Role of Cardiac CT
CT is an increasingly pivotal diagnostic tool for cardiovascular disease and preprocedural planning for structural intervention and device implantation. CT coronary angiography (CTCA) has gained prominence in UK clinical practice as it is now recommended in the National Institute for Health and Care Excellence guidelines as the first-line test for the investigation of anginal symptoms in those without known coronary artery disease (CAD).1 CTCA is an excellent rule-out test for CAD (figure 1) but has an increasingly robust positive predictive value, especially when combined with CT-fractional flow reserve,2 which is currently being funded as part of an NHS England Innovation programme. Recent evidence has demonstrated the addition of CTCA to standard of care in patients from rapid access chest pain clinics reduced non-fatal myocardial infarction rates by over 40%.3
Figure 1. Typical CT coronary angiogram images of a patient referred for investigation of coronary artery disease.
(A) 3D volume rendered images demonstrated the anatomical distribution of the left anterior descending (LAD) and diagonal vessels. (B) Centre-vessel tracking reconstructed images of the LAD demonstrated no significant coronary stenosis or atheroma.
In structural heart disease, such as prior to transcatheter aortic valve implantation, CT can provide accurate dimensions of the aortic annulus, root and coronary ostia to guide valve sizing and intravenous access route (figure 2).4 Prior to mitral valve intervention, detail on mitral valve annulus morphology, calcification, landing zone and anatomical relation to the left circumflex artery can be acquired to guide device sizing and implantation.5 Furthermore, CT is important in the workup for electrophysiology procedures to evaluate the size, position and morphology of the atria, pulmonary veins and left atrial appendage prior to radiofrequency ablation and left atrial exclusion.6 It is increasingly used in the assessment of both paediatric and adult congenital heart disease, especially when cardiac MRI is contraindicated.
Figure 2. Preprocedural reconstructed images demonstrating accurate dimensions and morphology to guide transcatheter aortic valve implantation (TAVI).
(A) Aortic annulus, (B) aortic root, (C) distance from aortic annulus to ostia of coronary arteries, (D, E) orthogonal views of the iliofemoral arteries for access routes, (F) 3D volume rendered reconstruction of the entire arterial tree from aortic root to femoral arteries.
Technology and image processing has rapidly progressed such that radiation doses have markedly reduced by 78% over 10 years,7 and with emerging cost-effectiveness evidence, CT has an expanding role for diagnosis of cardiovascular disease.
Role of Cardiologists
Increasingly, all cardiologists require a clear understanding of indications and limitations (table 1), contraindications, radiation burden and strengths of cardiovascular CT. Referring clinicians need to provide sufficient clinical details and indicate clear clinical questions. This allows adequate planning of image acquisition to obtain optimal images with least radiation and in turn enables reporters to produce high-quality relevant reports to guide patient care. While the indications and evidence base are expanding for cardiovascular CT, there is a clear shortfall in trained clinicians to meet UK service requirements.8 Thus, there is a need to train the next generation of cardiovascular imagers to meet this challenge nationally and internationally.
Table 1. Indications and limitations for cardiovascular CT.
| Indication | Detail |
|---|---|
| Coronary artery disease | Assessment of calcific and non-calcific plaque for assessment of coronary atherosclerosis with CT calcium scoring and CT coronary angiography |
| Assessment of patency of grafts after coronary artery bypass grafting | |
| Prior to transcatheter aortic valve implantation | Evaluation of anatomy and morphology of aortic dimensions to guide procedure and device sizing |
| Assessment of patency of intravenous access routes including iliofemoral and subclavian arteries | |
| Prior to mitral valve intervention | Evaluate anatomy and morphology of mitral valve apparatus to guide sizing of devices |
| Prior to radiofrequency ablation | Anatomy and morphology of atrial and pulmonary venous system |
| Prior to biventricular pacemaker | Delineate coronary venous drainage to guide lead placement |
| Adult congenital heart disease | Assessment of anomalies of the coronary arteries and complex congenital heart disease |
| Cardiac masses | Assessment of intracardiac and extracardiac mass anatomy and morphology |
Limitations
Use of ionising radiation, although doses have considerably reduced—2016 UK median dose 200 mGy cm (5–6 mSv).
Significant motion and arrhythmia can result in artefact and thus reduce image quality and diagnostic utility.
Stents and heavily calcific coronary lesions can lead to blooming artefact and thus difficulty in lesion quantification.
Test of anatomical disease rather than functional consequence of coronary artery lesions (unless in conjunction with CT-fractional flow reserve [FFR]).
Optimal imaging requires heart rate control, usually with intravenous/oral beta blocker.
Successful service delivery necessitates an integrated working relationship between cardiologists and radiologists and regular audit of radiation, image quality and reporting for continued quality control. Cardiologists in all disciplines need to engage with cardiac imaging specialists through multidisciplinary meetings and two-way feedback to ensure usefulness and diagnostic utility for patient benefit.
Accreditation
Formal accreditation requires demonstration of skills and knowledge through experience and participation in image acquisition, reporting and formal lectures.9 Currently, level I accreditation provides familiarity to cardiovascular CT and requires 50 CTCA reports, while level II accreditation requires accurate interpretation of cardiovascular CT and is achieved by reporting a case mix of 150 studies. Given the increasing role of cardiovascular CT in routine clinical practice there may be a case to incorporate level II training as a core requirement for cardiologists in both Europe and the UK. Level III accreditation is reserved for clinicians with considerable expertise in performing and reporting CT and capable to lead a clinical/academic unit or provide high-quality education in the field.
In summary, cardiovascular CT is an increasingly central non-invasive imaging test in cardiology with growing diagnostic and clinical application that will likely hold an increasingly important role in future cardiovascular care.
Funding
This study was funded by the Medical Research Council (grant number MR/P01979X/1).
Footnotes
Contributors EDN conceived the idea of this article. MSN and EDN jointly wrote this manuscript.
Competing interests None declared.
Patient consent for publication Not required.
Provenance and peer review Commissioned; internally peer reviewed.
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