Cardiovascular disorders

I./3.5.: Coronary CT

Coronary CT has become widespread in the recent years. In parallel with the development of technique, it has a more and more significant place in the diagnostics of patients with coronary heart disease. Its main advantage is its semi-invasive nature, as no direct coronary angiography is required for it. Recordings of very high quality can be made with the help of intravenously applied contrast media. During the examination the contrast agent is given through a cannula inserted to a peripheral vein, and very high-resolution images are made; then a detailed computerized reconstruction of these allow even the creation of spatial (three-dimensional) images. Currently, with the modern high-resolution, high-speed CT equipments also patient-friendly examinations can be performed which are associated with a low radiation exposure. For a recording of good quality a modern instrument with at least 256 slices is required; and it is very important that the patient should not have tachycardia.

For an optimal examination the patient’s heart rate at rest should be around 60 bpm. This can often be attained by administering a short-acting intravenous beta blocking agent before the examination. Among others, the examination offers an excellent diagnostic possibility for determining the calcium content (Ca score) that is in close connection with the long-term prognosis; for detecting the coronary anomalies; for excluding the coronary disease, or for the triple-rule-out outlined in the clinical part. It is recommended primarily for excluding coronary disease, if the non-invasive test results are contradictory in a patient with chest pain, or when the pre-test possibility of coronary disease is moderate. It is certainly not recommended in patients with unequivocal acute coronary syndrome or myocardial infarction, as the diagnosis is not at all dubious in such cases; at the same time the diagnostics should be continued by performing a coronary intervention in much cases (in patients with ST segment elevation myocardial infarction almost in 100%).

Further, patients who earlier underwent coronary artery bypass grafting (CABG) or aorto-coronary bypass grafting (ACBG) can be examined in order to determine the patency of their grafts, and patients who previously underwent a coronary intervention can be examined in order to detect any in-stent re-stenosis. Not all stents can be examined; usually the lumina of stents with a diameter of 3 mm or more are suitable for being evaluated. The method may also help planning the revascularization in special situations, e.g. by an accurate mapping of complex stenoses which affect the division of the left common principal trunk or another significant bifurcation.

Replacement of the “routine” coronary angiography by CT examination of the coronaries in patients who underwent heart transplantation is a novel field. Namely, the risk of developing coronary sclerosis and stenoses in the transplanted heart significantly increases during the post-transplantation years; in addition – understandably – this often develops without any complaints; therefore, depending on the local protocol of the transplantation center, usually a routine coronary angiography is performed yearly.

In its guidelines on myocardial revascularization, the European Society of Cardiology does not recommend CT examination of the coronaries for the purpose of screening. Namely, the later malignancies and the consequent increase of mortality, calculated on the base of radiation doses delivered by the previous “screening” CT examinations performed with equipments of an earlier generation in a population of patients in their twenties exceeded the number of lives saved by the screening on the long run. It should be added that the current up-to-date equipments work with radiation doses which are lower by orders of magnitude.