Most patients presenting to hospital with chest pain are discharged home without further tests once a heart attack has been ruled out. Current strategies to assess patients with a suspected heart attack involve blood tests to measure troponin, a protein released into the bloodstream when the heart muscle is damaged. Despite having had a heart attack ruled-out, some patients have unrecognised coronary heart disease and are at risk of having a heart attack in the future. However, we do not know what is the best approach to identify and treat these patients.

This study will use a heart scan known as computed tomography coronary angiogram (CTCA) to look for underlying coronary heart disease in patients who have had a heart attack ruled out. In an earlier study, we performed this scan in patients referred to the outpatient cardiology clinic with stable chest pain and found that this improved the diagnosis of coronary heart disease, leading to improvement in patient care that prevented many future heart attacks. Our research has also demonstrated that troponin levels below the threshold used to diagnose a heart attack identify those who are at greater risk of having a heart attack in the future. The aim of this study is to confirm whether these low levels of troponin can identify patients who have underlying coronary heart disease and may benefit from further testing and preventative treatment.

Using a newer, more sensitive troponin test, we now know that troponin levels even below the threshold used to diagnose a heart attack identify patients who are at risk of having a heart attack in the future. Our research in patients with stable chest pain demonstrated that computed tomography coronary angiogram (CTCA) improved the diagnosis of coronary heart disease, leading to improvement in patient care that prevented many future heart attacks. This study will build on these two major strands of research to confirm whether these low levels of troponin can identify patients who have underlying coronary heart disease and may benefit from further testing and preventative treatment.

The investigators will evaluate consecutive patients presenting to hospital with suspected acute coronary syndrome and cardiac troponin concentration within the normal reference range for the presence of underlying coronary artery disease. All participants will be invited for an outpatient CTCA.

Findings from this study will help inform a randomised controlled trial to evaluate the role of CTCA in patients who have a heart attack ruled out, but are identified as intermediate risk on troponin testing.

Inclusion Criteria:

• Presentation to hospital with acute chest pain or equivalent symptoms of suspected acute coronary syndrome
• Maximum high-sensitivity cardiac troponin I concentration below the 99th centile (16 ng/L for women and 34 ng/L in men)

Exclusion Criteria:

• Diagnosis of myocardial infarction during index presentation
• Clear alternative diagnosis for index presentation
• Recent CT or invasive coronary angiogram (within 1 year)
• Patient inability to undergo CT scanning, due to severe renal failure (estimated glomerular filtration rate <30 mL/min) or major allergy to iodinated contrast media
• Pregnancy or breast feeding
• Inability to give informed consent
• Further investigation for coronary artery disease would not in the patient's interest, due to limited life expectancy, quality of life or functional status

Adult patients (30 years and over) with acute chest pain or equivalent symptoms of suspected acute coronary syndrome and maximum high-sensitivity cardiac troponin I concentration below the 99th centile (16 ng/L for women and 34 ng/L in men)

Requests for IPD will be considered on an individual basis.