What type of irregular heart rhythm is indicative of bradycardia alternating with tachycardia?

Sick sinus syndrome is characterized by a malfunction of the sinus node, which can lead to a variety of heart rhythm abnormalities, including bradycardia that alternates with episodes of tachycardia. This irregular rhythm occurs due to the sinus node's inability to properly regulate the heart rate, causing periods where the heart beats too slowly followed by periods of rapid heartbeat.

In contrast, fibrillation typically involves rapid, chaotic electrical activity in the heart that doesn’t present as distinct bradycardia-tachycardia patterns. Ventricular tachycardia is a fast rhythm that originates from the ventricles, while supraventricular tachycardia primarily results from abnormal conduction pathways above the ventricles, neither of which is directly associated with the alternating pattern of bradycardia and tachycardia as seen in sick sinus syndrome.