ACHE and congenital heart disease: The underlying etiology of sinus node dysfunction is mostly attributed to SA node fibrosis, medications, and congenital heart diseases [5,6]. Fibrosis is the most common cause of dysfunction but medications like beta blockers, non-dihydropyridine calcium channel blockers, digoxin, antiarrhythmics, and acetylcholinesterase inhibitors can also cause SA node dysfunction.