Conduction recovery at the mitral isthmus triggers atrial fibrillation in a patient with rate-dependent 'block' and recurrent atrial fibrillation after previous pulmonary vein isolation and left atrial linear ablation.

During a redo procedure for paroxysmal atrial fibrillation (AF) recurrence, mitral isthmus-dependent atrial tachycardia due to a gap in the previous line and rate-dependent slow conduction in sinus rhythm were demonstrated. After initial achievement of mitral isthmus block, adenosine reproducibly triggered conduction recovery and initiated AF. Further ablation led to AF termination and stable bidirectional block.