Over the few past years, the diagnostic value of coronary computed tomography (CT) angiography (CTA) has been firmly established. The European Society of Cardiology Guidelines recommend coronary CTA as a class IIa indication in the presence of a low–intermediate pre-test probability risk of coronary artery disease (CAD). Technological advancements in the quantification and functional assessment of epicardial coronary stenosis by means of fractional flow reserve (FFR) derived from computed tomography (FFRCT) have raised the possibility of expanding coronary CTA use to guide decision-making regarding revascularization strategies in patients with CAD.
The expansion of coronary CTA usage to decision making needs consideration of some limitations of this technology. Firstly, despite recent improvements in mechanical and software-based spatial and temporal resolution, coronary CTA is still inferior to coronary angiography, especially in evaluating intermediate stenosis in patients with atrial fibrillation or in the presence of high-degree calcifications. Newer-generation scanners including flat panel CT, multisegment reconstruction, and dual-source CT technology represent valuable advantages but do not eliminate the gap. Moreover, although haemodynamic evaluation of intermediate stenosis can be performed by FFRCT, this technology is not readily available as FFR or an instantaneous wave-free ratio obtained during invasive coronary angiography. Finally, coronary CTA is more patient/operator-dependent regarding image acquisition and interpretation when compared to invasive coronary angiography.
The SYNTAX III REVOLUTION trial, presented in this issue of the European Heart Journal, is an international, multicentre study, randomizing two separate heart teams (composed of an interventional cardiologist, a cardiac surgeon, and a radiologist) to quantify, with either coronary CTA or conventional angiography, the anatomical complexity by using the SYNTAX score in patients with known de novo left main or three-vessel CAD. Each heart team, blinded for the other imaging modality, integrated clinical information using the SYNTAX score II and provided treatment recommendations among the three options: coronary artery bypass grafting (CABG), percutaneous coronary intervention (PCI), or equipoise between CABG and PCI. The primary endpoint of this study was agreement between the two heart teams on the revascularization strategy. For the secondary endpoint, the coronary CTA heart team made a further treatment recommendation, integrating anatomical and functional data from FFRCT values. Comparison of the SYNTAX and SYNTAX II scores and their components between the two heart teams are presented in Table 2 of the manuscript. An important consideration when analysing this table is that some differences (such as the amount of calcium and presence of left main disease) may be related to the different power of each imaging modality to identify specific characteristics (i.e. coronary CTA is better to detect calcium and to point out significant left main disease by visualizing the vessel lumen and the disease affecting the vessel wall). No significant differences in the number of coronary stenoses > 50%, and SYNTAX score calculated by using coronary CTA and conventional angiography, were observed (1108 vs. 1073 and 33.9 ± 12.0 vs. 30.3 ± 12.2, respectively). Regarding the final recommendations, the agreement on the revascularization strategy was almost perfect between the two groups. CABG was recommended in 28% of patients by coronary CTA and in 26% of patients by invasive coronary angiography. Equipoise CABG or PCI was suggested in 106 patients, with no difference between CTA and coronary angiography. Overall, the heart teams agreed on the coronary segments to be revascularized in 81.1% of cases. Most remarkable was the correlation between the SYNTAX II score evaluated by coronary CTA vs. coronary angiography, with a correlation coefficient of 0.98. An important departure from current practice has been to utilize physiological assessment to guide the decision to suggest CABG. FFRCT was available in 868 of the 1108 lesions and identified no flow-limiting stenosis in 116 lesions in 34% of the patients; thus, changing the treatment decision in 7% of the patients (in 13 patients the surgical procedure was changed to a percutaneous approach) and reducing the proportion of patients with haemodynamically significant three-vessel disease from 92.3 to 78.8%.
Take Home Figure.
A final stage of the study protocol allowed unblinding of the heart teams. The availability of coronary angiography to the CTA heart team changed decisions 9% of the times when decisions were initially based upon CTA, and in 6.3% of the patients initially evaluated according to FFRCT.
We do not need sophisticated statistical analysis to conclude that, in this study, there was an almost perfect agreement regarding the treatment decision when the heart team utilized CTA assisted by FFRCT or conventional coronary angiography (without pre-specified usage of FFR).
The authors correctly point out several limitations of this trial, such as the underrepresentation of patients with acute coronary syndromes and the lack of outcome data when the treatment decision was taken according to CTA evaluation. Additional limitations we consider relevant are:
We are not aware of the number of CTA examinations considered technically inadequate or even not performed for various clinical/technical reasons.
Coronary CTA examinations of optimal quality with experienced interpretations are not a universal guarantee. While these attributes might be 'normal' in highly experienced environments, we do not know what will happen in 'real-life' scenarios.
The availability of FFRCT and its validation in common practice are still objectives to be achieved.
This study was performed in patients with left main or three-vessel CAD and we do not know if the strategy of coronary angiography with ad hoc PCI would be more practical and cost-effective in patients with less-advanced CAD.
These limitations should alert the practicing cardiologist that CTA is not currently ready to be utilized for final therapeutic decision-making instead of coronary angiography.
In light of these considerations, we would like to rephrase the conclusions of this important and well-conducted study as follows: 'In patients with complex CAD, optimal CTA with FFRCT availability, evaluated by an experienced reader, might lead the heart team to almost similar therapeutic recommendations as conventional coronary angiography. A prospective study with clinical outcomes is needed to evaluate the feasibility and the value of this strategy'.
Eur Heart J. 2018;39(41):1576-1577. © 2018 Oxford University Press
Copyright 2007 European Society of Cardiology. Published by Oxford University Press. All rights reserved.