In the Netherlands, 180,000 new patients present with stable chest pain—the most common symptom of coronary artery disease (CAD)—annually [1
]. In the past few years, the preferred diagnostic strategy in these patients has evolved from a focus on functional testing to coronary computed tomography angiography (CCTA) [2
]. Treating cardiologists in the Netherlands are recommended to apply a more consistent management by using a single non-invasive first-line test for diagnosing CAD due to current variation in clinical practice [1
]. Implementation of CCTA in the work-up of patients with stable chest pain, however, may lead to unnecessary invasive testing, because CCTA has the ability to accurately rule out CAD [4
], but not the ability to correctly predict a haemodynamically significant stenosis on invasive coronary angiography (ICA) [6
Computed tomography-derived fractional flow reserve (FFRct) may overcome the shortcomings of CCTA. FFRct is a non-invasive method that uses the already acquired CCTA images as the basis to calculate coronary FFR values as they would be expected if measured invasively (see Fig. S1 in Electronic Supplementary material). FFRct applies computational fluid dynamics and deep-learning image-based modelling to estimate rest and hyperaemic coronary flow and pressure from CCTA [7
]. FFRct represents the ratio of maximal coronary blood flow through a stenotic artery to the blood flow in the hypothetical case that the artery is normal [8
]. Early validation studies, assessing the diagnostic performance of FFRct with invasive FFR as the reference standard, are promising. On a per vessel analysis, the sensitivity is 80–88% and the specificity is 61–86% [9
So far, observational data have shown that FFRct adds to the diagnostic strategy in patients with stable chest pain by reducing the rate of unnecessary ICA (defined as ICA showing unobstructed coronaries). The ADVANCE registry indicated that the availability of FFRct as an adjunct to CCTA would change the management of CAD in 66.9% of patients when compared with an initial CCTA-based treatment plan [12
]. This study also demonstrated the safety of patient management following the implementation of FFRct into the decision pathway, and the avoidance of invasive assessment in most patients with a negative FFRct [12
]. The PLATFORM study demonstrated a cancellation of ICA in 61% of CCTA + FFRct patients. No adverse clinical events occurred at 1 year in these patients, indicating safe deferral of ICA based on CCTA and FFRct [14
]. The recent FORECAST trial showed that a strategy of CCTA with selective FFRct in stable angina patients did not differ significantly from standard clinical care pathways in cost and clinical outcomes, but did reduce the use of other non-invasive tests and ICA [15
]. These studies suggest that FFRct can alter the management of patients and safely reduce the percentage of patients referred for ICA without significant CAD. An overview of the main findings of these current studies is presented in Tab. 1
Main characteristics of the studies on the use of FFRct in patients suspected with CAD
Sample size, n
The ADVANCE registry, 2018, 2020
Pragmatic, prospective, international, multicentre registry of patients being
investigated for clinically suspected CAD with documented stenosis of at least 30% on coronary CTA
– FFRct modified treatment recommendation in 66.9% of the patients when compared with CCTA alone, was associated with less negative ICA, predicted revascularisation, and identified subjects at low risk of adverse events through 90 days.
– 1-year outcomes show low rates of events in all patients, with less revascularisation and a trend toward lower MACE and significantly lower cardiovascular death or MI in patients with a negative FFRct compared with patients with abnormal FFRct values
The PLATFORM study, 2015, 2016
Prospective, consecutive cohort study with a comparative effectiveness observational design in symptomatic outpatients without known CAD, but with an intermediate likelihood of obstructive CAD, whose physician had planned non-emergent, non-invasive, or invasive cardiovascular testing to evaluate suspected CAD
– Among those with intended ICA (FFRct-guided = 193; usual care = 187), no obstructive CAD was found at ICA in 24 (12%) in the CTA/FFRct arm and 137 (73%) in the usual care arm. Invasive coronary angiography was cancelled in 61% after receiving CTA/FFRct results. Clinical event rates within 90 days were low in usual care and CTA/FFRct arms.
– 1-year outcomes show that in patients with planned ICA, care guided by CTA and selective FFRct was associated with equivalent clinical outcomes and quality of life, and lower costs, compared with usual care over 1‑year follow-up
The FORECAST trial, 2021
Open-label, multicentre, randomised, controlled clinical trial. Patients presenting at RACP, who require a cardiac test, were randomised to either routine care (management strategy based on NICE Chest Pain of Recent Onset Guidance—CG95) or CCTA with selective FFRct group in a 1:1 ratio
A strategy of CCTA with selective FFRct in patients with stable angina did not differ significantly from standard clinical care pathways in cost or clinical outcomes, but did reduce the use of non-invasive testing and ICA, which was 22% lower in the experimental group
Sub-study of the CRESCENT I and II trials, 2020
Secondary analysis using the CCTA data. Observational cohort study, which included patients with suspected CAD and a ≥ 50% stenosis on CCTA who had been randomised to cardiac CT in the CRESCENT I trial and II trials
The availability of FFRct would have reduced the number of patients requiring additional testing by 57%-points compared with CCTA alone. The initial management strategy would have changed for 30 patients. Reserving ICA for patients with a FFRct ≤ 0.80 would have reduced the number of ICA following CCTA by 13%-points
Prior FFRct studies involved populations of various countries with different work-up and were based on a non-randomised design with the exception of the FORECAST trial [13
]. There are no prospective data on the real-world use of FFRct in the Dutch population of stable chest pain patients. On top of that, there are no trials that randomise patients who have undergone CCTA to standard care or FFRct-guided care based on the presence of > 50% stenosis on CCTA.
The ‘Addition of FFRct in the diagnostic pathway of patients with stable chest pain to reduce unnecessary invasive coronary angiography’ (FUSION) trial is a multicentre, randomised, controlled trial that investigates the impact of adding FFRct analysis in the diagnostic pathway of stable chest pain patients with a 50–90% coronary stenosis on CCTA, on the rate of unnecessary ICAs, the cost-effectiveness, quality of life and clinical outcomes.
The FUSION trial is sponsored by the Dutch Ministry of Health and the Dutch National Health Care Institute (Zorginstituut Nederland) as part of the research programme ‘Potentially Promising Care’ (‘Veelbelovende Zorg’) that aims to assess medical technology to determine if it can be reimbursed in the standard health care package.
This multicentre, randomised clinical trial will evaluate the impact of adding the FFRct analysis to CCTA in the diagnostic pathway of stable chest pain patients with CCTA-derived stenosis on the rate of unnecessary ICA, cost-effectiveness, quality of life, and clinical outcomes from a Dutch perspective.
FFRct is a non-invasive technique that may change the way stable angina is diagnosed and managed. Patients who undergo ICA after CCTA often do not have a haemodynamically significant stenosis, which leads to 28–41% unnecessary ICAs in the Dutch population [16
]. By deriving coronary physiology from CCTA data, FFRct can be used to increase the diagnostic yield of the CCTA and, consequently, reduce the number of unnecessary ICAs as well as costs [13
In addition, FFRct may add to a proper selection of patients who may benefit from a revascularisation procedure [13
]. FFRct has been validated against invasive FFR, which is an essential invasive procedure guiding revascularisation in stable CAD by investigating the haemodynamic significance of epicardial coronary stenoses (FAME trial) [9
]. Although ICA with FFR could be performed in the management of patients with stable chest pain, the invasive approach has its challenges; not only the complications inherent to invasive testing, but also the inevitable patient discomfort and costs. Determining FFR using CCTA could provide both anatomical and physiological assessment of the coronary circulation without cardiac catheterisation.
To evaluate the impact of FFRct in the FUSION trial, selection of an appropriate target population is necessary. Given the high negative predictive value of CCTA, only little added benefit of FFRct is expected in patients without suspected obstructive disease on CCTA. On the other hand, functional evaluation is also not required in case of a very high grade stenosis (> 90%) on CCTA, because the probability of this stenosis to be haemodynamically significant on ICA is very high [8
]. Therefore, we will only include patients with a 50–90% stenosis on CCTA.
Similar to the design of the CRESCENT trial [17
], the FUSION trial design is based on improving the diagnostic strategy of stable angina pectoris patients and not merely on identifying which diagnostic test is superior. In the FUSION trial, we focus on patients in whom we expect FFRct to be most appropriate, namely patients with intermediate anatomic stenosis. On top of that, we have designed our study in such a way that we can estimate the number of false negative FFRct results and determine the effects of missing CAD diagnosis, by performing a post-hoc FFRct analysis in the control group based on the existing CCTA in each patient. The patients in the control group undergo routine care, which is not based on FFRct but, mostly, on ICA. This ensures that we can determine how often the FFRct results would have led to a false negative result. In the intervention group, patients with FFRct > 0.80 will include both the true and false negatives, and we will assess the outcome of these patients. These results combined will provide solid data on how often false negatives occur and what the consequences are. We will be able to make an assumption on the maximum risk these patients have for developing major adverse cardiac events in 1 year.
Major adverse cardiac events is not selected as the primary endpoint, as it would require a very high number of patients to be included in the trial. Since we can make accurate assumptions of the risk of major adverse cardiac events in the study population—and unnecessary ICAs is a clinically relevant endpoint—we have chosen the latter as the primary endpoint.
The FUSION trial has been designed to investigate the role of FFRct in the diagnostic strategy of patients with stable chest pain after CCTA and does not have the potential to answer questions about optimal treatment strategy in patients with symptomatic CAD. This was subject of the ISCHEMIA trial, which results support that the vast majority of patients with CAD (in a selected population of patients with an abnormal functional test) can be treated with an initial conservative strategy of medical therapy alone [21
]. These results do not undermine the prominent role of functional testing in the management of stable chest pain patients, whether this should be based on functional testing or based on FFR testing, such as in the FUSION trial.
First of all, it remains useful to confirm a clinical diagnosis in patients with quality-of-life-limiting symptoms. Secondly, as the ORBITA trial demonstrated, having symptoms and an anatomic stenosis is insufficient to detect the patients for whom revascularisation will improve quality of life [22
]. On top of that, ISCHEMIA targeted a specific patient population, as most patients referred for further testing in the current era would have been too low risk to be included in the trial, but also high-risk patients (unacceptable level of angina despite maximal medical therapy, left main disease on CCTA, ejection fraction < 35%) were excluded [21
In conclusion, the FUSION trial is designed to evaluate whether the use of FFRct could decrease unnecessary ICA in patients with stable chest pain in both academic and peripheral hospitals with multiple CCTA vendors. The FUSION trial aims to provide a new strategy in Dutch health care for the diagnostic workup of stable chest pain. As the FUSION trial is part of the research programme ‘Potentially Promising Care’ of the Dutch National Health Care Institute, the results of the study will be used for a fast-track procedure to assess if FFRct reimbursement can be included in the standard health care package.
Conflict of interest
S.P. Sharma, A. Hirsch, M.G.M. Hunink, M.J.M. Cramer, F.A.A. Mohamed Hoesein, C.A. Geluk, G. Kramer, J.W.C. Gratama, R.L. Braam, P.M. van der Zee, W. Yassi, S.L. Wolters, C. Gürlek, G. Pundziute, R. Vliegenthart and R.P.J. Budde declare that they have no competing interests. This study is financially supported by HeartFlow, Inc. In addition, the Erasmus Medical Centre has received support from HeartFlow, Inc. and Siemens for other studies unrelated to the FUSION trial.