Clinical studies and cases related to Cavis Wirecath
Finished clinical studies:
Sahlgrenska, Gothenburg, Sweden,
Simultaneous measurements with a Wirecath and a sensor-tipped wire showed that
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the hydrostatic error was removed
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drift was reduced
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pressure-derived CFR correlated to other CFR methods
when using Wirecath
Catharina, Eindhoven, The Netherlands
Clinical case reports:
Case presented at PCRonline, showing that hydrostatic error caused misclassification of an LAD stenosis.
Case presented at CRTonline, showing that hydrostatic error caused misclassification of an RCA stenosis.
Data on effect of hydrostatic pressure error
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A clinical consensus statement from the EAPCI/ESC identifies hydrostatic effects as one cause for normal FFR values to be different in LAD and non-LAD (0.92 and 0.96) (1).
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In the LAD (most common case), the average height difference is 5.8 cm (4.5 mmHg) in men and 4.3 cm (3.3 mmHg) in females (2).
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Hydrostatic pressure errors causes up to 22% vessel misclassification (2, 4, 5)
- 13% for hyperemic (FFR) measurements
- 21% for dPR measurements
- 22% for resting Pd/Pa measurements
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When avoiding hydrostatic errors in FFR measurements and keeping the 0.80 cut-off, the amount of significant lesions will be reduced with 17% (2, 4, 5)
The effect of removing hydrostatic error on existing study results
Is the cut-off 0.80 too high?
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Ahn et al. (6) studying 1001 lesions with FFR 0.75-0.80 found no significant difference in outcome between deferred and treated patients. This implies the optimal FFR cut-off is lower than 0.80. 563 of these lesions where deferred and in this group events were underrepresented in LAD and overrepresented in non-LAD. If the hydrostatic error would have been avoided, the results would have been more equal for LAD and non-LAD, suggesting that a more optimal cut-off would have been applied.
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Buccheri et al. (7) studying 5066 patients found that the 0.80 cut-off is too high which causes higher event rates in treated patients.
Why is Post-PCI FFR different in LAD and non-LAD?
Studies (8-9) show that post-PCI FFR is generally much lower in LAD than in non-LAD arteries. Hydrostatic-error free measurements would have made the rate of successful post-PCI FFR higher in the LAD and lower in non-LAD, and therefore the success rate in LAD and non-LAD would have been more similar.
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Collet et al. (8) studying 2760 patients found that the average difference in post-PCI FFR between LAD and non-LAD vessels was 0.064, consistent with the expectation regarding hydrostatic effects (LAD 0.04 lower from a 5-cm elevation, LCX or RCA 0.02 higher because of a 3- to 4-cm depression; net difference = 0.06). This may influence the predictive capacity of post-PCI FFR.
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Hwang et al. (9) studying 835 patients concluded the optimal cut-off values of post-PCI FFR for predicting target vessel failure were 0.82 and 0.88 in the LAD and non-LAD, respectively. These cut-offs correspond to the difference in hydrostatic error between LAD and non-LAD (2, 3).
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Shin et al. (10) studying 588 patients found that post-PCI FFR ≤0.80 were 55% more common among LADs than among non-LADs, while post-PCI Pd/Pa ≤0.92 were 250% more common among LADs than among non-LADs. The ability to predict target vessel failure (TVF) was poor for post-PCI Pd/Pa compared to post-PCI FFR and the same for iFR and dPR as for Pd/Pa.
Cost savings when avoiding hydrostatic errors
When avoiding hydrostatic errors in FFR measurements and keeping the 0.80 cut-off, the amount of significant lesions will be reduced with up to 17%, see table below from (5), which also seems beneficial to outcome (6-8). This will lead to less PCI and also less CABG since some three-vessel disease will be down-graded to one/two-vessel disease.
Table from Florie et al (5)
When the studies iFR-Swedeheart (11) and DEFINE-FLAIR (12) are merged, it shows that when iFR is used instead of FFR:
PCI is -3,26 %-units
CABG is -1,63 %-units
which saves 206€(PCI)+366€(CABG) = 572€* per patient in a cost analysis (11). A detailed calculation file is provided below.
The merged Wirecath study (13) and PW-COMPARE (14) shows that when avoiding hydrostatic errors
PCI is -6,67 %-units
Assuming the cost for both CABG and PCI is linearly related to amount of PCI, this gives:
6,67/3,26 x 206 = 421€ cost saving per patient related to less PCI
6,67/3,26 x 366 = 749€ cost saving per patient related to less CABG
In the Florie et al study (5), studying effect of avoiding hydrostatic errors
PCI is -8,14 %-units (corresponding to up to 17% PCI reduction)
Assuming the cost for both CABG and PCI is linearly related to amount of PCI, this gives:
8,14/3,26 x 572 = 1428€ cost saving per patient.
Conclusion: Cost savings between 421€ (absolute minimum) and 1428€ per patient are indicated.
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Johnson NP. et al. (2016) Data from: Continuum of vasodilator stress from rest to contrast medium to adenosine hyperemia for fractional flow reserve assessment. Dryad Digital Repository. https://doi.org/10.5061/dryad.f76nv. (CONTRAST)
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Ahn JM. et al. Fractional Flow Reserve and Cardiac Events IRIS-FFR Registry. Circulation. 2017 Jun 6;135(23):2241-2251.
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Buccheri S. et al. FFR in chronic coronary syndrome: a report from SCAAR EuroPCR 2023