Midregional Pro–A-Type Natriuretic Peptide for Diagnosis and Prognosis in Patients With Suspected Acute Myocardial Infarction
Are levels of midregional pro-A-type natriuretic peptide (MR-proANP) useful in determining early diagnosis and prognosis in patients with suspected acute myocardial infarction (AMI)?
MR-proANP, cardiac troponin T (cTnT), and high-sensitive cTnT (hs-cTnT) were measured at presentation in 675 consecutive patients presenting to the emergency room with suspected AMI. Patients were followed 360 days for mortality and AMI.
AMI was the final diagnosis in 18% of patients. Median MR-proANP levels were higher in patients with AMI compared to those with another diagnosis (189 vs. 83 pmol/L, p < 0.001); however, this did not improve diagnostic accuracy compared to hs-cTnT. 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 predicted mortality/AMI independently of and more accurately than cTnT, hs-cTnT, and TIMI risk score.
The authors concluded that MR-proANP improves risk prediction for 360-day mortality/AMI, but does not seem to help in the early diagnosis of AMI.
In response to hemodynamic stress or myocardial injury, the synthesis and liberation of natriuretic peptides (ANP and BNP) are increased. Thus, elevated levels of these peptides may be useful in the diagnosis of MI and also in determining prognosis following MI. Since ANP levels are several-fold higher than BNP and the stable midregion has been shown to correlate closely with synthesis of proANP, MR-proANP may be a particularly useful biomarker. The use of hs-cTns is highly sensitive and specific for diagnosis of MI, and it is not surprising that MR-proANP levels did not aid in early MI diagnosis. However, because these biomarkers also reflect hemodynamic stress, they could be useful in predicting adverse consequences following MI, as this study demonstrates. Further studies are needed to determine how use of MR-proANP levels might alter therapeutic strategies and lead to improved outcomes following MI.
Keywords: Prognosis, Natriuretic Peptides, Myocardial Infarction, Biological Markers, Early Diagnosis
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