Coronary Flow Reserve (CFR)

What to do when there are no obstructive lesions ?

What is the problem with current diagnostic tools used to measure CFR?

> There is an large unmet need to diagnose patients with non-obstructive coronary artery disease by measuring coronary flow reserve (CFR) 1, 2.

Existing invasive tools for measuring CFR have a number of disadvantages preventing their integration in standard care

> Alternatives are needed to help those patients and improve their outcome!

Promising research – Pressure-derived CFR with Wirecath

In-vitro study: Pressure-derived CFR vs. Thermodilution

Wirecath has been assessed regarding the possible use for pressure-derived CFR. 

In a Wetlab with pulsatile flow, we compared the accuracy of pressure-derived CFR with the thermodilution-CFR method by Abbott Medical.

CFR was overestimated by both methods to similar extent in this in-vitro model.

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

The in-vitro test was performed in a simulated coronary model. The artery was represented by a 3 mm inner diameter silicone tube. 55 different cases with different flow levels divided in 3 different stenosis types were evaluated by each method, thermodilution and pressure-derived CFR. 

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 ≤0.984 (Average = 0.97)
0.744 ≤ FFR ≤0.958  (Average = 0.88)
(In line with CorMicA trial patients2)

The pressure measurements by Wirecath were used to calculate the pressure-derived 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.

Pressure-derived CFR affected by diffuse or focal stenoses?

In the same Wetlab, we assessed the effect of focal versus diffuse stenosis on the accuracy of the pressure-derived CFR.

  • Accuracy was only slightly affected by the two simulated types of stenosis, diffuse or focal.
  • When merging diffuse and focal data, it shows a good correlation with true CFR.

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 patients2)

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.

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 below

Use a sensor-tipped wires for pressure-derived CFR?

  • All available sensor-tipped wires are prone to the hydrostatic error
  • This error introduces an average deviation of 3.5 mmHg to the measurements.
  • When adding the conservative average hydrostatic error of 1.0 mmHg, range -2 mmHg to +1 mmHg, randomly to Pd in order to simulate those sensor-tipped wires, the correlation between pressure-derived CFR and true CFR is abolished.
  • A resting Pd/Pa should be at maximum 0.98 to use pressure-derived CFR with Wirecath.

Sensor-tipped wires are not reliable for pressure derived CFR considering the effect of hydrostatic error!

Future research

Future research is required to further investigate the potential of using the Wirecath for pressure derived CFR measurements. It can be concluded

  • Pressure-derived CFR with excellent precision compared to thermodilution in a bench model.
  • Accuracy realized through the absence of hydrostatic error and drift.
  • Significant time saving advantage.

Opens new research field to help patients with non-obstructive CAD using accurate and simple CFR measurements.

About

Cavis Technologies was founded 2015. It’s an innovative start-up company supplying invasive cardiology care units with a unique device for improved control and safety.

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Contact

Cavis Technologies AB

Kungsängsvägen 29A

75323 Uppsala

Sweden

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