Exit Block
Failure of electrical impulses to conduct out of an ectopic focus or reentrant circuit, despite continued activation within.
Full Definition
Exit block refers to the phenomenon where electrical activity continues within an ectopic focus or reentrant circuit but fails to conduct to surrounding myocardium. This results in cessation of the clinical arrhythmia while the underlying mechanism persists. Exit block can occur spontaneously due to progressive conduction slowing or can be induced by antiarrhythmic drugs that preferentially affect the exit pathway. Understanding exit block is crucial for interpreting ablation endpoints, as successful therapy should eliminate the arrhythmogenic substrate rather than simply creating exit block. The concept is particularly relevant in ventricular tachycardia ablation and automatic ectopic arrhythmias.
Usage
Usage note: Always use as two words, not 'exitblock'. Distinguish from 'entrance block' in documentation.
In Context
- "The VT terminated due to exit block rather than substrate elimination." — Ablation procedure assessment
- "Flecainide administration resulted in exit block of the automatic atrial tachycardia." — Pharmacologic testing report