Guide to Invasive Coronary Pressure Ratios
This infographic provides an overview of Fractional Flow Reserve (FFR) and Instantaneous Wave-Free Ratio (iFR), essential tools for assessing the functional significance of coronary stenosis in patients with intermediate lesions.
Why Use Invasive Pressure Measurements?
- Invasive coronary pressure measurements help determine if intermediate coronary stenoses (40–70%) are causing ischemia.
- The 2021 Guidelines for Coronary Artery Revascularization recommend the use of FFR or iFR to guide PCI decisions in patients with angina or undocumented ischemia.
Principles of Pressure Measurements
- Coronary flow is proportional to the pressure gradient (Pa – Pd) divided by resistance across a lesion.
- Pa: Pressure proximal to the lesion (aorta).
- Pd: Pressure distal to the lesion.
- If there is no stenosis, Pd/Pa = 1.0. As stenosis worsens, Pd/Pa decreases linearly.
Note: Resistance fluctuates during the cardiac cycle, which impacts pressure readings.
Differences Between FFR and iFR
| Feature | FFR | iFR |
|---|---|---|
| Definition | Pd/Pa during hyperemia | Pd/Pa during the wave-free period |
| Resistance Control | Requires adenosine for hyperemia | Adenosine-independent |
| Cutoff Value | ≤ 0.80 | ≤ 0.89 |
| Key Trials | FAME, DEFER | iFR-SWEDEHEART, DEFINE-FLAIR |
| Notable Pearls | Adenosine can cause side effects | More sensitive to noise, drift |
| Limitations | Less reliable with microvascular dysfunction | May underestimate arteries with large territories |
Key Takeaways
- FFR provides the most accurate assessment by inducing maximal hyperemia with adenosine. However, it is invasive, requires pharmacological stress, and can cause side effects.
- iFR allows for a simpler, faster evaluation without adenosine, making it more practical in some cases. It is preferred for patients unable to tolerate adenosine.
Created by Cali R. Clark
Reviewed by Dr. Nazli Okumus and Dr. Ahmed Ghoneem
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