Case presentation
A 66-year-old man was referred for a third procedure for recurrent atrial fibrillation (AF) after two previous failed pulmonary vein isolations (PVIs). During the procedure, the right pulmonary vein was reconnected and re-isolated. The linear ablations targeting the left atrial roof, posterior mitral isthmus (MI), and cavotricuspid isthmus were also performed. After radiofrequency catheter ablation (RFCA) from the coronary sinus (CS), the atrial electrograms (EGMs) recorded in the CS changed to a proximal-to-distal activation sequence, and MI blocked was confirmed by the differential pacing maneuver (Figures 1A and 1B). The MI was then reconnected during the observation period (Figure 1C). Electrograms (EGMs) recorded in the distal part of the CS demonstrated double components during pacing from the left atrial appendage at a pacing cycle length (CL) of 600 ms. The first one was a low amplitude and frequency signal demonstrating a distal-to-proximal activation sequence, indicating the far-field left atrium (LA) EGMs. The second one was a high amplitude and frequency signal demonstrating both middle-to-distal and middle-to-proximal activation sequences, indicating the near-field CS EGMs. The interval between the stimulus and the first component recorded in the CS 1-2 to CS 5-6 gradually prolonged and shortened again, suggesting a Wenckebach periodicity. This phenomenon was repeatedly observed. Consolidation RFCA was performed to the endocardial MI lesion, resulting in MI block again.
The rate-dependent conduction block of the MI line has been reported as a potential pitfall in the assessment of MI block.1However, Wenckebach periodicity at the MI lesion has rarely been reported. An incomplete MI block increases the risk of developing peri-mitral atrial flutter (PM-AFL), which is the most frequent post-AF ablation macro-reentrant tachycardia.2
Both slow conduction and unidirectional block contribute to initiate and maintain the reentrant tachycardia.3It is noteworthy in the present case that it described a Wenckebach periodicity at the endocardial posterior MI lesion presenting with gradual conduction delay, and subsequent conduction block and conduction recovery. Because these findings demonstrate an early reconnection of MI lesion, and an arrhythmogenic substrate that can lead to development of reentrant tachycardia, that is, PM-AFL.