We hypothesized that midregional pro-A-type natriuretic peptide (MR-proANP), the stable midregional epitope of proANP, might be useful in the early diagnosis and risk stratification of patients with suspected acute myocardial infarction (AMI). In this multicenter study we measured MR-proANP, cardiac troponin T (cTnT), and high-sensitive cTnT (hs-cTnT) at presentation in 675 consecutive patients presenting to the emergency department with suspected AMI. The final diagnosis was adjudicated by 2 independent cardiologists. Patients were followed 360 days for mortality and AMI. AMI was the final diagnosis in 119 patients (18%). Median MR-proANP levels at presentation were significantly higher in patients with AMI (189 pmol/L, interquartile range 97 to 341) versus patients with another final diagnosis (83 pmol/L, 49 to 144, p <0.001). However, neither the combination of MR-proANP with cTnT nor its combination with hs-cTnT significantly improved diagnostic accuracy as quantified by area under the receiver operating characteristic curve (0.91 vs 0.89 for cTnT alone, p = 0.086; 0.95 vs 0.96 for hs-cTnT, respectively, p = 0.02). Cumulative 360-day mortality/AMI rates were 2.4% in the first, 3.6% in the second, 9.5% in the third, and 18.8% in the fourth quartiles of MR-proANP (p <0.001). MR-proANP (area under the curve 0.76) predicted mortality/AMI independently of and more accurately than cTnT (area under the curve 0.62), hs-cTnT (area under the curve 0.71), and Thrombolysis In Myocardial Infarction risk score (area under the curve 0.72). Net reclassification improvements offered by the additional use of MR-proANP were 0.388 (p <0.001), 0.425 (p <0.001), and 0.217 (p = 0.007), respectively. In conclusion, MR-proANP improves risk prediction for 360-day mortality/AMI but does not seem to help in the early diagnosis of AMI.
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