CT-CA may be an alternative to other non-invasive functional tests - such as ECG stress test, stress Echo or SPECT - in the diagnostic work-up of patients with suspected coronary artery disease (CAD) and in due time may even replace invasive coronary angiography (ICA).
An alternative to other functional tests
A recent report from the Working Group of Nuclear Cardiology and Cardiac CT of the ESC and European Council of Nuclear Cardiology clearly stated that state-of-the-art 64-slice CT is highly reliable in ruling out the presence of significant CAD. CT-CA is considered a strong gate-keeper for ICA and may be a viable alternative to other functional (coronary flow-limiting) tests.
Currently, we do not know the precise role of CT-CA in relation to functional testing, and this will once again fuel the debate about the importance of anatomy versus function in the diagnostic work-up of CAD. With current CT-technology (as with ICA) we should still expect a mismatch between the anatomical severity and the functionality of a coronary lesion, in particular with intermediate lesions. Combining both anatomy and function would constitute a highly desired comprehensive evaluation of a coronary lesion (or coronary territory).
Replacement of ICA
Current 64-slice CT-CA falls short of replacing ICA because the number of false-positives is rather high, resulting in a too-low positive predictive value (~80%). Interventionists and cardiac surgeons require precise detailed anatomical information to plan their revascularisation procedures, and this is beyond the image quality of current CT-CA.
CT-technology that improves spatial and temporal resolution is required to challenge ICA, which may be expected to occur in the near future.
Problems with CT-CA
Severe calcifications seriously hamper the diagnostic reliability of CT-CA and development of more refined detector technology may reduce this problem. The introduction of CT-scanners which scan the heart in one or a few heart beats may allow the use of CT-CA in patients with irregular heart beats or even with atrial fibrillation. CT-technical innovations, such as ECG-triggered pulse window and development of new CT-acquisition protocols (step and shoot), have been developed to significantly reduce the initially high radiation exposure to more acceptable doses within the range of those associated with ICA.
Consensus and future
Any new diagnostic technique should meet three criteria:
- Incremental diagnostic value (information) to already existing diagnostic techniques
- Better (or change in) patient management and outcome (mortality/morbidity)
- Cost-effectiveness
Because CT-CA is a technique still in its infancy (the first 64-slice CT reports only appeared in 2005), these criteria have only been partially met and the necessary information to fully address these issues requires a large number of studies.
Consensus in the appropriate use of CT-evaluation of coronary stenoses is still developing. So far, CT-CA is useful for ruling-out CAD in patients with atypical chest pain (intermediate pre-test likelihood of CAD), with equivocal functional test results, and with acute chest pain at low risk (normal ECG, no enzyme rise), and in patients evaluated before heart valve or non-cardiac surgery or evaluation of coronary anomalies.