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The ACIST RXi System is indicated for obtaining intravascular pressurements for use in the diagnosis and treatment of coronary and peripheral artery disease. The ACIST Navvus II MicroCatheter is intended for use with the ACIST RXi System

The ACIST Navvus II MicroCatheter is a single-lumen monorail catheter designed to be used with standard 0.014 in (0.36 mm) guidewires in the arterial vasculature. The MicroCatheter is compatible with the ACIST RXi family of system hardware which includes the RXi System and RXi Mini. Features unique to each system are denoted specifically.

The Navvus II MicroCatheter distal shaft is 26 cm in length with a pressure sensor located 5 mm from the distal tip. The elliptical distal shaft is 1.68 x 1.91F (0.020 in x 0.025 in) up to 10 mm from the distal tip; a maximum profile of 2.7F (0.036 in) occurs at the pressure sensor. The distal shaft smoothly tapers over the pressure sensor and down to the tip accepting the guidewire. A radiopaque marker band is located 2.5 mm from the distal tip.

The shaft proximal to the monorail section is 2.4F, allowing use in 5F or larger guide catheters. Two white positioning markers are located at 80 cm and 100 cm from the distal tip. The pressure sensor on the catheter utilizes optical sensing technology. Both the optical pressure signal and information for auto calibration are transmitted from the catheter to the RXi hardware.

The ACIST RXi System is designed to provide hemodynamic information for the diagnosis and treatment of coronary and peripheral artery disease. The system is intended for use in catheterization and related cardiovascular specialty laboratories to compute and display fractional flow reserve (FFR) and resting Pd/Pa.

FFR and resting Pd/Pa supplement the visual data provided by angiography and provides an assessment of the lesion severity.

Measurement of FFR and resting Pd/Pa requires simultaneously monitoring the blood pressures proximal and distal to a lesion. The ACIST RXi System includes a single-use MicroCatheter with a pressure sensor for acquisition of the distal pressure. The proximal pressure is acquired via the guide catheter which is monitored by the ACIST RXi System via an interface to the hospital's hemodynamic monitor.

Pd/Pa is the ratio of distal coronary arterial pressure to aortic pressured at resting conditions. The physician may then use the resting Pd/Pa value, along with knowledge of patient history, medical expertise and clinical judgment to determine if an additional measurement of FFR during hyperemia or therapeutic intervention is indicated.

The acceptance criteria and supporting study details for the ACIST Rapid Exchange (RXi) System and Navvus II MicroCatheter are described below.

1. Table of Acceptance Criteria and Reported Device Performance

The provided document focuses on demonstrating substantial equivalence to a predicate device rather than explicitly stating acceptance criteria for a novel device and then reporting performance against those criteria. Instead, it details design verification testing and relies on clinical post-market analysis and supported literature to establish the clinical utility of the derived Pd/Pa values.

For the Navvus II MicroCatheter, the document states that design verification testing demonstrated that the observed differences in Maximum Tip OD and Distal End of Sensor to Markerband did not affect the performance of the device, suggesting an implicit acceptance criterion of "performance unaffected" relative to the predicate.

For the RXi System, the document states that it is identical to the predicate and that the change is simply to include Pd/Pa in the labeling, implying that its performance is already established by the predicate.

The main clinical performance claim revolves around the Pd/Pa measurement and its correlation with FFR. While not explicitly a "device performance" in terms of physical function, the clinical utility of the device hinges on this.

2. Sample Size Used for the Test Set and Data Provenance

The document references a clinical post-market analysis: "ACIST-FFR Pd/Pa Post-hoc Sub-Group Analysis" and "Maini et al. meta-analysis."

• ACIST-FFR Pd/Pa Post-hoc Sub-Group Analysis: This analysis leveraged data from the original ACIST-FFR clinical study. The original study aimed to assess catheterization and standard techniques for Fractional Flow Reserve Measurement.
  • Sample Size for Test Set: Not explicitly stated for this sub-group post-hoc analysis. The original analysis was published in Circ Cardiovasc Interv. 2017 Dec; 10 (12). e005905, but the specific number of cases/patients used in this sub-group analysis for determining the optimal Pd/Pa cutpoint is not provided in the submitted document.
  • Data Provenance: Not explicitly stated (e.g., country of origin, retrospective/prospective). However, the nature of a "post-hoc sub-group analysis" of a clinical study implies the data was collected prospectively for the original ACIST-FFR study and then retrospectively analyzed for this specific purpose.
• Maini et al. Meta-analysis:
  • Sample Size for Test Set: Reported on 14 studies. The total number of individual patients or cases across these 14 studies is not specified in the FDA submission, but the meta-analysis itself aggregates data from multiple studies.
  • Data Provenance: The meta-analysis aggregated "published resting Pd/Pa diagnostic accuracy studies." This implies diverse geographical origins and likely a mix of prospective and retrospective original study designs.

3. Number of Experts Used to Establish the Ground Truth for the Test Set and Their Qualifications

• ACIST-FFR Pd/Pa Post-hoc Sub-Group Analysis: The ground truth for this analysis used an FFR cutoff value of ≤0.80 to define stenosis. This FFR measurement itself would be obtained by a clinician (e.g., interventional cardiologist) using the Navvus MicroCatheter. The determination of the FFR value and the interpretation of whether it indicates stenosis (≤0.80) is based on widely accepted clinical consensus and guidelines in interventional cardiology. The document does not specify the number of individual experts or their specific qualifications for establishing this ground truth within the study, but it relies on established FFR thresholds.
• Maini et al. Meta-analysis: This meta-analysis compared Pd/Pa to FFR. Therefore, FFR measurements from the 14 included studies served as the ground truth. Again, the number and qualifications of experts involved in the original FFR measurements or their interpretation across these diverse studies are not specified in this document, but FFR measurement and interpretation are standard practices by interventional cardiologists.

4. Adjudication Method for the Test Set

Not explicitly stated. Given that the ground truth for the clinical utility claims is FFR (a quantitative physiological measurement with an established cutoff), a formal adjudication process beyond standard clinical measurement and interpretation protocols is unlikely to have been detailed in this context. The "optimal cutpoint" derived was likely statistical (Receiver Operating Characteristic - ROC curve analysis).

5. Multi-Reader Multi-Case (MRMC) Comparative Effectiveness Study

No, a multi-reader multi-case (MRMC) comparative effectiveness study comparing human readers with AI assistance vs. without AI assistance was not done. The submission focuses on validating the device's ability to measure pressure and derive Pd/Pa, which subsequently aids clinicians in decision-making, rather than comparing AI-assisted vs. unassisted human interpretation of complex images or data.

6. Standalone (Algorithm Only Without Human-in-the-Loop Performance) Study

Yes, in a sense. The core "performance" of the RXi System (when coupled with the Navvus II MicroCatheter) in calculating Pd/Pa and FFR is a standalone algorithm function based on acquired pressure data. The "optimal cutpoint" of 0.91 for Pd/Pa in relation to FFR (≤0.80) was determined algorithmically (via ROC curve analysis) from a dataset. This demonstrates the performance of the device's computational output (Pd/Pa value) in relation to FFR, independent of real-time human interpretation during the calculation. However, the clinical application of these values always involves a human-in-the-loop (the physician making treatment decisions).

7. Type of Ground Truth Used

The primary ground truth used for the clinical utility claim regarding Pd/Pa was Fractional Flow Reserve (FFR).

• For the ACIST-FFR Pd/Pa Post-hoc Sub-Group Analysis, the derived optimal Pd/Pa cutpoint was established using an FFR cutoff value of ≤0.80 measured with the Navvus MicroCatheter to define stenosis. FFR is a physiological measurement, widely accepted as a gold standard for assessing the hemodynamic significance of coronary artery lesions.
• The Maini et al. meta-analysis also compared Pd/Pa to FFR as its gold standard.

8. Sample Size for the Training Set

The document does not explicitly mention a "training set" in the context of an AI/ML algorithm being trained.

• The "ACIST-FFR Pd/Pa Post-hoc Sub-Group Analysis" used data from the "ACIST-FFR clinical study." The overall sample size of this study is not provided in detail in the current document, only referenced by its publication. It's more akin to a validation set used to derive a cutpoint from existing data rather than an AI training set.
• Similarly, the Maini et al. meta-analysis is an aggregation of 14 separate studies, each with its own patient population.

9. How the Ground Truth for the Training Set Was Established

As no explicit "training set" for an AI/ML algorithm is described, this question is not directly applicable in the terms of the provided document. However, if interpreting the data used to determine the Pd/Pa cutpoint (from the ACIST-FFR study) as analogous to a "training set" for establishing a diagnostic threshold:

• The ground truth for this data was FFR (Fractional Flow Reserve) measurements within those clinical studies. FFR is established by simultaneously measuring pressure distal to a stenosis (Pd) and aortic pressure (Pa) under maximal hyperemia and calculating their ratio (Pd/Pa under hyperemia). A value of ≤0.80 is widely accepted as indicating a hemodynamically significant stenosis. These measurements are performed invasively using specialized catheters (like the Navvus MicroCatheter itself) and guide catheters, interpreted by trained interventional cardiologists based on established physiological principles.

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