Abnormal electrophysiology of sinoatrial node origin Sick sinus syndrome An abnormality involving the generation of the action potential by the sinus node and is characterized by an atrial rate inappropriate for physiological requirements. Manifestations include severe sinus bradycardia, sinus pauses or arrest, sinus node exit block, chronic atrial tachyarrhythmias, alternating periods of atrial bradyarrhythmias and tachyarrhythmias, and inappropriate responses of heart rate during exercise or stress. HP:0011704 SNOMEDCT_US:36083008 peter MSH:D012804 Sinoatrial node disease human_phenotype UMLS:C0037052 2012-04-10T11:31:17Z Heart block