Interview with Prof. Riemer H. J. A. Slart, Nuclear Medicine and Molecular Imaging, Faculty of Medical Sciences, University of Groningen
Coronary heart disease (CHD) can cause heart arrhythmia, heart insufficiency or heart attack. All the more important is an early, reliable diagnosis that helps to treat it and to reduce risk factors. But what is the best method for diagnosis? A recent study found that functional imaging methods can often spare patients the trouble and risks of a coronary angiography.
Prof. Riemer Slart
In this interview with MEDICA-tradefair.com, Prof. Riemer Slart talks about the advantages and disadvantages of different imaging methods, when invasive methods should be used to diagnose CHD and how this could change in the future.
Prof. Slart, we are talking about CHD and its diagnosis. What imaging methods can be used to diagnose this disease?
Prof. Riemer H. J. A. Slart: Coronary angiography, CAG, is a widely-used invasive method. There are also different non-invasive methods. On the one hand, there are nuclear techniques, where we use myocardial perfusion imaging with radio-isotopes, such as the SPECT technique, single photon emission computed tomography, or the PET technique, positron emission tomography. On the other hand, there is MR imaging that relies on myocardial perfusion imaging with contrast agents.
Compared to non-invasive methods, CAG has several disadvantages and even carries risks for the patients. What are those?
Slart: CAG exposes the patient to a higher radiation dose, higher than with the nuclear techniques. The injected contrast agent can also cause side effects. The catheter insertion can cause bleedings in the groin afterwards or even a compartment syndrome and, however less frequently, complications during the procedure itself. Furthermore, CAG is relatively expensive to use.
What are the advantages of functional imaging methods?
Slart: They are not as risky as the invasive procedure. The MR contrast agents do not have strong side-effects, radio-isotopes not at all. Using these methods, we can quantify different parameters, such as the perfusion of the heart, and we can evaluate the heart’s function at the same time. The methods are very accurate, they are more convenient for the patient and their costs are lower.
Are there also disadvantages?
Slart: Nuclear techniques still have a certain radiation dose, but it is much lower than with CAG.
The MRI can be a problem for some patients who have implants like pacemakers. They are not all allowed to enter the MR. Others react claustrophobic in the MR. This can actually be a significant number of patients.
Coronary angiography is aber to produce precise images of the coronary vessels, but the procedure is expensive and not without risks.
A lot of this speaks against using CAG. Are there some data that you cannot obtain with the non-invasive imaging methods, but with CAG only?
Slart: We can find out more about stenosis, the obstruction of the coronary arteries, when we use CAG. CAG is pretty accurate in this respect because its image resolution is high.
Still, there is another technique coming up these days, the CT angiography (CTA). We can also perform imaging of the coronary arteries and see the degree of stenosis with CTA. It is not as accurate as CAG yet, but it gets closer. This depends on how the technique will be improved further in the coming years. It could maybe replace CAG in the future.
How often are these different methods carried out, for example in Europe or in the US?
Slart: It depends not only on the country, but also on the individual hospital and the cardiologists there. There are guidelines, but the application of different imaging techniques is very wide for the work-up of patients. For patients with acute chest pain, CAG actually has to be used. But if cardiologists are very convenient with one of the techniques in other cases, they will of course prefer that one.
In general, CAG is used quicker in the UK than in the rest of Europe, where cardiologists are more focused on the non-invasive techniques in the work-up of patients suspected of coronary heart disease (CHD). The US is also more focused on non-invasive imaging, especially the nuclear techniques.
The examination of the coronary vessels is important to assess their degree of stenosis, narrowing. Besides coronary angiography, other imaging procedures are able to produce good pictures, too.
Recently, there was a study carried out in the UK, the "CE-MARC 2" study. What did this study look like?
Slart: The study evaluated the work-up of patients with CHD in the UK. British cardiologists work with the NICE guidelines, issued by the British National Institute for Health and Care Excellence. These guidelines state a specific cut-off value regarding the pre-test probability for CHD. The pre-test probability is the probability that a patient has a certain disease, before any diagnostic measures are taken. It relies, among others, on the risk factors of the patient. In the case of CHD and the NICE guidelines, it influences which diagnostic measures are taken by answering the question "When do we have to use non-invasive imaging or CAG techniques?".
In "CE-MARC 2", the cardiologists used the NICE guidelines to determine for one group of patients, which of them receive CAG. Two other groups received MRI or SPECT first. Just following the NICE guidelines, 40 percent of patients from the first group received CAG. In the two other groups, only around 18 percent underwent the invasive CAG. So, implementing a non-invasive procedure as the first diagnostic method dramatically reduced the number of patients who underwent invasive CAG.
What does this mean for the future of diagnosing CHD?
Slart: In the follow-up of the study, cardiovascular events such as infarction were equally low in all three groups. This means that the non-invasive methods are as safe a diagnosis as the conventional work-up from the NICE guidelines.
The European guideline, issued by the European Society of Cardiology (ESC), already anticipates this outcome. It states a pre-test probability for CAG of 85 percent, NICE states 60 percent. The cut-off value in Europe is much higher, so (unnecessary) invasive imaging is already used much less.
CAG is still necessary for patients with acute chest pain. This is also stated in the guidelines. It is also necessary for patients with a calculated high risk score. Non-acute patients who do not fulfill the risk criteria should receive non-invasive imaging first.