HeartFlow FFRCT for estimating fractional flow reserve from coronary CT angiography

HeartFlow FFR_CT (developed by HeartFlow) is coronary physiology simulation software used for the qualitative and quantitative analysis of previously acquired computerised tomography DICOM data. The software provides a non-invasive method of estimating fractional flow reserve (FFR) using standard coronary CT angiography (CCTA) image data. FFR is the ratio between the maximum blood flow in a narrowed artery and the maximum blood flow in a normal artery. FFR is currently measured invasively using a pressure wire placed across a narrowed artery.

After a clinician decides to request a HeartFlow test, anonymised data from a CCTA scan (of at least 64 slices) are sent from the local imaging system, by secure data transfer to HeartFlow's central processing centre in the US. A case analyst employed by the company then uses the image data to create 3D computer models of the coronary arteries, incorporating coronary flow characteristics. The results are presented in a report which is sent, by secure data transfer, to the referring clinician within 48 hours. The report includes both 3D images of the coronary anatomy and calculated functional information, including the estimated FFR values (known as FFR_CT values). Clinicians can then use the report to help guide the management of suspected coronary artery disease.

HeartFlow FFR_CT is intended for use in patients with stable, recent-onset chest pain and suspected angina. Because the safety and effectiveness of FFR_CT analysis has not been evaluated in other patient subgroups, HeartFlow FFR_CT is not recommended in patients who have an acute coronary syndrome or have had a coronary stent, coronary bypass surgery or myocardial infarction in the past month.

The company first received a CE mark in July 2011, covering all 1.X versions of the technology, including the current version, 1.7.

HeartFlow FFR_CT costs £700 per test. A higher price of £888 is used in the company submission and assessment report. The cost was reduced in May 2015.

The claimed benefits of HeartFlow FFR_CT in the case for adoption presented by the company were as follows:

• Analysis is done using standard CCTA scans, without the need for additional imaging, radiation or medication.

• It provides the same accuracy in excluding coronary artery disease as CCTA, and characterises the coronary arteries from both functional and anatomical perspectives, differentiating between ischaemic and non-ischaemic vessels in a way that CCTA cannot.

• It allows physicians to evaluate anatomical coronary artery disease and accurately determine which coronary lesions are responsible for myocardial ischaemia, avoiding unnecessary invasive diagnostic or therapeutic procedures and related complications.

• It reduces the need for revascularisation in patients after identifying anatomical stenosis by invasive coronary angiography (ICA) alone, by more accurately identifying if those stenoses are ischaemic.

• It improves the diagnostic accuracy for coronary artery disease compared with CCTA alone against the gold standard of invasive FFR, and provides both functional and anatomical assessment of coronary arteries.

• It has better diagnostic performance than CCTA alone, or other non-invasive or invasive tests (such as nuclear myocardial perfusion, magnetic resonance perfusion, stress echocardiography, exercise treadmill testing, invasive angiography or intravascular ultrasound) for detecting and excluding coronary artery lesions that cause ischaemia.

• It reduces costs arising from inconclusive or inaccurate diagnostic tests.

• It avoids staff and procedure costs for unnecessary ICAs.

• It avoids staff and procedure costs for unnecessary interventions (such as angioplasty).

• It provides a more effective use of high-cost invasive procedure suites, providing the opportunity to reduce waiting times for these facilities and increase patient turnaround.

The NICE guideline on chest pain recommends diagnostic testing for people in whom stable angina cannot be excluded by clinical assessment alone.

The guideline recommends offering 64‑slice (or above) CCTA as the first-line diagnosis test when clinical assessment indicates typical or atypical angina; or non-anginal chest pain but 12‑lead resting ECG has been done and indicates ST‑T changes or Q waves.

Subsequent diagnostic tests can be requested dependent on the CCTA results. The guideline recommends offering non-invasive functional imaging for myocardial ischaemia if 64‑slice (or above) CCTA has shown coronary artery disease of uncertain functional significance, or is non-diagnostic. Non-invasive functional imaging includes:

• myocardial perfusion scintigraphy with single-photon emission CT (MPS with SPECT)

• stress echocardiography

• first-pass contrast-enhanced MR perfusion

• MR imaging for stress-induced wall motion abnormalities.
  
  ICA should be offered as a second-line investigation when the results of non-invasive functional imaging are inconclusive.

When ICA is used to determine the presence and severity of coronary stenosis, it may be combined with the invasive measurement of FFR using a pressure wire. Although the NICE guideline on chest pain does not consider FFR, other guidelines (such as those of the European Society of Cardiology and American College of Cardiology) state that lesions with an FFR of 0.80 or less are functionally significant and revascularisation may be considered.