How accurate is Edwards' (Edwards) Flow Track hemodynamic system for measuring cardiac index and output in patients with atrial fibrillation (Afib)?

Accuracy of Edwards' Flow Track Hemodynamic System in Atrial Fibrillation

The Edwards' Flow Track hemodynamic system is likely to have reduced accuracy for measuring cardiac index and output in patients with atrial fibrillation due to the irregular ventricular response and beat-to-beat variability inherent in this arrhythmia.

Hemodynamic Challenges in Atrial Fibrillation

Atrial fibrillation presents unique challenges for hemodynamic monitoring systems due to several physiological factors:

Irregular Ventricular Response

• AF is characterized by an irregular ventricular response with variable RR intervals 1
• This irregularity creates beat-to-beat variability in stroke volume and cardiac output
• Research shows that irregular RR intervals alone (independent of rate) decrease cardiac output by approximately 15% compared to regular rhythm at the same average rate 2

Loss of Atrial Contribution

• The loss of synchronized atrial contraction ("atrial kick") in AF reduces stroke volume by 20-30% in normal individuals and even more in patients with heart disease 3
• This contributes to decreased cardiac output and can affect the accuracy of monitoring systems calibrated for normal cardiac physiology

Variable Ventricular Filling

• The varying cycle lengths in AF lead to inconsistent ventricular filling times
• Shorter RR intervals result in reduced ventricular filling and smaller stroke volumes
• Longer RR intervals allow for more complete filling and larger stroke volumes

Implications for Flow Track Monitoring

The Edwards' Flow Track system, which typically relies on pulse contour analysis for continuous cardiac output monitoring, faces several challenges in AF patients:

1. Beat-to-beat variability: The system must account for significant variations in stroke volume between consecutive beats 4

2. Calibration challenges: Most hemodynamic monitoring systems are calibrated based on regular cardiac rhythms, making their algorithms less reliable during irregular rhythms like AF

3. Averaging limitations: While the system may provide averaged values over time, these may not accurately reflect the true hemodynamic status due to the fundamental irregularity of AF

Clinical Recommendations

When using the Edwards' Flow Track system in AF patients:

• Consider the heart rate: Accuracy decreases further with rapid ventricular rates (>100 bpm) 1
• Extend measurement periods: Use longer averaging periods to improve reliability
• Verify with alternative methods: When critical decisions depend on precise measurements, consider validating with alternative techniques
• Monitor rate control: Ensure adequate rate control (60-80 bpm at rest, 90-115 bpm during moderate exercise) to improve measurement reliability 5

Potential Pitfalls

• Overreliance on absolute values: Focus on trends rather than absolute values in AF patients
• Failure to recognize rapid rates: Extremely rapid rates (>200 bpm) suggest accessory pathway conduction and require immediate intervention 5
• Ignoring underlying cardiomyopathy: Tachycardia-induced cardiomyopathy can develop with persistently elevated ventricular rates, further complicating hemodynamic assessment 1

In summary, while the Edwards' Flow Track system provides valuable hemodynamic data, clinicians should interpret its measurements with caution in AF patients, understanding the inherent limitations imposed by the irregular rhythm and altered cardiac physiology.