What causes arteriovenous (AV) fistulas to enlarge in patients undergoing dialysis?

From the Guidelines

Arteriovenous (AV) fistulas for dialysis enlarge primarily due to hemodynamic changes that occur after their creation, specifically the increased blood flow and wall shear stress triggered by the connection of an artery to a vein, as noted in the most recent study 1.

Causes of Enlargement

The process of enlargement involves vascular remodeling through mechanotransduction, where endothelial cells sense the increased pressure and flow, releasing growth factors and cytokines that stimulate vessel dilation and wall thickening. This remodeling causes the vein to "mature" - becoming larger, thicker-walled, and more suitable for repeated needle insertions.

• Hemodynamic changes: The high-pressure arterial blood flows into the low-pressure venous system, creating increased blood flow and wall shear stress in the vessels.
• Vascular remodeling: The process involves smooth muscle cell proliferation, extracellular matrix reorganization, and vessel wall hypertrophy.
• Mechanotransduction: Endothelial cells sense the increased pressure and flow, releasing growth factors and cytokines that stimulate vessel dilation and wall thickening.

Complications and Monitoring

While this enlargement is generally beneficial for dialysis access, excessive dilation can sometimes lead to complications like aneurysm formation. Patients should monitor their fistula for abnormal enlargement, pulsations, or skin changes and report these to their healthcare provider. Regular clinical assessment of the fistula helps ensure it develops appropriately for effective hemodialysis while minimizing complications, as recommended by the KDOQI guidelines 1.

• Aneurysm formation: Progressive enlargement of an aneurysm can eventually compromise the skin above the graft, leading to possible rupture.
• Monitoring: Patients should monitor their fistula for abnormal enlargement, pulsations, or skin changes and report these to their healthcare provider.

Management and Treatment

The management and treatment of AV fistula enlargement and related complications involve a multidisciplinary approach, including surgical consultation, endovascular management, and hypercoagulability testing, as discussed in the recent study 1.

• Surgical consultation: Vascular surgery consultation for possible revision for creation of a new fistula may be considered in the setting of clinical failure of endovascular treatment.
• Endovascular management: Endovascular management is the preferred alternative to open surgery as a first-line therapy for dialysis accesses thrombosis.
• Hypercoagulability testing: Hypercoagulability testing for associated thrombophilia may also be explored in patients with frequent or recurrent thrombotic occlusions of the hemodialysis access.

From the Research

Causes of Arteriovenous (AV) Fistula Enlargement

• The creation of an AVF can lead to increased flow of blood through the venous system, which may cause turbulence and endothelium injury, potentially resulting in stenosis or aneurysm formation 2.
• High-flow AVFs can disrupt overall circulatory dynamics, particularly in patients with cardiovascular compromise, and may lead to complications such as high-output cardiac failure, pulmonary hypertension, and dialysis-associated steal syndrome 3, 4.
• The pathophysiology of high-flow AVFs involves the shunting of blood from the high-resistance arterial system into the lower resistance venous system, increasing venous return and potentially leading to cardiac failure 4.
• The use of certain antihypertensive medications, such as calcium channel blockers, may be associated with a lower risk of AVF maturation failure, although the exact mechanisms are unclear 5.
• Flow reduction procedures, such as banding, can decrease AVF flow and alter hormone levels, including natriuretic peptides and renin-angiotensin-aldosterone system hormones, which may impact kidney function 6.

Risk Factors for AV Fistula Enlargement

• Pre-existing heart disease and cardiovascular compromise may increase the risk of complications associated with high-flow AVFs 3, 4.
• The presence of comorbidities, such as diabetes, hypertension, and peripheral vascular disease, can complicate AVF management and increase the risk of enlargement or failure 3.
• The type and location of the AVF, as well as the patient's individual anatomy and physiology, can also impact the risk of enlargement or complications 2, 3.