Discussion
To our knowledge, this paper is the first comparison of MDCT to TEE for
the purpose of TMVr planning. Current generation MDCT scanners, with at
least 64-slice technology capable of generating images with
sub-millimetric spatial resolution allow for comprehensive evaluation of
complex mitral anatomy. Quantitative information including leaflet
length and mitral apparatus dimensions can be obtained with MPR, while
volume rendering depicts a 3D assessment of the valve. In our study, we
found that patients evaluated for TMVR/r with MDCT had similar findings
of the mitral valve and valvular apparatus compared to TEE.
Our results found that measurements between MDCT and TEE were not
significantly different for MVA, flail width, commissural diameter, AP
diameter, posterior leaflet length and leaflet thickness. Previously,
Fuechtner et al found that MDCT can diagnose mitral valve prolapse with
high accuracy. Our study also found that MDCT can accurately identify
the pathological leaflet scallop location, discriminate between flail vs
billowing leaflets and characterize leaflet thickening. Shanks et al,
also found that 3D TEE has comparable mitral valve geometry to MDCT
(including similar posterior leaflet length measurement). Sizing of the
mitral annulus is traditionally done with MDCT, though our study found
that measurements were similar among imaging modalities. Additionally,
annular calcification is best assessed with MDCT, yet MAC severity was
also comparable.
We did find a discrepancy of the flail gap measurements. It is unclear
why MDCT tended to overestimate the flail gap. Prior studies have felt
that the four-chamber view on MDCT resulted in an overestimation of
billowing in prolapsed valves [5]. Our CT readers therefore used the
two- and three- chamber reformations on MDCT to measure flail gap,
however we still found a significant difference. We cannot rule out the
possibility that MDCT is more accurate than TEE, and perhaps we did not
appreciate the full extent of flail on TEE. Mitral regurgitation may be
a dynamic process and the volume load (with IV contrast) for MDCT along
with the sedation given during TEE may also lead to real life changes in
the mitral pathology measurements. We therefore can’t exclude the
possibility that the differences found were accurate. Identification of
cleft leaflet is best recognized with 3D TEE. There were two patients in
our study with cleft leaflet, and MDCT was only able to detect the cleft
in one of them. The slit-like appearance of a cleft leaflet can be
difficult to see on 2D TTE or TEE. Cleft leaflets are identified on 3D
TEE. With MDCT, using MPR projections is difficult to assess cleft
leaflet, but with VR 3D imaging we were able to identify one of the
cleft leaflets. However, adjusting the window of the 3D rendered image
can make assessment of thin/soft tissue structures of the mitral leaflet
a challenge, particularly clefts or pseudoclefts.