The right ventricular moderator band (MB) is increasingly being
recognized as a source for PVCs and PVC-mediated ventricular
fibrillation. Monomorphic PVCs, non-sustained monomorphic VT and
ventricular fibrillation are all documented arrhythmias originating from
the MB. The benign PVCs usually have a coupling interval in excess of
400 msec. When PVCs trigger VF, coupling intervals are typically short,
less than 300 msec. We report here a case of long-standing frequent
monomorphic PVCs with a coupling interval of > 400 msec
from the right ventricular distal conduction system embedded in the
moderator band that progressed to non-sustained ventricular tachycardia.
Following suppression of the arrhythmia with RF ablation, the arrhythmia
recurred with PVCs at a shorter coupling interval (<300 msec),
with frequent repetitive non-sustained polymorphic VT and triggering of
sustained ventricular fibrillation. The use of a cryoballoon to ablate
over the course of the moderator band resulted in complete and durable
suppression of ventricular arrhythmias.