Assessment of left atrial fibrosis progression in canines following rapid ventricular pacing using 3D late gadolinium enhanced CMR images

Figures

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  Fig 1. Flow-chart of study protocol and 3D LGE-CMR imaging time points. Six-step study protocol underwent by experimental canines. Control canines underwent the same sequence of events excluding the 5 weeks of rapid ventricular pacing (i.e., the third step in the flow-chart).

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  Fig 2. Image processing pipeline. Steps used to quantify MF in 3D IR-FLASH LGE-CMR images at baseline, in-vivo and in-situ time points.

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  Fig 3. Image processing workflow. Example workflow of LA blood pool and myocardial segmentation using axial dilate and Boolean remove algorithms in in-situ IR-FLASH CMR images. Manual segmentation of the LA blood pool is shown on the left. The axial dilate algorithm expands the blood pool segmentation, as demonstrated in the middle image. The Boolean remove algorithm subtracts the blood pool chamber (left) from the axially dilated segmentation (middle) to reveal the LA wall boundaries. Corrections are done manually to remove erroneous areas as needed, before revealing the final LA myocardial wall segmentation (right).

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  Fig 4. LA enhancement demonstrated in 3D LGE CMR at baseline, post-pacing (in-vivo) and post-mortem (in-situ). A single slice from 3D IR-FLASH LGE CMR acquisitions are demonstrated at baseline (left column), post-pacing (middle) and in-situ (right column) in experimental dog 7 at approximately the same slice location. LA enhancement is demonstrated in the anterior aspect of the LA in post-pacing and in-situ images. Post-pacing images are significantly corrupted by motion artifact due to irregular, elevated heart rate that occurred as a result of pacing.

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  Fig 5. Dot and line plot of %MF changes across time points. Dot and line plot demonstrating the change in percent fibrosis (%MF) over the LA volume for experimental (paced) dogs (right) and control dogs (left) on a per-animal basis. Baseline and post-pacing time points are indicated on the x-axis while LA fibrosis percentage is demonstrated on the y-axis.

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  Fig 6. Rendered 3D volumes of LA myocardium and enhancement regions in experimental animals. Evolution of LA enhancement volumes in three example dogs at baseline (left), post-pacing (middle) and in-situ (right). The LA myocardial volume is rendered in white color, while enhanced regions are depicted in green. The black regions demonstrate regions outside of the myocardium, such as the septum space between the left atrium to left ventricle (such as in Paced dog 9).

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  Fig 7. Rendered 3D volumes of LA myocardium and enhancement regions in control animals. Evolution of LA enhancement volumes in control dogs at baseline (left) and 5 weeks post insertion of pacing device (right) with no rapid ventricular pacing. In-situ 3D-IR-GRE MR images were not acquired in these canines.

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  Fig 8. Histopathological imaging of experimental (2) and control animals (1). Example histopathological images of left atrial samples acquired after Masson’s Trichrome staining. Fibrotic areas are shown in blue while normal tissue is shown in red.