<unk>  <unk> , also known as sick<unk>  syndrome (SSS), is a group of abnormal heart rhythms (arrhythmias) usually caused by a malfunction of the<unk> <unk> , the heart's primary pacemaker. Tachycardia-bradycardia syndrome is a variant of sick<unk>  syndrome in which the arrhythmia alternates between fast and slow heart rates.
Sinus node dysfunction
Pacemaker crosstalk
Cardiac fibrosis
Primary tumors of the heart
Ventricular dyssynchrony
Coronary vasospasm
Ectopic pacemaker
Ventricular remodeling