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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