Infectious agents such as bacterial endocarditis and Chagas disease commonly result in atrioventricular conduction problems rather than sinus node dysfunction. Damage to SA node or the sinus nodal artery may occur after cardiothoracic surgery from valve replacement, correction of congenital heart disease or heart transplant. Infiltration of the SA node by sarcoidosis, amyloidosis, hemochromatosis, collagen vascular disease or metastatic cancer results in SA node dysfunction. Heart failure and atrial tachyarrhythmias have been shown to induce cellular remodeling of the sinus node in animal models. Recent studies have identified several mutations in the ion channels explaining familial and congenital forms of sick sinus syndrome. While the most common intrinsic factor leading to sinus node dysfunction is age-related degeneration of the SA node, sinus node dysfunction can be a result of congenital disorders, arrhythmias, infiltrative disorders and surgery. The etiologic factors leading to sinus node dysfunction can be classified into two categories: intrinsic pathology to the sinus node itself, typically results from fibrosis of the nodal tissue and external causes that affect the SA node function.
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