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Research connected to Cavis Wirecath pressure guide wire

Clinical studies involving Wirecath are ongoing. Please contact us for more information.

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Clinical importance of simple and accurate CFR measurements

There is a large unmet need to diagnose patients with non-obstructive coronary artery disease (NOCAD) by measuring coronary flow reserve (CFR) (1) and Resistive Reserve ratio (RRR) (2).

 

Existing invasive tools for measuring CFR and RRR have a number of disadvantages preventing their integration into standard care. The thermodilution technique has weak test-retest reliability as manual injections cause data variability (3). The Doppler technique is highly dependent on the skill/experience of the operator and there is insufficient quality of Doppler traces in up to 30% of measurements (4).

RRR is easily derived by pressure from CFR by the formula RRR = Pd rest/Pd hyp x CFR (2).

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Pressure-derived CFR with
Cavis Wirecath

In-vitro study: Accuracy in pressure-derived CFR vs. thermodilution-CFR

Wirecath has been assessed regarding possible use for pressure-derived CFR. In a wetlab with pulsatile flow, we compared the accuracy of pressure-derived CFR using Wirecath with thermodilution-CFR using a commercially available pressure wire. CFR was overestimated by both methods to a similar extent in this in-vitro model.

Result: Pressure-derived CFR had better correlation with true CFR compared to thermodilution.

How we tested in the wetlab


The in-vitro test was performed in a simulated coronary model. The artery was represented by a 3 mm inner diameter silicone tube. 40 different cases with different flow levels were evaluated in each stenosis type, focal and diffuse. The reference sensor was made by weighing exiting water on a scale to measure the true coronary flow ratio (CFR flow) with less than 2% error. The flow velocity range was 9-40 cm/s during rest and 17-73 cm/s during hyperemia representing clinically relevant velocities5. Pd/Pa and FFR in all cases: 0.926 ≤ Pd/Pa ≤0.982 (Average = 0.96) 0.744 ≤ FFR ≤0.953 (Average = 0.87)
(In line with CorMicA trial patients (5)) The pressure measurements by Wirecath were used to calculate the CFR according to CFR= (1-FFR) / (1-Pd/Pa). Delta P values below 1 mmHg were excluded since not possible to measure with sufficient accuracy.





In-vitro study: Effects of focal vs. diffuse disease on accuracy in pressure-derived CFR

In the wetlab, we assessed the effects of focal versus diffuse disease on the accuracy of pressure-derived CFR.

 

Result: Accuracy was only slightly affected by the two simulated types of disease, diffuse and focal. When merging diffuse and focal data, there was a good correlation with true CFR.

Focal stenosis
Constriction with a length of 12 mm and an inner diameter of 1.7 mm

Diffuse stenosis

300 mm tube with an inner diameter of 3.2 mm and a slight constriction as shown in the image above

How we tested in the wetlab


The in-vitro test was performed in a simulated coronary model. The artery was represented by a 3 mm inner diameter silicone tube. 40 different cases with different flow levels were evaluated in each stenosis type, focal and diffuse. The reference sensor was made by weighing exiting water on a scale to measure the true coronary flow ratio (CFR flow) with less than 2% error. The flow velocity range was 9-40 cm/s during rest and 17-73 cm/s during hyperemia representing clinically relevant velocities5. Pd/Pa and FFR in all cases: 0.926 ≤ Pd/Pa ≤0.982 (Average = 0.96) 0.744 ≤ FFR ≤0.953 (Average = 0.87)
(In line with CorMicA trial patients (5)) The pressure measurements by Wirecath were used to calculate the CFR according to CFR= (1-FFR) / (1-Pd/Pa). Delta P values below 1 mmHg were excluded since not possible to measure with sufficient accuracy.





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Coronary Flow Reserve (CFR) measurements

What to do when there are no obstructive lesions?

Approximately 40% of angiography patients have non-obstructive coronary artery disease (1).

  • Rarely receive a definitive diagnosis

  • Are frequently labelled and managed inappropriately

  • Often continue to remain symptomatic

In-vitro study: Effects of hydrostatic error on accuracy in pressure-derived CFR

To simulate Pd-values with hydrostatic errors, the conservative average hydrostatic error of 1.0 mmHg (range -2 mmHg to +1 mmHg) was added randomly to Pd.

 

Result: The correlation between pressure-derived CFR and true CFR was abolished.

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Future research

Future research is required to further investigate the potential of using the Cavis Wirecath for NOCAD diagnosis.

Summary:

  • Pressure-derived CFR can be measured with excellent precision compared to thermodilution in a bench model

  • Accuracy realized through absence of hydrostatic error and drift

  • Significant time saving advantage

  • Also easy to derive Resistive Reserve Ratio (RRR) from pressure measurements

 

With Wirecath, a new research field is opened up, to diagnose patients with NOCAD.