APPENDIX: LOWER EXTREMITY: ARTERIOVENOUS FISTULA

PATIENT STORY

A 58-year-old healthy man initially presented to the emergency room with gunshot wound (GSW) birdshot injuries to the back of his left leg that occurred on a hunting trip. His initial examination showed normal pulses without any localized neurologic deficits. He was reevaluated in the clinic 1 month later with a thrill in the popliteal fossa and diminished pedal pulses. A duplex ultrasound study confirmed an arteriovenous fistula (AVF) at the level of the proximal posterior tibial artery (PTA) or distal popliteal artery. An endovascular intervention resulted in successful coverage of the AVF and improvement of distal limb perfusion (Figure 1).

ETIOLOGICAL DEFINITION AND CLASSIFICATION

• An AVF is an abnormal connection between an artery and vein with a persistent endothelialized tract. They are often classified as either congenital or acquired.

• Congenital AVFs are rare and often secondary to persistent embryonic vessels that fail to distinctively differentiate into an artery or vein.

• Acquired AVFs are more common and often secondary to the following causes: traumatic, iatrogenic, therapeutic, and degenerative aneurysmal changes.

ETIOPATHOLOGY OF ACQUIRED AVFs

1. Traumatic injury most commonly following stab wounds (63%), GSW (26%), or blunt trauma (1%).^1,2

2. Iatrogenic injury most commonly occurs after percutaneous vascular interventions. The common femoral artery (CFA) is the most common site of iatrogenic AVFs.^3,4

3. Therapeutic procedures performed for complex hemodialysis vascular access in patients with inadequate access at more conventional sites (eg, femoral vein transposition).

4. Degenerative aneurysmal changes resulting in rupture of an arterial aneurysm into a contiguous vein (Figure 2A and B).^{5,6,7, and 8}

PATHOPHYSIOLOGY OF ACQUIRED AVFs

• The natural history of an AVF is often determined by the size and adequacy of the inflow and outflow vessels, as well as the size and location of fistula tract.

• Some AVFs spontaneously close, but most continue to enlarge.

• In chronic AVFs the proximal artery and proximal vein enlarge with an associated increase in flow through the respective vessels. These vessels also undergo tortuous changes as they enlarge. If the fistula outflow resistance is very low, it can result in a distal arterial steal phenomenon that can ...