Echocardiographic, Electrocardiographic, and Radiographic Analysis in the Green Iguana (Iguana iguana)
Department of Small Animal Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, USA
Cardiac disease can cause significant morbidity and mortality in captive reptiles, but antemortem diagnosis and monitoring are hindered by a lack of standardization in diagnostic procedures. The authors have developed methods to standardize echocardiography, electrocardiography and cardiac radiography in apparently healthy adult iguanas. Echocardiographic anatomy was identified with reference to necropsy specimens and published descriptions.1,2 Echocardiographic examination allowed reliable visualization of the great vessels, atria, and ventricle, as well as the associated valves. Intracardiac chamber diameters tended to increase with body size, while great vessel diameters were less reliably correlated. The indistinct endocardial surface of the ventricular myocardium prevented measurement of internal diameter, but the measured change in outer diameter between systole and diastole may provide an index of systolic function. Systolic function was also assessed by pulse-wave Doppler measurement of ventricular outflow velocities. Color Doppler imaging showed that insufficiency of the atrioventricular and left aortic valves was common, with atrioventricular regurgitation present in over 60% and aortic regurgitation in over 75% of the population. A six-lead electrocardiogram allowed reliable identification of P waves, QRS complexes, and T waves, with complexes and timing similar to those previously reported in reptiles.3,4 Radiographic visualization in the right lateral view allowed repeatable measurement of the width of the heart perpendicular to the sternum, which may prove a useful indication of generalized cardiomegaly. This study describes a method for standardizing cardiac diagnostic testing which may facilitate diagnosis and monitoring of heart disease in iguanas and other lizards.
The authors thank Reptile Hospice and Sanctuary of Texas for access to their collection for this study.
1. Holland, M. F., S. Hernandez-Divers, et al. 2008. Ultrasonographic appearance of the coelomic cavity in healthy green iguanas. J. Am. Vet. Med. Assoc. 233(4): 590–596.
2. Girling, S. J. and B. Hynes. 2004. Cardiovascular and haemopoietic systems. BSAVA Manual of Reptiles. S. J. Girling and P. Raiti. Quedgeley, England, British Small Animal Veterinary Association.
3. Murray, M. 2006. Cardiology. Reptile Medicine and Surgery. D. Mader. St. Louis, MO, Saunders: 181–195.
4. Kik, M. J. L. and M. A. Mitchell. 2005. Reptile cardiology: a review of anatomy and physiology, diagnostic approaches, and clinical disease. Sem. Avian Exotic Pet Med. 14(1): 52–60.