Invasive Cardiac Assessment
Coronary Physiology
Pressure wire assessment inside the coronary arteries determines the functional significance of narrowings — answering not just whether a blockage is present, but whether it is actually limiting blood flow and causing symptoms. Dr Nijjer co-developed iFR, the technique now adopted worldwide and embedded in international guidelines.
P
Understanding Blood Flow in the Heart
What Is Coronary Physiology?
Coronary angiography shows the anatomy of the coronary arteries — the shape of a narrowing and its approximate degree of stenosis. But anatomy alone is an imperfect guide to treatment. A narrowing that looks significant on an angiogram may carry sufficient blood flow at rest and during exercise, causing no ischaemia. Conversely, a lesion that appears moderate on the image may critically limit perfusion. Treating solely on the basis of appearance leads to unnecessary stenting in some patients and missed interventions in others.
Coronary physiology resolves this uncertainty. A thin pressure-sensing wire, finer than a human hair, is passed across the narrowing to measure the pressure drop it creates. This provides a direct, real-time measure of whether the lesion is haemodynamically significant — limiting blood flow in a way that is causing or is likely to cause symptoms. Multiple large randomised trials have shown that physiologically-guided decisions produce better patient outcomes than anatomy-guided decisions alone.
The DEFER, FAME, and FAME 2 trials established FFR-guided intervention as superior to angiography-guided treatment. The DEFINE-FLAIR and iFR-SWEDEHEART trials subsequently demonstrated that iFR — developed at Hammersmith Hospital — produces equivalent clinical outcomes to FFR without the need for adenosine.
Dr Nijjer and iFR. Dr Nijjer was a principal investigator in the development of iFR (Instantaneous wave-free ratio) at Imperial College and Hammersmith Hospital — a technique now used in tens of thousands of patients worldwide and incorporated into European and US cardiology guidelines. He has published over 50 papers on coronary physiology and is a recognised international expert in pressure wire assessment, iFR pullback, and functional coronary intervention planning.
Physiological Assessment Tools
Pressure Wire Indices
Several indices can be measured from a pressure wire. Each has a specific measurement window, clinical evidence base, and threshold for significance. Dr Nijjer selects the most appropriate index for each patient and clinical context.
Pioneered at Hammersmith Hospital, Imperial College
iFR
Instantaneous Wave-Free Ratio
≤ 0.89
Haemodynamically
significant → treat
significant → treat
AdenosineNot required
WindowDiastolic rest period — natural low-resistance phase
Key trialsDEFINE-FLAIR · iFR-SWEDEHEART · ADVISE registry
- No adenosine side-effects (chest tightness, breathlessness)
- Non-inferior to FFR in major outcome trials
- Faster acquisition — ideal for multi-vessel disease
- Enables iFR pullback for vessel mapping
- Incorporated in ESC and ACC/AHA guidelines
FFR
Fractional Flow Reserve
≤ 0.80
Haemodynamically
significant → treat
significant → treat
AdenosineRequired — IV or intracoronary bolus
WindowMaximal hyperaemia (full coronary vasodilation)
Key trialsDEFER · FAME · FAME 2
- Most extensive long-term outcome evidence
- Established standard prior to iFR
- Preferred in equivocal iFR zone (0.86–0.93)
- Validated across all coronary territories and lesion types
RFR · dPR
Pd/Pa · QFR
Pd/Pa · QFR
Non-Hyperaemic Resting Indices
≤ 0.89
Approximate threshold
(varies by index)
(varies by index)
AdenosineNot required
PrincipleResting pressure ratio — similar concept to iFR, different measurement windows or algorithms
QFRAngiography-derived FFR — no wire required, computed from angiogram images
- Available on most modern pressure wire platforms
- Broadly similar diagnostic performance to iFR
- QFR useful for planning when wire not yet placed
Vessel Mapping
iFR Pullback
iFR
Pullback
Mapping Pressure Loss Along the Artery
A standard iFR measurement tells you that a vessel is haemodynamically significant — but not precisely where along its length the pressure is being lost. In a diseased artery with multiple narrowings or long segments of diffuse plaque, identifying the dominant site of pressure loss is critical for planning treatment.
iFR pullback involves slowly withdrawing the pressure wire from the distal tip of the artery back towards the guiding catheter while recording iFR continuously. This generates a real-time physiological map of the entire vessel, showing exactly where iFR falls and by how much. The pattern of pressure loss — whether focal or diffuse — determines the optimal treatment strategy.
Dr Nijjer co-developed the pullback technique and led the ADVISE Pullback Registry, demonstrating that it accurately predicts the post-intervention iFR — a form of virtual PCI performed before any stent is deployed. This allows precise planning: the operator can identify which lesion to treat, whether a single stent or multiple stents are needed, and what the physiological result is likely to be.
Focal Disease Pattern
The iFR trace is normal proximally, then drops sharply at a discrete stenosis, and remains stable distal to it. This indicates that a single dominant lesion is responsible for all the haemodynamic impairment. Stenting that segment is predicted to normalise physiology — and the pullback allows verification before the stent is placed.
→ Targeted stenting likely to normalise iFR
Diffuse Disease Pattern
The iFR declines gradually along the entire length of the artery without a dominant focal drop. No single lesion accounts for the total pressure loss. Stenting any one segment will improve but not normalise iFR, and multiple stents carry their own risks. In this pattern, optimal medical therapy is often preferred over intervention.
→ Medical therapy often preferable to stenting
Beyond Obstructive Disease
Microvascular & Vasomotor Testing
Many patients with genuine cardiac symptoms have normal or near-normal coronary arteries on angiography. In these cases, the problem lies not in an obstructive plaque but in the behaviour of the smaller vessels and the vessel wall itself. Dr Nijjer performs a comprehensive range of specialist tests to diagnose these conditions.
ACh
Coronary Spasm Testing
Coronary spasm — an inappropriate constriction of the coronary artery in response to triggers such as cold, stress, or spontaneously — is a significant and frequently missed cause of angina and acute coronary events. Symptoms often occur at rest, at night, or without the exertional pattern typical of obstructive disease.
Provocation testing uses intracoronary acetylcholine (ACh) infused in graded doses during angiography, with continuous ECG and pressure monitoring. Two distinct patterns are identified:
- Epicardial vasospasm: ≥90% transient narrowing of a main coronary artery accompanied by angina and ischaemic ECG changes. Treated with calcium channel blockers and long-acting nitrates.
- Microvascular spasm: Angina and ECG changes occur without visible epicardial narrowing — spasm confined to the small vessels. Often responds to calcium channel blockers, with avoidance of vasoconstrictive triggers.
MB
Myocardial Bridging
In some individuals, a segment of the coronary artery — most commonly the left anterior descending artery — runs within the heart muscle rather than on its surface. During each heartbeat, the contracting muscle squeezes the artery, temporarily reducing or obstructing flow. This is visible on angiography as the characteristic "milking effect."
While mild bridging is common and usually benign, severe bridging can cause exertional angina, ischaemia, and — rarely — life-threatening arrhythmias. The functional significance is assessed with a pressure wire during both rest and provocative testing.
- iFR quantifies the haemodynamic impact of the bridge during the diastolic period
- FFR during dobutamine stress unmasks dynamic obstruction not apparent at rest
- Treatment: beta-blockers, calcium channel blockers; surgical myotomy reserved for refractory severe cases
MVA
Microvascular Angina
Microvascular angina — also termed cardiac syndrome X or ischaemia with non-obstructive coronary arteries (INOCA) — affects a substantial proportion of patients presenting with chest pain, particularly women. Symptoms are genuine and can be severely limiting despite a normal angiogram and no obstructive disease.
Diagnosis requires specific physiological measurements that assess the function of the microvasculature directly:
- Coronary Flow Reserve (CFR): The ratio of maximal to baseline coronary blood flow. CFR below 2.0 indicates impaired microvascular vasodilatory capacity.
- Index of Microcirculatory Resistance (IMR): A thermodilution-derived measure of microvascular resistance. IMR above 25 units indicates elevated resistance within the small vessels, independent of epicardial disease.
- Treatment: ACE inhibitors, calcium channel blockers, beta-blockers, ivabradine, and targeted lifestyle modification each play a role depending on the precise physiological profile identified.
What to Expect
The Pressure Wire Procedure
01
Access & Preparation
A fine sheath is placed in the radial artery at the wrist (or femoral artery at the groin) under local anaesthetic. A guiding catheter is advanced to the mouth of the coronary artery. Heparin anticoagulation is given. The procedure typically takes 30–60 minutes for a straightforward physiological assessment.
02
Diagnostic Angiogram
Contrast dye outlines the coronary arteries under X-ray. Dr Nijjer identifies which lesions require physiological assessment and selects the appropriate pressure wire index — iFR, FFR, or microvascular testing — based on the angiographic findings and clinical context.
03
Wire Placement
The pressure wire is advanced through the guiding catheter and across the narrowing into the distal vessel. Correct positioning is confirmed. Baseline pressure measurements are recorded with the wire tip at rest. The wire-to-aortic pressure ratio (Pd/Pa) provides an initial resting index before iFR or FFR is formally calculated.
04
Index Measurement
iFR is recorded automatically over several heartbeats. If FFR is required, adenosine is given intravenously or directly into the coronary artery to induce maximal vasodilation. For iFR pullback, the wire is slowly withdrawn whilst continuously recording. For microvascular testing, additional protocols including thermodilution and acetylcholine infusion are performed.
05
Results & Decision
Dr Nijjer reviews the physiological data immediately and discusses the findings with you. If the lesion is haemodynamically significant, angioplasty and stenting may proceed in the same session or be planned as a separate procedure. If non-significant, intervention is deferred and medical treatment optimised. You are typically discharged the same day.
Questions About Your Coronary Arteries?
Dr Nijjer offers expert physiological assessment of coronary disease — from straightforward iFR measurement to complex multi-vessel pullback analysis and specialist microvascular testing.