The IMPACT Study (Influence of Sensor-Equipped Microcatheters on Coronary Hemodynamics and the Accuracy of Physiological Indices of Functional Stenosis Severity)

Multicenter clinical evaluation of a piezoresistive-MEMS-sensor rapid-exchange pressure microcatheter system for fractional flow reserve measurement

Objectives

This multicenter, prospective clinical study investigates whether the microelectromechanical‐systems‐(MEMS)‐sensor pressure microcatheter (MEMS‐PMC) is comparable to a conventional pressure wire in fractional flow reserve (FFR) measurement.

Background

As a conventional tool for FFR measurement, pressure wires (PWs) still have some limitations such as suboptimal handling characteristics and unable to maintain the wire position during pullback assessment. Recently, a MEMS‐PMC compatible with any 0.014″ guidewire is developed. Compared with the existing optical‐sensor PMC, this MEMS‐PMC has smaller profiles at both the lesion crossing and sensor packaging areas.

Methods

Two hundred and forty‐two patients with visually 30–70% coronary stenosis were enrolled at four centers. FFR was measured first with the MEMS‐PMC, and then with the PW. The primary endpoint was the Bland–Altman mean bias between the MEMS‐PMC and PW FFR.

Results

From the 224‐patient per‐protocol data, quantitative coronary angiography showed 17.9% and 55.9% vessels had diameter < 2.5 mm and stenosis >50%, respectively. The two systems' mean bias was −0.01 with [−0.08, 0.06] 95% limits‐of‐agreement. Using PW FFR≤0.80 as cutoff, the MEMS‐PMC per‐vessel diagnostic accuracy was 93.4% [95% confidence interval: 89.4–96.3%]. The MEMS‐PMC's success rate was similar to that of PW (97.5 vs. 96.3%, p = .43) with no serious adverse event, and its clinically‐significant (>0.03) drift rate was 43% less (9.5 vs. 16.7%, p = .014).

Conclusions

Our study showed the MEMS‐PMC is safe to use and has a minimal bias equal to the resolution of current FFR systems. Given the MEMS‐PMC's high measurement accuracy and rapid‐exchange nature, it may become an attractive new tool facilitating routine coronary physiology assessment.

Extent of the difference between microcatheter and pressure wire-derived fractional flow reserve and its relation to optical coherence tomography-derived parameters

Background

Although previous studies demonstrated that microcatheter-derived fractional flow reserve (mc-FFR) tends to overestimate lesion severity compared to pressure wire-derived FFR (pw-FFR), the clinical utility of mc-FFR remains obscure. The extent of differences between the two FFR systems and its relation to a lesion-specific parameter remain unknown. In this study, we sought to compare mc-FFR with pw-FFR and determine the lower and upper mc-FFR cut-offs predicting ischemic and non-ischemic stenosis, using an ischemic and a clinical FFR threshold of 0.75 and 0.80 as references, respectively. We further explored optical coherence tomography (OCT) parameters influencing the difference in FFR between the two systems.

Methods and results

In this study, 44 target vessels with intermediate de novo coronary artery lesion in 36 patients with stable ischemic heart disease were evaluated with mc-FFR, pw-FFR and OCT. Bland-Altman plots for mc-FFR versus pw-FFR showed a bias of −0.04 for lower mc-FFR values compared to pw-FFR values. The mc-FFR cut-off values of 0.73 and 0.79 corresponded to the 0.75 ischemic pw-FFR and 0.80 clinical pw-FFR thresholds with high predictive values, respectively. The differences in the two FFR measurements (pw-FFR minus mc-FFR) were negatively correlated with OCT-derived minimum lumen area (MLA) (R = −0.359, p = 0.011). The OCT-derived MLA of 1.36 mm² was a cut-off value for predicting the clinically significant difference between the two FFR measurements defined as >0.03.

Conclusion

Mc-FFR is clinically useful when the specific cut-offs are applied. An OCT-derived MLA accounts for the clinically significant difference in FFR between the two systems.

Diagnostic Accuracy of Microcatheter Derived Fractional Flow Reserve

Microcatheter derived fractional flow reserve (FFR_MC) system has an increased profile compared with pressure-wire derived fractional flow reserve (FFR_W). Consequently, the FFR_MC system itself may increase the degree of coronary artery stenosis and lower the measured FFR value. This can affect the diagnostic accuracy of the FFR_MC system and inadvertently result in erroneous therapy for patients. Our aim was to evaluate the diagnostic accuracy FFR_MC measurements and provide a means for clinicians to interpret individual FFR_MC results with respect to FFR_W. Correlation between FFR measurement techniques was analyzed in this lesion level analysis of 413 patients and 441 lesions from 6 studies. The reference standard to determine physiological significant stenosis was FFR_W value ≤0.80. The mean values for FFR_MC and FFR_W were 0.80 ± 0.11 and 0.83 ± 0.09, respectively. Bland-Altman analysis demonstrated a bias toward overestimation of FFR by FFR_MC (bias, -0.03 [0.05]). The overall lesion level diagnostic accuracy of the FFR_MC system was 80.4% (95% confidence interval [CI] 76.2% to 84.0%). The diagnostic accuracy for FFR_MC values <0.75, 0.75 to 0.85 and >0.85 were 83.7% (95% CI 71.4% to 92.4%), 72.3% (95% CI 59.8% to 75.6%), and 99.2% (95% CI 94.8% to 99.8%), respectively. Using the FFR_W threshold of ≤0.80, 16.3% of lesions would have had inappropriate revascularization according to FFR_MC measurements. Receiver-operating characteristics suggested the optimal cut-off value of FFR_MC to determine ischemia was 0.78. In conclusion, the diagnostic accuracy of FFR_MC varies markedly across the spectrum of disease with marked deterioration for values between 0.75 and 0.85. This may result in clinicians to inadvertently revascularize patients with FFR measurements >0.80.

Fractional flow reserve guided percutaneous coronary intervention optimization directed by high-definition intravascular ultrasound versus standard of care: Rationale and study design of the prospective randomized FFR-REACT trial

BACKGROUND

Post percutaneous coronary intervention (PCI) fractional flow reserve (FFR) is a significant predictor of major adverse cardiac events (MACE). The rationale for low post procedural FFR values often remains elusive based on angiographic findings alone, warranting further assessment using an FFR pullback or additional intravascular imaging. It is currently unknown if additional interventions intended to improve the PCI, decrease MACE rates.

STUDY DESIGN

The FFR REACT trial is a prospective, single-center randomized controlled trial in which 290 patients with a post PCI FFR <0.90 will be randomized (1:1) to either standard of care (no additional intervention) or intravascular ultrasound (IVUS)-directed optimization of the FFR (treatment arm). Eligible patients are those treated with angiographically successful PCI for (un)stable angina or non-ST elevation myocardial infarction (MI). Assuming 45% of patients will have a post PCI FFR <0.90, approximately 640 patients undergoing PCI will need to be enrolled. Patients with a post PCI FFR ≥ 0.90 will be enrolled in a prospective registry. The primary end point is defined as a composite of cardiac death, target vessel MI and clinically driven target vessel revascularisation (target vessel failure) at 1 year. Secondary end points will consist of individual components of the primary end point, procedural success, stent thrombosis and correlations on clinical outcome, changes in post PCI Pd/Pa and FFR and IVUS derived dimensions. All patients will be followed for 3 years.

CONCLUSION

The FFR-REACT trial is designed to explore the potential benefit of HD-IVUS-guided PCI optimization in patients with a post PCI FFR <0.90 (Dutch trial register: NTR6711).

Fractional flow reserve derived from microcatheters versus standard pressure wires: a stenosis-level meta-analysis

Aims

To determine the agreement between sensor-tipped microcatheter (MC) and pressure wire (PW)-derived fractional flow reserve (FFR).

Methods and results

Studies comparing FFR obtained from MC (FFRMC, Navvus Microcatheter System, ACIST Medical Systems, Eden Prairie, Minnesota, USA) versus standard PW (FFRPW) were identified, and a meta-analysis of numerical and categorical agreement was performed. The relative levels of drift and device failure of MC and PW systems from each study were assessed. Six studies with 440 lesions (413 patients) were included. The mean overall bias between FFRMC and FFRPW was -0.029 (FFRMC lower). Bias and variance were greater for lesions with lower FFRPW (p<0.001). Using a cut-off of 0.80, 18 % of lesions were reclassified by FFRMC versus FFRPW (with 15 % being false positives). The difference in reported drift between FFRPW and FFRMC was small. Device failure was more common with MC than PW (7.1% vs 2%).

Conclusion

FFRMC systematically overestimates lesion severity, with increased bias in more severe lesions. Using FFRMC changes revascularisation guidance in approximately one out of every five cases. PW drift was similar between systems. Device failure was higher with MC.

ACIST-FFR Study (Assessment of Catheter-Based Interrogation and Standard Techniques for Fractional Flow Reserve Measurement)

BACKGROUND

Measurement of fractional flow reserve (FFR) to guide coronary revascularization lags despite robust supportive data, partly because of the handling characteristics of traditional coronary pressure wires. An optical pressure-monitoring microcatheter, which can be advanced over a traditional coronary guidewire, facilitates FFR assessment but may underestimate pressure wire-derived FFR.

METHODS AND RESULTS

In this prospective, multicenter trial, 169 patients underwent FFR assessment with a pressure wire alone and with a pressure microcatheter over the pressure wire. An independent core laboratory performed quantitative coronary angiography and evaluated all pressure tracings. The primary end point was the bias or difference between the microcatheter FFR and the pressure wire FFR, as assessed by Bland-Altman analysis. The mean difference between the microcatheter and the pressure wire-derived FFR values was -0.022 (95% confidence interval, -0.029 to -0.015). On multivariable analysis, reference vessel diameter (P=0.027) and lesion length (P=0.044) were independent predictors of bias between the 2 FFR measurements. When the microcatheter FFR was added to this model, it was the only independent predictor of bias (P<0.001). The mean FFR value from the microcatheter was significantly lower than from the pressure wire (0.81 versus 0.83; P<0.001). In 3% of cases (95% confidence interval, 1.3%-6.7%), there was clinically meaningful diagnostic discordance, with the FFR from the pressure wire >0.80 and that from the microcatheter <0.75. These findings were similar when including all 210 patients with site-reported paired FFR data.

CONCLUSIONS

An optical, pressure-monitoring microcatheter measures lower FFR compared with a pressure wire, but the diagnostic impact appears to be minimal in most cases.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov. Unique identifier: NCT02577484.

A Practical Guide for Fractional Flow Reserve Guided Revascularisation

The presence and extent of myocardial ischaemia is a major determinant of prognosis and benefit from revascularisation in patients with stable coronary artery disease. Fractional Flow Reserve (FFR) is accepted as the reference standard for invasive assessment of ischaemia. Its ability to detect lesion specific ischaemia makes it a useful test in a wide range of patient and lesion subsets, with FFR guided intervention improving clinical outcomes and reducing health care costs compared to assessment with coronary angiography alone. This article will review the basic principles in FFR, practical tips in FFR guided revascularisation and the role of emerging non-hyperaemic indices of ischaemia.