Aortic stenosis (AS) has become a major cause of morbidity and mortality among a growing population of older adults. Transcatheter aortic valve implantation (TAVI) has rapidly evolved in response to this clinical challenge. The appropriate patient for a TAVI procedure typically has symptomatic senile degenerative AS of a trileaflet valve. However, other indications are growing or being evaluated such as aortic regurgitation, bicuspid valve or valve-in-valve in degenerative bioprosthetic surgical valves. The purpose of this review is to discuss and to evaluate the factors in a degenerative AS patient which can aid in the decision to refer for TAVI.
Indications for transcatheter aortic valve implantation
Current recommendations by the European Society of Cardiology (ESC) in Guidelines on the management of valvular heart disease are that TAVI should be carried out in patients with a life expectancy >1 year, they should be deemed inoperable (or high-risk) by a cardiac surgeon and they should be likely to gain improvement in quality of life; there should be no absolute contraindication (Table 1). As a consequence of the present insufficient scoring systems for the definition of the individual risk associated with TAVI, we have observed a shift in the use of TAVI towards the so-called intermediate-risk patient population in Europe. This fact is already reflected by promising results in the intermediate-risk population of trials and registries such as NOTION and GARY. However, these data are being analyzed in the randomized controlled SURTAVI trial and the PARTNER IIA trial comparing the outcomes of TAVI and surgical aortic valve replacement (SAVR), respectively, in intermediate-risk patients. The results of these trials and the durability of the transcatheter valve will further clarify the expansion of the indication for TAVI to intermediate-risk patients. This review focuses on high-risk patients.
Table 1. Contraindications for TAVI.
|Absolute contraindications||Relative contraindications|
Absence of a "Heart Team" and no cardiac surgery on the site.
Appropriateness of TAVI, as an alternative to SAVR, not confirmed by a “Heart Team”.
Estimated life expectancy <1 year. Improvement of quality of life by TAVI unlikely because of comorbidities.Severe primary associated disease of other valves with major contribution to the patient’s symptoms that can be treated only by surgery.
Inadequate annulus size (<18 mm, >29 mm).
Thrombus in the left ventricle.
Elevated risk of coronary ostium obstruction (asymmetric valve calcification, short distance between annulus and coronary ostium, small aortic sinuses).
Plaques with mobile thrombi in the ascending aorta, or arch.
For transfemoral/subclavian approach: inadequate vascular access (vessel size, calcification, tortuosity).
Bicuspid or non-calcified valves.
Untreated coronary artery disease requiring revascularization.
For the transapical approach: severe pulmonary disease, LV apex not accessible.
LV: left ventricle; LVEF: left ventricular ejection fraction; SAVR: surgical aortic valve replacement; TAVI: transcatheter aortic valve implantation
A key recommendation from the ESC Guidelines is that individual cases should be discussed within a multidisciplinary “Heart Team” and should only be performed in hospitals with cardiac surgery on-site.
Optimal patient selection is critical to a successful TAVI procedure. This is very much a multidisciplinary approach, a collaborative exercise for the heart valve team. The responsibilities of the Heart Team include case screening, deciding the optimal treatment strategy, planning the procedure details, as well as detailing the post-procedure management.
The thought process behind patient selection can be divided into a clinical assessment and then anatomical assessment.
Clinical suitability is the primary requirement for the selection of a patient for TAVI and includes different aspects such as:
- Symptoms evaluation
- Surgical risk scoring
- Patient frailty
The appropriately selected TAVI patient must be symptomatic but the typical AS patient is older. In this population effort-related symptoms are difficult to assess because of comorbidity. Indeed, no clear relation between symptoms or NYHA class and mortality in older patients has been proved. Symptoms are commonly misinterpreted as part of the aging process.
Surgical risk scoring
The risk assessment is currently guided by calculation of either the logistic EuroSCORE (LES) or the Society of Thoracic Surgeons (STS) score. A patient is considered high-risk when the logistic EuroSCORE is >20%, the EuroSCORE II is >10% or the STS score is >10% (ACC/AHA guidelines now consider >8%). However, conventional risk scores do not provide a reliable estimate of exact operative mortality in an individual patient with valvular heart disease and especially in patients who are candidates for TAVI.
Several characteristics which may increase surgical risk (radiation, porcelain ascending aorta, multiple prior chest surgeries), or which may contraindicate TAVI (small aortic annulus, short distances between the coronary ostium and annulus) are not included in the STS score or EuroSCORE, giving these scores poor discriminatory ability for adverse outcomes following TAVI. In the absence of a perfect quantitative score, European Guidelines recommend that the risk assessment should rely principally on the clinical judgment of the “Heart Team”, in addition to the combination of scores.
Comorbidity and patient frailty
As TAVI is reserved mainly for patients at high risk and who are older, they have elevated comorbidity. Comorbidity (chronic obstructive pulmonary disease, pulmonary hypertension, liver disease, prior stroke, anemia, chronic kidney dysfunction, cognitive deterioration) has great influence on the prognosis. For these reasons the inclusion in the preoperative evaluation of the Charlson comorbidity index is useful for predicting events in patients undergoing TAVI. In some studies patients with severe symptomatic AS and high comorbidity (Charlson index ≥5) have a poor prognosis in the short term and do not seem to benefit from interventional treatment. Although frailty is a relatively easy concept to describe, it is much more difficult to define and measure clinically. Different tests for the measurement of frailty are described but only indices that include poor mobility predict better/worse survival.
However, discussion on individual patient management should take place in the Heart Team with a balanced evaluation between survival and expected quality of life versus risk of complications.
All patients presenting for TAVI need evaluation of the arterial vasculature and aortic valve complex (left ventricular outflow tract, annulus, sinus of Valsalva, sinotubular junction and ascending aorta) in order to determine the annular size and approach (transfemoral, apical, transaortic, subclavian).
The main limitation of a transfemoral approach is the arterial diameter, while tortuosity and calcification have also been described as important determinants for the selected route. Currently, a minimal diameter larger than 6 mm is necessary. There are smaller aortoiliac tract diameters measured on computed tomography angiography (CTA) compared to projection measurements on angiographic images. CTA shows calcium distribution in the artery that can help in the procedure.
Aortic valve complex
An accurate evaluation of annular size is of maximal importance. Underestimation of its dimensions could lead to selection and deployment of a smaller valve, with possible complications such as paravalvular regurgitation (PAR), poor hemodynamics, valve migration and embolism. Overestimation of annular size and deployment of a larger valve can lead to incomplete unfolding (with PAR as a consequence) or annular rupture.
Transthoracic echocardiography (TTE), transesophageal echocardiography (TEE), multislice computed tomography (MSCT) and iliofemoral angiography are complementary imaging techniques which can be used to evaluate aortic valve function and anatomy.
Traditionally, sizing has been based upon a direct measurement of annulus diameter in the long-axis plane by 2D echocardiography techniques. This method has limitations, and several other methods have been used to measure the annulus diameter.
In patients referred for TAVI, measurements of the aortic annulus using TTE, TEE, and MSCT were close but not identical. The method used has important potential clinical implications on TAVI strategy. The annulus size is in general 1 mm smaller by TTE than by TEE, and the TEE measurement is 1 to 1.5 mm smaller than MSCT measurements.
Echocardiography (TTE or TEE) remains the technique most used to assess the aortic annulus; nevertheless, with more means of data acquisition in the near future, 3D imaging modalities such as CT and 3D echocardiography are preferred for assessing the anatomy and dimensions of the aortic annulus and root before TAVI. 3D transesophageal echocardiography and MSCT have been shown to be superior to 2D echocardiography for the prediction of PAR and have been shown to alter the choice of valve prosthesis. In a controlled clinical trial, the use of MSCT led to a reduced incidence of PAR. For these reasons, 3D techniques will probably become the primary imaging modality to do this. However, it is likely that new prostheses with sealing cuffs to mitigate PAR may further reduce its incidence without the need for aggressive oversizing.
An important point is the distribution of calcification, especially calcification of the device landing zone, particularly if located inferior to the annulus, because is associated with residual PAR after TAVI. Indeed, the incidence of paravalvular leakage differs significantly according to the prosthesis type implanted.
The measurements necessary before TAVI include:
- Identification and quantification of aortic stenosis
- Number of valve cusps
- Extent and distribution of calcification
- Sinus dimensions
- Effective annular diameter
- Height of the coronary ostium above the valve annulus
- Basal septal hypertrophy
- Presence and severity of mitral valve disease
Patient selection for TAVI is based on accurate assessment of aortic stenosis, both clinical and anatomical. The Heart Team is key in the risk evaluation of this population. 3D imaging modalities are preferred for assessing the anatomy and the dimensions of the aortic annulus before TAVI. In any case, we should tailor our patient selection and prosthesis selection on a case-to-case basis.
This article is supported in the form of an unrestricted educational grant by Edwards Lifesciences.