Case Report
A 27-year-old woman having frequent exercise-induced palpitation without
ECG documentation underwent electrophysiology study.
Slightly
shortened H-V interval (21ms) with mild preexcitation was seen at
baseline (Figure 1A). Programmed atrial extrastimuli and atrial pacing
were associated with inapparent surface delta wave, while intracardiac
ventricular signals were still preexcited given the activation at basal
right ventricle (HIS) remaining earlier than apex (Figure 1B). The H-V
interval was constant (32ms) when A-H prolonged during programmed atrial
extrastimuli,
consistent
with an extra fasciculoventricular AP. Ventricular pacing and
extrastimuli showed poor retrograde conduction solely over the AV node.
When high-dose isoproterenol was given, the preexcitation progressively
became prominent (Figure 2A). A wide QRS tachycardia demonstrating 1:1
V-A relationship was then initiated by ventricular pacing without
visible His before QRS. Instead, a presumable retrograde His could be
observed after ventricular electrogram on HISd with an H-A interval of
around 100ms.
Entrainment
from atrium was associated with unchanged QRS morphology and an A-V-A
response following overdrive cessation, which excluded ventricular
tachycardia and confirmed antidromic AVRT utilizing an
isoproterenol-sensitive atrioventricular AP (Figure 2B).
Mapping of the pathway was performed during sinus rhythm with low
isoproterenol infusion rate to avoid catheter instability. Mild
preexcitation caused by atrioventricular pathway conduction was present
in this setting. When the ablation catheter was positioned near the
earliest ventricular activation site at 12 o’clock site of tricuspid
annulus, 15 millimeters away from the nearest His, split potentials with
an interval of 30ms were recorded by the proximal electrode pair (ABLp)
between atrial and ventricular signals (Figure 3A). The potentials were
significantly later than all atrial signals which made it highly
unlikely to be an atrial component. The second one was also visible on
distal ABL according to the nearly identical timing, followed by an
early local ventricular electrogram with QS unipolar pattern. The
interval between the double potentials and QRS onset/local V was
variable with spontaneous change of preexcitation (Figure 3B),
suggesting that the potentials were also irrelevant to the ventricle,
and thus could both be considered as AP potentials, demonstrating an
example of intra-pathway delay. Gently withdrawing the catheter made the
split potentials shifting to ABLd (Figure 3C) and caused frequent ectopy
showing QRS with maximal preexcitation pattern identical to tachycardia,
indicating pathway automaticity. The atrial signals were not followed by
the split potential when V-A dissociation occurred, further confirming
the identity AP potentials. Radiofrequency application at this site was
also associated with accelerated pathway rhythm
(Supplemental
Figure).
The H-V interval was back to 32ms after ablation, which could not be
changed by atrial pacing or isoproterenol infusion, suggesting the block
of atrioventricular AP conduction. The patient has been free of
arrhythmia for 6 months.