Relationship Between Apelin and New-onset Atrial Fibrillation After Coronary Artery Bypass Grafting: a Prospective Cohort Study and Retrospective Case-Control Clinical Trial

Atherosclerosis is a systematic and progressive pathological process, which commonly occurs in the intima of large and medium-sized arteries. The disease can lead to degenerative, proliferative, non-inflammatory lesions; thickening, hardening, and loss of elasticity of the vascular wall, and vascular stenosis; and reduced arterial blood flow. Eventually, organ damage occurs. Coronary atherosclerotic heart disease is the most common chronic degenerative disease caused by atherosclerosis.

Coronary artery bypass grafting (CABG) can effectively increase myocardial blood supply, prevent myocardial infarction, and improve quality of life, and is associated with low rates of surgical complications and mortality. However, new-onset atrial fibrillation is a common complication after coronary artery bypass grafting, with an incidence rate of 30%. It induces hemodynamic instability, is often accompanied by left-ventricular systolic dysfunction and congestive heart failure, and increases the risk of stroke.

Several studies have shown that the initiation and maintenance of atrial fibrillation is strongly associated with inflammation, which affects the electrical and structural remodeling of the heart. The role of C-reactive protein (CRP), a marker of inflammation, has been widely investigated. C-reactive protein is a non-specific acute-phase protein, and is elevated in many cardiovascular diseases, including coronary atherosclerotic heart disease, heart failure and hypertension. Elevated C-reactive protein levels are not only associated with simple and post-surgical atrial fibrillation, but also with cardioversion and recurrence of atrial fibrillation after ablation. However, there is no elevation of C-reactive protein levels in lone atrial fibrillation, indicating that inflammation is associated with cardiovascular disease, but not with atrial fibrillation per se. One of the aims of the present study is to determine how C-reactive protein levels in patients with new-onset atrial fibrillation change after coronary artery bypass grafting.

Apelin has anti-inflammatory effects in different tissues. Ellinor et al. showed that levels of apelin-12 were remarkably low in patients with atrial fibrillation. Recurrence of atrial fibrillation is high in patients with persistent atrial fibrillation and low apelin-12 levels after electrical cardioversion.

Apelin is an endogenous ligand of the G-protein coupled receptor APJ, and exhibits homology to angiotensin II. The signaling system stimulated by apelin regulates many physiological functions and pathological processes. The main target of apelin is the cardiovascular system; it dilates blood vessels, and has antifibrotic and positive inotropic effects. Falcone et al. showed that the risk of recurrence of atrial fibrillation was 3.1 times greater in patients with low apelin levels than those with high apelin levels. Furthermore, Yang et al. concluded that apelin levels were lower in patients with different types of atrial fibrillation than in controls, indicating that apelin might contribute to the initiation and maintenance of atrial fibrillation.