Background Non-traumatic out of hospital cardiac arrest (OOHCA) is one of the leading causes of death in western world. Acute coronary syndrome (ACS) is the most common aetiology of OOHCA with a culprit artery lesion identified on invasive angiography. However, 1/3rd of patients with OOHCA have unobstructed coronaries on angiography. Non-invasive tissue characterisation by cardiovascular magnetic resonance (CMR) has the potential to establish the final diagnosis in patients with OOHCA with obstructed coronaries as well as with unobstructed coronary arteries.

Methods We retrospectively reviewed the database in our tertiary cardiothoracic centre from October 2009 to November 2013. We identified 54 consecutive patients who were referred for a CMR following an OOHCA. A comprehensive CMR protocol with cine, oedema and scar imaging was used. All scans were done within 6–8 weeks of the index event and was reported by a consultant with >10years of experience in CMR.

Results Out of the 54 patients (16 female, age range 21–84 years), 29 (54%) had coronary artery disease, in which the culprit was treated by primary angioplasty and 25 (46%) patients had unobstructed coronaries. Of the latter, 3 had hypertrophic cardiomyopathy, 4 had myocarditis or cardiac sarcoid, 2 had non-ischaemic dilated cardiomyopathy, 2 had LV non-compaction (LVNC) cardiomyopathy, 7 had nonspecific abnormalities and 9 had completely normal CMR scan. In all patients (n = 29) with significant CAD on angiography CMR identified a myocardial infarction (100%). So in total, 40/54 (74%) of OOHCA, a cause was found on CMR. In 11/25 (44%) of OOHCA with unobstructed coronaries a diagnosis was made whereas in 9/25 (36%), a normal CMR was suggestive of a primary arrhythmic cause, thereby guiding further therapy (ICD).

Conclusions In adults surviving a non-traumatic OOHCA with unobstructed coronaries on angiogram, CMR could identify the underlying aetiology in the large majority of cases. This has potential implications for treatment and prognosis.