Abstract

With aging populations of bottlenose dolphins (Tursiops truncatus) under professional care, marine mammal clinicians are confronted with new challenges in identifying and diagnosing heart disease in this species, as cardiac abnormalities may become increasingly more evident. Here, we report an asymptomatic 55-year-old female bottlenose dolphin diagnosed with second degree Mobitz type 2 atrioventricular (AV) block on routine examination.¹ Auscultation revealed a grade 3/6 systolic fixed murmur, with left caudal point of maximal intensity.² Echocardiography upon initial diagnosis revealed mild degenerative valve disease. Additionally, analysis of blood-based cardiac biomarkers showed marked elevation of B-type natriuretic peptide at 27.72 ng/ml (mean in healthy dolphins 1.7 ng/ml ±1.1, n=53, unpublished data). Regular voluntary, in-water electrocardiograms were performed to monitor for progression of AV block, as well as the contributions of changes in vagal tone on conduction disturbances.³ Two years after initial diagnosis, the ratio of non-conducted P waves progressed intermittently from 2:1 to 3:1 conduction. A modified stress test was performed and showed partial improvement in AV conduction.⁴ To further characterize the AV nodal disease, atropine sulfate was administered intravenously at a dose of 0.01 mg/kg without adverse effects.⁵ Evaluation of electrocardiogram following administration suggested a combination of enhanced vagal tone and AV node dysfunction as the etiology, likely attributed to degenerative aging processes as seen in other mammalian species.¹ Based on the complete cardiac evaluation, pacemaker implantation is not currently indicated; however, monitoring for disease progression is ongoing. Comprehensive cardiac evaluation is critical in monitoring cardiac health in geriatric dolphins to promote healthy aging.

Acknowledgements

The authors thank the veterinary technicians and training staff at the National Marine Mammal Foundation and U.S. Navy Marine Mammal Program for their excellent care and assistance with this case, as well as James Bailey and George Le-Bert for their consultation on this case.

*Presenting author

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