CT imaging
Preoperative and postoperative evaluation of LA, LAA and adjacent
structures was performed by CCTA (Somatom Definition, Siemens Medical
Solutions, Forchheim, Germany). The temporal resolution is 330 ms, the
detector collimation is 64*0.6 mm, the tube voltage of 120 kV and tube
current of 380 mA. 100 ml contrast medium was injected with 50 ml saline
flush followed through elbow vein at the rate of 5 ml/s.
Image analysis was performed by the Extended Brilliance Workspace
version 4.5 (Philips Healthcare Cleveland, OH, USA). All images were
analyzed by two blinded, experienced
radiologists. Evaluating the
consistency of the measurement results between
the two radiologists, the mean
values of each CT indicator were taken for follow-up analysis. In case
of disagreement in the evaluation process, the two radiologists
reevaluated and discussed to reach a consensus.
Measurements were made of the maximum diameter of LAA orifice at the
preoperative CCTA images. The double-oblique orthogonal view of LAA
orifice is obtained by the method of multi-planar imaging reconstruction
(Figure 1). The orifice was defined as the plane between the circumflex
artery and a point 15 ± 5 mm from the tip of the limbus, reflecting as
closely as possible the site where the proximal aspect of the Watchman
device would be expected to expansion.
Preoperative left atrial volume (LAV) and left atrial appendage volume
(LAAV) were measured by Mimics Medical 17.0 (Materialise NV, Leuven,
Belgium). The thinfilm cross sectional images generated by CCTA were
imported into the Mimics in the DICOM data format. Images at the end
systolic cardiac phase (when the LA cavity was largest) were selected as
original data. Tissues connected to LA were then separated based on 3D
model. Separation of LA and left ventricle was bounded by the mitral
valve annulus. Pulmonary veins (PV) and LAA were separated by the PV
ostia and LAA orifice, respectively (Figure 1). LAV and LAAV were
automatically calculated by Mimics. The specific details were described
as our previous essay[6].
PDL and device endothelialization were evaluated at the postoperative
CCTA images. CT workspace was used to reconstruct the original CCTA
images in 3D multi-planar, and the axial plane should be at the level of
LA. For the Watchman device, first observe the position of the nitinol
skeleton of the device. Afterwards, move the coronal axis within the
transverse window perpendicular to the coves of the parachute of the
device. Afterwards, align the axes on the two other viewers also
perpendicular to the coves of the parachute of the device. Lastly, the
center of the axes should be placed to the center of the screw-hub. With
all of the above imaging steps, the LAA occluder view for
post-implantation evaluation (LOVE) could be
established[7].
Quantitative contrast assessment of LAA was carried out by
measuring the average linear
attenuation coefficient (Hounsfield units [HU]) in the LAA distal to
the implanted device, using a circle diameter of 3 mm for the region of
interest. PDL was defined as the
average linear attenuation coefficient of LAA was more than 100 Hu, and
continuous contrast enhancement was
observed from LA to LAA along the side of the
device[8]. Incomplete endothelialization was
defined as the average linear
attenuation coefficient of LAA was more than 100 Hu, and continuous
contrast enhancement was observed from LA to LAA through the fabric of
the device (“fabric leak” from diffusion of contrast through the
non-endothelialised polyethylene terephthalate membrane). The average
linear attenuation coefficient less than 100 Hu was defined as LAA
complete occlusion[7].