critical isthmus
A narrow corridor of conductive tissue essential for maintenance of a reentrant circuit, representing an optimal ablation target.
Full Definition
A critical isthmus is a narrow corridor of conductive tissue that represents an essential component of a reentrant arrhythmia circuit. These areas are characterized by slow conduction and are bounded by anatomical or functional conduction barriers. The isthmus represents the narrowest part of the reentrant circuit where ablation can effectively terminate the arrhythmia with minimal tissue damage. Common examples include the cavotricuspid isthmus in typical atrial flutter and mitral isthmus in perimitral flutter. Successful ablation across the entire width of the critical isthmus creates bidirectional conduction block and eliminates the substrate for reentry.
Usage
Usage note: Essential concept in ablation strategy; isthmus identification often requires detailed mapping techniques.
In Context
- "Radiofrequency ablation across the critical isthmus between the mitral annulus and left inferior pulmonary vein terminated the perimitral flutter." — Ablation procedure report
- "Entrainment mapping confirmed the critical isthmus location for the macro-reentrant ventricular tachycardia." — Electrophysiology study findings