# Resolution of Exercise-Induced Syncope After Stenting of the Azygos Vein in a Dog with Segmental Aplasia and Azygos Continuation of the Levopositioned Caudal Vena Cava

## TL;DR

A 1-year-old dog with a rare blood vessel defect was successfully treated with a stent, resolving its fainting episodes during exercise.

## Contribution

This is the first report of stent implantation for treating segmental aplasia and azygos continuation of the caudal vena cava in dogs.

## Key findings

- Stent implantation in the azygos vein resolved exercise-induced syncope in a dog with a rare vascular anomaly.
- Computed tomographic angiography identified diaphragm compression as the cause of venous insufficiency.
- The dog remained symptom-free for six months post-surgery without medication.

## Abstract

In the present report, we describe the case of a 1-year-old dog with a very rare congenital anomaly of the abdominal blood vessels. A portion of the greatest vein of the body, which is responsible for returning the blood from the hindlegs and the belly to the heart, was missing due to a congenital developmental defect. A connection with another vein helped with the venous return. However, each time when the dog became excited or went for a walk, the venous return to the heart was insufficient to such a degree that multiple fainting episodes occurred every single day for several months. Advanced diagnostic imaging revealed that a compression of the “helping” vein by the diaphragm was responsible for the clinical signs. Implantation of a stent with a minimal invasive catheter technique prevented the vein from compression and resulted in immediate resolution of all clinical signs. The dog is free from any clinical signs 6 months after the surgery without any medication. This is the first report that describes this procedure for the treatment of this rare condition.

A 1-year-old Maltese–Poodle mixed breed dog was referred to the cardiology service because of severe exercise intolerance and daily exercise-induced syncopal episodes. Physical examination revealed no abnormalities. Echocardiography showed intermittent underfilling of the heart. Abdominal ultrasound examination revealed a segmental aplasia of the caudal vena cava between the kidneys and the liver, and azygos continuation of the cava. The azygos vein dorsal to the right kidney showed a severe aneurysm with stasis of blood. Computed tomographic angiography showed that the right crus of the diaphragm was probably responsible for the intermittent compression of the dilated azygos vein, which was thought to have subsequently led to insufficient venous return to the heart. The underfilled ventricles could not produce sufficient cardiac output, which caused the assumed cerebral hypoperfusion due to presumed systemic arterial hypotension. Under general anesthesia a self-expanding nitinol stent was implanted into the azygos vein at the level of the diaphragm. All clinical signs resolved immediately after surgery. The dog remained free from clinical signs (6 months after surgery). This is the first report that describes the successful treatment of this congenital vascular anomaly. Ultrasonography of the caudal vena cava should be performed in dogs with unexplained syncope.