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Physiology
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Guide PCI with coronary physiology

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Physiology fundamentals

 

FFR and iFR can be obtained during routine coronary angiography by using a pressure wire to calculate the ratio between coronary pressure distal to a stenosis and the aortic pressure proximal. When resistance is constant, this ratio represents the potential decrease in coronary flow distal to the coronary stenosis.

 

Learn more about index definition and the wave-free period by clicking below.

Wave icon

Index definition

wave-free icon

Wave-free period

Index definition

Pd Pa vessels

FFR =

Distal Coronary Pressure (Pd)

Proximal Coronary Pressure (Pa)

(During maximal hyperemia)

The FFR modality uses hyperemic agents to achieve a state of constant resistance.

Change in pressure = 

change in flow x constant resistrance

Pd Pa equation

Fundamental equation for relating pressure flow derived from Poiseuille's Law for fluid dynamics

iFR =

Distal Coronary Pressure (Pd)

Proximal Coronary Pressure (Pa)

(During wave-free period)

The iFR modality measures pressure during the wave-free period of the cardiac cycle when resistance is naturally constant.

Benefits of iFR’s wave-free period2,3,4

The cardiac cycle

Pressire, resistance, and intensity during the wave-free period

  • Noise from compression and suction waves is minimized
  • Resistance is constant so ΔP is proportional to ΔQ (flow)
  • Velocity is higher so betterpower to discriminate

iFR (instant wave-Free Ratio)

Unlike FFR, iFR does not require administration of vasodilators because hyperemia is not necessary when measuring pressure during the wave-free period of the cardiac cycle.

 

iFR is proven to reduce procedure time, patient discomfort and cost compared to FFR.2,3,4

Simplifying workflow

 

The iFR modality provides a hyperemia-free measurement in as few as five heartbeats.

iFR vs. FFR: same wire, same system, fewer steps

iFR workflow

iFR workflow

FFR workflow

IntraSight iFR

Single dichotomous cut-point back by data2,3

iFR cut point

Both DEFINE FLAIR and iFR Swedeheart were designed with the dichotomous cut-point of iFR in the iFR arm. With comparable MACE rates to FFR, these results mean the 0.89 cut-point for iFR is proven and backed by more than 4500 patients of outcome data

iFR cut point

iFR Scout pullback technology

 

iFR Scout pullback technology reveals the physiologic profile of the entire vessel, so when you encounter diffuse disease or serial lesions you can make informed treatment decisions.

  • Provides beat-by-beat pressure measurements across the entire vessel, artery by artery
  • Establishes the physiological significance of each vessel and/or individual lesion (focal or diffuse)
  • Provides a clear view of the functional gain
  • Facilitates multiple assessments before, during and after the procedure (without the need for hyperemia)

iFR Scout pullback technology vs. FFR pullback

Green check icon

Benefits of iFR Scout pullback technology5

No hyperemic agent required

Simple graphical display of iFR values through the vessel

Maps the ischemic contribution of each lesion without the confounding effects observed with FFR pullback1

Easily bookmark areas of interest

Orange x icon

Limitations of FFR pullback

Requires IV hyperemia

Can be difficult to interpret

There is an interdependency of pressure gradients in serial lesions

Requires a second FFR pullback after treating the first lesion to assess the “updated” severities of the remaining lesions

No hyperemic agent required

Requires IV hyperemia

Simple graphical display of iFR values through the vessel

Can be difficult to interpret

Maps the ischemic contribution of each lesion without the confounding effects observed with FFR pullback1

There is an interdependency of pressure gradients in serial lesions

Easily bookmark areas of interest

Requires a second FFR pullback after treating the first lesion to assess the “updated” severities of the remaining lesions

iFR Co-registration

Easily determine lesion location with iFR Co-registration.

FFR (Fractional Flow Reserve)

iFR cut point

Philips physiology wires enable measurement of both FFR and iFR, both supported by key industry guidelines including ESC Class IA designation.6

 

FFR ischemia scale

An FFR lower than 0.75-0.80 is generally considered to be associated with myocardial ischemia.7

  • FFR < 0.75 was validated against the 3 gold standard tests to correlate with ischemia with 100% specificity
  • FFR between 0.75 and 0.80 may indicate ischemia
  • FFR > 0.80 is highly likely to be non‑ischemic
  • AUC guidelines reflect the FAME cutoff of 0.80 
    (≤ 0.80 Treat, > 0.80 Defer)

Omni wire orange

OmniWire: the world’s first solid core pressure wire

With an all new workhorse design only OmniWire pressure guide wire combines confidence in wire performance with proven iFR outcomes2,3 and iFR Co-registration, making it easy to benefit from physiology throughout the case.

1. Tonino PA, De Bruyne B, Pijls NH, et al. Fractional flow reserve versus angiography for guiding percutaneous coronary intervention. N Engl J Med. 2009;360:213–24.

2. Davies JE, et al., Use of the Instantaneous Wave-free Ratio or Fractional Flow Reserve in PCI. N Engl J Med. 2017 May 11;376(19):1824-1834.

3. Gotberg M, et al., iFR-SWEDEHEART Investigators.. Instantaneous Wave-free Ratio versus Fractional Flow Reserve to Guide PCI. N Engl J Med. 2017 May 11;376(19):1813-18233.

4. Patel M. “Cost effectiveness of instantaneous wave-Free Ratio (iFR) compared with fractional flow reserve (FFR) to guide coronary revascularization decision-making.” Late-breaking clinical trial presentation at ACC March 10, 2018.

5. Nijjer S, et al. Pre-Angioplasty Instantaneous Wave-Free Ratio (iFR) Pullback Provides Virtual Intervention and Predicts Hemodynamic Outcomes for Serial Lesions and Diffuse Coronary Artery Disease. JACC: Cardiovasc Interv 2014; 12:1386-1396.

6. Neumann, F-J et al. 2018 ESC/EACTS Guidelines on myocardial revascularization. European Heart Journal (2018).

7. Pijls NH, De Bruyne B, Peels K, et al. Measurement of fractional flow reserve to assess the functional severity of coronary-artery stenosis. N Engl J Med 1996 Jun 27. 334(26): 1703-8.

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