Discussion
The differential diagnoses of WCT with LBBB morphology similar to that
during SR, an HH interval preceding a VV interval, and presenting with
1:1 VA conduction include bundle-branch reentry ventricular tachycardia
(BBR-VT), any supraventricular tachycardia (SVT) with LBBB such as AVN
reentrant tachycardia (AVNRT), orthodromic reciprocating tachycardia
(ORT) with AV accessory pathway (AP), ORT with
node-fascicular/node-ventricular (NF/NV) AP, junctional tachycardia
(JT), and atrial tachycardia (AT). Antidromic reciprocating tachycardia,
pathway-to-pathway tachycardia, and any SVT with a bystander AP were
unlikely because His deflection preceded the QRS onset with the HV
interval identical to that during SR (Figure 1). During WCT, AH block
and the subsequent VA perturbation followed without termination (Figure
2). This finding could exclude ORT with AV AP, ORT with NF/NV AP, JT,
and BBR-VT because these tachycardias include the ventricle or His as a
part of the circuit. AVNRT with infra-Hisian block also was an unlikely
diagnosis because there was VA perturbation without termination of the
tachycardia (Figure 2). Although we did not confirm the dual pathway
physiology of the AVN by an extra pacing maneuver, gradual prolongation
of AH leading to the fixed AH interval after AH block during WCT (Figure
2) was not inconsistent with the transition of the antegrade pathway
from the fast to the slow pathway. Based on these findings, AT was
diagnosed.
VA relationships were interrupted by atrial pacing from the two
different sites of the right atrium without termination of the
tachycardia.1, 2 Mapping was performed during WCT, and
the earliest atrial activation site was near the His region. RFCA was
performed and the WCT was terminated. This was complicated by complete
AV block. Before ablation, the patient was informed of the potential
risk of AV block with the necessity for a pacemaker and of being the
potential candidate for cardiac resynchronization therapy (CRT) because
of class 2 congestive heart failure with an impaired EF and LBBB;
therefore, CRT was implanted.
We described a case of AT
presenting with a wide QRS-complex, 1:1 VA conduction, HH variability
preceding VV variability and short VA. The differential diagnoses of WCT
with 1:1 AV conduction are challenging, and some pacing maneuvers should
be encouraged. However, in our case, only one ECG tracing, a transient
VA perturbation following AH block during WCT, immediately ruled out
other SVT and VT, which is the most important differential diagnosis.
An observation of the spontaneous phenomenon during EP study is
occasionally sufficient to make a diagnosis.