Instantaneous Wave-Free Ratio (iFR)
Instantaneous Wave-Free Ratio (iFR)
1. What does the Instantaneous Wave-Free Ratio (iFR) measure?
A. Blood flow velocity during systole
B. Pressure gradient across a coronary lesion during a specific diastolic period
C. Total myocardial oxygen consumption
D. Heart rate variability
Explanation: iFR is a pressure-derived index that measures the pressure gradient across a coronary stenosis during the diastolic “wave-free” period when microvascular resistance is naturally minimized.
2. During which part of the cardiac cycle is iFR specifically measured?
A. Entire diastole
B. Entire systole
C. Wave-free period in diastole
D. Isovolumetric contraction phase
Explanation: iFR is calculated during a specific part of diastole called the wave-free period, where microvascular resistance is stable and minimized, eliminating the need for pharmacologic vasodilation.
3. Which pharmacologic agent is required during an iFR procedure?
A. Adenosine
B. Dobutamine
C. Nitroglycerin
D. None
Explanation: iFR does not require any pharmacologic vasodilators such as adenosine because it utilizes the naturally low resistance wave-free period in diastole.
4. An iFR value < 0.89 suggests:
A. Normal coronary artery
B. Hemodynamically significant stenosis
C. Elevated left atrial pressure
D. Microvascular dysfunction
Explanation: An iFR value below 0.89 indicates a physiologically significant coronary artery lesion that may benefit from revascularization.
5. How does iFR compare to FFR in terms of vasodilator requirement?
A. iFR does not require vasodilators; FFR does
B. Both require vasodilators
C. Only FFR avoids vasodilators
D. Neither requires vasodilators
Explanation: Unlike FFR which requires pharmacologic hyperemia (typically using adenosine), iFR is performed without vasodilators, making it less invasive and more patient-friendly.
6. The iFR cutoff value used to guide PCI is:
A. 0.75
B. 0.92
C. 0.89
D. 0.95
Explanation: The widely accepted iFR threshold for guiding PCI is 0.89. A value ≤0.89 suggests the lesion is ischemia-producing.
7. iFR is most commonly measured using:
A. IVUS catheter
B. Balloon angioplasty catheter
C. Guide catheter only
D. Pressure-sensing guidewire
Explanation: iFR is performed using a specialized pressure-sensing guidewire that measures distal and aortic pressure to calculate the ratio during the wave-free period.
8. Which study validated the use of iFR as non-inferior to FFR in guiding revascularization?
A. COURAGE
B. DEFINE-FLAIR
C. SYNTAX
D. ISCHEMIA
Explanation: The DEFINE-FLAIR trial demonstrated that iFR was non-inferior to FFR in terms of clinical outcomes for guiding coronary revascularization.
9. Which of the following is a major advantage of iFR over FFR?
A. No need for adenosine
B. Better imaging quality
C. Higher specificity
D. Direct measurement of flow
Explanation: iFR avoids the use of adenosine, making it simpler, less time-consuming, and more comfortable for patients compared to FFR.
10. iFR values are most reliable in:
A. Severe left main disease
B. Atrial fibrillation
C. Stable coronary lesions in sinus rhythm
D. Bypass graft evaluation
Explanation: iFR is most accurate in stable lesions during sinus rhythm. Irregular rhythms or diffuse disease may reduce reliability.
11. Which parameter is directly measured to calculate iFR?
A. Myocardial perfusion
B. Cardiac output
C. Left ventricular pressure
D. Distal coronary and aortic pressures
Explanation: iFR is based on the ratio of distal coronary pressure to aortic pressure during the wave-free diastolic period.
12. Which of the following most likely leads to a falsely normal iFR value?
A. Use of contrast agent
B. Stenosis in LAD
C. Serial lesions in same vessel
D. High heart rate
Explanation: Serial or tandem lesions can alter pressure gradients between segments, potentially giving a falsely reassuring iFR value.
13. Which patient factor can make iFR measurement less accurate?
A. Atrial fibrillation
B. Obesity
C. Age
D. Female sex
Explanation: Atrial fibrillation causes irregular heart cycles, disrupting the diastolic wave-free period used in iFR measurement.
14. What is the mathematical formula used in iFR?
A. Mean Pd / Mean Pa during entire cardiac cycle
B. Systolic Pd / Pa
C. Mean distal coronary pressure (Pd) / aortic pressure (Pa) during wave-free diastole
D. (Pd-Pa) × HR
Explanation: iFR is calculated as the mean distal coronary pressure divided by the aortic pressure during the specific diastolic “wave-free” period.
15. iFR is not recommended in:
A. Intermediate LAD lesion
B. Stable angina with RCA stenosis
C. Borderline LMCA lesion
D. Hemodynamically unstable patient
Explanation: iFR is not validated for use in hemodynamically unstable patients due to the altered physiology and pressure dynamics.
16. A patient with iFR = 0.91 would typically:
A. Require urgent stenting
B. Require adenosine challenge
C. Not require revascularization
D. Be recommended for bypass surgery
Explanation: iFR ≥ 0.90 suggests no significant ischemia and typically excludes the need for revascularization.
17. The main physiologic principle behind iFR is:
A. Coronary perfusion during systole
B. Low and stable microvascular resistance in wave-free diastole
C. Flow independence from pressure
D. Use of reactive hyperemia
Explanation: iFR is based on the concept that microvascular resistance is lowest and most stable during a certain phase of diastole, allowing reliable assessment without pharmacologic stress.
18. What is the typical duration of the wave-free period in diastole?
A. Entire diastole
B. 200 ms after systole
C. Mid-to-late diastole
D. 100 ms after end-diastole
Explanation: The wave-free period occurs in mid-to-late diastole and is characterized by minimal and stable microvascular resistance.
19. What is a key limitation of iFR?
A. Requires hyperemia
B. Poor in detecting proximal lesions
C. High cost compared to angiography
D. Limited accuracy in diffuse or serial disease
Explanation: iFR can be less reliable in vessels with multiple or diffuse lesions due to pressure recovery effects and difficulty isolating a single lesion’s impact.
20. Which company developed iFR?
A. Boston Scientific
B. Volcano Corporation
C. Abbott Vascular
D. Medtronic
Explanation: The iFR technology was developed by Volcano Corporation, which was later acquired by Philips. It offers an alternative to FFR without pharmacologic stress.
21. In clinical practice, iFR is especially useful for evaluating:
A. Acute STEMI
B. Cardiac tamponade
C. Intermediate coronary lesions
D. Ventricular aneurysm
Explanation: iFR is most commonly used in evaluating intermediate coronary stenoses to guide revascularization decisions without inducing hyperemia.
22. What does an iFR value of 0.85 typically indicate?
A. Likely ischemia-producing stenosis
B. Normal functional perfusion
C. Borderline lesion
D. Microvascular angina
Explanation: An iFR < 0.89, such as 0.85, typically suggests a significant lesion that warrants revascularization.
23. Compared to FFR, iFR generally results in:
A. More stents placed
B. Fewer stents placed
C. No difference in revascularization rate
D. More complications
Explanation: Studies show that iFR-guided PCI results in fewer stents being placed without compromising clinical outcomes.
24. Which iFR-guided trial included cost-effectiveness analysis?
A. FAME-3
B. ISCHEMIA
C. DEFINE-FLAIR
D. SCOT-HEART
Explanation: DEFINE-FLAIR trial not only evaluated clinical safety of iFR but also demonstrated its cost-effectiveness compared to FFR.
25. The DEFINE-FLAIR trial enrolled approximately:
A. 200 patients
B. 2,500 patients
C. 8,000 patients
D. 20,000 patients
Explanation: DEFINE-FLAIR was a large multicenter trial enrolling over 2,400 patients comparing iFR and FFR for PCI guidance.
26. What is the significance of the wave-free period?
A. Reflects systolic myocardial contraction
B. Includes aortic valve closure
C. Occurs in early systole
D. Represents a time of stable coronary resistance
Explanation: The wave-free period is a phase during diastole when microvascular resistance is stable and minimized, ideal for assessing coronary pressure gradients.
27. Which vessel’s lesions are most commonly evaluated with iFR?
A. Left circumflex
B. Right coronary artery
C. Left anterior descending artery
D. Posterior descending artery
Explanation: Intermediate lesions in the LAD are most frequently evaluated using iFR due to their clinical importance and prevalence.
28. In iFR, the pressure ratio is obtained without using:
A. Diastolic measurements
B. Hyperemic agents
C. Electrocardiogram
D. Catheterization lab
Explanation: iFR avoids pharmacologic agents like adenosine by using resting pressure during a specific diastolic window.
29. What defines a “gray zone” iFR value?
A. iFR between 0.86 and 0.93
B. iFR between 0.60 and 0.70
C. iFR > 0.95
D. iFR < 0.75
Explanation: iFR values between 0.86 and 0.93 may require clinical judgment or additional testing, as they lie in a borderline or “gray” range.
30. What is one advantage of iFR over stress imaging?
A. Detects microvascular disease
B. Detects myocardial infarction
C. Provides lesion-specific functional assessment
D. Measures global cardiac function
Explanation: iFR provides direct physiological assessment of individual coronary stenoses, unlike stress imaging which evaluates global myocardial perfusion.
Instantaneous Wave-Free Ratio (iFR)
| 🔢 No. | Instantaneous Wave-Free Ratio (iFR) 📌 Point |
|---|---|
| 1 | iFR is a non-hyperemic pressure-derived index used to assess coronary artery stenosis. |
| 2 | It is calculated during a specific period in diastole when resistance is naturally minimized. |
| 3 | Unlike FFR, iFR does not require pharmacologic vasodilation (e.g., adenosine). |
| 4 | iFR is measured as the ratio of distal coronary pressure (Pd) to aortic pressure (Pa). |
| 5 | The “wave-free period” is the part of diastole when microvascular resistance is stable and low. |
| 6 | iFR cutoff value of ≤0.89 is considered hemodynamically significant. |
| 7 | A value >0.89 usually indicates no need for revascularization. |
| 8 | It offers improved patient comfort compared to FFR due to no adenosine requirement. |
| 9 | iFR and FFR have high diagnostic concordance (~80–85%). |
| 10 | iFR uses physiologic measurements at rest, not during stress. |
| 11 | It can be performed in the cath lab using standard pressure wires. |
| 12 | It is particularly useful in intermediate coronary lesions (40–70% stenosis). |
| 13 | The iFR pullback technique allows mapping of pressure gradients along a vessel. |
| 14 | iFR has been validated by DEFINE-FLAIR and iFR-SWEDEHEART trials. |
| 15 | These trials confirmed non-inferiority of iFR to FFR for guiding PCI. |
| 16 | iFR values are less influenced by heart rate and blood pressure variations. |
| 17 | It is less time-consuming than FFR-guided measurements. |
| 18 | iFR avoids the side effects of adenosine such as chest pain, flushing, and AV block. |
| 19 | It provides a cost-effective strategy for functional lesion assessment. |
| 20 | Can be used in patients where adenosine is contraindicated (e.g., asthma, AV block). |
| 21 | Uses pressure-sensing coronary wires, often the same as for FFR. |
| 22 | It reflects functional significance of a lesion more than anatomical severity. |
| 23 | Post-PCI iFR can help evaluate adequacy of stenting. |
| 24 | It is incorporated into many modern intravascular imaging systems. |
| 25 | The wave-free period begins ~25% into diastole and lasts until end-diastole. |
| 26 | Lesion-specific ischemia detection by iFR improves decision-making in multivessel disease. |
| 27 | Some lesions with iFR >0.89 but significant on angiography may still be functionally insignificant. |
| 28 | Hybrid iFR-FFR strategy may be used when iFR is borderline (0.86–0.93). |
| 29 | Physiologic assessment like iFR can outperform angiography in guiding revascularization. |
| 30 | iFR helps in personalized treatment strategy, minimizing unnecessary stenting. |
1. What is the Instantaneous Wave-Free Ratio (iFR)?
• iFR is a non-hyperemic index to assess coronary stenosis severity.
• It is calculated using pressure measurements during diastole.
• Specifically measured in the wave-free period of diastole.
• Unlike FFR, iFR does not need adenosine or other vasodilators.
• Used to guide PCI decisions based on physiological significance.
2. How is iFR calculated?
• It’s a ratio of distal coronary pressure (Pd) to aortic pressure (Pa).
• Only uses data from a specific part of diastole: wave-free period.
• Excludes periods of variable resistance like systole or early diastole.
• No pharmacologic hyperemia is induced for calculation.
• Calculated automatically using pressure wire systems.
3. What is the clinical threshold for iFR?
• An iFR value ≤ 0.89 indicates hemodynamically significant stenosis.
• Such lesions often benefit from revascularization like PCI.
• Values ≥ 0.90 are generally considered non-significant.
• iFR thresholds were validated in clinical trials like DEFINE-FLAIR.
• Provides a binary decision similar to FFR cut-off at 0.80.
4. What is the wave-free period?
• It is a segment in mid-to-late diastole.
• Microvascular resistance is naturally minimized during this period.
• Allows assessment without vasodilators.
• Ideal for measuring steady-state pressure conditions.
• Forms the physiologic basis of iFR.
5. What equipment is needed for iFR?
• A pressure-sensing guidewire is essential.
• Requires an iFR-compatible monitoring system.
• No need for hyperemic drugs like adenosine.
• Can be done during routine diagnostic coronary angiography.
• Offers rapid assessment without additional medications.
6. What are the advantages of iFR over FFR?
• iFR does not require vasodilator agents like adenosine.
• Reduced procedure time and patient discomfort.
• Lower cost due to fewer drugs and materials.
• Equally accurate in stable coronary disease (as per trials).
• Better tolerance in patients with asthma or hypotension.
7. What are limitations of iFR?
• Less validated in acute coronary syndromes.
• May be inaccurate in atrial fibrillation due to irregular diastole.
• Less reliable in serial or diffuse coronary disease.
• Not suitable for use in hemodynamically unstable patients.
• May miss dynamic obstructions or spasm-induced stenoses.
8. What are the key trials supporting iFR?
• DEFINE-FLAIR trial compared iFR to FFR.
• Showed non-inferiority of iFR in guiding PCI decisions.
• SWEDEHEART trial also confirmed comparable outcomes.
• Trials demonstrated fewer side effects with iFR use.
• Promoted widespread clinical adoption of iFR.
9. When is iFR preferred over FFR?
• When adenosine is contraindicated or poorly tolerated.
• In routine catheter lab assessments of intermediate lesions.
• In stable patients with borderline angiographic lesions.
• When rapid physiologic assessment is desired.
• For improved patient comfort and shorter procedure.
10. What are alternatives to iFR?
• Fractional Flow Reserve (FFR) is the main alternative.
• Non-invasive options: stress MRI, nuclear imaging.
• Angiographic indices: QFR (Quantitative Flow Ratio).
• Intravascular ultrasound (IVUS) for anatomical assessment.
• Optical coherence tomography (OCT) for high-resolution imaging.
Instantaneous Wave-Free Ratio (iFR)
The wave-free period begins ~25% into diastole and lasts until end-diastole.
Comparison table between Instantaneous Wave-Free Ratio (iFR) and Fractional Flow Reserve (FFR)
| Feature | iFR (Instantaneous Wave-Free Ratio) | FFR (Fractional Flow Reserve) |
|---|---|---|
| Definition | Pressure ratio measured during the wave-free period of diastole | Ratio of distal coronary pressure to aortic pressure during maximal hyperemia |
| Hyperemia Requirement | No (resting index) | Yes (requires adenosine or other vasodilators) |
| Procedure Time | Shorter | Longer (due to time needed for drug-induced hyperemia) |
| Patient Comfort | Better (no hyperemia, fewer side effects) | Lower (due to adenosine-related symptoms: flushing, chest pain) |
| Accuracy vs. FFR | High correlation, non-inferior in large trials (e.g., DEFINE-FLAIR, iFR-SWEDEHEART) | Gold standard for many years, widely validated |
| Cut-off Value | ≤ 0.89 indicates significant stenosis | ≤ 0.80 indicates significant stenosis |
| Clinical Adoption | Increasing use, especially in Europe and U.S. | Still commonly used and well-established |
| Cost | Lower (no need for adenosine) | Higher (due to hyperemic agent and longer procedure) |
| Guideline Support | Supported by ESC, ACC/AHA guidelines | Strongly supported in all major guidelines |
| Use in Complex Lesions | May be less sensitive in certain lesion types | More established in complex anatomy (e.g., serial lesions) |
