What are the potential issues with an arteriovenous fistula (AVF) that is always running at a high blood flow rate (BFR)?

High Blood Flow Rate in AVF: Potential Complications

An AVF consistently running at high blood flow rate (BFR) can lead to high-output cardiac failure, particularly when indexed flow exceeds 603 ml/min/m²·⁷, and should prompt cardiac evaluation and consideration of flow reduction procedures. 1

Cardiac Complications

High-Output Heart Failure (HOHF)

• HOHF is defined as cardiac output >8 L/min with resting cardiac index >2.5-4.0 L/min/m² and low systemic vascular resistance, and represents a critical complication of high-flow AVFs. 2
• Patients with elevated cardiac index (4.0-6.0 L/min/m²) demonstrate significant reverse cardiac remodeling after AVF flow reduction, including decreased left ventricular mass, left atrial diameter, right ventricular diameter, and pulmonary systolic pressure. 3
• Cardiac index elevation, rather than absolute AVF flow rate alone, better identifies patients who will benefit from flow reduction procedures. 3

Cardiac Remodeling Indicators

• When AVF blood flow is indexed for body size (height²·⁷), a threshold of ≥603 ml/min/m²·⁷ identifies patients at high risk for HOCF with 100% sensitivity and 86% efficiency. 1
• Patients exceeding this indexed threshold demonstrate more severe left ventricular mass increase (63±18 vs. 47±7 g/m²·⁷), larger left ventricular diastolic volumes, increased left atrial volumes, and higher incidence of diastolic dysfunction (70% vs. 17%). 1
• Cardiac output reduction of >2000 ml/min after manual AVF compression strongly suggests hemodynamically significant high flow requiring intervention. 1

Vascular Access Dysfunction

Stenosis Development

• High BFR creates turbulent flow conditions that promote endothelial injury and neointimal hyperplasia, the primary cause of vascular access failure. 4
• Clinical indicators of stenosis include high venous and arterial pressures at prescribed blood flow, reduced dialysis clearance without other cause, and excessive bleeding after needle withdrawal. 5
• Physical examination findings suggesting stenosis include high-pitch discontinuous systolic-only bruit, abnormal thrill (weak/discontinuous), and alterations in pulse quality with water-hammer characteristics. 5

Venous Hypertension and Edema

• Downstream venous stenosis forces blood through collateral veins, producing venous hypertension that manifests as persistent arm swelling and can progress to chronic venostasis with skin ulceration. 6
• Central venous stenosis is the leading cause of persistent arm swelling in AVF patients and requires fistulography with dilute contrast for definitive diagnosis, as standard ultrasound may miss major outflow obstruction. 6, 7

Monitoring and Intervention Thresholds

Physical Examination Monitoring

• KDOQI recommends routine physical examination monitoring (inspection, palpation, auscultation) to detect signs of pathology, ideally conducted when the patient is not on dialysis. 5
• The "One-Minute Access Check" provides rapid assessment for detecting early dysfunction. 5
• Look for ipsilateral extremity edema, failure of fistula to collapse with arm elevation (outflow stenosis), abnormal thrill characteristics, and inability to achieve target dialysis blood flow. 5

Intervention Criteria

• Pre-emptive angioplasty is reasonable when persistent clinical indicators are present with underlying stenosis, though KDOQI does not recommend intervention for stenosis without clinical indicators. 5
• Percutaneous transluminal angioplasty should be performed for stenosis >50% of lumen diameter when associated with clinical or physiologic abnormalities. 8
• For high-flow AVF causing cardiac symptoms, treatment options include flow reduction procedures (banding), AVF ligation, or conversion to peritoneal dialysis. 2

Critical Pitfalls to Avoid

• Do not rely solely on absolute AVF flow measurements (e.g., ≥2000 ml/min) without indexing for body size, as this provides poor discrimination for identifying patients at risk for cardiac complications. 1
• Failing to perform cardiac evaluation in patients with high-flow AVF and symptoms of volume overload can lead to progressive heart failure, as many cases are reversible with early intervention. 2
• Delaying fistulography when persistent arm swelling extends beyond 2 weeks risks missing central venous stenosis, which standard ultrasound frequently fails to detect. 6
• Patients with underlying heart disease (aortic stenosis, cardiomyopathy) are at particularly high risk for decompensation with high-flow AVF and require lower thresholds for intervention. 2
• Normal cardiac index (2.5-3.8 L/min/m²) patients do not demonstrate reverse remodeling after AVF reduction, so intervention should be reserved for those with elevated cardiac index. 3