Hypothesis and Background: A high prevalence of downwardly sloping type 3 Aortic Arch (AA) in elderly humans with Left Ventricular Hypertrophy (LVH) led us to hypothesize that Major Aortic Arch Branches (MAAB) acting through the AA and ascending Aorta are pivotal in subtending the heart in its anatomic position. Based on established commonality in comparative anatomy of terrestrial mammals we tested our hypothesis in the even-toed ungulate model.
Methods and Results: We observed 5 animals (2 sheep and 3 goats) at a licensed abattoir as they were being dressed, in a requested order. In vertical orientation, midline incision bisecting the entire chest and anterior abdominal wall was made and after retracting the ribs the heart was visualized. In stepwise fashion: abdominal organs, diaphragm, lungs and Vertebropericardial Ligaments (VPL) were removed; in all animals, the heart maintained its position in the thorax after the above steps. Subsequently, Sternopericardial Ligaments (SPL) were transected and the heart still maintained its position. Only after ascending aorta was severed just above the Aortic valve, did the heart lose its position and drop down to the pelvis.
Conclusion: In even-toed ungulate animal model, MAAB acting through AA and ascending aorta are pivotal in subtending the heart in its usual anatomic position. Invoking basic principles of comparative anatomy it would be safe to extrapolate that same may run true in humans. Indirect evidence of above in humans may reside in a high prevalence of downwardly sloping type 3 AA in elderly with LVH.