Clinical Use of Coronary CT Angiography

CHANGE OF PARADIGM

During the last decades we have witnessed a tremendous ‏progress in imaging technologies. Probably the ‏most impressive results have been achieved in cardiac ‏imaging. The landscape of diagnostic tools used for cardiovascular ‏diagnostics has dramatically changed. All cardiovascular ‏imaging technologies have improved, but the ‏most spectacular changes have occurred in echocardiography, ‏coronary and cardiac computed tomgraphy (CT) angiography, ‏cardiac magnetic resonance and hybrid modalities ‏(position emission tomography computed tomography ‏[PET -CT] and position emission tomography magnetic resonance ‏imaging [PET -MRI]). These have moved from the area ‏of research tools into routinely used ones.

Several trends in this area are obvious. First of all, progress of ‏cardiac imaging is related to amazing improvements in scanning ‏technology. In some ways cardiac imaging is a kind of ‏‘probing stone’ for scanners. For example, it is quite difficult to ‏show improvements in diagnosis ‏of pulmonary nodules using widedetector ‏or dual-source scanners ‏in comparison with ‘traditional’ ‏low-end 16-row systems (here ‏we are speaking about diagnostic ‏accuracy, not radiation exposure ‏to patients or image quality). In the case of cardiac ‏computed tomography angiography (CTA ), the difference for ‏the better in the case of technically more advanced scanners ‏is quite obvious.

It is interesting to note that the ability to detect and grade ‏coronary stenosis performance of ‘traditional’ 64-row scanners ‏in general is quite similar to newer and more expensive ‏scanners. Latest trials have shown that neither coronary ‏catheterisation nor cardiac CTA are perfect in grading ‏coronary lesions into haemodynamically significant and ‏not significant ones. First of all this fact concerns so called ‏intermediate stenosis, causing luminal narrowing to 50-70 ‏percent. This is why one of the major directions in cardiac ‏radiology is functional imaging. In case of CCTA it can be ‏done with the help of perfusion myocardial CT or noninvasive ‏assessment of coronary blood flow. The last one could ‏be done with help of CT fractional flow reserve (CT FFR) analysis ‏or assessment of transluminal arterial gradient (TGA). ‏Both these approaches (especially CT FFR) are promising ‏tools for studies of coronary flow through stenotic lesions.

New generations of CT scanners can perform both CCTA and ‏myocardial perfusion CT with fewer non-interpretable scans. ‏It is their major advantage over standard 64-row scanners. ‏

In the past results of CCTA in multiple single- and multicentre ‏trials had been compared with invasive coronary angiography ‏(ICA) using the latter as a ‘gold standard’. Quite naturally ‏CCTA was inferior to ICA in grading of coronary lesions. ‏But after accumulation of a wealth of practical and scientific ‏data, today we are witnessing a quite different situation.

In cardiology and cardiac surgery we are witnessing a rapid ‏transition from the ‘traditional’ approach to grading of individual ‏coronary artery lesions towards the ‘modern’ one, which is ‏based on a combination of anatomy and physiology to determine ‏the physiological consequences of coronary stenosis: ‏does it cause myocardial ischaemia or not?

With the introduction and ‏rapid evolution of invasive ‏fractional flow reserve ‏(FFR) technology, a new gold ‏standard has been developed ‏to invasively assess ‏the physiological severity ‏of a coronary artery stenosis. Several trials using FFR have ‏demonstrated that ICA also has limited capabilities to determine ‏the physiologic significance of intermediate (50-70 ‏percent) coronary stenosis. In some recent trials it was shown ‏that in case of head-to-head comparison of ICA with CCTA ‏using FFR as a new reference, the diagnostic performance of ‏both modalities for grading of coronary stenosis was comparable ‏(Budoff et al. 2016).

What is even more important is that CCTA has the ability ‏to see the vessel wall, to assess the structure of atherosclerotic ‏plaques and even to detect (in some cases) the ‏vulnerable plaques. CCTA provides three-dimensional imaging ‏of the whole heart, including the myocardium, all the heart ‏chambers and valves.

So it looks like the answer to the popular question: “When ‏does CCTA replace ICA?” is “Tomorrow!”. Why tomorrow, not ‏today? As has been said earlier, even the best models of ‏modern scanners still cannot provide artefact-free anatomica and physiological imaging in one hundred percent of cases, ‏and most of them are not so common in public healthcare. ‏Usually they are used in medical centres dedicated to cardiac ‏imaging and research.

But having almost 30 years’ experience in cardiac imaging, ‏I am quite enthusiastic about this transition. Let’s look ‏back: a long time ago (in the 1980s) both CT and MRI replaced ‏catheter angiography for diagnostic workup of aortic disease. ‏After the appearance of spiral and multislice CTA this modality ‏practically replaced catheterisation in diagnosis of pulmonary ‏thromboembolism, carotid and peripheral arterial disease. ‏The next target is coronary imaging and we are almost there. ‏Hunting for vulnerable plaques will continue and hybrid cardiac ‏imaging (PET -CT, SPE CT-CT, MRI -CT) is steadily developing ‏from a research tool into a clinical one.

Use of cardiac imaging is rapidly expanding and today we ‏have plenty of scientific data providing us with reasons to ‏use CCTA more widely in clinical routine. It is important to ‏notice that CCTA has proven independent prognostic value ‏and it can even improve patient outcomes (SCOT -Heart Trial) ‏(Williams et al. 2016). Indications for use of CCTA are given ‏in modern U.S. and European cardiological and radiological ‏guidelines (one can refer to publications from the American ‏College of Cardiology (ACC), Society of Cardiovascular Computed ‏Tomography (SCCT), the European Society of Cardiology ‏(ES C) and the American College of Radiology (ACR) - plus the ‏recent iGuide from the European Society of Radiology (ESR). ‏But it looks like even these modern recommendations and ‏guidelines would be substantially changed and updated in ‏favour of CCTA when some recent important trials of 2015- ‏2016 are taken into consideration.

Generally speaking, technical progress of CCTA in combination ‏with rigorous research in this area has resulted in rapid ‏transformed use of this diagnostic modality. Probably in the ‏next few years we will see the situation when imaging of all ‏vessels - big and small - will be done noninvasively with the ‏help of CTA (or MRA) and ICA will move completely into the ‏area of intervention (placement of stents, grafts, artificial ‏valves, occluders etc.). It is going to be a ‘win-win’ situation ‏both for physicians and patients because it will increase the ‏number of right procedures performed rapidly and effectively ‏for the right patients.