A cardiac magnetic resonance imaging (CMR) directed strategy improves the diagnostic yield of invasive coronary angiography (ICA) in stable coronary artery disease (CAD). Evidence on the diagnostic accuracy of CMR to detect obstructive CAD in non-ST elevation myocardial infarction (NSTEMI) is limited as is its role to identify myocardial infarction with non-obstructive coronary arteries (MINOCA) in the current high-sensitivity cardiac troponin (hs-cTn) era.
To investigate the diagnostic role of CMR in suspected NSTEMI, especially to detect obstructive CAD.
This study is a sub-analysis of a randomized controlled trial that investigated whether a non-invasive imaging first strategy safely reduced the number of ICA compared to routine clinical care in suspected NSTEMI (acute chest pain, non-diagnostic electrocardiogram, hs-cTnT levels >14 ng/L). All patients underwent CMR prior to ICA (1 day, range 0-6 days). A stepwise approach was used to assess the diagnostic accuracy of CMR to detect obstructive CAD (stenosis =70%). Regional abnormalities in =2 adjacent segments on cine, T2-weighted and delayed enhancement imaging suggestive of underlying CAD were evaluated first and when normal or non-diagnostic, on adenosine-stress perfusion imaging as a second step (Figure).
Of 51 patients included (63±10 years, 51% male), 34 (67%) had obstructive and 17 (33%) had non-obstructive CAD. The sensitivity, specificity and overall accuracy of step one and two were 71%, 71% and 71% vs. 80%, 92% and 86%, respectively. When both steps were combined, the sensitivity, specificity and overall accuracy were 94%, 65% and 84%, respectively. In the 17 patients with non-obstructive CAD, CMR still showed an MI in 5 (29%) and stress cardiomyopathy in one. When CMR was normal or non-diagnostic, MINOCA was diagnosed on clinical judgement in 4 additional and remained unknown in 7 patients.
CMR, particularly stress perfusion imaging, accurately detects obstructive CAD in hs-cTnT-positive suspected NSTEMI. Non-obstructive CAD is common with almost one-third having MINOCA by CMR.