NPPA and atrial fibrillation: Another important aspect is that the plasma concentration of Atrial Natriuretic Peptide (ANP) >300 ng/L during the arrhythmia was the second predictor of spontaneous conversion (OR 3.24; 95% CI 2.30 to 6.46): the higher the value of ANP during the AF episode, the higher the probability of SCV.