious and sterile, and feature high quality imaging equipment, and facilities for cardiac support. A hybrid suite is ideal but in practice very few centres in Europe have the availability of such equipment and most procedures are performed in catheterisation laboratories.
TAVI is currently carried out using two different approaches: retrograde transfemoral or transaxillary and antegrade transapical, since the transseptal approach has been abandoned.
The specific issues related to the different approaches are:
In the transfemoral approach the common femoral artery can be either prepared surgically or approached percutaneously. Closure of the vascular access can be achieved surgically or by using a percutaneous closure device, depending on the size of the device and the experience of the team. The same principles hold true for the transaxillary approach. Finally, a retroperitoneal approach of the iliac artery has been used in a few cases.
The transapical approach requires an anterolateral mini-thoracotomy, pericardiotomy, identification of the apex, then puncture of the left ventricle using a needle through purse string sutures. Subsequently, an introductory sheath is positioned in the LV and the prosthesis is implanted using the antegrade route.11
Both approaches share the same main principles. Most teams perform the procedure under general anaesthesia, although sedation and analgesia may suffice for the transfemoral approach. However, it should be kept in mind that the presence of an anaesthetist with specific expertise in cardiology is mandatory for peri-procedural care because of the severe clinical condition of these patients.The use of general anaesthesia allows for peri-procedural TOE monitoring to help correctly position the valve and moreover to detect complications. After crossing the aortic valve, BAV is performed to predilate the native valve.
Positioning the prosthesis at the level of the aortic valve is a crucial step and may use in combination:
(1) Fluoroscopy to assess the level of valve calcification and aortography to determine the position of the valve and the plane of alignment of the aortic cusps.
(2) Echocardiography: TOE is helpful, in particular in cases with moderate calcification. The additional value of three dimensional real-time TOE is currently being evaluated. According to the limited current experience with intracardiac echography, it does not seem to add to TOE in this setting (figure 5).
When positioning is considered correct, the prosthesis is released. Rapid pacing is used at this stage in balloon expandable valves to decrease cardiac output, stabilising the prosthesis during inflation, but not in self-expanding devices. Immediately after TAVI, aortography and, whenever available, TOE are performed to assess the location and degree of aortic regurgitation, the patency of the coronary arteries, and to rule out complications such as haemopericardium, and aortic dissection (figure 6). The haemodynamic results are assessed using pressure recordings and/or echocardiography.Similarly to what is done when using surgical valve replacement, BAV could be used as a bridge to TAVI in patients presenting with very low LV ejection fraction or in acute heart failure. This stepwise approach performed at an interval of a few days or weeks may decrease the risk of intervention. After the procedure, the patient should stay in intensive care for at least 24 h and be closely monitored for several days in regard to haemodynamics, vascular access, and rhythm disturbances, especially late atrioventricular block. On an empirical basis, dual antiplatelet therapy is usually given for 3–6 months and aspirin is continued life long. If vitamin K blockers are needed the duration of dual antiplatelet treatment should be made shorter or a single agent should be considered.
More than 10 000 TAVI procedures have been performed worldwide; however, it should be acknowledged that the evidence in the field remains limited to a number of single centre reports, seldom including over 100 cases, published in peer review journals, but mixing early and late experience as well as first and subsequent generation devices.12–14 The second source of information is from registries15–17 mostly reported in oral presentations with all the inherent limitations. In addition the analysis of the results suffers from the lack of common definitions as regards success and complications across the series.
The patients treated were mostly over 80 years old, at high risk (eg, Logistic EuroScore >20% in most cases), or with contraindications for surgery. The series are also heterogeneous as regards the approach or device used. Most series report the use of one or the other approach, or device, and few use both approaches or devices. In most reports the transfemoral approach is the default approach and therefore the patients treated using the transapical approach usually have a higher risk profile and more comorbidities, which should be kept in mind when analysing the results.
The overall results are shown in tables 1–3.
The reports considering the management of severe AS in the era of TAVI show that around 60% of the patients screened by a multidisciplinary team for the procedure are currently treated by TAVI if both approaches are available, while 10–20% are operated on, and finally around 30% are treated medically because severe comorbidity limits their life expectancy and precludes any functional benefit from TAVI.14
The two types of devices are used more or less equally. Overall, two thirds of cases have been performed using the transfemoral approach and only preliminary reports describe the experience of the transaxillary route in around 200 patients.
Procedural success is over 90% in experienced centres and in the most recent registries.12–17
Valve function is good with a final valve area ranging from 1.5–1.8 cm2 and mean gradients around ≤10 mm Hg, which is at least equivalent to that of a surgically implanted prosthesis.18 Interestingly, recent observations using MSCT showed that in up to 20% of cases the shape of the prosthesis may be elliptic after implantation, which may favour paravalvular aortic regurgitation.10
Mortality at 30 days ranges from 5–18% for the transfemoral approach12–14 and 10–19% when using the transapical approach.12 14 16 17 Coronary obstruction is a rare (<1%) but dramatic complication. It may be due to external compression of the left main coronary artery by bulky valve calcification or obstructive low positioned coronary ostia. Acute myocardial infarction occurs in 2–5% of cases. Mild aortic regurgitation, mostly paravalvular, is observed in over 50% of cases,12–17 and moderate regurgitation occurs in around 20% of cases. The availability of larger prostheses and their more careful matching with the size of the aortic annulus, in order to slightly oversize the device, has led to a decrease in the incidence of severe aortic regurgitation to <10%. Prosthesis embolisation is rare, around 1%. Stroke rate ranges from 2–9% with a trend towards a lower incidence of stokes when using the transapical approach.12–17
Vascular complications remain a significant cause of morbidity in the transfemoral approach, with an incidence ranging from 10–15% with the balloon expandable device, decreasing to 2–4% with the self expandable one which has a lower profile.12–15
Atrioventricular block occurs in 4–8% of cases with the balloon expandable devices, necessitating pacemaker implantation in up to 30% with self expandable devices. The presence of previous right bundle branch block and the onset of left bundle branch block during the procedure are predictors of the need for pacemaker implantation after TAVI.19
Surgical conversion is rare but requires the immediate availability of cardiac support and surgical back up, at least in operable patients, in cases of life threatening complications such as coronary occlusion, massive aortic regurgitation or valve migration in the LV.
Long term results up to 6 years (though only 1 to a maximum of 3 years in most studies) show a survival rate of 70% at 1 year and 60% at 2 years,12–14 16 17 with a significant improvement in clinical condition and quality of life parameters in most cases, which is of the utmost importance in this elderly population.20 The majority of late adverse clinical events are due to comorbidities (figure 7). Anecdotal cases of valve endocarditis or thromboembolism have been reported. The risk of bleeding could be a concern in elderly patients when receiving a combination of antiplatelet agents plus vitamin K blockers. The degree of aortic regurgitation remains stable over time and mild to moderate aortic regurgitation did not require re-intervention or cause severe haemolysis during this limited follow-up. Serial echocardiographic studies have consistently shown good prosthetic valve function and no structural deterioration of valve tissue has been reported so far.12 14 A few cases of secondary surgical intervention have been performed, mostly in cases of inadequate valve positioning. Preliminary reports have shown that LV ejection fraction improves after TAVI while the degree of functional mitral regurgitation decreases.
There are currently no studies comparing either one device against the other or one approach against the other.
Finally, case reports have shown the feasibility of ‘valve in a valve implantation’ for either acute failure of TAVI caused by intraprosthetic aortic regurgitation or for degenerated valve prostheses, either stented or stent-less; however, it is too early to draw any definite conclusions on this attractive potential indication.
It is necessary to accumulate more evidence on the results of TAVI. The results of the first randomised trial (PARTNER US), comparing TAVI with either medical treatment or surgical valve replacement according to the patient's condition, will be reported during the coming year. Data should be accumulated from registries with longer follow-up to assess safety and durability, with special focus on the timing and the mode of valve failure, the consequences of mild to moderate aortic regurgitation, and the feasibility of re-intervention, either percutaneous or surgical. These data will help to define better the indications of the technique and the respective place of each approach. Overall the availability of TAVI has already increased the number of referrals for intervention in patients with severe AS, which is a good thing taking into consideration the current underuse of surgery in this population. At this stage TAVI is not recommended for patients who simply refuse surgery on the basis of personal preference because of the awareness of TAVI. The respective roles of TAVI and surgical valve replacement are likely to change in the future with an anticipated increase in the use of TAVI, which will hopefully be based on evidence more than on uncontrolled off label use of the devices. Furthermore it is also likely that the availability of TAVI will lead to a lowering of the age of implantation of surgical bioprosthesis with the expectation of performing a secondary ‘valve in a valve’ procedure. Further improvements in imaging will also play an important role to refine valve sizing in order to reduce the incidence of aortic regurgitation. Computerised systems derived from conventional angiography will allow three dimensional reconstruction of the aortic root anatomy to facilitate valve placement. Progress in delivery systems and valve manufacturing will eventually overcome what are currently the main limitations of TAVI: lower profile enabling a decrease of the sheath size for the transfemoral approach; and a wider range of prosthetic valve dimensions to adapt to the annulus size better. The new generation devices are also expected to be repositionable, retrievable, and more durable.
The current results suggest that TAVI is feasible and provides haemodynamic and clinical improvement for up to 3 years in patients with severe symptomatic AS at high risk or with contraindications for surgery. Pending questions mainly concern safety and long term durability. Surgeons and cardiologists must work as a team to select the best candidates, perform the procedure, and, finally, evaluate the results. Today these techniques are targeted at high risk patients but they may well be extended to lower risk groups in the future, if the initial promise holds true after careful evaluation.
Transcatheter valve implantation for aortic stenosis: key points
Degenerative aortic stenosis is the most frequent valve disease and is most often observed in elderly patients.
The selection of patients for and performance of transcatheter aortic valve implantation (TAVI) requires close medico-surgical collaboration.
The current candidates for TAVI are patients at high risk or with contraindications for surgery whose life expectancy is not too limited.
Non-invasive evaluation based on echocardiography and multislice CT is key in the evaluation of the feasibility of TAVI.
Transfemoral and transapical approaches are the most frequently used.
With careful screening and experience, the current techniques, either via the transfemoral or transapical approach, achieve a high immediate success rate.
Valve function after TAVI is good in terms of haemodynamics. Mild aortic regurgitation is frequent; however, severe aortic regurgitation is rare.
After a follow-up of up to 3 years haemodynamic and functional results are satisfactory, especially when taking into account the patient's risk profile.
Pending questions remain on safety and long term durability of the valve prosthesis.
Indication for TAVI may well be extended to lower risk groups in the future, if the initial promise holds true after careful evaluation.
You can get CPD/CME credits for Education in Heart
Education in Heart articles are accredited by both the UK Royal College of Physicians (London) and the European Board for Accreditation in Cardiology—you need to answer the accompanying multiple choice questions (MCQs). To access the questions, click on BMJ Learning: Take this module on BMJ Learning from the content box at the top right and bottom left of the online article. For more information please go to: http://www.heart.bmj.com/misc/education.dtl
RCP credits: Log your activity in your CPD diary online (http://www.rcplondon.ac.uk/members/CPDdiary/index.asp)—pass mark is 80%.
EBAC credits: Print out and retain the BMJ Learning certificate once you have completed the MCQs—pass mark is 60%. EBAC/ EACCME Credits can now be converted to AMA PRA Category 1 CME Credits and are recognised by all National Accreditation Authorities in Europe (http://www.ebac-cme.org/newsite/?hit=men02).
Please note: The MCQs are hosted on BMJ Learning—the best available learning website for medical professionals from the BMJ Group. If prompted, subscribers must sign into Heart with their journal's username and password. All users must also complete a one-time registration on BMJ Learning and subsequently log in (with a BMJ Learning username and password) on every visit.
Description of the first transcatheter aortic valve implantation procedure in a human.
Document issued by both medical and surgical scientific societies to set the stage for the use of transcatheter aortic valve implantation.
Comparative evaluation of the predictive value of the risk scores for aortic valve replacement.
Semi-quantitative score for evaluation of life expectancy.
Pioneering publication on the role of echocardiography during transcatheter aortic valve implantation.
Pioneering work on the role of MSCT during transcatheter aortic valve implantation.
The largest single centre series using the balloon expandable prosthesis.
The largest single centre study using the self expandable device.
The largest report on the transapical approach.
Largest North American registry on the transapical approach.
Competing interests In compliance with EBAC/EACCME guidelines, all authors participating in Education in Heart have disclosed potential conflicts of interest that might cause a bias in the article. AV undertakes consulting for Edwards Lifesciences, and DH acts as a physician for Edwards Lifesciences.
Provenance and peer review Commissioned; not externally peer reviewed.
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.