Patient Selection and Echocardiographic Assessment

Indications for TAVI are still evolving. Patients currently excluded from TAVI (with the currently available Edwards Sapien series of prostheses) are those eligible for conventional surgical valve replacement, or in whom the aortic annular diameter is <18 or >26 mm, or if a reasonable quality or duration of life is unlikely after TAVI. Preprocedural transthoracic echocardiography (TTE) is an essential component in the evaluation of patients for TAVI. As described previously, preliminary assessment by TTE consists of a standard transthoracic examination, with special attention paid to the aortic annular dimension, the severity and mechanism (subvalvular, valvular, or supravalvular) of aortic stenosis, and the distribution and severity of valve calcification. Transesophageal echocardiography (TEE) is recommended if the aortic annular diameter cannot be accurately assessed because of poor transthoracic imaging windows. The annular diameter is essential for sizing the aortic prosthesis. At our institution, a 23-mm valve is considered suitable for an aortic annulus between 18 and 22 mm, while a 26-mm valve is implanted when annular diameter is 23 to 26 mm. Other important elements to note on preprocedural TTE include left ventricular size and function, wall thickness, pulmonary artery pressure, and the presence and severity of mitral and aortic regurgitation.

TEE should be performed routinely during TAVI to guide valve deployment. Prior to valve deployment, it is important to carefully assess aortic anatomy, including the aortic annulus, left ventricular outflow tract, and aortic sinuses. Careful attention should be paid to the volume and distribution of aortic valve calcium. Heavy aortic and or mitral calcification can interfere with prosthesis visualization at the time of deployment, especially at the ventricular aspect. It is also important to note the size of the aortic sinuses. The combination of small aortic sinuses with bulky calcified aortic leaflets in the setting of a small annular diameter may increase the incidence of aortic annular rupture. Careful baseline assessment of left ventricular function, wall motion abnormalities, mitral regurgitation, and pericardial fluid is vital in rapid problem solving should procedural complications occur.

TEE at the time of valve deployment and immediately after deployment has been described previously. Prompt assessment and communication of any adverse periprocedural findings on TEE to the implanting physician is paramount. Serious complications of TAVI, such as annular rupture, coronary artery occlusion, prosthesis malposition, and severe aortic regurgitation, may occur. These can be minimized with clear communication and a team-based approach to valve deployment.

Transcutaneous Aortic Valve Implantation Outcomes and Comparison With Surgical Aortic Valve Replacement

For TAVI to be a viable first-line treatment for aortic stenosis, a number of factors need to be addressed. In comparison with the surgical standard, TAVI must be shown to be noninferior with respect to morbidity and mortality, valve hemodynamics, and valve durability in equivalent population groups. Procedural success and short-term and intermediate-term outcomes to 1 year after the procedure with TAVI have already been described. Bauer et al details a single-center experience with echocardiographic data out to 2 years after TAVI. Similar to previous studies, Bauer et al detail similar short-term and intermediate-term outcomes after TAVI with regard to improvement in aortic valve area, reduction in peak and mean aortic valve pressure gradients, reduction in end-systolic left ventricular volume, improvement in left ventricular ejection fraction, and postimplantation aortic regurgitation severity. Bauer et al also show that at 2 years after TAVI, ejection fraction, left ventricular volumes, aortic valve gradients, and aortic valve area were similar to the 1-year follow-up values.

The improvement in ejection fraction occurs early and is due to a reduction in end-systolic volume. These results are best explained by an early reduction in afterload following successful TAVI and argue against significant late remodeling, at least out to 2 years. As stated by Bauer et al, a number of factors have been described in the setting of SAVR that adversely influence reverse remodeling. These include left ventricular hypertrophy, coexisting coronary artery disease, diastolic dysfunction, and sphericity index. In addition, a recent prospective cardiac magnetic resonance imaging study demonstrated that the degree of myocardial fibrosis predicts long-term outcome after surgical aortic valve replacement. The influence on remodeling of these and other factors, such as vascular impedance, is yet to be delineated in the TAVI group. More advanced techniques, such as three-dimensional (3D) echocardiography and magnetic resonance imaging, may be required to flesh out our understanding of remodeling in these patients.

Larger patients or those with small aortic annuli who are at risk for patient-prosthesis mismatch might potentially derive special benefit from TAVI. Severe patient-prosthesis mismatch (indexed valve effective orifice area ≤ 0.65 cm ² /m ² ) has been associated with increased morbidity and mortality rates at short-term and midterm follow-up after SAVR. For a given annular size, hemodynamics are likely to be superior with TAVI compared with SAVR, with the possible exception of certain newer generation mechanical valves. This is largely because the Sapien valve does not have a sewing ring or occluders, allowing it to realize more of its potential orifice area. The choice of TAVI, especially in patients with small annular dimensions, reduces the incidence of patient-prosthesis mismatch or may avoid the need for an aortic enlargement procedure.

An increased incidence of aortic regurgitation is noted after TAVI compared with SAVR. The aortic regurgitation can be valvular or paravalvular, often at the commissures of the native aortic valve, and may be more common with heavily calcified native aortic valves. Earlier concerns that aortic regurgitation would emerge as a significant limitation with TAVI have not so far materialized. The majority of aortic regurgitation is paravalvular but is mild in severity and decreases over time. Paravalvular aortic regurgitation has not been associated with hemolysis.

Transcutaneous Aortic Valve Implantation Outcomes and Comparison With Surgical Aortic Valve Replacement

For TAVI to be a viable first-line treatment for aortic stenosis, a number of factors need to be addressed. In comparison with the surgical standard, TAVI must be shown to be noninferior with respect to morbidity and mortality, valve hemodynamics, and valve durability in equivalent population groups. Procedural success and short-term and intermediate-term outcomes to 1 year after the procedure with TAVI have already been described. Bauer et al details a single-center experience with echocardiographic data out to 2 years after TAVI. Similar to previous studies, Bauer et al detail similar short-term and intermediate-term outcomes after TAVI with regard to improvement in aortic valve area, reduction in peak and mean aortic valve pressure gradients, reduction in end-systolic left ventricular volume, improvement in left ventricular ejection fraction, and postimplantation aortic regurgitation severity. Bauer et al also show that at 2 years after TAVI, ejection fraction, left ventricular volumes, aortic valve gradients, and aortic valve area were similar to the 1-year follow-up values.

The improvement in ejection fraction occurs early and is due to a reduction in end-systolic volume. These results are best explained by an early reduction in afterload following successful TAVI and argue against significant late remodeling, at least out to 2 years. As stated by Bauer et al, a number of factors have been described in the setting of SAVR that adversely influence reverse remodeling. These include left ventricular hypertrophy, coexisting coronary artery disease, diastolic dysfunction, and sphericity index. In addition, a recent prospective cardiac magnetic resonance imaging study demonstrated that the degree of myocardial fibrosis predicts long-term outcome after surgical aortic valve replacement. The influence on remodeling of these and other factors, such as vascular impedance, is yet to be delineated in the TAVI group. More advanced techniques, such as three-dimensional (3D) echocardiography and magnetic resonance imaging, may be required to flesh out our understanding of remodeling in these patients.

Larger patients or those with small aortic annuli who are at risk for patient-prosthesis mismatch might potentially derive special benefit from TAVI. Severe patient-prosthesis mismatch (indexed valve effective orifice area ≤ 0.65 cm ² /m ² ) has been associated with increased morbidity and mortality rates at short-term and midterm follow-up after SAVR. For a given annular size, hemodynamics are likely to be superior with TAVI compared with SAVR, with the possible exception of certain newer generation mechanical valves. This is largely because the Sapien valve does not have a sewing ring or occluders, allowing it to realize more of its potential orifice area. The choice of TAVI, especially in patients with small annular dimensions, reduces the incidence of patient-prosthesis mismatch or may avoid the need for an aortic enlargement procedure.

An increased incidence of aortic regurgitation is noted after TAVI compared with SAVR. The aortic regurgitation can be valvular or paravalvular, often at the commissures of the native aortic valve, and may be more common with heavily calcified native aortic valves. Earlier concerns that aortic regurgitation would emerge as a significant limitation with TAVI have not so far materialized. The majority of aortic regurgitation is paravalvular but is mild in severity and decreases over time. Paravalvular aortic regurgitation has not been associated with hemolysis.