How to manage cardiac output in a patient with an arteriovenous (AV) fistula?

Management of Cardiac Output in Patients with Arteriovenous Fistulas

For patients with arteriovenous (AV) fistulas who develop high-output cardiac failure, surgical correction of the high-flow fistula through banding or closure is recommended as the definitive treatment to improve cardiac function. 1

Pathophysiology and Hemodynamic Effects

AV fistulas create significant hemodynamic changes through:

• Left-to-right extracardiac shunting that increases cardiac workload
• Increased venous return to the heart
• Reduced peripheral vascular resistance
• Increased cardiac output to maintain adequate tissue perfusion

These changes can lead to:

• Increased cardiac workload
• Left ventricular hypertrophy
• High-output cardiac failure in susceptible patients

Diagnosis of High-Output Cardiac Failure

Clinical Presentation

• Dyspnea on exertion
• Orthopnea
• Peripheral edema
• Pulmonary congestion
• Elevated jugular venous pressure
• Presence of a continuous murmur over the AV fistula

Diagnostic Criteria

1. Cardiac output >8 L/min or cardiac index >3.9 L/min/m²
2. Evidence of volume overload (elevated filling pressures)
3. Normal or increased left ventricular ejection fraction
4. Exclusion of other causes of heart failure

Diagnostic Testing

• Echocardiography to assess:
  • Chamber dimensions
  • Ventricular function
  • Valvular function
  • Estimated cardiac output
• Doppler ultrasound of the AV fistula to measure flow rates
• Cardiac catheterization (in selected cases) to measure:
  • Cardiac output
  • Fistula flow (via temporary occlusion test)

Management Algorithm

Step 1: Risk Assessment

Identify patients at high risk for high-output cardiac failure:

• Elderly patients
• Pre-existing cardiac disease
• High-flow AV fistula (>1.5-2 L/min)
• Fistula flow >20-30% of cardiac output

Step 2: Medical Management

For mild to moderate symptoms:

• Optimize volume status with diuretics
• Standard heart failure therapy:
  • ACE inhibitors/ARBs
  • Beta-blockers (use with caution as they may reduce cardiac output)
  • Digoxin (for rate control if atrial fibrillation present)

Step 3: Intervention for Refractory Cases

For severe or refractory symptoms:

• Fistula flow reduction by banding
• Fistula ligation or closure
• Creation of alternative access with lower flow

Special Considerations

During Cardiac Surgery

For patients with AV fistulas undergoing cardiac surgery:

• Consider bicaval cannulation instead of single two-stage venous cannulation to achieve adequate cardioplegic arrest 2
• Monitor for excessive venous return during cardiopulmonary bypass
• Temporary occlusion of the fistula may be necessary during critical phases of surgery

Monitoring Parameters

• Regular assessment of cardiac function with echocardiography
• Monitoring of fistula flow rates
• Assessment of cardiac output and filling pressures

Preventive Strategies

• Create fistulas with appropriate size to minimize excessive flow
• Regular monitoring of fistula flow rates
• Early intervention for high-flow fistulas before cardiac decompensation occurs

Pitfalls and Caveats

• Do not attribute all heart failure in dialysis patients to AV fistulas without proper evaluation
• Temporary occlusion of the fistula can help determine its contribution to cardiac failure
• Fistula closure should be considered only after confirming its contribution to cardiac failure
• Ensure alternative dialysis access is available if fistula closure is planned

By following this structured approach, clinicians can effectively manage cardiac output in patients with AV fistulas and prevent or treat high-output cardiac failure when it occurs.