Non-contrast 3-dimensional Cardiac Magnetic Resonance Imaging as Pre-procedural Guidance for Trans-catheter Aortic Valve Replacement in Assessing the Aortic Valve Apparatus

1. Background/Rationale:

Optimizing procedural and patient outcomes relies heavily on tomographic imaging data guidance for patients being evaluated for trans-catheter aortic valve replacement or implantation (TAVR) by providing accurate information of the aortic valve apparatus (aortic annulus and its pertinent neighboring structures). Though selection of the trans-catheter heart valve size was initially driven by echocardiographic data, recently aortic annulus sizing by electrocardiographic gated cardiac computed tomographic angiography (CCTA) is now widely accepted as the "gold-standard" for this purpose. 8 However, CCTA requires administration of iodinated contrast. Most of the patients being considered for (TAVR) have chronic kidney disease. In these patients, avoiding contrast administration and at the same time being able to accurately assess the aortic annulus apparatus (AVA) 1 2 will be of paramount importance. Also with CCTA, the presence of significant or exuberant aortic annulus calcification can make the annulus border delineation challenging, and in some instances practically impossible to demarcate the boundary of the annulus in some of its sectors. This is due to the blooming and shadowing artifacts caused by the calcification.

In these patients, when not contraindicated, a non-contrast cardiac magnetic resonance imaging (CMRI) has been suggested as an alternate method to size the AVA. A free-breathing non-contrast navigator-gated 3D whole-heart acquisition can also be obtained to mimic the volumetric acquisition of a CT image. 1 4 However, in this study by Roos et al that is referenced for this recommendation, the authors used the 3D data set only to measure coronal and single oblique sagittal dimensions of the aortic valve annulus. This was adopted because the coronal view is similar to the anterior-posterior view on aortic root angiography, and the reconstructed sagittal view has the same orientation as the mid-esophageal long-axis view on trans-esophageal echocardiogram. It is now established well beyond doubt that this is not the most accurate way to size the aortic annulus, as the aortic valve annulus is a dynamic complex elliptical or ovoid 3D entity that is also subject to constant shape deformation across the cardiac cycle in addition to being influenced by the thoracic and intra-thoracic anatomy or variations. Ideally, this needs to be done creating a plane that precisely corresponds to the aortic annulus/basal ring which includes all 3 lowest insertion points of the aortic valve cusps (hinge points) by multi-planar reconstructions. A review of literature shows that this method of post-processing CMRI 3D data sets using multi-planar reformats has not so far been validated against the currently available "gold standard" CCTA.

In CMRI, the conventional 2-dimensional (2D) breath-hold cine MRI has been used to assess cardiac anatomy and function. However, this technique requires cooperation from the patient, and in some cases the scan planning is complicated. However, similar to standard echocardiography, most MRI sequences are 2D (i.e. the plane of imaging has to be chosen at the time of the examination and cannot be changed by subsequent manipulation of the data set).2 On the contrary, 3-dimensional (3D) cardiac MRI can overcome some of these problems because it requires minimal planning and can be reformatted in any plane with post-processing. Cardiac MRI using 3D whole heart acquisition protocol may be a practical option for these patients, as this test is able to assess the aortic annulus complex without contrast administration, and without the blooming and shadowing artifacts caused by calcification in some instances. 2. Study Objectives

2.1. Scope and Duration To assess agreement between cMRI and CCTA, 35 subjects with aortic valve stenosis who are referred for pre-TAVR imaging will be selected for the study. The investigators estimate it will take approximately 6 months to reach our target enrollment of 35 patients. There will not be any follow-up visits.