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Objective Plasma norepinephrine (NE) level can be a guide to mortality in patients with heart failure. This study aimed to evaluate the significance of plasma NE level compared with plasma natriuretic peptides (atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP)) levels in patients with atrial fibrillation (AF). Methods Included in this study were 137 consecutive patients referred for catheter ablation of lone AF (paroxysmal in 90 and persistent in 47 patients). Blood samples for measurements of ANP, BNP and NE were drawn in the supine position before the procedure. Results ANP, BNP and NE levels were greater in patients with persistent AF than in patients with paroxysmal AF (median (25th-75th centile)=28 (18-49) vs 69 (36-106), p<0.0001; 28 (15-50) vs 94 (39- 156), p<0.0001; and 315 (223-502) vs 382 (299-517) pg/mL, p=0.04, respectively). NE level correlated weakly with ANP and BNP levels (r=0.28 and r=0.23, respectively, p<0.01 for both). BNP and NE levels differed between patients with and without recurrence of AF (55 (26-135) vs 35 (18-64), p=0.005 and 431 (323-560) vs 302 (225-436) pg/mL, p<0.001, respectively). Of note, only NE level was significantly greater in patients with symptomatic sick sinus syndrome (SSS) (n=21) than in those without SSS (560 (466-632) vs 321 (242-437) pg/mL, p<0.0001). Logistic regression analysis showed NE level to be the only independent discriminator for SSS (OR 1.006, 95% CI 1.002 to 1.010, p=0.001). Conclusions An increase in plasma NE level was observed in patients with AF and SSS. Although this implies a pathophysiological link between clinical manifestation of SSS and the autonomic nervous dysfunction, further studies are needed to clarify the mechanisms for this novel finding. [ABSTRACT FROM AUTHOR]