Implantation of a Cardiac Resynchronization Therapy Device (CRT) in a Western Lowland Gorilla (Gorilla gorilla gorilla) with Cardiac Disease
Cardiovascular disease causes significant morbidity and mortality in captive great apes. Fibrosing cardiomyopathy with left- or right-sided insufficiency is common and is more prevalent in males over 30 years old.1 A 24-year-old, male western lowland gorilla (Gorilla gorilla gorilla) at the Birmingham Zoo was diagnosed with cardiac failure in March 2003. Evaluation of cardiac disease and progression was made using trans-esophageal and trans-thoracic echocardiography and electrocardiography (ECG). At initial diagnosis, the cardiac disease was categorized as a class 3 failure on a scale of 1–4 (4 most severe in humans). Treatment for cardiac disease was attempted with furosemide and enalapril, but the gorilla’s cardiac function worsened over the next 16 months despite therapy. Repeat cardiac function evaluations performed every 7 months documented the progression of disease to class 4 end-stage cardiac failure. At this time, carvedilol, bumetanide, enalapril, acetylsalicylic acid and metolazone were added to the medication regimen, and the animal was evaluated to determine candidacy for implantation of a biventricular cardiac resynchronization therapy (CRT) device as treatment for this disease. ECG data from this animal was compared with values from multiple normal gorillas in other institutions, as human values appear to be significantly dissimilar.
This gorilla was successfully treated through surgical implantation of a biventricular CRT device. A portable fluoroscopy unit was used intraoperatively to evaluate the motion of the heart, location of the vascular structures, and placement of the pacing leads in the right atrium (RA), right ventricle (RV) and left ventricle (LV) as accessed by the coronary venous vessels. The implantation team consisted of an electrophysiologist, echocardiologist, veterinary cardiologists, a physician to perform anesthesia, and multiple specialty veterinarians. Additionally, team members were needed to implant, program and evaluate the CRT for the procedure. Placement of the RA, RV and LV leads and device required 5.5 hours, an extended length due to technical difficulties and anatomic differences versus humans.
Electrical timing of the paced cardiac chambers was selected to maximize cardiac output as determined by the ECG. Interrogation and programming of the CRT device requires that it be within 2 inches of the reading/programming wand, which necessitated training of this animal for proper positioning. Training has allowed frequent evaluation of the CRT device, which constantly records the ECG and any abnormal cardiac rhythms for later retrieval. Appetite, cardiopulmonary function, activity level, attitude, and training all improved over a 6-month period after CRT implantation until the pacing leads were dislodged during an altercation with a companion animal. The leads and device were replaced during a surgery identical to the initial procedure, with minor equipment modifications to accommodate the mechanical difficulties encountered in gorillas. This accidental loss of the CRT device confirmed its clinical value, as the animal’s health and cardiac function decreased significantly after loss then improved again after re-implantation, allowing for the release of this gorilla onto exhibit only 10 days later.
Although requiring special equipment and surgical skill, CRT implantation appears to be a viable option for treatment of non-ischemic dilated cardiomyopathy and hypokinetic cardiac disease in gorillas. Differences in human and gorilla anatomy and activity must be considered and managed during surgery and postoperative care. Although equipment designed for humans was utilized successfully in this animal, improvements could be made which might significantly decrease surgical time and decrease the risk of postoperative device complications in gorillas. In the future, special technical and surgical equipment designed specifically for gorillas with cardiac disease could streamline CRT implantation, allowing for an increased quality and length of line in these endangered apes.
Thanks to the primate and maintenance staff at the Birmingham Zoo for their time and care of this animal. Also, thanks to Linda Garmon with Guidant Corporation for her continued time and devotion to training for CRT interrogation, and to the Wildlife Conservation Society and Zoo New England for providing comparative cardiac data from normal gorillas.
1. Loomis, M.R. 2003. Great Apes. In: Fowler, M.E., R.E. Miller, eds. Zoo and Wild Animal Medicine. 5th ed., Elsevier Science: St. Louis, MO. P. 386.
2. Proceedings of the Auburn University College of Veterinary Medicine Annual Conference, 2005. (Reprinted with permission.)