Research related to Cavis Wirecath
Pressure-derived CFR was shown to correlate to bolus thermodilution-CFR and echocardiography-CFR in a Wirecath study, see Latest study abstract (link)
Pressure-derived MRR was shown to correlate to invasive doppler derived MRR when avoiding hydrostatic errors in a study by Zsolt K. et al. (link).
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), resistive reserve ratio (RRR) (2) or microvascular resistance reserve (MRR) (3)
Existing invasive tools for measuring CFR 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 (4). 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 (5).
Pressure-derived CFR using the formula CFRmax=(1-FFR)/(1-Pd/Pa) has been proposed (6). However, this method is highly affected by hydrostatic errors, especially in patients having non-significant FFR and Pd/Pa values. For example, a true Pd/Pa of 0.98 while a hydrostatic pressure affected value of 0.96 will have large impact on the CFR when using the formula above.
RRR is easily derived by pressure from CFR by the formula RRR = Pd rest/Pd hyp x CFR (2).
MRR is easily derived by pressure from CFR by the formula MRR = Pa rest/Pd hyp x CFR (3).
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. 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 existing 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 velocities (5).
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 patients (7)) The pressure measurements by Wirecath were used to calculate pressure-derived CFR according to CFR = (1-FFR) / (1-Pd/Pa) (6).
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 negative angle edge and an inner diameter of 1.7 mm
300 mm tube with an inner diameter of 3.2 mm
Diffuse stenosis
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).
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Rarely receive a definitive diagnosis
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Are frequently labelled and managed inappropriately
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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.
