Right-Atrial Muscular Ridge as an Isthmus for Macro-Re-Entrant Atrial Tachycardia in Partial Atrial Standstill.

BACKGROUND

Partial atrial standstill is a rare disorder with extensive atrial electrical silence that can coexist with atrial tachycardia (AT). However, the mechanism of AT in this population remains unclear.

CASE SUMMARY: A 54-year-old man was referred for AT and complete atrioventricular block. High-resolution electroanatomic mapping revealed extensive electrically silent areas involving the sinus venarum and right atrial septum, consistent with partial atrial standstill. In contrast, a preserved right atrial muscular ridge (arcuate ridge and crista terminalis) formed the critical isthmus of a macro-re-entrant circuit. Ablation of this ridge, followed by cavotricuspid isthmus ablation, terminated the AT. A permanent pacemaker was subsequently implanted. The patient remained free of atrial tachyarrhythmia for 7 years.

DISCUSSION: Preserved muscular ridges can be key conduction pathways and ablation targets in an extensively scarred atrium.

TAKE-HOME MESSAGES: Muscular ridges can serve as a conduction pathway of macro-re-entrant AT in an extensively scarred atrium.