106 - Comparison of Cardiac Anatomy in Tortoises Using CT Scans and Imaging Analysis Software

Poster Board Number: 106
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Abstract Body : There is currently a limited amount of visualized information available for cardiovascular anatomy in tortoises. While limited information is available for their aquatic turtle counterparts, it is likely that the cardiovascular system of fully terrestrial tortoises will differ due to dramatic ecological and locomotor differences. Here, three tortoise species were perfused with BriteVu contrast agent: a leopard tortoise (Stigmochelys pardalis), desert tortoise (Gopherus agassizii), and forest hinge-back (Kinixys erosa). S. pardalis was MicroCT scanned on an NSI scanner, while G. agassizii and K. erosa were scanned on an Epica GT-30 medical CT scanner. Using Avizo 3D software (2021.1), the heart and great vessels of each specimen were segmented and 3D rendered for comparative purposes.
The heart was positioned in the midsagittal plane, bordered by the liver and stomach caudally, forelimb girdles laterally, and neck cranially. The heart was subtriangular with rounded edges and no distinct apex, contrasting from the prominently tapering apex of aquatic turtles. G. agassizii had a rounder, more oval heart than the other two tortoise species. G. agassizii had the thickest pericardial sac surrounding the heart, while S. pardalis has a much thinner but still distinct sac. The pericardium for K. erosa was only visualized by the negative space between the ventricle and other organs, making it the thinnest of the three species. As in other turtles, three chambers were present, a single large ventricle caudally and two smaller atria cranially. The trabeculae carneae of the ventricle were prominent and muscular, in contrast to the comparatively thin-walled atria. The two atria of G. agassizii were asymmetrical in size and shape, with the right atrium being 15% larger than the left with more prominent pectinate muscles. The two atria of K. erosa are similar in size, however they differ in shape, with the right being more oval and the left atrium more subtriangular.
The great vessels of G. agassizii are large and well visualized. The brachiocephalic trunk courses parallel to the left pulmonary artery, before the left and right aortic arches branch out. In K. erosa, a wide gap between the left and right atrium provides a clear view of the brachiocephalic trunk, and its branches can be seen emerging from the ventricle. The sinus venosus in K. erosa is larger than that of G. agassizii. The left pulmonary vein in both specimens is large and can be seen merging with the sinus venosus, while the right pulmonary vein is tucked deeper into the cardiovascular tissue. In S. pardalis, the brachiocephalic trunk appears as the right and left atrium separate, showing the trunk connecting to the ventricle. As in G. agassizii, the brachiocephalic trunk of S. pardalis also initially runs parallel to the left pulmonary artery.
Some notable cardiovascular differences exist in structures among tortoise species. G. agassizii has larger and thicker blood vessels than K. erosa, although the size of the heart is similar in both species. The heart in S. pardalis is larger than the other two species, although the shape is less defined. We observed some functional differences between the hearts of the tortoise species and previously published aquatic turtles, such as a less prominent apex, more symmetrical atrial volumes, and relatively thicker blood vessels. These differences may relate to the different adaptive pressures of living and swimming in a fast-moving stream versus locomoting on land.