The goal of this observational study is to better understand the role of measuring troponin (a protein measured by a blood test) and coronary imaging in patients presenting with rapid atrial fibrillation (AF)

The main questions this study aims to answer are:

1. Are patients with a fast, irregular heartbeat (rapid AF) and damage to the heart (myocardial injury) more likely than those without damage to the heart to have blocked heart arteries (obstructive coronary artery disease)
2. Are patients with a fast, irregular heartbeat (rapid AF) and damage to the heart (myocardial injury) with further evidence that their heart hasn't been getting enough oxygen (myocardial ischemia) more likely to have imaging evidence of myocardial infarction than those without myocardial ischemia

To do this, we will measure troponin in patients with rapid AF and then carry out further investigations of the heart (electrocardiogram, echocardiogram, CT scan and cardiac MRI)

Inclusion Criteria:

1. Age 18 years and over
2. Primary presentation with symptoms related to atrial fibrillation
3. Atrial fibrillation with a ventricular rate >100 bpm on a 12-lead electrocardiogram
4. Able to provide informed consent

Exclusion Criteria

1. Previous myocardial infarction
2. Previous coronary revascularisation procedure
3. Patients in renal failure (eGFR <30ml/min/1.73m2) or major allergy to contrast media
4. Pregnancy or breast feeding
5. Deemed unsuitable for participation in the study by the attending clinician
6. Previous enrolment in the trial

Patients presenting to an Emergency Department or Acute Medical Unit with rapid atrial fibrillation