Abstract

Cardiovascular disease is a significant cause of mortality in all of the captive ape species and has even been diagnosed in some wild gorillas and chimpanzees.² Historically, postmortem cardiac evaluation has been performed by numerous independent prosectors using varying protocols. While this allows diagnosis of an individual case, the lack of standardization hinders analysis of data across populations, as lesions and measurements can vary depending on sampling site. Standardized necropsy protocols are critical for collecting data, which can be compared within and among species to accomplish the goals of the Great Ape Heart Project based at Zoo Atlanta, including a clinicopathological database to improve diagnosis, treatment, and our understanding of cardiovascular disease in apes. In human medicine, there are agreed-upon criteria and sections to examine in postmortem evaluation of hearts.³ Much of this methodology is directly applicable to the study of cardiac disease in apes but is different from the techniques commonly taught in pathology labs during veterinary school. Therefore, the goal of this presentation is to introduce both clinicians and pathologists to best practices for evaluating ape hearts at necropsy. Both basic and more advanced protocols (see below rationale) will also be available in free downloads in both iBook and Android formats.¹

In preparation for the cardiac necropsy, the prosector needs to have available a digital camera, 1 cm or greater ruler or size marker appropriate for use with photographs, a scale appropriate for weighing the heart, and a piece of string/twine in addition to tools and any diagrams needed for prosection. With the body in dorsal recumbency, open the chest cavity and before any tissues are sampled or manipulated, take a photograph of the heart in situ. After the pluck is removed, separate the heart from the lungs by cutting the major vessels 5 cm from the base of the heart. Particular attention should be given to including both superior and inferior vena cava (these are often inadvertently lost). Flush out clots (ideally with saline, but water can be used) and weigh the heart. Next, a series of photographs will be taken with a ruler in the image so that measurements can be determined. Place the heart with the anterior side and both auricles facing up and the apex at the bottom, such that the right auricle is on the left and the left auricle is on the right, and take a photograph. Rotate the heart 90° to the left (left auricle is now facing the camera) and photograph; rotate the heart another 90° to the left (posterior view) and photograph; and rotate the heart a final 90° to the left (right auricle is facing the camera) and photograph. Pick up the heart and take a photograph of the heart base (with the vessels facing the camera). Examine the heart for gross lesions and describe. To measure the circumference, wrap a string around the heart at the level of the coronary groove and then lay the length of string that outlines the circumference on a ruler.

At this point, the heart can be fixed and further sectioning deferred. If you wish to stop at this point, make a single transverse cut, perpendicular to the long axis, through the heart at 3 cm (chimpanzees, orangutans, and bonobos) or 4 cm (gorillas) from the apex, rinse out any remaining clots, weigh the heart, and suspend the heart in formalin to fix. Suspension can be achieved by tying a string around the great vessels or “building” a cradle of paper towel or a surgical bonnet. Both sections of the heart can then be submitted to the pathologist for further evaluation. At this point, the prosector must also choose whether the basic or advanced protocol will be followed. The basic protocol will sample key features of myocardium and valves, but does not circumferentially evaluate myocardium, or key aspects of the conduction system (sinoatrial node, atrioventricular node, bundle) or coronary arteries. The advanced protocol will provide this comprehensive evaluation (see below). If the basic protocol is chosen, the prosector may choose to continue with the cardiac examination. To continue with the prosection, lay the heart with the anterior side facing up and make repeated 1-cm parallel transverse slices, perpendicular to the long axis (the posterior and anterior myocardium thickness will be equal) through the myocardium (continue to 3 cm for chimpanzees, orangutans, and bonobos and 4 cm for gorillas) starting at the apex. On this final (mid-ventricular) slice, mark the posterior wall (loop of suture, surgical staple, surgical ink or small notch). Photograph the three or four slices together and then fix the third/fourth slice in formalin.

The remainder of the heart should be opened along the lines of flow. Open the atrium from posterior vena cava to the auricle. Cut from the back (posterior side) of the right atrium into the right ventricle and out the pulmonary artery. Use string to measure the right atrioventricular (tricuspid) valve circumference. Photograph the inside of the right side of the heart with a ruler alongside the heart (not on the heart, please!). Section the right atrium and ventricle with valve and fix in formalin. Using string, measure the circumference of the pulmonic valve. Next, open the left atrium from pulmonary vein to auricle and then make a single longitudinal cut perpendicular to this through the middle of the left ventricular free wall. Examine the left atrioventricular (mitral) valve and endocardium for lesions. Measure the left atrioventricular valve circumference using the string method. Photograph the inside of the left side of the heart with a ruler alongside the heart. Take a longitudinal section through the left atrium, atrioventricular valve, and ventricle and fix in formalin. Cut through the mitral valve along the septum and into the aorta to open the aorta. Measure the aortic valve circumference using the string method. Take a longitudinal section of the septum from the aorta into the left ventricle and fix in formalin. Take a cross-section (“donut”) of aorta 1.5 cm from the aortic valve and fix. In addition to the cardiac portion of the necropsy, don’t forget to open the entire length of the thoracic and abdominal aorta and examine for lesions, such as dissections and atherosclerosis. For the advanced protocol, taking sections of thoracic and abdominal aorta (regardless of whether lesions are present) is valuable for the GAHP.

The advanced protocol includes several more assessments that will provide valuable data for future GAHP analyses, and which may potentially provide critical diagnostic information in unexpected cardiac deaths. These assessments include determination of vascular dominance (determining whether the right coronary or left circumflex branch of the left coronary artery feeds the apex), more detailed evaluation of the coronary arteries at multiple levels, and evaluation of the conduction system.³ Protocols for these procedures are detailed in the iBook and Android apps. Additionally, directions for post-fixation sampling and identification of standard blocks are also included so that pathologists are aware of which sections of submitted fixed tissues should be examined histologically. By standardizing our approaches in this way, we can establish reference ranges for each ape species, compare lesions within and among ape species, develop detailed consensus among pathologists on histological criteria for classifying lesions, and provide high-quality data that can be used in future studies into the pathogenesis of ape cardiovascular disease.

Acknowledgments

Funding and in-kind support was provided by many organizations and individuals, including: the Institute of Museum and Library Services National Leadership Grant (to the Great Ape Heart Project based at Zoo Atlanta, Grant # LG-26-12-0526-12); Drs. Hayley Murphy and Marietta Dindo-Danforth (GAHP), Cardiovascular Pathology Laboratory, CVM, TAMU; Brad Gilleland and the Educational Resources Center, College of Veterinary Medicine, UGA; and Dr. William Foster and Birmingham Zoo Incorporated.

Literature Cited

1.  McManamon R, Ellis AE, Lowenstine LJ, et al. A new approach to ape postmortem cardiac evaluation. Am Coll Vet Pathol Annu Conf. 2013:D-22.

2.  McManamon R, LJ Lowenstine. Cardiovascular disease in great apes. In: Miller RJ, ME Fowler, eds. Fowler’s Zoo and Wild Animal Medicine, Current Therapy. 7th ed. St. Louis, MO: Elsevier; 2012:408–415.

3.  Sheppard MN. Approach to the cardiac autopsy. J Clin Pathol. 2012;65(6):484–495.