Cardiology · Coronary Interventions
FFR / RFR
Measuring whether a blockage is truly starving the heart
Also known as: fractional flow reserve · FFR test · resting full-cycle ratio · pressure wire study · coronary physiology · FFR-guided PCI
Medically reviewed by Dr Kunal Ajay Patankar, DrNB (Cardiology) · July 2026
What it is
Think of your coronary arteries as pipes feeding the heart muscle. An angiogram is a photograph of the pipes — it shows where one looks narrowed, but a photograph can't tell you whether the pressure at the tap beyond it has actually dropped. A narrowing that looks alarming may still deliver plenty of flow; one that looks modest may be choking the muscle. Judging it by eye gets this wrong surprisingly often.
FFR and RFR settle it by measuring, not guessing. A wire finer than the lead in a pencil carries a pressure sensor across the narrowing and reads the pressure just beyond it against the pressure just before it. If the blockage is squeezing off flow, the pressure downstream falls and the ratio drops below a known cut-off. If flow is preserved, the ratio stays high — and you have proof the narrowing can be safely left alone.
The only difference between the two is the condition of measurement. FFR is read at maximum flow, forced by a few seconds of a drug called adenosine, which is when a serious blockage shows its hand. RFR reads the same pressure relationship at rest, in the quiet part of each heartbeat, with no drug at all. Both point to the same decision: stent the blockages that are truly limiting flow, and safely leave alone the ones that aren't.
Who it's for
- A blockage of borderline severity (roughly 40–70%) where the angiogram alone can't settle whether it needs treatment
- Several narrowings, to identify which one is truly responsible for symptoms
- To safely avoid a stent when a narrowing looks concerning but isn't limiting flow
- Multi-vessel or left-main disease, to plan stenting versus bypass surgery
- Checking a bystander lesion, or a segment near a previous stent
Signs you might need it
- Angina or breathlessness together with a borderline narrowing found on angiography
- Symptoms that don't clearly match what the angiogram shows
- A narrowing your cardiologist judges as 'intermediate' — not clearly mild, not clearly severe
How we confirm you need it
- Coronary angiography first shows the narrowing and its rough severity
- When the angiogram leaves genuine doubt about how significant a lesion is, FFR or RFR is measured in the same sitting
- The pressure-wire number, not the eye, then decides whether the lesion is treated
How it happens, step by step
1
Done during your angiogram
FFR/RFR is not a separate admission — it is added during coronary angiography or angioplasty, through the same wrist catheter, once a borderline narrowing is seen.
2
Passing the pressure wire
A wire with a tiny pressure sensor near its tip is guided across the narrowing. It reads the blood pressure just beyond the blockage and compares it with the pressure just before it.
3
FFR — measuring at maximum flow
For FFR, a short-acting drug (adenosine) briefly opens the small vessels to create maximum flow, the condition under which a significant blockage reveals itself. You may feel a few seconds of flushing or breathlessness that passes quickly.
4
RFR — measuring at rest
RFR reads the pressure ratio at rest, across the natural resting part of the heartbeat, with no drug needed — quicker, and without adenosine's brief side effects.
5
Reading the number, deciding together
The value appears at once. Below the cut-off, the blockage is flow-limiting and a stent is likely to help; above it, the narrowing is not significant and is better left to medicines. We talk it through with you before doing anything.
Inside a real procedure
Real, de-identified views from Dr Kunal Patankar's own cases — shared so you can see what this actually looks like.
The benefits
- Turns a borderline picture into an objective, measured decision
- Prevents unnecessary stents — sparing you a device, lifelong dual antiplatelet medication, and its risks
- Makes sure a genuinely significant blockage is not left untreated
- Guideline-recommended, and shown in large trials to improve outcomes over treating on the angiogram alone
- RFR needs no drug, so for many patients it is quick and free of adenosine's brief discomfort
The risks
- The pressure wire carries the same small, rare risks as any coronary wire — vessel spasm or, very rarely, injury to the artery
- Adenosine (for FFR) commonly causes a few seconds of flushing, chest heaviness or breathlessness, and briefly slows the heart — it wears off within seconds of stopping the drug
- Adenosine is used with caution in people with significant asthma; RFR, needing no drug, is the alternative in that situation
- Overall the added risk is very small, weighed against the value of getting the treatment decision right
Alternatives we'll discuss
Angiogram (visual) assessment alone
Deciding from the picture without measuring. Fine for clearly mild or clearly severe blockages, but for the borderline lesions in between, the eye is often wrong — which is exactly the gap FFR and RFR fill.
Non-invasive stress testing
A stress echo or nuclear scan can show whether a region of muscle is short of blood, before or instead of the cath lab. It points to a problem but, unlike a pressure wire, cannot measure a specific lesion from inside the artery.
Intravascular imaging (OCT / IVUS)
OCT and IVUS look at the artery wall and measure the narrowing's dimensions, rather than its effect on flow. Physiology (FFR/RFR) and imaging answer different questions and are often used together.
Preparing for it
- Usually no separate preparation — it is done within your planned angiogram or angioplasty
- If FFR with adenosine is planned, avoid caffeine (coffee, tea, cola, chocolate) for about 12–24 hours beforehand, as it blunts the drug
- Tell your team if you have asthma, so RFR or an alternative is chosen instead of adenosine
- Otherwise, the same simple preparation as a coronary angiogram
Recovery
- Nothing extra — your recovery is that of the angiogram or angioplasty it was part of
- Any adenosine effect (flushing, a heavy chest, breathlessness) lasts only seconds and is gone before you leave the table
- Same wrist-band care and same-day discharge as a diagnostic angiogram, when no stent was needed
Results & durability
- The number is known immediately and drives the decision then and there
- A non-significant value (FFR above 0.80, RFR above 0.89) means no stent — medicines and risk-factor control instead, with the reassurance that the narrowing was measured, not guessed
- A significant value means the stent goes exactly where it will help, often in the same sitting
- Either way, the treatment matches the physiology of your own arteries
Cost & insurance
What affects the cost
- FFR/RFR adds the cost of the pressure wire — and, for FFR, the adenosine — to your angiogram
- That is frequently offset by avoiding a stent you don't need, and the years of medication that follow one
- Cover under insurance varies by policy; we explain what applies to you before proceeding
- For a figure specific to your case, please book a consultation rather than rely on generic online prices
Common questions
Why do I need FFR or RFR if the angiogram already shows the blockage?
An angiogram shows how a narrowing looks, not whether it is actually starving the muscle of blood. Many borderline blockages look worse than they behave, and some look milder than they are. FFR and RFR measure the real effect on flow, so a stent goes in only where it will genuinely help.
What is a normal or 'safe' value?
For FFR, above 0.80 means the blockage is not flow-limiting and a stent can be safely deferred; 0.80 or below favours treating it. For RFR, the cut-off is 0.89. We discuss your exact numbers with you on the spot.
Will I feel anything?
The wire itself is painless. With FFR, the adenosine can cause a few seconds of flushing, a heavy chest or breathlessness while it works — uncomfortable but brief and harmless. RFR needs no drug, so there is nothing to feel.
What is the difference between FFR and RFR?
Both measure the pressure a blockage causes. FFR does it at maximum flow, created with adenosine; RFR does it at rest, without any drug. They answer the same question by different routes, and large studies show they agree closely and lead to equally good outcomes.
Does a good value mean I don't need a stent?
Often yes — and that is the point. A non-significant value means the narrowing is not the culprit, and you are spared a stent you don't need, along with its lifelong medication and small risks. Medicines and risk-factor control take over.
Is it safe?
Very. It adds a fine wire, and for FFR a brief drug, to a procedure you are already having. Serious complications are rare, and the information it gives prevents both unnecessary stents and missed significant disease.
Should I stop my coffee or tea before it?
If FFR with adenosine is planned, we usually ask you to avoid caffeine — coffee, tea, cola, chocolate — for about 12–24 hours beforehand, because caffeine blunts adenosine's effect. RFR is unaffected. Your team will give you exact instructions.
Does it cost much more than an angiogram?
It adds the cost of the pressure wire, and adenosine for FFR, to the angiogram. That cost is often offset many times over by avoiding an unnecessary stent — both the device and the years of medication that would follow it.
References
- 2024 ESC Guidelines for the management of chronic coronary syndromes ↗
- 2021 ACC/AHA/SCAI Guideline for Coronary Artery Revascularization ↗
Medically reviewed by Dr Kunal Ajay Patankar, DrNB (Cardiology) · Last reviewed July 2026. This page is educational and not a substitute for a personal consultation.
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