Figure legends
Figure 1. A : Twelve-lead ECGs before and after the operation,
and during the tachycardia. After the operation, QRS duration was
prolonged to 132ms with slight left axis deviation which was noted by a
deep S wave in lead II. The tachycardia showed a left bundle branch
block (LBBB)-like morphology with superior axis deviation and the QRS
width of 200 ms.
B : Induction of the tachycardia. At the baseline, an HV
interval was 76 ms. Pacing from right ventricular apex (RVA) produced a
spike potential (Spike, red arrows) followed by a fragmented potential
(Fg, red underlines) (Spike-Fg) in a bipolar electrode (His 1-2) placed
at the His bundle. When the stimulation interval was shortened, the
fragmented component was further prolonged with reversal of the sequence
to Fg-Spike, thereby inducing the tachycardia. During the tachycardia
with a cycle length of 420 ms, the Fg to QRS interval was 189 ms and the
QRS to Spike interval was 87 ms. Each dotted vertical line indicates
onset of the QRS complex. Shown are the surface ECGs and intracardiac
electrograms recorded from the low lateral right atrium (LLRA), His
bundle (His) area, and right ventricular apex (RVA). Fg = fragmentated
potential. Spike = spike potential. 1-2 = distal pairs of electrodes of
the catheter. S = stimulus.
Figure 2. A : Pacing from RVA during the tachycardia. Post
pacing interval of 624ms was much longer than the tachycardia cycle
length of 430ms.
B : Twelve-lead ECGs during the burst pacing. Paced QRS
morphologies from RVA with the cycle length of 400 ms during baseline
(RVA(B)) and tachycardia (RVA(Tachy)) were identical, which indicated
absence of constant and progressive fusion. The stimulation captured His
bundle potential (i.e., Spike potential) (His p) and fragmented
potential (Fg p). B = baseline rhythm. Tachy= tachycardia, His p= His
bundle (i.e., Spike potential) pacing, Fg p= fragmented potential
pacing.
C : Pacing at the His bundle area during the tachycardia. The
pacing captured His bundle, i.e., Spike potential. The stimulus to QRS
interval of 71 ms quasi-equaled the HV interval during the baseline
rhythm. The post pacing interval was 578 ms and the interval from the
last stimulation to fragmentation was 380 ms. The fragmented potential
to QRS interval was 198 ms during the tachycardia (left panel). The
pacing captured the fragmented potential (Fg) selectively with the
stimulus to QRS interval of 162 ms and concealed fusion. The interval
from the last stimulation to the fragmented potential was 479 ms (middle
panel). At the pacing cycle length of 340 ms, the stimulus to QRS
interval gradually increased and the tachycardia was terminated with a
seeming Fg-Spike block. A direct ventricular capture immediately after
termination produced a different QRS morphology from that during the
tachycardia (right panel). Abbreviations are the same as in Figure 1.
Figure 3. A : A proposed mechanism of this tachycardia. AV node
= atrioventricular node. RBB = right bundle branch. LBB = left bundle
branch. Fg = fragmented potential. Spike = spike potential. See text for
details.
B: Before the radiofrequency catheter ablation. A brief
fragmented potential was recorded from bipolar electrodes of the
ablation catheter (ABL). The electrogram was 49 ms earlier than the
onset of QRS complex at the successful ablation site. At this site,
concealed entrainment with the stimulus to QRS interval of 46 ms was
observed. The His bundle catheter was displaced to a more distal
(ventricular) site. ABL = ablation catheter. Other abbreviations are the
same as in Figure 1