Majid Haghjoo, M.D, Arash Arya, M.D, Mohammad Reza Dehghani, M.D,
Mohammad Ali Sadr-Ameli, M.D
Department of Pacemaker and Electrophysiology, Rajaie Cardiovascular
Medical and Research Center, School of Medicine, Iran University of
Medical Sciences, Tehran, Iran.
Address for
correspondence: Majid Haghjoo MD, Department of Pacemaker and
Electrophysiology, Rajaie Cardiovascular Medical and Research Center,
Mellat Park, Vali-e-Asr Avenue, Tehran 1996911151 Iran. P.O.Box:
15745-1341 E-mail:majid.haghjoo@gmail.com
ECG
in sinus rhythm with ventricular preexcitation and changing QRS
morphology was seen that was initially interpreted as the
multiple accessory pathway from elsewhere. (
Figure 1A).
The following
mechanisms are potentially involved in the electrogenesis of changing
QRS morphology in WPW syndrome: 1) multiple accessory pathways
1; 2) simultaneous occurrence of aberrant
atrioventricular conduction with accessory pathway conduction
2; 3) ventricular fusion of preexcited
sinus impulse with ectopic impulse.
Electrophysiologic study showed short PR (75 ms) interval with wide QRS
(152 ms) and negative HV (-12 ms) interval. No change in delta wave
polarity was observed during HRA and CS pacing. In full preexcitation,
no breakthrough was seen in the CS. During incremental ventricular
pacing, atrial breakthrough site is initially recorded on the HRA
catheter and then changed to distal pole of CS catheter with
progressive decrease in pacing cycle length. During ventricular pacing
at cycle length of 500 ms (S1), earliest atrial activity is recorded on
HRA catheter.
Changing QRS could not be
explained by presence of
multiple APs
because only right-sided AP had bidirectional conduction and no distal
CS breakthrough was seen simultaneous with changing QRS morphology. The
possibility of
aberrant conduction
is excluded by presence of negative HV interval in the beats with
differing QRS morphology. No sinus cycle length variation before and
after the beats with different morphologies are against the occurrence
of functional LBBB. The prematurity of ventricular electrogram in His
recording catheter with variable HV (H-electrogram is recorded after
V-electrogram in second beat and before V-electrogram in third beat)
and fixed V-RB intervals (interval from ventricular electrogram in His
to the RB potential) are compatible with
ventricular fusion of preexcited sinus
impulse with ectopic ventricular impulse originating from
parahissian area (explaining LBBB and inferior axis morphology of the
beats with changing QRS) but not from the His bundle or RBB
itself (because H-electrogram and RB potential is recorded after
V-electrogram in the second beat with greater degree of ventricular
fusion)(
Figure 1B).
Figure
1- A: This electrocardiographic tracing shows sinus rhythm with
ventricular preexcitation and changing QRS morphology in the second and
third beats of the tracing. B:
Intracardiac electrograms and surface ECG recording during the
variation of the QRS complexes. The second and third complexes are
beats with different degrees of fusion. Note that A-A, H-H, V-V (RVA),
and AH intervals are the same in all beats. The main difference of
fusion beats with preexcited sinus beats is the variation of HV
interval in fusion beats with fixed V-RB interval, indicating the
retrograde invasion of the RBB by ectopic impulse arising form the low
RVOT area.
HRA=high right atrium; His=his bundle; RVA=right ventricular apex; CS=coronary sinus; RVOT=right ventricular outflow
tract; RBB=right bundle branch
References
1. Josephson ME, Caracta AR, Lau SH.
Alternating type A and type B Wolf-Parkinson-White syndrome. Am Heart
J. 1974; 87:363.
2. Mendoza IJ, Castellanos A,
Sung RJ. Wolf-Parkinson-White syndrome type B with
tachycardia-dependent (phase 3) block in the accessory pathway and in
left bundle-branch coexisting with rate-unrelated right bundle-branch
block. Br Heart J. 1990; 43:481-486.
