What does the term "reentry circuit" refer to in arrhythmias?

The term "reentry circuit" refers to a continuous loop of electrical activity that can lead to tachycardia. This phenomenon occurs when an electrical impulse travels around a circuit formed by abnormal conduction pathways, allowing it to re-enter a previously excited area. In normal physiology, electrical impulses follow a one-way conduction pathway, but with a reentry circuit, the impulse reactivates tissue that has not yet fully recovered from its previous activation. This can create sustained rapid heartbeats, such as atrial flutter or certain types of ventricular tachycardia.

The mechanism of a reentry circuit commonly involves a combination of unidirectional block (where conduction travels in one direction due to blocked pathways) and slowed conduction (which allows time for the impulse to return to its original point of excitation). This can perpetuate the arrhythmia as the electrical signal continues to cycle through the loop. In essence, this continuous activation can lead to significant and sometimes dangerous heart rates, highlighting the importance of recognizing and managing these circuits in clinical practice.