Next Generation FFR Microcatheter Technology
Fractional flow reserve (FFR) assesses the reduction in flow resulting from a coronary artery stenosis. It is an essential tool in the evaluation of the physiological significance and proper treatment of coronary stenosis in the catheterisation laboratory since many stenotic lesions identified at angiography are of intermediate severity, and their impact on myocardial perfusion cannot be determined accurately from angiography alone.1 Multiple studies have demonstrated the efficacy and safety of FFR,2 including the 2009 Fractional Flow Reserve Versus Angiography for Multivessel Evaluation (FAME) study.3,4 However, the technique is underutilised: a 2012 report of the National Cardiovascular Data Registry reported that only 6.1 % of patients in the US underwent FFR assessment prior to percutaneous coronary intervention (PCI) for intermediate coronary stenosis (40–70 % stenosis).5
Most FFR measurements are performed using a 0.014" guidewire incorporating a distal pressure sensor. This is more difficult to guide through tortuous lesions. In addition, assessment of diffuse disease or multiple lesions requires wire pullback, which results in the loss of wire position. As the use of FFR is increasing worldwide and increasingly complex lesions are being treated, there is a need for improved technologies to improve speed, accuracy and ease of use. In addition, post-stenting FFR has been proposed as an effective tool to assess the effect of treatment on coronary flow. However, FFR wiring after stenting requires additional time and could lead to wire placing behind the stents struts.
The ACIST RXi® rapid exchange system (ACIST Medical Systems) features an ultrathin monorail microcatheter (Navvus™; ACIST Medical Systems) with an optical pressure sensor located close to the distal catheter tip (see Figure 1). This system allows the use of any 0.014" coronary guidewire appropriate for the patient’s anatomy. It enables repeated pullbacks and advancements, as well as the ability to move the sensor up and down the artery to determine the site of change in pressure gradient, without losing wire position.6,7 Furthermore, it allows an easy and fast assessment of post-stenting FFR.
However, the larger diameter of the catheter (0.022" mean diameter, compared with the 0.014" guidewire) could influence FFR measurement. The ACIST Diagnosis of Coronary Arterial Disease with a Rapid Exchange Monorail Pressure Sensor for the Measurement of Fractional Flow Reserve (ACCESS-NZ) study compared the Navvus/RXi system with a conventional pressure wire and found that fewer patients had clinically significant (>±0.03) drift with the Navvus catheter (13 %) than with the pressure wire (33 %) when FFR was measured with both systems.8
On-going studies are evaluating the clinical utility of the Navvus microcatheter systems, including the FFR-Stent Evaluated at Rotterdam Cardiology Hospital (FFR-SEARCH) registry and the Assessment of Catheter-based Interrogation and Standard Techniques for Fractional Flow Reserve measurement (ACIST–FFR) study. This article describes two presentations given at EuroPCR (16–19 May 2017, Paris) that discussed the latest findings of these studies.
Summary and Concluding Remarks
The increased use of FFR – particularly in multivessel disease and tandem lesions – has necessitated more efficient and accurate techniques, and it is increasingly important to understand the benefits and limitations of available FFR technologies. The use of microcatheter-based FFR technology can overcome the limitations of pressure wire technology such as accessibility in challenging anatomy, maintaining wire position, pressure-measurement drift and ease of obtaining post-intervention FFR. The microcatheter system can thus simplify PCI procedures as well as avoid technical errors. Preliminary data from the FFR-SEARCH registry has indicated that post-PCI, almost half of patients have FFR values below 0.90 even when stent placement appears adequate on angiography. The ACIST-FFR trial has shown that the clinical impact of the difference between microcatheter and conventional pressure wire FFR measurements is minimal in most cases.
These data have added to the body of clinical evidence supporting the use of microcatheter-based FFR. Furthermore, while FFR has previously been considered a diagnostic tool to assess whether a lesion has to be treated or not, these studies have led to an expanded view of FFR as a tool to understand and evaluate the results of PCI procedures. These studies have stimulated further research into optimising procedures and should facilitate the more widespread use of FFR.
Written By : Katrina Mountfort
Reviewers : Roberto Diletti, Matthew J Price
Citation : Interventional Cardiology Review 2017;12(2 Suppl 1):1–8.
DOI : https://doi.org/10.15420/icr.2017:12:2.S1