Discussion
In this case report, we have described a phenomenon of split AP
potentials in a patient with a slowly-conducting atrioventricular
pathway. The tachycardia can be clearly diagnosed as antidromic AVRT
based on the intracardiac electrograms and atrial entrainment.
Usually, APs with stable excellent anterograde conduction are necessary
for the initiation and maintenance of antidromic AVRTs. Free wall bypass
tracts, including those with decremental conduction, are most commonly
seen in antidromic AVRT [4,5]. Based on the
findings above, our patient had a short atrioventricular pathway with
baseline slow conduction in a rare (para-His) region. The evidence of
decremental property was yet insufficient given the AP block during
atrial pacing at long cycle lengths.
Recording of pathway potentials is useful in guiding AP ablation, which
is usually manifested as a single sharp spike 10 to 30 ms before the
onset of the delta wave during anterograde
conduction[1]. However, two discrete potentials
between A and V were recorded near the earliest ventricular activation
site in our case, which were considered as AP potentials by careful
analysis of electrograms during different levels of preexcitation. This
pattern of double pathway potentials is similar to the split His
potentials in the setting of intra-His conduction delay, which reflected
the conduction disturbance within the slow atrioventricular pathway.
Although mapping during tachycardia was not attempted, we believe that
the conduction could be significantly improved by isoproterenol, as
evidenced by the rapidly altered QRS configuration to a near maximal
preexcitation pattern.
Catecholamine-dependent preexcitation and antidromic tachycardia was not
uncommon[6,7]. In our patient, both of the
anterograde AP and retrograde AV nodal conduction was simultaneously
improved by isoproterenol, which served as the prerequisite of the
tachycardia.
To
our knowledge, this is the first report of split AP potentials
reflecting the slow conduction over the pathway in a case of antidromic
tachycardia.
In addition, the fixed short H-V interval despite decremental conduction
in AV node showed the characteristic of an extra fasciculoventricular
AP[8], which would not participate in AV reentry
and did not require ablation.
Informed consent was obtained from the patient.