Characterization of reentrant circuits in left atrial macroreentrant tachycardia: critical isthmus block can prevent atrial tachycardia recurrence.

Left atrial macroreentrant tachycardia (LAMRT) has not been characterized in detail. Twenty-eight patients with LAMRT, including 4 patients with ablated typical atrial flutter (AFL), underwent electroanatomic mapping of the left atrium (LA) between February 1999 and October 2001. LA maps were performed during LAMRT in 26 patients and during sinus rhythm in 2 patients. Electrically silent areas or continuous lines of double potentials were identified as acquired anatomic barriers in all patients. In 23 of 26 patients with LAMRT mapping, 42 reentry circuits with a protected isthmus were identified. The isthmus was 11.8+/-5.9 mm wide, with the maximal amplitude of 0.07 to 3.61 mV. Radiofrequency pulses terminated all LAMRTs in 23 patients and resulted in conduction block across the isthmus in 20 patients. In 2 patients with sinus mapping, all identified isthmuses were ablated. Additionally, AFL was induced and ablated in 6 patients. Atrial tachycardia recurred in 4 patients: 3 patients without validated block across the isthmus presented with recurrence of the same LAMRT, and 1 patient without ablated cavotricuspid isthmus presented with AFL. All tachycardias were abolished during a second procedure. Of 25 patients with identified isthmuses, 20 patients were without atrial arrhythmia and 5 had only atrial fibrillation during a median follow-up of 14 months. The reentry circuit with a protected isthmus can be identified in 89% patients with LAMRT by electroanatomic mapping. The isthmuses were amenable to radiofrequency applications in most patients. No atrial tachycardia recurred in any patients with isthmus block.