Figure3: The earliest retrograde atrial activation at AMC with 50msec earlier relative to distal CS terminated the arrhythmia and resulted in VA dissociation (a) The fluoroscopic view of successful site of ablation at LAO and AP projection at Aorto-mitral continuty
During post ablation study, 30 minutes later, there was no evidence of AP conduction. AH and HV intervals were 80 and 50msec, respectively. The patient was free of palpitation during 3 months post ablation follow up.
Discussion
PJRT is in differential diagnosis with other two types of arrhythmia with long RP-short PR interval including atypical atrioventricular nodal tachycardia (AVNRT) and Atrial tachycardia. In this case, we easily ruled out atrial tachycardia by observing arrhythmia termination with ventricular overdrive pacing and V-V interval changes preceding A-A interval during tachycardia. His synchronous pacing could not reset nor advance the arrhythmia. Decremental conduction during ventricular and HRA extrastimulation and AV nodal jump during HRA extrastimulation was recorded during study. Entrainment response from ventricular site with indexes of (PPI-TCL) and (SA-VA) were consistent with AVNRT (3,4). However, Alteration in CS activation sequence during arrhythmia initiation could challenge the diagnosis of AVNRT.
Not surprisingly, the mapping catheter induced PVC during catheter manipulation in LVOT did reset the arrhythmia (Fig 2d) , in close proximity to the earliest site of retrograde atrial activation and successful ablation site at Aorto- Mitral continuity.
The findings during EPS were consistent with decremenatal properties of AP. In the presence of decremental properties of AP, it is often impossible to confirm an AP as the retrograde limb using the standard technique of atrial preexcitation by a ventricular premature beat while the His is refractory, because the retrograde conduction decrements after premature ventricular stimulation (5).
This AMC separates the LV myocardium and the LVOT from the LV inflow. The AMC also relates to the LA of the noncoronary sinus of valsalva.(6) Albeit that the region of the AMC consists of a membranous structure and without any significant neighboring myocardium, some data suggests that remnant fascicles of Purkinje tissue are related to the conduction system, which may be the source of abnormal signals that have been successfully targeted for ablation.(7)
Contrary to few reports of PJRT and concealed AP ablated at left anteroseptal area from transseptal approach (8-10), we used retrograde approach for mapping the region. As a result the V: A ratio at successful ablation site was 8:1 delineating the ventricular insertion site of AP. In comparison to transseptal approach that localized the atrial insertion site near His bundle catheter, ventricular insertion was far apart from His bundle. This safe position was accompanied with minimal risk of AV block and seemed to be preferred.
Another unique characteristic of this tachycardia was participation of slow pathway in the path of arrhythmia which resulted in lengthening of antidromic arm and consequently much less delay in orthodromic arm. Subsequently unlike typical PJRT with long RP-short PR, we encountered an arrhythmia that atrial potential was recorded at mid V-V interval.
In summary, we present an unusual form of PJRT whose ventricular insertion was successfully ablated in the AMC.
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