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HeartFlow FFRcT is a post-processing software for the clinical quantitative and qualitative analysis of previously acquired Computed Tomography (CT) DICOM data for clinically stable symptomatic patients with coronary artery disease. It provides FFRcT, a mathematically derived quantity, computed from simulated pressure, velocity and blood flow information obtained from a 3D computer model generated from static coronary CT images. FFRcT analysis is intended to support the functional evaluation of coronary artery disease.

The results of this analysis are provided to support qualified clinicians to aid in the evaluation and assessment of coronary arteries. The results of HeartFlow FFR-c are intended to be used by qualified clinicians in conjunction with the patient's clinical history, symptoms, and other diagnostic tests, as well as the clinician's professional judgment.

The device is only for prescription use.

FFR v1.4 is post-processing image analysis software developed for the clinical quantitative and qualitative analysis of previously physician-acquired DICOM-compliant cardiac CT images and data, to assess the anatomy and function of the coronary arteries. The software displays the resulting coronary anatomy combined with functional information using graphics and text, including a computed and derived quantification of blood flow. termed FFR - to aid the clinician in the assessment of coronary artery disease.

The HeartFlow FFR cr software is housed at Heart Flow, Inc. The health care provider electronically sends the patient's CT scan data to HeartFlow. Inc. where a 3D computer model of the coronary arteries is developed and simulates blood flow in the models using computational fluid dynamics. A resulting report is electronically sent to the physician with the estimated fractional flow reserve (FFR) values (called FFRct values) displayed as color images of the patient's heart (Figure 1) and an associated color interpretation table (Table 1) indicating the error associated with each measurement range in the HFNXT clinical study.

Here's a breakdown of the acceptance criteria and the study detailing the device's performance:

Acceptance Criteria and Device Performance (HFNXT Study)

Note: The document states that the prespecified target goals identified by the sponsor for sensitivity and specificity were 65%, respectively. However, it also clarifies that these target goals were not agreed upon by the FDA. The table reflects the FDA's acceptance based on the reported lower one-sided 95% confidence bounds being "significantly above the pre-specified target goals of 65% and 55%, respectively, and were considered acceptable." This implies the FDA may have had slightly different internal thresholds but accepted these results.

Additional Per-Subject Diagnostic Performance (FFR_CT vs. Site-Read cCTA with FFR ≤ 0.80 as reference standard):

Study Details for HeartFlowNXT (HFNXT)

1. Sample Size used for the Test Set and Data Provenance:

   • Sample Size: 254 adult subjects comprise the intention-to-diagnose (ITD) population. In total, 484 vessels were analyzed for direct comparison of invasive FFR and FFR_CT.
   • Data Provenance: Prospective, multicenter, nonrandomized study conducted at 11 sites in 8 countries across Canada, Europe, and Asia. Data was collected from September 2012 to August 2013.

2. Number of Experts used to establish the ground truth for the test set and the qualifications of those experts:

   • The document states that "All invasive FFR data was reviewed by an independent FFR/QCA core laboratory." The number of experts or their specific qualifications (e.g., years of experience, subspecialty) are not explicitly detailed in the provided text.

3. Adjudication Method for the test set:

   • The document implies a core lab review for invasive FFR data, suggesting a centralized and likely standardized method, but a specific "adjudication method" like 2+1 or 3+1 for discrepancies is not explicitly described for the final ground truth determination. The FFR_CT and cCTA data were interpreted in a blinded fashion, but the process for resolving disagreements or establishing the definitive FFR ground truth isn't detailed.

4. If a multi-reader, multi-case (MRMC) comparative effectiveness study was done:

   • The HFNXT study compared the diagnostic performance of FFR_CT against cCTA alone. While it assesses the effectiveness of FFR_CT, it doesn't explicitly describe itself as a typical MRMC study designed to show how much human readers improve with AI vs. without AI assistance.
   • Effect Size with AI vs. without AI assistance: The study showed "Per-subject FFR_CT specificity compared to site-read cCTA demonstrated superior diagnostic ability (p<0.001)". Specifically, for per-subject diagnostic accuracy, FFR_CT was 81.1% (95% CI: 75.8%-85.4%) while site-read cCTA was 52.8% (95% CI: 46.6%-58.8%). This indicates a substantial improvement in diagnostic accuracy with FFR_CT.

5. If a standalone (i.e. algorithm only without human-in-the-loop performance) was done:

   • Yes, the HFNXT study primarily evaluated the standalone performance of FFR_CT (version 1.4) in comparison to invasive FFR. While humans are involved in acquiring the CT images and analyzing the invasive FFR, the FFR_CT algorithm itself generates the FFR_CT values based on the CT data semi-autonomously at HeartFlow, Inc., making this a standalone performance evaluation of the software's output. The "operator testing" mentioned under human factors dealt with the ability of HeartFlow analysts to use the software, but the primary clinical validation is of the FFR_CT output itself.

6. The type of ground truth used:

   • The ground truth used was direct measurement of invasive Fractional Flow Reserve (FFR) during cardiac catheterization. Ischemia was defined by an FFR ≤ 0.80.

7. The sample size for the training set:

   • The document does not explicitly state the sample size for the training set used for FFR_CT v1.4. It mentions that two prior studies (Discover-FLOW and DeFACTO) were conducted with earlier versions of the software (v1.0 and v1.2) and that the DeFACTO study provided "supportive data" for the de novo submission. However, it doesn't specify if or how data from these prior studies were specifically used in the training of v1.4, nor does it provide the size of any dedicated training dataset for v1.4.

8. How the ground truth for the training set was established:

   • This information is not explicitly provided. For HeartFlowNXT, the ground truth was invasive FFR. It is reasonable to infer a similar ground truth (invasive FFR) would have been used for any training data, given the device's purpose. However, the specific methodology for establishing ground truth for the training data (including any expert involvement or adjudication) is not detailed in the provided text.

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