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.

Rate dependent exit block across the pulmonary veins has been previously described immediately following catheter ablation. We report the case of rate dependent PV block seen at repeat ablation 7 years after the index procedure. To our knowledge, this is the first report of chronic rate dependent exit block (i.e. Rate dependent exit block discovered 7 years after circumferential PV antral isolation). We believe that, as with CTI ablation, rate independent pulmonary vein isolation should be confirmed.

We report a case of superiorly directed sinus p-waves in a young patient who had extensive right atrial scarring due to prior right atriotomies. This sinus p-wave axis then changed to inferiorly directed after catheter ablation of the cavo-tricuspid isthmus (CTI). Normal p-wave morphology during sinus rhythm has been described as having an axis between 0 to +75 degrees. However, this is contingent upon an otherwise healthy atrium without conduction abnormalities. Our case highlights a young patient who has undergone two mitral valve surgeries, and as a result, two right atriotomies for cardiopulmonary bypass. During follow-up after the second surgery, his unusual p-wave axis was noted and it was unclear whether it was due to an atrial escape rhythm that had overtaken the sinus node or abnormal conduction of sinus rhythm. Electroanatomic activation mapping proved that he indeed had a sinus rhythm with conduction abnormality along the sites of his previous atriotomies. Additional ablation on the other side of the sinus node exit resulted in pseudo-normalization of his p-wave axis morphology. Four week follow up showed persistent inferiorly directed P wave, a finding in this patient consistent with persistent block across the caval tricuspid isthmus.