What characterizes sick sinus syndrome?

Sick sinus syndrome is characterized by alterations in heart rate, specifically the presence of both bradycardia (slow heart rate) and tachycardia (fast heart rate). This condition results from dysfunction of the sinus node, which is responsible for initiating and regulating the heart's rhythm. Patients may experience episodes of excessive slowing of the heart rate followed by periods of rapid heartbeats, reflecting the erratic nature of sinus node activity.

The syndrome does not merely present persistent tachycardia or solely bradycardia, as the hallmark of sick sinus syndrome involves fluctuating heart rates that require close monitoring and management. It is also not exclusively caused by atrioventricular block, which is a different arrhythmogenic condition related to the conduction pathways in the heart. Additionally, while severe hypotension can occur in cases where the heart rate fluctuations lead to inadequate cardiac output, it is not a defining characteristic of sick sinus syndrome. Instead, the key feature remains the alternating pattern of bradycardia and tachycardia.