Digital Theses Archive


Tesi etd-03272019-163059

Type of thesis
Ischemic Mitral Valve Regurgitation: The Quest for Valve Repair Prognostic Factors.
Scientific disciplinary sector
SCIENZE MEDICHE - Translational Medicine
  • CT
  • Ischemic Mitral Regurgitation
  • Mitral Valve Imaging
  • Mitral Valve Surgical Anatomy
  • MRI.
Exam session start date
Background: New minimally invasive and percutaneous techniques are being developed to repair and replace the mitral valve (MV). These procedures rely upon the knowledge of the exact structure of the MV and its surrounding structures. However, there has not been a standard method identified to accurately assess the MV apparatus. Therefore, we sought first to perform an anatomic study to evaluate various structures associated with the MV apparatus in 40 cadaveric human hearts. <br>The anatomic study will serve as baseline for comparison with a subsequent pilot imaging study, consisting of retrospective in vivo assessment of MV and associated structures with cardiac computed tomography (CT) and magnetic resonance imaging (MRI). Main anatomic structures were qualitatively assessed on both imaging methods using a 5 point Likert scale. Imaging measurements were compared with anatomic study measurements.<br>Anatomical Study: Forty human cadaveric hearts from rejected donors with normal MV anatomy were studied. The hearts were dissected in a standardized approach as to preserve the valve structure. Measurements of several MV anatomic features were taken and compared to other spatially related cardiac structures. Dissections and measurements were performed by a single trained individual. The median annular circumference and area were 101mm (98-105) and 8.11cm2 (7.33-8.85) respectively. Body surface area correlated with the secondary chordae length of segment A2 (r = 0.584), A3 (r = 0.484), and tertiary chordae length of segment A2 (r = 0.569). The length of segment A2 correlated with annulus circumference (r = 0.640) and annulus area (r = 0.626). The circumflex artery was between 7.4-9.0mm on average cranial and 4.3-5.7mm posterior to the annulus. While, the coronary sinus was between 5.6-9.6mm on average cranial and 3.5-4.9mm posterior to the annulus. The annulus area &amp; circumference are independent of body surface area (BSA), gender, and age.<br>The MV apparatus complexity has been a large factor in hindering progress in MV repair techniques and more recently in transcatheter aortic valve repair and replacement. However, a better understanding of the MV apparatus radiographically could help strengthen transcatheter technology. <br>At this time transesophageal echocardiograms (TEE) are utilized for cardiac structure but cardiac MRI and cardiac CT are starting to add value in clinical practice ad to be used as an adjunct. However, no well-defined protocol is present for this technique.<br>Imaging Study: This was a pilot monocentric trial with the aim to study mitral valvular and subvalvular apparatus comparing two imaging modalities, Cardiac MRI and Cardiac CT scan. A retrospective search was performed in UT Southwestern’s Picture and Archive System for dynamic cardiac CT (4D-CT) obtained between January and June of 2017 in a subject with at least one prior cardiac MRI within the prior 12 months. A total of 12 subjects were identified in the search.<br>Cardiac CT were acquired with multi-detector scanners with 320 rows (Acquilion One, Toshiba, Japan) or 64 rows (iQon CT, Philips, the Netherlands), using 80 kVp, 100 kVp, or 120 kVp and automatic tube current modulation according to body size and clinical protocol and retrospective ECG-gating.<br>MRI scans were acquired using a 1.5 T MR scanner (Achieva, Philips, the Netherlands), using ECG-gated steady-state free-precession sequence with segmented k space reconstruction, resulting in 20 temporally resolved images equally spaced through the cardiac cycle.<br>Two readers assessed images, one radiologist with cardiothoracic training and 9-year experience with cardiac imaging, a cardiac surgeon and a medical student trained during a three months’ period by the same radiologist. The structures that were measured were the mitral annulus circumference, mitral annulus area, anterior and posterior papillary muscle (PM) length and length to apex, A2/P2 length, P1-3 Annulus to coronary sinus midpoint, P1-3 Annulus to circumflex artery midpoint, septal thickness, anterior/posterior PM to annulus distance, and distance to left atrial appendage ostium from posterior mitral annulus.<br>Overall, this pilot study was able to show that the cardiac CT images were far superior in evaluating subtler structures in comparison to cardiac MRIs. For the quality analysis, cardiac CT and cardiac MRIs images were read and assessed for the quality of certain cardiac structures on a Likert (Likert Rensis 1932) scale of 1-5. The scale reads as a 5 = excellent, 4 = good, 3 = fair, 2 = poor, 1 = unusable. Our cardiac imaging quality analysis allowed us to compare the quality of the MRI and CT.<br>Due to the difficulty in analyzing images from the MRI, another method to quantitatively analyze the images was developed. The analysis shows that the CT images have a higher quality score in every structure in comparison to the MRI images. The MRI images have lower quality scores in every structure but have a lower standard deviation (SD) in comparison to the CT images.<br>