Patients undergoing coronary artery bypass grafting (CABG), aortic (valve) or mitral valve surgery are at risk of developing postoperative and new-onset atrial fibrillation (AF), but adequate risk prediction is currently impossible. This study aims to discover tissue and circulating microRNAs and protein biomarkers that may help to unravel the pathophysiological processes underlying AF and are potential tools for risk stratification and prognosis or may become future targets of therapy.

This study will be a single-center cohort study of 150 patients undergoing cardiac surgery, which will constitute the beginning of the follow-up period. Left atrial appendages, whole blood and epicardial mappings will be collected. Patients will be followed for 2 years with regular holter investigations to detect postoperative and new-onset AF.

Study procedures:

The left atrial appendage (LAA) will be removed for research and intended prophylactic purposes, using a surgical stapler or surgical knife prior to the standard procedure. Epicardial mappings may be performed during cardiac surgery with a 48-multi-electrode. Patients will be followed with regular 24-hour Holter investigations.

This study will be an exploratory study with a required inclusion of 150 patients, based on the estimated event rate. Patients will be recruited by the investigators during pre-operative assessment.

Clinical data will be gathered at baseline and stored in a customized microsoft access entry database. Statistical analysis will be performed in collaboration with the Bioinformatics Laboratory from the Academic Medical Center.

Inclusion Criteria:

• Elective sternotomy for either coronary artery bypass surgery or aortic (valve) surgery or mitral valve surgery
• CHA2DS2 VASC score ≥ 2
• Sinus rhythm
• Age between 18 and 80 years
• Legally competent and willing and able to sign informed consent

Exclusion Criteria:

• Unable or unwilling to comply with study procedures
• Documented or reported history of atrial fibrillation, atrial flutter (duration > 5 minutes) or ventricular tachycardia
• Emergency or redo of CABG
• Emergency valvular surgery or pericarditis or endocarditis
• NYHA class IV heart failure symptoms or left ventricular ejection fraction < 35%
• Pregnancy or of childbearing potential without adequate contraception
• History of previous radiation therapy of the thorax
• Active malignancy
• Active inflammtion or auto-immune disease
• Surgery for congenital anomalies
• Circumstances that prevent follow-up (no permanent home or address, transient, etc.)

All consecutive patients are eligible that are referred to the investigators' tertiary cardiothoracic center for mitral valve surgery, (aortic) valve surgery or coronary artery bypass surgery and meet in- and exclusion criteria.