Introduction
Approximately 350 000 patients present acutely with chest pain to emergency departments (ED) in the UK each year. These patients are assessed for suspected acute coronary syndrome (ACS) using assays of serial biomarkers and 12-lead ECGs.1 ,2 If the tests prove normal, patients are often discharged with a diagnosis of ‘troponin negative’ chest pain. Further assessment for possible coronary heart disease is inconsistent and is largely dependent on the individual clinician. A quick, safe, accurate and cost-efficient diagnostic tool for patients with suspected ACS is desirable.
Invasive coronary angiography (ICA) remains the gold standard for identifying clinically significant coronary heart disease (CHD). The invasive nature of ICA, however, is associated with a risk of complications (eg, vascular injury, myocardial infarction), cost, radiation exposure and compromise in patient experience. Furthermore, referrals for ICA often require inpatient transfer of patients to a regional centre, as only around 35% of UK hospitals have onsite coronary revascularisation facilities.3 This study was undertaken in Jersey General Hospital, in the Channel Islands, where there is no onsite coronary angiography service. Aeromedical transfer of patients referred for ICA is, furthermore, associated with clinical risk and expense.
In cases where ACS is suspected despite non-diagnostic ECG and troponin findings, the European Society of Cardiology (ESC) currently recommends functional testing to ascertain inducible ischaemia, and further guide decisions on invasive strategies.4 Furthermore, those with a predetermined low-intermediate risk of CHD should be considered for CTCA as an alternative to ICA.4 Despite these recommendations, uncertainty continues as to which non-invasive imaging modality should be used as first-line for the triage of patients with suspected ACS and low-intermediate risk of CHD.
Diagnostic non-invasive imaging techniques can be categorised as anatomical (CTCA) or functional (stress-echocardiography, nuclear medicine and stress MRI). Before evaluating the role of these individually, it would be prudent to add that in real practice, choice of investigation is greatly determined by interhospital variability in available resource and clinician expertise. In terms of functional assessment, stress echocardiography is preferred to exercise testing due to its superior diagnostic accuracy5 and prognostic outcomes.6 ,7 Advantages of stress echocardiography include availability, low cost and its radiation-free nature. The advantage of cardiac MRI (CMR) is its ability to assess both perfusion and regional wall changes. Favourable short-term and mid-term prognostic outcomes are reported in patients with suspected ACS and normal CMR findings.8 Its role in the acute setting of coronary assessment is of course limited by cost and resource. In patients with equivocal ECG changes and cardiac enzymes, combined stress–rest myocardial scintigraphy has been shown to enhance the assessment of ischaemia, and is again associated with favourable outcome.9 ,10
CTCA provides a reliable non-invasive alternative to ICA.11 Clinical studies have demonstrated that CTCA facilitates non-invasive risk stratification of CHD with a negative test indicating a favourable prognosis.12 ,13 A systematic review of 21 trials evaluating the diagnostic accuracy of CTCA reported a pooled specificity and sensitivity of 89% and 99%, respectively, when used to investigate clinically significant CHD.14 Heavily calcified coronary arteries on CTCA results in blooming artefact and overestimation of coronary lesions.15 Dual energy CT imaging has the potential to attenuate the radiological effects of beam hardening and blooming artefact when imaging heavily calcified vessels.16 Iyengar et al17 examined the diagnostic accuracy of high-definition CTCA (HD-CTA) compared with ICA. HD-CTA addresses the shortcomings of CTCA by improving spatial resolution and reducing blooming artefact from coronary calcification without exposing patients to higher doses of radiation. From their interim results, they concluded that HD-CTA has excellent accuracy compared to ICA in patients with high pretest probability of, or established, CHD. Furthermore, its incorporation in an acute chest pain service is feasible and provides early triaging of patients with suspected ACS who present with non-diagnostic troponin and ECG findings.17
Accordingly, CTCA could serve as a gatekeeper for ICA in selected patients presenting with suspected ACS, with particular benefit for those hospitals without onsite coronary revascularisation facilities. The objective of this study was to conduct a retrospective analysis of inpatients with suspected or confirmed ACS who were referred for ICA at a tertiary centre. The primary outcome measure was evidence of CHD at ICA requiring percutaneous or surgical coronary intervention. This cohort analysis enabled us to identify the number of patients who met the ESC-recommend criteria for consideration of CTCA as a primary investigation for suspected ACS. The secondary aim was to calculate the total cost of inpatient referral for this subgroup, and evaluate the role of local inpatient CTCA as a cost-effective alternative investigation to tertiary ICA in the context of suspected or confirmed ACS.