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.