Case Report - Arteriovenous fistulas

Case Report "Catnip"

Victoria Demello

University of Georgia, College of Veterinary Medicine

ABSTRACT:

Arteriovenous fistulas (AV fistulas) have been reported in humans and animals. This condition is rare and can be either congenital or acquired. Acquired arteriovenous fistulas are often due to trauma including surgery. Congenital fistulas are due to vascular malformations. These fistulas are often reported in peripheral vasculature within veterinary medicine. We describe a case of suspected arteriovenous fistula versus suspected unclassified cardiomyopathy in a 5-month-old feline that quickly progressed to left- and right-sided congestive heart failure. Gross pathology and histopathology lesions revealed all chambers as dilated with interfiber edema. Extensive alveolar edema and frequent hemorrhage was noted in the lungs. Numerous hemosiderin macrophages within alveolar lumen were present.

CASE REPORT:

“Catnip”, 5-month old male intact DSH, presented to University of Georgia’s College of Veterinary Medicine’s (UGA CVM) Cardiology service for evaluation of a murmur diagnosed by the primary veterinarian. The cat was found when he was 9-weeks-old. He received his first round of kitten shots and was tested for FeLV and FIV. He was negative for both diseases. 3 weeks later, during the next vaccine appointment (12-week-old kitten), a right-sided grade IVV/VI systolic murmur was noted. The primary veterinarian recommended an echocardiogram. The cat did not have any clinical signs or symptoms reported at that time. The owner declined further diagnostic testing.

3 weeks later, at the next vaccine appointment, a grade V/VI right-sided systolic murmur was diagnosed by the primary veterinarian. An abdominal component to the cat’s breathing that was not present before was also noted. The owner reported the cat’s abdomen was becoming increasingly distended and the patient did not play as much as his littermate. The cat was bright, alert, and responsive at home, eating/drinking/urinating/defecating normally. Due to the increase in murmur severity and presence of clinical signs, a referral appointment to University of Georgia’s College of Veterinary Medicine’s Cardiology service was made.

On physical exam at the University of Georgia’s College of Veterinary Medicine’s Cardiology service, a grade IV/VI right systolic parasternal murmur was diagnosed. Temperature, and heart rate were within normal limits (99.3°F, 168 beats per minute). The jugular vein was distended and the respiration rate was increased with an abdominal component (72 breaths per minute). Increased inspiratory noise was also noted. Blood Pressure was 100mmHg (systolic). Packed cell volume/Total solids: 35%/5.6.

Thoracic radiographs (3-view) were performed and revealed severe generalized cardiomegaly with pulmonary arterial and venous distension and both left- and right-sided cardiac failure.

Echocardiogram findings showed right atrium dilation, right ventricle dilation. The tricuspid valve leaflets, right ventricular outflow tract including the pulmonic valve cusps and main pulmonary artery were within normal limits. The left atrium was severely dilated and was the left ventricle. The mitral valve leaflets, interventricular septum, left ventricular free wall were all normal as were the aortic valve cusps and ascending aorta. Abdominal effusion was present on echocardiogram. No cardiac masses or thrombi were present. Electrocardiogram showed sinus tachycardia.

The patient was suspected to have unclassified cardiomyopathy or a peripheral arteriovenous fistula. The patient was euthanized due to cardiomyopathy and secondary severe pulmonary edema.

Gross pathologic findings were dilation of all cardiac chambers with the most significant change within the right atrium. Wall thicknesses were measured (right atrium 1 mm; right ventricle 3 mm; left atrium 2mm; left ventricle 8mm). Pulmonary artery was enlarged with a circumference of 6mm. Circumference of the aorta was 5mm. Just medial to the left kidney, in the dorsal abdomen, was a large plexus of engorged vessels between the aorta and caudal vena cava. Measured as 4cm in length and 1.5cm in diameter. There was blood present in the trachea and the lungs were dark and diffusely and moderately congested.

Histopathology of the heart revealed modest interfiber edema in all but was most severe in the right atrium and right ventricle. Extensive alveolar edema and frequent hemorrhage was noted in the lungs. Numerous hemosiderin macrophages within alveolar lumen were present.

DISCUSSION

AV fistulas are abnormal connections between an artery and vein. This abnormal connection causes abnormal blood flow throughout the body creating murmus. AV fistulas are most common secondary to penetrating trauma injuries in both veterinary and human medical literature. There have only been a handful of reported AV fistulas in veterinary literature with a majority occurring due to trauma (secondary to gun shots, animal bites, etc).

One case (Bolton et al) illustrated a congenital AV fistula in a 3 month old feline presented for acute dyspnea. This fistula was identified due to the abnormal murmur heard during a routine physical exam. On presentation, the feline had cyanotic oral mucous membranes and a gallop rhythm on cardiac auscultation. Further diagnostics (thoracic radiographs, ECG, CBC and serum chemistry) revealed an enlarged heart. Angiography was performed, as well, which showed a plexus of blood vessels between the aorta and caudal vena cava. This paper was published in 1976 before echocardiography was readily available. Angiography was able to illustrate a clear picture of the AV fistula. This fistula was able to be surgically ligated prior to permanent cardiac musculature changes. This cat survived but ultimately lived a shortened life span. Due to the complications and prognosis of untreated AV fistulas, prompt identification, diagnosis, and intervention is key.

In the case of Catnip, his AV fistula was discovered too late. He presented to the UGA Cardiology service with fulminant congestive heart failure characterized by severe dilation of all 4 cardiac chambers. Catnip was euthanized due to his poor prognosis.

Catnip was approximately 12 weeks old when his murmur was fist ausculted. Murmurs are created due to the abnormal turbulent blood flow within the heart or vessels. Murmurs in young animals (animals less than 6 months old) are not an uncommon finding. These murmurs are referred to as physiologic murmurs. These murmurs are characterized by an absence of structural cardiac disease. Students are often taught that grade 1/6 to 2/6 in young animals (less than 6 months of age) without any clinical signs are most often physiologic or “innocent” murmurs. Murmurs that meet this criteria often disappear with time. However, murmurs grade 3/6 and higher should always undergo cardiologic evaluation including echocardiogram. These murmurs are pathologic (arising from structural cardiac disease) in nature regardless of the age of the animal.

It is important to understand the grading of murmurs and the difference between physiologic and pathologic murmurs because of cases like this. A veterinarian’s physical exam is the most important way to detect a problem early. Moving forward, a detailed understanding of cardiac murmurs, and education of owners with animals that have murmurs is essential to early detection of AV fistulas.

References:

1. “Arteriovenous Fistula of the Aorta and Caudal Vena Cava Causing congestive heart failure in a cat”. Bolton, Gary, Edwards, N. Joel, Hoffer, R.E.. Journal of the American Veterinary Medical Association. July/August 1976

2. “Peripheral Acquired Arterivenous Fistula: A report of 4 cases and literature review”. Bouayad, H., Feeney, D.A., Lipowitz, AJ, Levine, S.H., Hayden, D.W.. Journal of the American Animal Hospital Association. June 1986.

3. “Arteriovenous fistulas: Pathophysiology, Diagnosis, and Treatment”. The Small Animal Compendium. May 1989