Abstract

Understanding pinniped cardiac function has been a primary focus for researchers investigating diving physiology. However, cardiac disease, as in most mammalian species, is increasingly of concern in aging populations of sea lions living under human care. Electrocardiograms (ECG) are part of routine cardiac health evaluations and, especially in human medicine, long-term recording of ECG is invaluable in identifying early issues and associating cardiac disease with specific activities. Unfortunately, long-term ECG recording in marine mammals has been historically limited due to their aquatic environment and has necessitated the use of invasive techniques to place instruments. The purpose of this study was to evaluate the use of an insertable cardiac monitor (Medtronic Reveal XT Model 9529^™) in adult female Steller sea lions (Eumetopias jubatus) as part of a large cardiac physiology and health monitoring project in this species. The monitor is placed under the blubber overlying the heart using a single incision of less than 2 cm in length in sea lions undergoing general anesthesia. The incision is closed in two layers using 3-0 polydioxanone suture material with no external sutures. Mean total surgical time was less than 11 minutes. The device measures 62 mm x 19 mm x 8 mm and includes two electrodes that continuously monitor the sea lions’ ECG. Researchers and clinicians obtain recordings using an externally held receiver that is held adjacent to the sea lion thorax for approximately 60 seconds. Up to 27 min of ECG data can be stored at any one time, and battery life is expected to be at least 3 years. To date, 6 sea lions have been implanted. All animals showed excellent wound healing with minimal swelling and no indication of tissue reaction to either sutures or the instrument. ECGs obtained are clear with minimal electronic interference. Preliminary data shows that sea lion ECG patterns are similar to those of terrestrial species but the timing and electrical conductivity is significantly different.

Acknowledgements

The authors wish to thank the veterinary technicians and marine mammal training staff at the Vancouver Aquarium for their incredible devotion to these animals and their health.

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