Understanding the technology
About This Technology.
The Physiologic Testing System measures blood pressure before and after a coronary artery narrowing using a thin wire with a pressure sensor during catheterization. The ratio between the two pressures, given as an FFR or iFR value, shows whether the narrowing reduces blood flow to the heart muscle. The result helps your doctor decide whether a stent is needed.
Why the Shape of a Narrowing Is Not Enough
Coronary angiography shows how narrow an artery is, but it does not always answer a key question: does the narrowing actually reduce blood flow to the heart muscle? A narrowing that looks moderate on the images can have a large effect on flow, and the reverse is also possible. Physiologic measurement answers this question with a number.
How the Measurement Works
During catheterization, your doctor inserts a thin guide wire with a pressure sensor near its tip. The wire is advanced past the narrowing, and the blood pressure beyond the narrowing is compared with the pressure at the start of the coronary artery.
- FFR (fractional flow reserve) is measured while the small vessels of the heart muscle are widened with a medication, usually adenosine, so that blood flow resembles the flow during heavy exertion. A value of 0.80 or lower generally indicates a narrowing that limits flow.
- iFR (instantaneous wave-free ratio) is measured at rest, during the filling phase between two heartbeats, without a vessel-widening medication. The commonly used threshold is 0.89 or lower.
How the Result Is Used
If the value shows that flow is limited, your doctor may proceed to stent placement during the same procedure or discuss bypass surgery. If the value is normal, the narrowing is usually treated with medication and lifestyle changes, so that stents are placed only where they are needed. With blockages in several arteries, the measurement helps decide which arteries need treatment.
What You Will Experience
The measurement is done in the cath lab as part of coronary angiography or PCI, with the same preparation. You will not feel the sensor wire inside the artery. If your doctor uses adenosine for FFR, you may feel warmth, shortness of breath, or chest pressure while the medication is given. These sensations fade soon after it is stopped. An iFR measurement does not need this medication.
Limitations of the Test
FFR and iFR values can be affected by certain conditions, such as an ongoing heart attack, disease of the small blood vessels in the heart muscle, or severe narrowing of the aortic valve. The measurement also does not show the shape or content of plaque; for that, your doctor uses IVUS or OCT. Your doctor interprets the result together with your symptoms and other tests before deciding on treatment.
Clinical use
Uses and Benefits.
Whether this technology suits your condition is decided by a doctor after an evaluation.
- Assessing whether a moderate narrowing reduces blood flow to the heart muscle
- Helping decide between stent placement and treatment with medication
- Choosing which arteries to treat when several are narrowed
- Assessing a narrowing when symptoms and other test results do not match
- Assessing narrowings in other arteries after a heart attack, as your doctor judges appropriate
Benefits for the Doctor's Assessment
Measures Flow, Not Just the Shape of a Narrowing
Angiography shows how narrow an artery is. FFR and iFR show whether that narrowing actually reduces blood flow to the heart muscle.
Results Available During the Procedure
The value appears on screen during the procedure, so the decision to place a stent can be made right away without a repeat catheterization.
An Option Without Vessel-Widening Medication
With iFR, the measurement is taken at rest without adenosine, so you do not feel the effects of that medication. The DEFINE-FLAIR and iFR-SWEDEHEART trials compared iFR with FFR for guiding PCI.
Recommended for Moderate Narrowings
The 2024 ESC guidelines for chronic coronary syndromes recommend FFR or iFR to assess moderate narrowings before PCI when there is no prior evidence of reduced flow from other tests.
Brief Technical Information
- Examination type
- Pressure measurement inside the coronary artery (coronary physiology)
- Measuring device
- Guide wire with a pressure sensor
- Medication used
- FFR uses a vessel-widening drug such as adenosine; iFR does not
- Radiation
- None from the sensor wire; the procedure is guided by cath lab X-ray
- Typical anesthesia
- Local anesthesia at the puncture site
- Service location
- Cath lab, Coronary Intervention Procedures
