The Use of Transesophageal Echocardiography to Assess Cardiovascular Health in Captive Lowland Gorillas (Gorilla gorilla gorilla)
Complete cardiac diagnostic testing, even without evidence of clinical cardiac disease, is warranted due to the high prevalence and acute nature of cardiac disease in captive gorillas. Antemortem diagnostic techniques, previously described in gorillas, include electrocardiography, echocardiography, blood pressure measurements, oximetry, radiology, cardiac catheterization and coronary angiography. Annual cardiac examinations of the gorillas at the Franklin Park Zoo include a 12-lead electrocardiogram, a thoracic radiograph, Doppler flow imaging, transthoracic and transesophageal echocardiography. Transesophageal echocardiography (TEE) with a Hewlett-Packard echocardiograph machine model SONOS 2000/2500 with an OMNIPLANE TEE transducer (5 MHz), has allowed enhanced imaging of the heart and great vessels in an attempt to monitor and hopefully intercede in the development of any cardiovascular diseases.
The incidence of cardiovascular disease as a cause of mortality in adult, captive lowland gorillas has been reported to be as high as 41% in the Species Survival Plan (SSP) population.4 These statistics have elucidated the need for further investigation into cardiovascular disease as a cause of death in captive lowland gorillas (Gorilla gorilla gorilla).1,4,5 The most commonly used cardiovascular diagnostic techniques in gorillas to date have included electrocardiograms, transthoracic echocardiographs (TTE), thoracic radiographs, and blood pressure measurements. The use of TEE presents an additional diagnostic tool to aid in the early detection of cardiovascular disease in large apes.
Previously described cardiovascular diseases of gorillas include aortic dissection, fibrosing cardiomyopathy, congenital defects, and coronary artery disease.1-8 Many of these conditions are diagnosed postmortem due to the acute nature of the final stages of these diseases. The increasing use of TEE, as part of the annual physical examination of captive lowland gorillas, may be a way to detect some of the more subtle cardiovascular changes that occur early on in the progression of these diseases. The more commonly used diagnostic tool is transthoracic echocardiography. This involves sending ultrasonic sound waves across the chest wall, in between the ribs and through the air in the lungs. All of these sound wave interfaces can interfere with the quality and definition of the image.
Another limiting factor of TTE is the compromised view of the aorta. In humans, TTE provides 4–5 windows in which the heart can be visualized. Because of the massive chest and more cranial-dorsal positioning of the heart in the thoracic cavity observed in gorillas, the view is limited to two windows and the sound waves have to travel further before returning to the transducer, thereby creating a less defined image. These limited windows provided by TTE allow only a small portion of the ascending aorta and aortic root to be visualized. Transesophageal echocardiography allows for unobstructed imaging of the heart, the entire aorta including the ascending, transverse and descending aorta, the aortic root, the abdominal aorta, the left coronary artery, any small valvular discrepancies, and the left atrial appendage. The TEE transducer actually scans from the back of the heart in 180 degree sweeps and the sound waves do not travel through the lungs and the ribs like they would with a transthoracic echocardiograph, thereby creating a clearer, more complete picture. By having a sharper image with an unlimited viewing window, subtle changes in cardiac musculature, cardiac function, and vasculature function and integrity may be apparent at an earlier stage in the disease process.
Human cardiologists are now routinely using TEE to further diagnose and treat cardiovascular disease in cardiac patients. Transesophageal echocardiography, where available, should be considered as part of a normal annual cardiac examination on captive gorillas. When used in conjunction with transthoracic echocardiography, electrocardiograms, and other diagnostic techniques, a complete database can be established on the cardiovascular health of captive gorillas. This may lead us to a better understanding of the factors leading up to these diseases and hopefully a means of prevention or early treatment.
This work was made possible by the generosity of New England Baptist Hospital, Hewlett-Packard, and the cardiology and ultrasound staff of the New England Baptist Hospital.
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