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Place of imaging in aortic valve intervention

I had the pleasure to co-chair with Dr. Unger (Brussels, Belgium) on Friday December 9th afternoon a fantastic session on the place of imaging in aortic valve intervention.

First, Dr. Pressman gave us his interpretation of the guidelines in the presentation entitled: “AV interventional: the place of imaging in the guideline”. He highlighted that assessment of aortic valve disease severity has three components, namely anatomic, hemodynamic and its consequences including symptoms. In aortic stenosis (AS) the class I indications for aortic valve intervention are, in severe AS patients, the presence of symptoms, the need for another open-heart surgery or the presence of an impaired left ventricular ejection fraction, below 50%. Interestingly, the assessment of severe AS is not as easy as expected, and the non-circular shape of the left ventricular outflow tract and pressure recovery have to be considered. In asymptomatic patients with severe AS, exercise testing is recommended to unmask symptoms or a decrease in systolic blood pressure or exercise tolerance. Moreover, exercise stress echocardiography is also useful to evaluate the increase in mean gradient. Additionally, in asymptomatic patients, the presence of very severe (peak aortic jet velocity≥5 or 5.5 m/s), rapid progression (increase in peak aortic jet velocity≥0.3 m/s) or excess hypertrophy (without clear definition) prompted a class IIb indication for aortic valve replacement. Regarding transcatheter intervention, the use of transoesophageal or transthoracic echocardiography (i.e. complete anesthesia vs. sedation) during the procedure remains an important debate, as well as treatment of bicuspid patients in whom the left ventricular outflow tract is larger and heavy bulky calcification is feared. Indeed, calcification of the landing zone of the prosthesis has been shown to predict the presence and severity of paravalvular leak. In aortic regurgitation (AR), class I recommendations for surgery are: severe AR with symptoms, the need for another open-heart surgery or decreased LV ejection fraction. Severity of AR could be evaluated by vena contracta, proximal isovelocity surface area and holodiastolic flow reversal in the descending aorta. Class IIa or IIb indications for surgery are left ventricular end systolic diameter≥50mm or indexed ≥25, left ventricular end diastolic diameter≥65 or 70mm according to American or European guidelines. In mixed AS/AR, peak aortic jet velocity has been shown to be useful to predict events. However no specific recommendation has been made regarding these patients.

Then, Dr. Delgado talked about the “Role of the imager in the heart team” especially in transcatheter aortic valve intervention (TAVI). A heart team should be composed of cardiologists, cardiac surgeons, anesthesiologists, imaging specialists (echocardiography, computed tomography and magnetic resonance) as well as other specialists such as geriatricians. The role of the imager would be in patient selection, procedure planning, peri-procedural and post-procedural evaluation: thus, at any step. Dr. Delgado focused on the two first steps (the other steps were covered by the following lecturers). In patient selection, the assessment of aortic disease is essential, as well as the degree of calcification of the valve, aortic root and LV outflow tract. Besides echocardiography, computed tomography is also essential for sizing of the valve with measurement of the aortic annulus in systole. When images cannot be acquired in systole, 3D echo could be a good alternative. The preferred access is the transfemoral route and computed tomography would be important to assess calcification of peripheral arteries. Also, it could help in the transaortic route to decide how to access the aorta or in the transapical route to locate the apex of the heart. Angiography has also an important role in evaluating coronary artery disease, sizing the aorta and peripheral arteries. Echocardiography remains essential to evaluate LV ejection fraction, given that up to 40% of patients will have an impaired LV ejection fraction. However, as opposed to surgery, a decreased LV ejection fraction has no impact on outcome after TAVI. Mitral regurgitation also has to be evaluated by echocardiography given that up to 30% of patients have ≥3+ mitral regurgitation. Moreover, mitral regurgitation increases 30-day mortality with probably more impact in self-expendable valves. Interestingly, mitral regurgitation may improve after TAVI. Finally, tricuspid regurgitation and pulmonary hypertension are also factors of increased 1-year mortality. Thus imagerscan help better select patients for TAVI and plan the intervention.

Leaving TAVI aside for a while, Dr. Chambers focused on surgical prosthesis and the importance of prosthesis patient mismatch (PPM). All prostheses are obstructive compared to a native aortic valve, however, PPM has to be noticed when moderate (indexed aortic valve area: AVAi ≤0.85cm2/m2) or severe (AVAi ≤0.65cm2/m2). PPM is actually a common finding after surgery, with up to 70% of moderate PPM in aortic as well as in the mitral position, and up to 11% of severe PPM. It has been shown that severe PPM has an impact on 30-day mortality in patients with normal LV function and that even moderate PPM has an impact on 30-day mortality in patients with impaired LV function. In late outcome, the effect is probably more complex, with more importance in young, diabetic, non-obese patients and when LV ejection fraction is decreased. PPM also has a negative effect on LV mass decrease, especially in patients older than 70 years of age. Finally, PPM seems to accelerate deterioration of the bioprothesis. Importantly, label sizes of the valves are not related to annulus diameter or prosthesis effective orifice area. It is thus important to use the prosthesis effective orifice area provided in the literature in order to calculate the index effective orifice area before surgery and avoid severe and/or moderate PPM. However, strategies such as aortic root enlargement have failed to improve outcomes of patients and in a borderline patient for TAVI referral, TAVI would be the best strategy to avoid PPM given that the hemodynamic performance of TAVI prostheses is better than surgical ones and PPM after TAVI is less frequent than after surgery. However, strategies to avoid PPM have to be individualized for each patient.

Last but not least, Dr. Pierard reviewed the role of imaging in complications after AV intervention. Complications after AV intervention may appear during the procedure, as well as long term after it, and in all cases, imaging is essential. However, the major question is the necessity of echocardiography or the sufficiency of fluoroscopy. Early during the procedure, complications of severe AR could occur after balloon valvuloplasty. At that time, the treatment would be rapid deployment of the prosthesis. During valvuloplasty, echocardiography can also reveal the risk of coronary occlusion that is a rare but important complication and could possibly be avoided by the use of echocardiography. AR after valve deployment could occur due to malpositioning of the prosthesis or as a consequence of annulus calcification. In any case, the rapid detection and gradation of the leakage is essential to decide on further corrective procedures. Indeed, an AR index could be calculated by dividing the systolic blood pressure by the LV end diastolic pressure measured by catheter. An AR index<25% has been shown to predict increased 1-year mortality in patients with moderate AR, but also in patients without AR. Thus, this index is probably related to more than only AR. Cardiac magnetic resonance is useful for AR quantification, and is probably more reproducible than echocardiography. However, access is limited, and it cannot be used intra-procedurally. Nevertheless, a regurgitant fraction of 30% was shown as a better predictor of poor clinical outcome. Increasing class of AR severity increased the mortality at 1 year, thus the management of AR during the procedure is essential. After prosthesis deployment, any degree of AR should be quantified by echocardiography and if AR is mild to moderate in a vulnerable patient or moderate and more, AR should be corrected. Corrective procedures that can be applied include balloon post-dilation, valve in valve (i.e. implantation of a second transcatheter valve within the first one) or percutaneous leak closure. Migration of the valve, ventricle perforation, aortic dissection and aortic root rupture may be visualized by echocardiography and by angiography. Finally, mid and long term dysfunction of the prosthesis, such as structural deterioration, thrombus, pannus or endocarditis could be evaluated by transthoracic echocardiography. Numerous complications of TAVI can be revealed by imaging. Preventing complications should be the first step. Acute peri-procedural complications are often better visualized by transoesophageal echocardiography than by fluoroscopy, and given that rapidity of detection is often essential, echocardiography should be used routinely for peri-procedural assessment of transcatheter prosthesis.

This session thus emphasized the important role of imaging in selecting patents for aortic valve intervention, planning the type and access of the procedure, managing acute intra-procedural complications and following patients after the procedure. Multimodality imaging including transthoracic and transesophageal echocardiography, computed tomography, angiography and possibly cardiac magnetic resonance imaging is key to success in aortic valve intervention.

The content of this article reflects the personal opinion of the author/s and is not necessarily the official position of the European Society of Cardiology.