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Turbulent flow as a cause for underestimating coronary flow reserve measured by Doppler guide wire
Markus Ferrari1, Gerald S Werner, Philipp Bahrmann
1Clinic of Internal Medicine I, Friedrich-Schiller-University, Jena, Germany. markus.ferrari@med.uni-jena.de
Insights
Doppler guide wires accurately measure coronary flow velocity (CFVR) in laminar flow but may underestimate it by up to 22.5% in turbulent flow. Cardiologists should consider this potential underestimation in 20% of patients when assessing CFVR.
Area of Science:
- Interventional Cardiology
- Cardiovascular Physiology
- Biomedical Engineering
Background:
- Doppler-tipped coronary guide-wires (FW) are essential for quantitative coronary blood flow analysis.
- Coronary flow velocity reserve (CFVR) can remain reduced post-angioplasty, necessitating accurate measurement.
- The impact of turbulent flow on intra-coronary Doppler measurements is not fully understood.
Purpose of the Study:
- To investigate the influence of flow profile changes on the accuracy of intra-coronary Doppler flow velocity measurements.
- To determine the validity of Doppler guide-wire measurements under conditions of laminar versus turbulent flow.
- To assess the clinical implications of turbulent flow on CFVR assessment.
Main Methods:
- In vitro experiments using a pulsatile flow model with glass pipes and heparinized blood to simulate laminar and turbulent flow.
- Average peak velocity (APV) measured with 0.014-inch Doppler guide-wires.
- In vivo measurements in 75 patients during coronary angiography with induced hyperemia via adenosine, alongside quantitative angiography for luminal diameter.
Main Results:
- In vitro, Doppler guide-wire measurements correlated significantly with perfusion volumes under laminar flow (r2 > 0.85).
- Under turbulent flow (Reynolds number > 500), volume calculations underestimated actual perfusion by up to 22.5%.
- In vivo, 20% of patients exhibited maximum APV exceeding the critical Reynolds number threshold, indicating potential underestimation of CFVR.
Conclusions:
- Doppler guide-wires are valid for coronary flow velocity measurement below a critical Reynolds number of 500.
- Turbulent flow can lead to underestimation of CFVR by up to 22.5%, impacting clinical decision-making.
- Clinicians should be aware of potential flow velocity underestimation in approximately 20% of patients due to turbulent flow.
Background:
Doppler-tipped coronary guide-wires (FW) are well-established tools in interventional cardiology to quantitatively analyze coronary blood flow. Doppler wires are used to measure the coronary flow velocity reserve (CFVR). The CFVR remains reduced in some patients despite anatomically successful coronary angioplasty. It was the aim of our study to test the influence of changes in flow profile on the validity of intra-coronary Doppler flow velocity measurements in vitro. It is still unclear whether turbulent flow in coronary arteries is of importance for physiologic studies in vivo.
Methods:
We perfused glass pipes of defined inner diameters (1.5-5.5 mm) with heparinized blood in a pulsatile flow model. Laminar and turbulent flow profiles were achieved by varying the flow velocity. The average peak velocity (APV) was recorded using 0.014 inch FW. Flow velocity measurements were also performed in 75 patients during coronary angiography. Coronary hyperemia was induced by intra-coronary injection of adenosine. The APV maximum was taken for further analysis. The mean luminal diameter of the coronary artery at the region of flow velocity measurement was calculated by quantitative angiography in two orthogonal planes.
Results:
In vitro, the measured APV multiplied with the luminal area revealed a significant correlation to the given perfusion volumes in all diameters under laminar flow conditions (r2 > 0.85). Above a critical Reynolds number of 500--indicating turbulent flow--the volume calculation derived by FW velocity measurement underestimated the actual rate of perfusion by up to 22.5 % (13 +/- 4.6 %). In vivo, the hyperemic APV was measured irrespectively of the inherent deviation towards lower velocities. In 15 of 75 patients (20%) the maximum APV exceeded the velocity of the critical Reynolds number determined by the in vitro experiments.
Conclusion:
Doppler guide wires are a valid tool for exact measurement of coronary flow velocity below a critical Reynolds number of 500. Reaching a coronary flow velocity above the velocity of the critical Reynolds number may result in an underestimation of the CFVR caused by turbulent flow. This underestimation of the flow velocity may reach up to 22.5 % compared to the actual volumetric flow. Cardiologists should consider this phenomena in at least 20 % of patients when measuring CFVR for clinical decision making.
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