Fractional Flow Reserve (FFR) Measurement 

Updated: Dec 30, 2019
Author: Eiman Jahangir, MD, FACC; Chief Editor: Karlheinz Peter, MD, PhD 

Overview

Background

Fractional flow reserve (FFR) measurement involves determining the ratio between the maximum achievable blood flow in a diseased coronary artery and the theoretical maximum flow in a normal coronary artery. An FFR of 1.0 is widely accepted as normal. An FFR lower than 0.75-0.80 is generally considered to be associated with myocardial ischemia (MI).[1]

FFR is easily measured during routine coronary angiography by using a pressure wire to calculate the ratio between coronary pressure distal to a coronary artery stenosis and aortic pressure under conditions of maximum myocardial hyperemia.[1] This ratio represents the potential decrease in coronary flow distal to the coronary stenosis. More recently, computed tomography (CT)-based FFR computations have been used to evaluate the functional severity of coronary artery stenoses, with FFRs derived from outflow boundary conditions based on conventional morphology generally agreeing with those based on positron-emission tomography (PET) conditions.[2]  However, FFRs measurements based on conventional morphology had a tendency to overestimate functional severity, particularly in the setting of reduced vasodilatory response under hyperemia (and thus abnomal myocardial perfusion).[2]

Over the past two decades, FFR measurement has been increasingly used in cardiac catheterization laboratories. It provides a quantitative assessment of the functional severity of a coronary artery stenosis identified during coronary angiography and cardiac catheterization.

A severe coronary artery stenosis can limit myocardial blood flow, resulting in MI. In most cases, the severity of a coronary artery stenosis is judged by visual inspection by the cardiologist during cardiac angiography. A lesion is generally considered severe and flow-limiting if the narrowing of the luminal diameter is estimated to be 70% or greater.[3]

During angiography, the cardiologist typically assesses the patient’s symptoms and clinical characteristics, evaluates the angiographic appearance of the coronary tree, and then decides whether revascularization with angioplasty, stenting, or coronary bypass surgery is most appropriate.[3]

However, the ability of the cardiologist to discriminate between lesions that can cause MI and lesions that are physiologically insignificant on the basis of coronary angiography alone is limited.[4] The use of FFR measurement provides the cardiologist with a straightforward, readily available, quantitative technique for evaluating the physiologic significance of a coronary stenosis.

Indications

Indications for FFR measurement are as follows:

  • To determine the physiologic and hemodynamic significance of an angiographically intermediate coronary stenosis

  • To identify appropriate culprit lesion(s) in multivessel coronary artery disease (CAD)

  • To measure the functional importance of stenosis in the presence of distal collateral flow

  • To identify the precise location of a coronary lesion when the angiographic image is unclear

Note that this procedure is not intended for use in the setting of a total vessel occlusion.

Outcomes

In a study designed to test the hypothesis that experienced interventional cardiologists could identify patients with FFRs below 0.75 by means of coronary angiography, FFR was measured in 83 angiographically moderate coronary lesions, which were also visually assessed by 3 interventional cardiologists; the reviewers’ classification matched the FFR in only about half of the lesions, and concordance between reviewers was poor.[5]  In this study, when visual assessment was compared with FFR, it resulted in good sensitivity (80%) and negative predictive value (91%) but poor specificity (47%) and positive predictive value (25%).[5] Angiographic assessment of an angiogram by experienced interventional cardiologists did not predict the significance of most moderate coronary lesions.

In the DEFER study, which assessed patients with single-vessel CAD and angiographically intermediate coronary stenosis, patients with an FFR above 0.75 were randomized to either medical management or stent implantation; at 5-year follow-up, those who did not receive a stent had the same risk of death or acute MI as those who did, which suggests that patients with an FFR higher than 0.75 do not benefit from revascularization of the stenosis.[6]

The Fractional Flow Reserve versus Angiography for Multivessel Evaluation (FAME) study, which studied the role of FFR in the evaluation of multivessel CAD, reported results suggesting that a revascularization strategy using FFR yields superior clinical outcomes in patients with multivessel CAD.[7]  In this study, patients with multivessel CAD identified by angiography were randomized to undergo either angiography alone or FFR plus angiography.[7] Patients in the angiography-only arm underwent stenting of all angiographically severe lesions. Patients in the FFR-plus-angiography arm underwent stenting only if FFR was 0.80 or less. At 2-year follow-up, patients who underwent FFR-driven stenting had fewer stents than those in the angiography-only group, along with reductions in mortality, MI, and repeat revascularization.

More recently, investigators retrospectively (2016-2018) evaluated FFR in 246 German patients with CAD undergoing transcatheter aortic valve implantation (TAVI) who had coronary lesions with a diameter stenosis of at least 50%.[8] They found concomitant CAD in 53.3% of TAVI patients.[8]  Postprocedure FFR measurements performed in those with a positive FFR up to and including 0.80 did not significantly change 6-8 weeks after TAVI, which the investigators indicated confirmed the validity of FFR for assessing coronary lesions in this specific clinical setting.[8]

 

Periprocedural Care

Patient Education and Consent

Before the cardiac catheterization, the cardiologist should explain all of the potential risks and benefits to the patient, including the possible need for unplanned coronary intervention. Discussion of the intervention should include information regarding placement of a stent and other invasive techniques used for evaluation, including fractional flow reserve (FFR) measurement.

Risks specific to the FFR procedure include the need for additional contrast use and radiation exposure, as well as a slightly increased risk of coronary arterial dissection with FFR wire passage. Besides explaining the risks and benefits, the physician should answer any other questions the patient may have regarding the procedure.

Preprocedural Planning

After a diagnostic cardiac catheterization has been performed and a stenosis has been identified (see the image below), the cardiologist makes the decision as to whether FFR measurement is likely to be useful.

Fractional flow reserve measurement (FFR). Angiogr Fractional flow reserve measurement (FFR). Angiography of the right coronary artery demonstrates an intermediate-grade lesion in the mid vessel. Intermediate-grade lesions such as this should be further evaluated with fractional flow reserve measurement.

Equipment

Volcano Corporation (San Diego, Calif)[9] and St Jude Medical, Inc (St. Paul, Minn)[10] are the 2 main producers of the devices and systems used to measure FFR.

FFR equipment manufactured by Volcano includes the following:

  • ComboMap Pressure and Flow System - This is a combined system that displays both pressure and flow

  • ComboWire XT Guide Wire - This wire allows simultaneous measurement of intravascular pressure and Doppler flow and, thus, is capable of measuring stenotic and microvascular resistance; it is available in 2 models, one with Doppler flow and pressure sensors at the tip of the wire and the other with a Doppler flow sensor at the tip and a pressure sensor 1.5 cm from the tip

  • PrimeWire Guide Wire - This wire allows measurement of intravascular pressure; the pressure sensor is at the tip, and the wire comes in 185-cm and 300-cm lengths

  • FloWire Doppler Guide Wire - This wire allows measurement of coronary arterial blood flow velocity and coronary flow reserve; the flow sensor is at the tip, and the wire comes in 175-cm and 300-cm lengths, along with a straight or a J tip

FFR equipment manufactured by St Jude Medical includes the following:

  • RadiAnalyzer Xpress - This combined system takes pressure, flow, and temperature measurements using 1 PressureWire and 1 instrument (see the image below)

    Fractional flow reserve measurement (FFR). RadiAna Fractional flow reserve measurement (FFR). RadiAnalyzer Xpress when initially powered on.
 

Technique

Approach Considerations

Typically, conscious sedation is administered as part of the cardiac catheterization. Unless the patient is uncomfortable, no other anesthesia is required. The patient is placed in the supine position.

To measure fractional flow reserve (FFR), the operator crosses the coronary stenosis with an FFR-specific guide wire designed to record the coronary arterial pressure distal to the stenosis. The pressure transducer is located approximately 20 mm proximal to the distal tip of the wire, and it can be seen fluoroscopically.

Once the transducer is distal to the stenosis, a hyperemic stimulus is administered by injection through the guide catheter, and the FFR is monitored for a significant change. To achieve maximum hyperemia, adenosine is typically used: a 15-30 µg bolus in the right coronary artery, a 20-40 µg bolus in the left coronary artery, or intravenous (IV) infusion for 3-4 minutes at 140 µg/kg/min. The mean arterial pressures from the pressure wire transducer and from the guide catheter are then used to calculate FFR.

An FFR value lower than 0.75 indicates a hemodynamically significant stenosis. An FFR value higher than 0.8 indicates a stenosis that is not hemodynamically significant. Values between 0.75 and 0.80 are indeterminate and should be considered in the context of patient’s clinical history to determine if revascularization is necessary.

Specific Approaches to FFR Measurement

Volcano systems

Open the product packaging with sterile technique, and place the spiral on the sterile field. With the wire in the spiral, remove the cable from the spiral by pulling on the plug, and connect it to a compatible instrument. Verify that the nose is rotated to the locked position.

After the wire has been zeroed, carefully remove the connector body from the spiral clip, and withdraw the guide wire from the spiral. At this time, the guide wire tip may be shaped with standard tip-shaping practices, if desired.

Wet the working length of the guide wire with normal saline, and insert the wire through the appropriate introducer components and guiding catheter into the desired blood vessel. Slowly advance the guide wire tip under fluoroscopic guidance, using contrast injections to verify its location. Be careful not to kink the proximal contact bands of the wire. Ensure that the tip is rotating freely and that no resistance is felt when torque is applied.

Locate the pressure sensor adjacent to the tip of the guide catheter, and perform a normalization procedure with the instrument. Advance the sensor to the desired measurement location, and perform measurements with the instrument. If the FFR is greater than 0.75 at baseline, proceed with administering a hyperemic stimulus (eg, intracoronary adenosine in a dose of 15-40 µg or IV adenosine at 140 µg/kg/min), and monitor measurements.

Finally, withdraw the pressure sensor and verify that pressures are equal.

St Jude Medical system

Open the product packaging with sterile technique, and place the PressureWire on the sterile field. Remove the gray connector from its holder and connect it to the RadiAnalyzer Xpress. Place the coil flat, and flush with 10 mL of saline. Press Enter on the RadiAnalyzer Xpress to calibrate the PressureWire (see the video below).

Fractional flow reserve measurement (FFR). Demonstration of calibration and use of a RadiAnalyzer Xpress.

Advance the sensor element so that it is just outside the guide catheter opening (see the first image below). Verify that aortic pressure and PressureWire pressure are equal at that position (see the second image below). If the 2 pressures are not equal, position the aortic transducer at the level of the patient’s heart, remove the guide wire introducer needle, close the valve tightly, flush any contrast remnants, press Equalize, and hold for 3 seconds.

Fractional flow reserve measurement (FFR). Pressur Fractional flow reserve measurement (FFR). PressureWire is placed outside of the guide catheter but proximal to the lesion to equalize pressure wire and aortic pressures.
Fractional flow reserve measurement (FFR). RadiAna Fractional flow reserve measurement (FFR). RadiAnalyzer Xpress demonstrating aortic and PressureWire pressures prior to crossing the lesion. Notice that the ratio is not equal to 1, indicating that further adjustments to the instruments are needed. Red line = aortic pressure. Green line = pressure at the wire tip.

Advance the sensor element to a point distal to the stenosis of interest (see the image below). Wait for stable baseline pressure values to be obtained.

Fractional flow reserve measurement (FFR). Pressur Fractional flow reserve measurement (FFR). PressureWire is placed distal to the lesion in the right coronary artery.

Induce maximum hyperemia with intracoronary adenosine (15-40 µg) or IV adenosine (140 µg/kg/min). When maximum hyperemia is reached, press Stop/View to stop recording. The instrument then calculates the FFR automatically (see the image below).

Fractional flow reserve measurement (FFR). With th Fractional flow reserve measurement (FFR). With the administration of intravenous adenosine, the fractional flow ratio decreases to 0.67, indicating that the lesion is hemodynamically significant and will benefit from revascularization. Red line = aortic pressure. Green line = pressure at the wire tip.

Complications

Complications associated with cardiac catheterization include the following:

  • Coronary vessel dissection, occlusion, or perforation

  • Embolism (coronary, cerebral, or other arterial)

  • Coronary artery spasm

  • Local or systemic infection

  • Acute renal failure

  • Myocardial infarction

  • Stroke

  • Serious arrhythmias

  • Death

 

Medication

Medication Summary

The goal of pharmacotherapy is to measure the fractional flow reserve (FFR) to decide whether a coronary intervention would be beneficial.

Diagnostic agents

Class Summary

A hyperemic agent such as adenosine may be used to evaluate FFR.

Adenosine (Adenocard, Adenoscan)

Adenosine slows conduction time through the AV node. It can interrupt atrioventricular reentrant tachycardia (AVRT) by blocking conduction in the AV node to restore normal sinus rhythm in paroxysmal supraventricular tachycardia (PSVT), including PSVT associated with Wolff-Parkinson-White (WPW) syndrome. It should not be given to patients with preexcitation unless by a cardiac electrophysiologist.

Locate the pressure sensor adjacent to the tip of the guide catheter, and perform a normalization procedure with the instrument. Advance the sensor to the desired measurement location, and perform measurements with the instrument. If the FFR is greater than 0.75 at baseline, proceed with administering a hyperemic stimulus (eg, intracoronary adenosine in a dose of 15-40 µg or IV adenosine at 140 µg/kg/min), and monitor measurements.

Finally, withdraw the pressure sensor and verify that pressures are equal.

 

Questions & Answers