MULTIMODALITY IMAGING ASSESSMENT OF THE ANATOMY OF THE AORTIC VALVE APPARATUS IN TAVI PATIENTS: IMPLICATIONS FOR PROSTHESIS SIZING AND PARAVALVULAR REGURGITATION

Aortic stenosis (AS) has become the most frequent type of valvular heart disease in Europe and North America. As it primarily presents as calcific AS in adults of advanced age (2–7% of the population >65 years), its prevalence is expected to increase further in the future with an aging population. Severe AS is associated with debilitating symptoms (shortness of breath, angina, dizziness, or syncope), and reduced survival if left untreated. According to European Society of Cardiology guidelines, aortic valve replacement (AVR) is the definitive therapy for all patients with symptoms and severe AS, or severe AS with left ventricular systolic dysfunction. However, approximately the 30% of patients referred for AVR are denied surgery because of advanced age, left ventricular dysfunction or comorbidities. Over the last few years, transcatheter aortic valve implantation (TAVI) has been demonstrated to be a feasible and effective therapeutic alternative to traditional AVR for high-risk surgical patients. Clinical trials have shown TAVI to have outcomes similar to surgical AVR up to 2 years after the procedure and excellent outcomes have been confirmed by registry data, with overall survival of 76% at 1 year. TAVI is an invasive technique whose success depends on multidisciplinary team approach, where imaging fulfils a definite part. Pre-procedure imaging is vital to assess the severity of AS, identify eligible candidates, plan the interventional approach, and select the appropriate prosthesis according to the anatomical features. Imaging is pivotal during and after the procedure, guiding prosthesis deployment, providing information regarding valve position, identifying immediate complications, and assessing outcomes. Before TAVI, accurate evaluation of the aortic root dimensions and anatomy is essential for the selection of eligible candidates for the procedure and to ensure the appropriately sized valve prosthesis is chosen. The objective of this thesis is to investigate the incremental value of a multimodality imaging approach to the evaluation of the anatomy of the aortic valve apparatus in TAVI candidates. Chapter 1 illustrates the feasibility and accuracy of 3D transthoracic echocardiography (TTE) compared to 2D TTE and multidetector computed tomography (MDCT) for the measurement of aortic annulus dimensions in the preoperatory evaluation of 100 patients candidates to TAVI. 3D TTE evaluation was feasible in the majority of the patients with low intra and inter observer variability. 3D TTE and MDCT measurements did not differ significantly, with excellent agreement in the selection of cases with too small or too large annulus (recognized exclusion criteria for TAVI) while, as expected due to the oval shape of the aortic annulus, the 2D TTE annulus area, geometrically derived from 2D TTE diameter, was considerably lower in comparison both with 3DTTE and MDCT planimetric surface area. A good agreement in the choice of prosthetic size in cases scheduled for the procedure was found between the 3D TTE and MDCT. Subsequently, even though it’s known that MDCT provides precise information about the annulus anatomy and remains the gold standard for the pre-operative assessment of TAVI candidates, 3D TTE may play a role in those patients that can’t be studied by MDCT for several reasons such as impaired renal function, severe breathlessness, and arrhythmias. 3D TTE does not require breath-old and contrast infusion, may be obtained at the bedside, in more critical cases, and also in the presence of arrhythmias. Chapter 2 shows that cardiac magnetic resonace (CMR), due to its multiplanar reformatting capabilities, allows accurate short-axis visualization of the aortic annulus and precise measurement of the virtual ring corresponding to the site of prosthesis deployment with high reproducibility and accuracy as compared to MDCT. Moreover, it can estimate the coronary ostia height and aortic valve leaflet dimensions that is a key step for patient selection and procedural planning in order to prevent coronary obstruction during TAVI. In Chapter 3 122 aortic patients were studied to evaluate the capability of 3D transesophageal echocardiography (TEE) to estimate preoperatively the distance between the aortic annulus and the left main ostium (AoA-LM), its accuracy in comparison with MDCT-derived measurements, the ability of the 3DTEE-derived measurements in predicting the stent landing zone as defined by the overlap of the prosthesis with mitral leaflet. The results demonstrated that 3D TEE may estimates the AoA-LM distance as an alternative technique to MDCT. Moreover, 3D TEE allows an immediate evaluation of the distance between the mitral leaflet and aortic prosthesis after the implantation. This measurement was feasible in most of the cases (90%) and also accurate. In fact the 3D TEE computed prosthesis was similar to the prosthetic nominal value. Pre and post 3D TEE data concerning the valve and prosthesis morphology and simultaneous real time evaluation of the aortic root including the LM coronary ostium give new insights regarding TAVI and its complications. Chapter 4 suggests that intraoperative 2D and 3D TEE may allow the identification of predictors of significant paravalvular aortic regurgitation (PAR) following successful TAVI. In particular, incomplete device expansion due to aortic valve calcifications is believed to be one of the contributing factors to PAR post-TAVI. In fact, heavily calcified native aortic valves may not allow a perfect apposition of the device along the annulus circumference. Our data, collected in 135 TAVI patients, show that the calcifications of the commissure between the right coronary and non-coronary cusp is related to significant post-procedural PAR. Moreover, the measurement of an “area cover index”, defined as the percentage difference between planimetered aortic annulus area and the nominal prosthesis area, should be considered during patient selection for TAVI. As a low “area cover index” predicts the development of significant post-procedural PAR, this index could be utilized as an additional parameter when choosing the prosthetic size in all those patients with borderline 2D TEE annulus size. Probably a certain degree of prosthetic oversizing is needed in order to minimize the development of significant PAR after the procedure. Chapter 5 shows that, in accordance with previous results, the lack of congruence between prosthesis and annulus size is associated with significant PAR. MDCT is a valuable modality for detecting the mismatch between prosthesis area and aortic annulus area and for predicting PAR. In details, a mismatch of 61.5 mm2 between prosthesis size and aortic annulus area measured by MDCT is a predictor of PAR. In conclusion, advanced cardiac imaging modalities (3D echocardiography, MDCT and MRI), besides standard 2D echocardiography and angiography, play a crucial role in the diagnostic process and management of TAVI patients, allowing proper selection and planning, optimizing the procedure and increasing TAVI success. Echocardiography is the cornerstone of pre-procedure evaluation, complemented by MDCT. Both 3D TTE/TEE and MDCT have a higher predictive value for PAR than 2D echo measurements and have been shown to change valve sizing strategy compared with 2D echo. During TAVI, 2D, and particularly 3D, TEE can be used for guidance and, allowing the visualization of the left main ostium and the measurements of its distance from the annulus, increases the procedure safety. In the future, as patients undergoing TAVI might be younger, CMR might gain significance by the absence of radiation issues.