Can cardiac magnetic resonance imaging safely defer invasive coronary angiography in patients with suspected non-ST-elevation myocardial infarction?

Introduction Patients with suspected non-ST-elevation myocardial infarction (NSTEMI) constitute a majority of patients evaluated for suspected MI (1, 2). Early cardiac magnetic resonance (CMR) could reclassify diagnoses and thereby influence management in over half of suspected NSTEMI cases (3, 4). T1- and T2 mapping can detect oedema as a sign of acute myocardial injury and may expand the utility of CMR to patients with prior MI (5). In this pilot study, we aimed to evaluate whether T1-/T2-mapping combined with late gadolinium enhancement (LGE) could identify patients with suspected NSTEMI in whom invasive coronary angiography (ICA) might be safely deferred, and whether Troponin T (TnT) levels could select optimal candidates for CMR prior to ICA. Methods Patients with suspected NSTEMI referred for ICA were prospectively enrolled to undergo CMR prior to ICA. Of 36 patients recruited, 4 were unable to complete CMR. CMR imaging was performed using a 1.5T Siemens Sola and included cine imaging, T1- and T2 mapping, and LGE. Images were acquired in short-axis and 3 long-axis projections. Images from 32 patients were interpreted by 2 independent blinded observers with consensus adjudication by 3 readers in cases of discrepancy. Acute MI was defined as elevated T1 (>1100 ms) and T2 (>55 ms) with corresponding ischemic-pattern LGE. Non-ischemic acute findings were defined as elevated T1 and T2 with non-ischemic LGE pattern. Chronic MI was defined as LGE in the absence of elevated T1 and T2. Subsequent clinical management including revascularization decisions were blinded to CMR . Results Of 32 patients, 17 had no acute findings on CMR and 15 had evidence of acute events. 22 patients were revascularized, of which 10 had acute MI on CMR, 2 had myocarditis, 2 had chronic MI, and 8 had normal CMR findings. Two patients experienced ICA complications: 1 transient aphasia and 1 peri-procedural MI. Patients with acute findings on CMR (11 acute MI, 5 acute non-ischemic findings) exhibited significantly higher mean TnT than those without acute findings (400 ± 605 vs. 74 ± 137 ng/L, p < 0.001). No patients with TnT levels < 140 ng/L showed CMR evidence of acute MI. CMR identified an acute event in all but two patients with TnT > 140 ng/L, and in none with TnT < 50 ng/L*. A TnT threshold of 140 ng/L had 93.8% sensitivity and 88.2% specificity for acute findings on CMR. Conclusions There is a clear discrepancy between revascularization decisions based on ICA findings and CMR evidence of acute MI in patients with suspected NSTEMI. In patients with higher Troponin T levels (>140 ng/L) CMR found a diagnosis in most cases and could safely have deferred urgent ICA in 35% of patients. The findings in patients with lower Troponins warrant further studies to understand if revascularization was done in patients with chronic coronary syndrome detected en passant or if T1/T2 CMR sensitivity is too low to be used in this patient category. *TnI = 42ng/L for 1 patientCentral illustration Patient characteristics