Hydrostatic error

What is the problem with all sensor-tipped wires?

  • All currently available pressure wires are affected by this physical phenomenon causing the so-called hydrostatic error1, 2, 3
  • Incremental change in blood pressure caused by the natural force of hydrostatic pressure
  • In the male LAD (most common case), the average height difference is 5.8 cm (4.5 mmHg)2.
  • The average error in all arteries is 3.5 mmHg (= 0.035 Pd/Pa quote) taking into account the sex and vessel prevalence of stable CAD 2, 3.

How sensor-tipped wires are affected by the hydrostatic error

All currently available wires are sensor-tipped wires having the pressure sensor located at the distal end of the wire. A hydrostatic error occurs due to the height difference between ostium and the distal measurement point1.

Usually, a wire equalization shall minimize pressure differences between Pa and Pd before procedure start. However, since the distal pressure sensor is advanced into the distal coronary vessel after equalization, the height difference between sensor and catheter tip leads to a significant signal error.

This is of particular importance since the hydrostatic error is not obvious to the physician.

Wirecath´s immunity

Wirecath are equalized at ostium according to regular procedure.

The pressure from the water filled Wirecath evens out the local hydrostatic pressure in the body.

Error avoided by physical law which is realized due to the external pressure sensor.

All fluid-filled objects are exposed to hydrostatic pressure  

  • This pressure is naturally exerted by the weight of the fluid above a certain measurement point. For example, higher pressure can be observed at the bottom of a fluid-filled container compared to the top.
  • The same principles apply to the human body. Higher blood pressure is measured at the feet-level compared to the head when standing.
  • The incremental change in blood pressure due to gravity accounts for 0.77 mmHg per cm height difference1

Wirecath´s immunity against the hydrostatic error

Wirecath is immune to the hydrostatic error, since its water filled interior compensates the hydrostatic pressure in the body

Misclassification due to hydrostatic error

> Hydrostatic error is of significant size compared to the cut-off limits of all indices2,3

> The error has a lot more effect on resting indices as compared to FFR1 

> Causes 24% vessel misclassification (16% hyperemia, 24% at resting Pd/Pa4,5,6, 22% at dPR6,7)

Precise pullback for PCI planning with the Wirecath®

Pullbacks during rest avoid cross-talk between lesions and are useful for PCI planning 8.

  • No hydrostatic error is added to the measurement signal.
  • PCI planning will be accurate when using the Wirecath®, especially during rest.
  • Therefore, the treatment decision might change.

Class effect among resting indices

Instantaneous wave-free ratio (iFR) and similar diastolic indices have emerged over the last few years. However, the these indices are not available in monitoring systems with integrated FFR software. 

  • Without any restrictions, resting Pd/Pa may be used, having an excellent agreement to iFR9.
  • Recent studies demonstrate that resting Pd/Pa and iFR have equivalent diagnostic performance 10, 11.
  • A weakness of iFR, compared to Pd/Pa, is that iFR works differently in the right coronary artery compared to the left coronary artery12

Based on the CONTRAST4 study results, 763 patients included,  and RESOLVE13, 1768 patients included, it was shown that

  • Pd/Pa has excellent correlation with iFR of r ≤ 0.974,13.
  • Not affected by the patient conditions i.e. acute coronary syndrome/stable angina9.
  • When iFR is measured twice in the same vessel twice, the same correlation of r = 0.96 between repeated measurements was shown4.

ACC/AATS/AHA/ASE/ASNC/SCAI/SCCT/ STS 2017 Appropriate Use Criteria for Coronary Revascularization in Patients With Stable Ischemic Heart Disease

  • ”Newer physiological measurements that do not require hyperemia measure […] during the whole cardiac cycle or the wave-free portion of the cycle […] have similar diagnostic concordance with FFR […]” 14.
  • ”Substitution of 1 of the newer physiological measurements for FFR may be considered provided the appropriate reference values are used” 14.

1. Kawaguchi Y. et al. Impact of Hydrostatic Pressure Variations Caused by Height Differences in Supine and Prone Positions on Fractional Flow Reserve Values in the Coronary Circulation. J Interv Cardiol. 2019; 2019: 4532862.

2. Härle T. et al.  Effect of Coronary Anatomy and Hydrostatic Pressure on Intracoronary Indices of Stenosis Severity. JACC Cardiovasc Interv. 2017 Apr 24;10(8):764-773.

3. Al-Janabi F. et al. Coronary artery height differences and their effect on fractional flow reserve. Cardiol J. 2019 Mar 26.

4. Johnson NP. et al. Continuum of Vasodilator Stress From Rest to Contrast Medium to Adenosine Hyperemia for Fractional Flow Reserve Assessment. JACC Cardiovasc Interv. 2016 Apr 25;9(8):757-767. (CONTRAST)

5. 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)

6. Cavis Technologies data on file.

7. Svanerud J. et al. Validation of a novel non-hyperaemic index of coronary artery stenosis severity: the Resting Full-cycle Ratio (VALIDATE RFR) study. EuroIntervention. 2018 Sep 20;14(7):806-814.

8. Kikuta Y. et al. Pre-Angioplasty Instantaneous Wave-Free Ratio Pullback Predicts Hemodynamic Outcome In Humans With Coronary Artery Disease Primary Results of the International Multicenter iFR GRADIENT Registry. JACC Cardiovasc Interv. 2018 Apr 23;11(8):757-767.

9. Kobayashi Y. et al. Agreement of the Resting Distal to Aortic Coronary Pressure With the Instantaneous Wave-Free Ratio. J Am Coll Cardiol. 2017 Oct 24;70(17):2105-2113.

10. Ahn JM. et al. IRIS-FFR: Prognostic Performance of Five Resting Pressure-Derived Indexes of Coronary Physiology. Retrieved April 11, 2019, from https://www.tctmd.com/slide/iris-ffr-prognostic-performance-five-resting-pressure-derived-indexes-coronary-physiology.

11. Lee JM, et al. Similarity and Difference of Resting Distal to Aortic Coronary Pressure and Instantaneous Wave-Free Ratio. J Am Coll Cardiol. 2017 Oct 24;70(17):2114-2123.

12. Gore A. et al. TCT-154 Diagnostic Accuracy of iFR Versus FFR in the Left Versus Right Coronary Artery. J Am Coll Cardiol. 2018 Sep 21;72(13): .

13. Jeremias A. et al.  Multicenter core laboratory comparison of the instantaneous wave-free ratio and resting Pd/Pa with fractional flow reserve: the RESOLVE study. J Am Coll Cardiol. 2014 Apr 8;63(13):1253-1261. 

14. Patel MR. et al. ACC/AATS/AHA/ASE/ASNC/SCAI/SCCT/STS 2017 Appropriate Use Criteria for Coronary Revascularization in Patients With Stable Ischemic Heart Disease: A Report of the American College of Cardiology Appropriate Use Criteria Task Force, American Association for Thoracic Surgery, American Heart Association, American Society of Echocardiography, American Society of Nuclear Cardiology, Society for Cardiovascular Angiography and Interventions, Society of Cardiovascular Computed Tomography, and Society of Thoracic Surgeons. J Am Coll Cardiol. 2017 May 2;69(17):2212-2241.

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