Arteriovenous Anastamoses

Introduction

This is a peripheral connection between an artery and a vein . It can be caused by a penetrating trauma (e.g. venepuncture), neoplasia, a mass ligation of vessels during surgery, aneurysmal rupture or the erosion of vessels by infection.
An arteriovenous anastomosis causes there to be a low resistance pathway for blood to flow form high pressure arterial circulation to the low pressure venous circulation, which promotes preferential flow through the fistula. The result of this is increased venous return, causing an increased cardiac output and therefore leading to significant volume overload on the heart. It can also cause inadequate perfusion of the area perfused by the artery.

Clinical Signs

Signs may include the area to be warm and swollen. There may be a palpabral thrill and pulsation over the area and a continuous machinery murmour may be audible. The animal may exhibit the Branham sign , which is when the fistula is occluded it causes a sudden rise in systemic vascular resistance and a drop in heart rate.

Diagnosis

Clinical signs and history of trauma or surgery etc can be indicative of the condition. Doppler ultrasound or angiography of the area is required for a definitive diagnosis. Both of these techniques will demonstrate abnormal flow.

Treatment and Control

The preferred treatment option is surgical and involves surgical ligation of the vessels to and from the affected area, resulting in prevention of flow through the affected area. This does have a tendancy to recur if inadequate ligation of the vessels was performed. If the anastomosis is very severe then radical surgery or amputation of the region may need to be performed.

Prognosis

Good if treated. Persistant flow can lead to high output heart failure.

References

Boswood, A (2008) Cardiovascular System Study Guide, Royal Veterinary College.
Ettinger, S.J. and Feldman, E. C. (2000) Textbook of Veterinary Internal Medicine Diseases of the Dog and Cat Volume 2 (Fifth Edition), W.B. Saunders Company.
Fossum, T. W. et. al. (2007) Small Animal Surgery (Third Edition), Mosby Elsevier.