# Reference Values for Postmortem Examination of the Heart in the Macropod (Macropodidae) and Koala (Phascolarctidae)

## TL;DR

This study provides heart reference values for macropods and koalas to improve postmortem cardiac assessments in these Australian marsupials.

## Contribution

The paper introduces species-specific postmortem cardiac reference values for macropods and koalas, which were previously unavailable.

## Key findings

- Heart weight to body weight ratios in macropods are comparable to domestic species.
- Koalas show lower heart weight to body weight ratios and higher variability in left-to-right ventricle ratios.
- Reference values help identify cardiac disease in macropods and koalas through postmortem examination.

## Abstract

Morphological assessment of the heart is an integral component of postmortem investigation of sudden death and cardiac disease in domestic animals and wildlife species. Reference values for these parameters have been published for domestic species, however, no postmortem reference values for these morphometrics are available for Australian marsupials, such as macropods (Macropodidae: kangaroos, wallabies, tree kangaroos, and others) and koalas (Phascolarctos cinereus). Species-specific reference values presented in this study facilitate objective and improved postmortem cardiac assessment in macropods and koalas.

Morphometric cardiac reference values are reported for macropods and koalas (Phascolarctos cinereus). Body weight (BW), heart weight (HW), left ventricle (LV) wall, interventricular septum (S), right ventricle (RV) wall thickness, and LV+S and RV weights were measured at postmortem examination of 48 macropods and 32 koalas that had no evidence of cardiovascular disease. The HW/BW% (0.43–0.96%) and (LV+S)/RV (2.80–4.22) for macropods were comparable to domestic species. In koalas, the HW/BW% (0.25–0.51%) was lower, and the (LV+S)/RV (3.06–5.41) ranged higher than in macropods and domestic species. The LV:RV of koalas (1.0–10.8) was more variable than in macropods (1.17–4.27). Two macropods with cardiac disease were assessed on postmortem examination against the generated reference values. An adult male common wallaroo (Osphranter robustus) was found dead with copious serous peritoneal effusion, chronic passive hepatic congestion with centrilobular fibrosis, and dilation of the RV, while the LV:RV was elevated, supportive of RV thinning. A 21-year-old female zoo-housed Matschie’s tree kangaroo (Dendrolagus matschiei) had a flaccid thin-walled RV, LV cardiomyocyte hypertrophy, interstitial myocardial fibrosis and myofiber degeneration, pulmonary oedema, and serous pericardial effusion. The (LV+S)/RV and LV:RV were elevated and RV:S decreased, supporting left hypertrophic cardiomyopathy. Species-specific reference values presented in this study facilitate objective and improved postmortem cardiac assessment in macropods and koalas.