Introduction: The diagnostic importance of NT-proBNP in heart failure (HF) is well established but a cut-off level for prognostic value has been less studied. Moreover, natriuretic peptides are known to rise in a wide variety of clinical scenarios different from HF, in-cluding atrial fibrillation (AF) and older age. Hence the prognostic cut-off values of NTproBNP in these situati-ons are of particular importance.

Objective: To determine the prognostic cut-off value of NT-proBNP in patients with heart failure with and without AF, in two different age groups (<75 years old and 75 years and older).

Methods: HF patients admitted to our clinic from Ja-nuary 2011 to December 2014 were retrospectively in-cluded in this study. We have excluded acute coronary syndromes, pulmonary embolisms, as well as read-missions of the same patient. Clinical, laboratory and echocardiographic parameters were recorded for all patients on admission. Survival status was assessed in August 2018. The patients were subdivided in 4 groups, according to age and presence of AF or sinus rhythm (SR). Group AF ≥75 consisted of patients with AF aged 75 years and older (198 patients, 64.71%), SR ≥75 – pa-tients with SR aged 75 years and older (142 patients, 46.86%), AF <75 – patients with AF younger than 75 years (125 patients, 38.82%) and SR <75 – patients yo-unger than 75 years with SR (99 patients, 31.03%).

Results: The study group included 1354 patients, with a mean age of 72.3 ± 10.57 years. 53.26% were fema-les. 59% had AF. During the follow-up period 44.73% patients were deceased. In the entire group, regardless of AF or age, an NTproBNP >1467 pg/ml had 64.36% sensitivity (Se) and 67.78% specificity (Sp) for morta-lity prediction with an AUC of 0.69, 95%CI 0.67-0.72, p<0.0001. In subgroup AF >75, NT-proBNP >2212 pg/ ml had 58.08% Se and 61.11% Sp for mortality predic-tion, with an AUC of 0.62, 95%CI 0.56-0.67, p=0.0004. In subgroup SR >75, NT-proBNP >1046 pg/ml had 64.79% Se and 68.94% Sp for mortality prediction, with an AUC of 0.70, 95%CI 0.65-0.75, p<0.0001. In subgroup AF <75, NT-proBNP >1467 pg/ml had 69.6% Se and 63.45% Sp for mortality prediction, with an AUC of 0.69, 95%CI 0.63-0.74, p<0.0001. In subgroup SR <75, NT-proBNP >726 pg/ml had 68.69% Se and 62.73% Sp for mortality prediction, with an AUC of 0.68, 95%CI 0.63-0.73, p<0.0001.

Conclusions: Higher cut off values for NT-proBNP were better predictors of mortality in HF patients with AF aged 75 years and older, compared to those in SR and younger. Patients with AF had prognostic NT-proBNP cut off values two times higher compared to those in SR. The presence of AF in patients with HF un-der 75 years impacts the cut off values of NT-proBNP predicting mortality to the same extent as age 75 years and older in patients in SR.