Incidence of stable coronary artery disease (CAD) is expected to increase in the coming decades. Coronary angiography is the gold standard for the treatment of an acute coronary syndrome; however, its relevance as a first-line test in cases of stable CAD remains debatable. The European Society of Cardiology (ESC), American College of Cardiology/American Heart Association (ACC/AHA), and National Institute for Health and Care Excellence (NICE) guidelines on stable CAD suggest that non-invasive stress testing is the preferred diagnostic strategy among most stable patients. Only stable patients with the highest pretest probability, or those with signs of ischaemia on resting electrocardiogram (ECG), benefit from an immediate invasive approach.
Exercise stress testing, single-photon emission computed tomography (SPECT), and stress echocardiography are the most commonly used non-invasive tests, followed by cardiovascular magnetic resonance (CMR) and positron emission tomography (PET). These tests should identify the individuals who ought to undergo invasive coronary angiography. The major drawback for these non-invasive tests applies to their low specificity. The latter leads to an overuse of coronary angiography, with studies showing that <50% of patients sent for invasive angiography ultimately prove to have significant CAD.
Until recently, coronary CT angiography (CCTA) was commonly used to rule-out CAD depending on its high negative predictive value. The PROMISE and SCOT-HEART studies provided compelling evidence that CCTA is a safe tool for the diagnosis of stable CAD. Nevertheless, similar to other non-invasive tests, a substantial proportion of unnecessary invasive coronary angiographies (ICA) are executed as lesion severity, assessed by CCTA, shows an unreliable relationship to lesion-specific ischaemia and stenosis severity is often overestimated. As a result, invasive fractional flow-reserve (FRR) measurement is still the gold standard for the diagnosis of lesion-specific ischaemia in the cath lab.
Recently, a new tool has proven to be able to increase accuracy of CCTA in diagnosing obstructive CAD. Non-Invasive HeartFlow® FFRCT (HeartFlow, Redwood City, California, USA) has been validated against invasive FFR in three trials: following the initial 2011 DISCOVER-FLOW study, the DeFACTO and NXT studies were published in 2012 and 2014, respectively. Subsequently, the outcome and resource trial, PLATFORM, proved that in patients with stable chest pain and planned invasive coronary angiography, care guided by CCTA and selective FFRCT was associated with equivalent clinical outcomes and quality of life, as well as lower costs, compared with usual care over 1-year follow-up.
We performed a retrospective analysis of 48 patients, who presented with stable chest pain, positive exercise ECG, and intermediate (50–70%) CCTA stenosis, who were referred for ICA and FFR examination. We determined the diagnostic accuracy of FFRCT versus CCTA using FFR as the reference standard and evaluated the potential impact of clinical adoption of FFRCT to guide clinical decision making. ‘Unnecessary’ ICA-FFR examinations were defined as ICA with measured FFR >0.80.
FFRCT had higher diagnostic accuracy than CCTA (83% versus 29%) with higher positive predictive values (69% versus 29%) and a 6-fold reduction in false positives. Using an invasive FFR-guided therapy, 34/48 patients (71%) proved to have non-obstructive CAD (FFR >0.80) and were treated medically while only 14 patients (29%) had FFR ≤0.80 and were revascularised (8 percutaneous coronary interventions, 6 coronary artery bypass grafts). There were no major adverse cardiac events in the patients who were treated with optimal medical therapy. Use of a FFRCT-guided strategy would have reduced unnecessary ICA-FFR procedures by 85%, thereby reducing the inherent risk of an invasive procedure. Assuming a cost of €1,000 per FFRCT analysis, an overall cost reduction of 30% would have been achieved. Furthermore, radiation dose exposure would have been reduced by 63%, assuming an average dose of 2.1 mSv for CTA and 4.8 mSv for ICA.
In conclusion, utilisation of FFRCT analysis in the evaluation of symptomatic patients with intermediate CTA stenosis results in fewer unnecessary invasive ICA-FFR examinations with significantly reduced costs, risks, and radiation dose exposure. These findings are in line with previously published data.