Cases of Sudden Death in a Sheep Model Implanted with Aortic Bioprostheses

Background: Sheep have long been established as an animal model in heart valve research for the preclinical safety assessment of prosthetic and bioprosthetic cardiac valves. Complications unrelated to the implant or surgical procedure are uncommon, but do represent a significant loss of data when they occur. Here we report the pre-term deaths of 3 sheep implanted with a bioprosthetic aortic valve. Aims: (1) To present potential physiological limitations of bioprosthetic aortic valves and the effect on the host animals’ ability to compensate for environmental stressors and (2) Consider these findings as they relate to the future long-term management of these animals during the in-life stage of studies. Methods: The early deaths of 3 sheep implanted with a novel bioprosthetic aortic valve were retrospectively analyzed including medical records, surgical records, pathology, and historical weather data. Results: Necropsy of all sheep revealed a stenotic left ventricular outflow tract and general findings consistent with acute congestive heart failure as a cause of death secondary to heat stress. Historical weather data identified high ambient temperatures, low wind speeds, and moderate humidity on the days the sheep died. Conclusion: The placement of bioprosthetic valve in the aortic position in sheep can result in significant compromise to the left side of the heart. It should be assumed that these sheep have a decreased cardiac reserve, limited ability to compensate in response to environmental stressors, and are at increased risk of adverse cardiac events including those possible during a heat wave. This should be considered when determining the appropriate post operative care of these animals.