Can we tell if AF is new?

One of the dilemmas in selecting appropriate therapy for atrial fibrillation in the emergency situation is determining whether the AF is of acute onset or not. AF causes release of natriuretic peptide from the heart, so measuring these peptides may give a clue to the recency of onset if the kinetics are known. This of course can only apply to those patients without heart failure, who have another cause for elevated natriuretic peptide levels.
A study of N-terminal pro-BNP levels in patients with acute onset AF, and without clinical or radiological evidence of heart failure, showed the pattern of rise and fall. The key finding in this study is the rapid rise of plasma NT-proBNP levels to peak followed by a rapid decline, probably due to depletion of the granules in atrial myocytes in which pro-BNP is stored.
The authors describe the following implication of the study:
According to our observations, a rising trend is markedly indicative of the fact that AF onset did not happen more than 24–48 h before presentation. As a consequence, obtaining two to three plasma NT-proBNP levels within 24 h of presentation in patients with AF without heart failure who cannot satisfactorily pinpoint the time of onset may assist in determining whether the onset of the arrhythmia was recent. Such information is pertinent to decisions concerning anticoagulation and cardioversion.
Short-term fluctuations of plasma NT-proBNP levels in patients with new-onset atrial fibrillation: a way to assess time of onset?
Heart. 2010 Jul;96(13):1033-6