Abstract

Transesophageal echocardiography (TEE) is used along with transthoracic echocardiography (TTE) to evaluate the human heart. Recently, efforts have been made to apply the technique used in humans to establish a database of cardiac reference values in non-human primates. The technique has subsequently been used in a variety of other domestic and exotic species. Detailed imaging of the cetacean heart via TTE is often impossible due to the thick body wall. The purpose of this study was to determine the usefulness of TEE to evaluate the cetacean heart and establish a database of reference values in normal adult Atlantic bottlenose dolphins.

Two adult, male, captive born, Atlantic Bottlenose dolphins (Tursiops truncatus), ages 9 and 13 were evaluated. Both animals were in apparent good health prior to examination based on physical examination and blood evaluation. Both animals were placed on foam pads in sternal recumbency and given 5 mg midazolam i.m. twenty minutes prior to the procedure. A 3-lead ECG was applied and monitored throughout the procedure. Echocardiography was performed using transthoracic and transesophageal imaging. Transesophageal imaging was performed using the Acuson V5M multiplane transesophageal transducer. The transducer has a 10 mm footprint and is 190 mm long with controls much like a typical flexible endoscope. It operates at three frequencies, 7, 5, and 3.5 MHz.

Excellent images for evaluation were obtained from both dolphins, with ready evaluation of the aortic valve and left ventricle. Evaluation of the aortic valve and left ventricle demonstrated images of comparable quality to those obtained in humans, permitting the identification of the three aortic leaflets and the left main coronary artery. Left ventricular systolic global and regional assessment was readily obtained in both a longitudinal and short axis plane. A short axis image through the base of the heart demonstrated the main pulmonary artery, its bifurcation, and the pulmonary valve. This view also permitted visualization of the tricuspid valve. Stemal recumbency limited the detail of some images due to the presumed tendency of the heart to fall away from the esophageal probe, The different cardiac position changed the visualized cross-sectional shape compared to humans evaluated in dorsal recumbency, necessitating non-traditional probe angulation. In addition, the cetacean heart is different than the human heart in both shape and structure. Nevertheless, much more detailed images of the heart as well as adjacent structures (such as liver) were obtained with TEE compared to TTE. The procedure was minimally invasive and well tolerated by the animals. Complete TEE was performed in less than ten minutes. Repeating the procedure with more dolphins is required to gain experience with the unique views and to generate normal cetacean values. Established reference values can be used for animals with suspected cardiac abnormalities plus as part of a detailed wellness exam.

Acknowledgements

We would like to thank the Sea World Ohio animal care and training staff for their support and Jim Otton and the Acuson team for providing the ultrasound equipment.