Introduction: The universal criteria for acute myocardial infarction (MI) has a troponin rise as a core criterion for the diagnosis, supplemented by clinical criteria. In patients who are Troponin Positive with Non Obstructive Coronary Arteries (TP-NOCA), non-ischemic causes for the troponin rise must be evaluated since alternative therapies may be appropriate. This study demonstrates the utility of diagnostic assessments to identify the underlying cause of TP-NOCA in a real world setting.
Methods: Consecutive patients undergoing angiography for MI were captured in the Coronary Angiogram Database of South Australia registry with patients classified as TP-NOCA on the basis of a troponin rise with <50% stenosis on angiography. Comprehensive medical record review was undertaken for all TP-NOCA patients to identify underlying ischemic/non-ischemic causes including angiographic review for coronary disorders (coronary slow flow, subtle coronary dissection or spasm), early MRI (myocarditis, takotsubo, subendocardial MI). The underlying cause was identified based on clinical assessments and discharge reports.
Results: In 3277 consecutive MI angiographic procedures, 11% were identified as TP-NOCA at the time of angiography, with subsequent evaluation confirming non-ischemic causes in 135 (38%) and possible ischemic causes (MI with NOCA, MINOCA) in the remaining 219 (62%). Of these 219 MINOCA patients, objective evidence of coronary vasomotor dysfunction (n=20) or subendocardial MI on MRI (n=28) was confirmed in only 22%, with the remaining having a presumed ischemic cause. Of the 135 non-ischemic TP-NOCA patients, subsequent diagnostic evaluations confirmed takotsubo (56%), myocarditis (30%), other cardiomyopathies (12%) and pulmonary embolism (2%).
Conclusions: In a real-world setting, only 52% of patients received investigations that confirmed the underlying cause of TP-NOCA. MRI remains the key tool to confirm the presence of MI and exclude non-ischaemic causes. The development of a clinical algorithm to evaluate the presence of an underlying ischemic cause may be useful in management. More so, treating physicians should routinely initiate more investigations for all TP-NOCA patients without an obvious aetiology after angiography.