Chest pain in the emergency department: choosing the right test when troponin is equivocal

Risk stratification:

1. Clinical: typical ischaemic chest pain, diaphoresis, and ECG changes (ST depression V4–V6) place her at high risk by HEART score (likely ≥7: history 2, ECG 2, age 2, risk factors 2, troponin 2) and by TIMI risk score. The 1-hour troponin delta (18 → 22 ng/L) is small but above the upper reference limit, consistent with possible non-ST-elevation myocardial infarction (NSTEMI) or unstable angina.
2. ECG: ST depression in V4–V6 suggests ischaemia in the LAD/LCx territory and is a high-risk feature.
3. Haemodynamics: stable, pain-free, no heart failure - she is not in cardiogenic shock and does not require immediate revascularisation on an emergency basis.

Strategy:

1. Admit and treat medically (aspirin, P2Y12 inhibitor per local protocol, anticoagulation, beta-blocker, statin, GTN) with continuous monitoring.
2. Invasive coronary angiography within 24 hours is indicated for high-risk NSTE-ACS (GRACE >140, dynamic ST changes, troponin rise). This should be arranged for the next available catheter lab slot, ideally within 24 hours, and the cardiology team should be informed now even though the registrar is in theatre.
3. CTCA is not the right test in this acute setting because: (i) it is not available after hours; (ii) in a patient with a high pre-test probability and positive troponin/ECG changes, CTCA may be non-diagnostic due to calcification and motion, and a negative CTCA would not safely exclude significant disease in this high-risk group; (iii) the definitive test is invasive angiography, which allows both diagnosis and treatment.
4. Do not discharge on the basis of a small troponin rise; the ECG changes and clinical picture warrant admission and early invasive assessment.
5. Communicate with the cardiology registrar (or on-call consultant) by phone, document the discussion, and hand over clearly to the admitting team.

Strategy in a low-risk patient:

1. CTCA is a reasonable first-line test in low-risk patients with no known coronary disease, normal ECG, and negative serial troponins, where it is available. It has a high negative predictive value and can safely discharge patients with normal or near-normal coronary arteries.
2. Timing: perform during the index admission or as an outpatient within a short interval, depending on local pathways. A negative CTCA allows early discharge and avoids invasive angiography.
3. Alternatives: functional testing (stress echocardiography, myocardial perfusion imaging, stress MRI) may be appropriate depending on local availability and patient factors (e.g. inability to hold breath, arrhythmia, high calcium score).

Advantages of CTCA:

• High sensitivity and negative predictive value for obstructive coronary disease.
• Non-invasive, rapid, and can be performed in the emergency setting.
• Provides anatomical information about plaque burden and can detect non-obstructive disease that functional tests may miss.
• Can identify alternative diagnoses (e.g. aortic dissection, pulmonary embolism) if a triple-rule-out protocol is used.

Limitations:

• Radiation dose (though modern protocols reduce this substantially).
• Contrast requirement (allergy, renal impairment).
• Calcification can cause overestimation of stenosis, particularly in older patients.
• Motion artefact with high or irregular heart rates; beta-blockers may be needed.
• Limited functional information - CTCA shows anatomy, not physiology; CT-derived fractional flow reserve (FFR-CT) can help but is not universally available.
• Incidental findings may generate anxiety and further testing.
• Not appropriate in high-risk or unstable patients, where invasive angiography is preferred.

Radiation safety considerations:

1. Justification: CTCA is justified only if the result will change management. In the low-risk scenario, a negative scan can safely discharge the patient and avoid invasive angiography; in the high-risk scenario, invasive angiography is preferred.
2. Optimisation: use prospective ECG-triggered acquisition where possible, tube voltage reduction (e.g. 100 kVp or lower in slim patients), iterative reconstruction, and a narrow z-axis coverage to minimise dose. Typical effective doses are 1–5 mSv with modern protocols, compared with 5–15 mSv for older retrospective protocols.
3. Diagnostic reference levels: ensure the local protocol is benchmarked against national DRLs and that dose is recorded in the dose management system.
4. Pregnancy: confirm she is not pregnant (she is 58, so unlikely, but document).

Consent discussion:

1. Explain the purpose of the test and what it will and will not show (anatomy, not function; may need further tests if abnormal).
2. Explain the radiation dose in plain terms (e.g. equivalent to a few years of background radiation) and the small theoretical long-term cancer risk, balanced against the benefit of excluding significant coronary disease.
3. Explain the contrast: warm flush, metallic taste, rare allergic reaction, and the small risk of contrast-induced nephropathy (her eGFR is 70, so risk is low; ensure hydration and document).
4. Explain the need to lie still, breath-hold, and possibly take beta-blockers to slow the heart rate.
5. Explain that incidental findings may be identified and may require follow-up.
6. Document the discussion and the patient's agreement; provide written information if available.
7. Escalate if there is any uncertainty about capacity or consent; involve a senior clinician.