Abbott's PressureWire™ X Guidewire measures resting full-cycle ratio (RFR), a resting index that can be measured as an alternative to FFR depending on the clinical situation.1 Like FFR, RFR can identify functionally significant epicardial coronary stenosis. Unlike FFR, RFR is a non-hyperemic index that does not require adenosine infusion.1
Functionally equivalent to the instantaneous wave-free ratio (iFR‡) resting index, Abbott's RFR resting index scans through diastole and systole for the largest drop in pressure. Unlike iFR‡ or diastolic pressure ratio (dPR‡), RFR is calculated from the lowest value of Pd/Pa over the entire cardiac cycle.2
"The major advantage of RFR over iFR‡ is that RFR does not require identification of a specific landmark or selection of a specific time point during diastole. By calculating the minimum Pd/Pa over the entire cardiac cycle, RFR calculates the maximum pressure gradient across the stenosis during resting status."
– Lee, et al. Circulation 2019
The cutoff value of RFR is 0.89:1,3,4
All resting pressure-derived indices closely correlate with one another, revealing the same discriminatory ability to guide intervention.2 The large IRIS-FFR retrospective study (1,506 patients, 1,833 lesions) examined deferred lesion failure among 5 resting indices—resting Pd/Pa, iFR‡, RFR, dPR‡, and DFR‡—and concluded that all resting indices had similar outcomes in deferred lesions.4
Here are the cutoff values for the various non-hyperemic pressure ratios.5
RFR has been studied in over 3,500 lesions and 2,500 patients, showing equivalence to iFR.‡
Major RFR Studies
|Number of Lesions||Number of Patients|
|ILUMIEN I + PREDICT3||313||299|
General guidelines are outlined below.
|When to Use Non-Hyperemic Index (RFR)|
|Left Anterior Descending10||+++||++|
|Acute Coronary Syndrome11||+++||++|
|When to Use FFR|
|Left Main Coronary Artery14||-||+++|
|Post-PCI Side Branch Interrogation16||-||+++|
‡ Indicates a trademark of a third party company or its respective owner.
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