This study aims to investigate N-terminal pro brain natriuretic peptide (NT-proBNP) as a biomarker to rule out heart failure in patients with atrial fibrillation. Atrial fibrillation and heart failure often co-exist. Heart failure is important to identify, as part of the medical treatment for patients with atrial fibrillation can be fatal if the patient has concomitant heart failure. Performing an echocardiography is considered "gold standard" for assessing cardiac function but echocardiography may not always be readily available during acute hospitalization. The cardiac biomarker NT-proBNP can be used to rule out acute heart failure in patients with sinus rhythm. However, atrial fibrillation affects levels of NT-proBNP in the blood and it is therefore unknown, how the biomarker performs in atrial fibrillation patients.

Background and hypothesis:

Atrial fibrillation is the most common cardiac arrhythmia with a prevalence of approximately 2% in the general population and even higher among elderlies. Atrial fibrillation is associated with an increased morbidity, mortality and risk of heart failure. Patients with atrial fibrillation are at risk of developing tachycardia-induced cardiomyopathy. Furthermore, heart failure of any other cause and atrial fibrillation often co-exist and these patients are at high risk of adverse outcomes and hospitalization. Therefore, early identification of heart failure among patients with atrial fibrillation is important in order to initiate the optimal treatment strategy. However, as recent onset atrial fibrillation and heart failure may present with similar symptoms, excluding heart failure in atrial fibrillation patients is a clinical challenge. The gold standard for evaluating heart failure is echocardiography. However, the access to echocardiographic evaluation may be limited in some hospitals receiving patients with atrial fibrillation. In situations where acute heart failure cannot be ruled-out, clinicians may choose to prescribe digoxin instead of e.g. beta blockers that are preferred for heart rate control. Digoxin is associated with a substantially higher mortality in large cohorts and is not recommended as a first line treatment. Methods other than echocardiography to rule-out heart failure in patients with atrial fibrillation is therefore warranted.

N-terminal pro-brain natriuretic peptide (NT-proBNP) is an established biomarker in identifying and determining long-term prognosis of heart failure in the general population. However, levels of NT-proBNP are known to be higher in atrial fibrillation patients, regardless of underlying structural heart disease.Therefore, it is not possible to rule-out heart failure in patients presenting to the Emergency Department with new-onset atrial fibrillation using existing algorithms for NT-proBNP and heart failure. Accordingly, the aim of this study is to prospectively measure NT-proBNP in atrial fibrillation patients to identify a NT-proBNP threshold making heart failure unlikely.

Perspectives: This study will evaluate if NT-proBNP may be feasible to rule-out heart failure in patients presenting with atrial fibrillation without the use of echocardiography. Early rule-out of heart failure will allow the use of more safe medication for rate control e.g. beta-blockers instead of digoxin.

Inclusion Criteria:

• Admission to hospital with atrial fibrillation
• On-going atrial fibrillation documented on an ECG

Exclusion Criteria:

• <18 years
• Other arrhythmias than atrial fibrillation
• Hemodynamically unstable
• Terminal renal failure (in dialysis)
• Pregnancy

Patients presenting to the Emergency Department with atrial fibrillation.