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International Journal of Arrhythmia 2012;13(3): 41-46.
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Introduction
Arrhythmogenic right ventricular dysplasia
(ARVD) is a progressive, genetically determined,
infiltrative myocardial disease with characteristic
structural and functional abnormalities primarily
involving the right ventricle (RV). At a later stage,
it may also affect the left ventricle (LV).1 The most
common affected areas are the infundibulum, apex,
and the inferoposterior subtricuspid areas,
collectively known as the triangle of dysplasia.2 The
most common cause of sustained monomorphic VT
associated with structural heart disease is reentry
related to ventricular scars. Multiple VTs with
different QRS morphologies can be caused by
multiple exits from the same scar region or changes
in activation remote from the circuit that are
caused by functional regions of block.3 Peritricuspid
ventricular reentry is a frequent mechanism of VT
in patients with ARVD that can be identified by
detailed 3-dimensional (3D) electroanatomical
mapping.4 Electrical storm is defined as the
occurrence of 3 or more episodes of sustained VT
separated by 5 minutes, during a 24-h period, or
the presence of incessant VT (defined as persistent,
sustained VT or continuous episodes of VT
separated by brief periods of normal rhythm).5
We performed radiofrequency catheter ablation
(RF ablation) for VT in patients with ARVD using a
3D mapping system (Carto-3) to relieve frequent
ICD shock.
Case
A 48-year-old man was referred to our hospital
in May 2005 for palpitation associated with
sustained VT that was terminated by direct current
(DC) cardioversion. The patient had never been
hospitalized before the event. Physical examination
was normal, as were 12-lead ECG and chest X-ray.
Two-dimensional echocardiography presented
normal left ventricular function and right
ventricular dilation and hypokinesia. The coronary
angiogram was also normal. He was discharged
against medical advice to undergo ICD
implantation.
Cardiac magnetic resonance imaging (MRI)
revealed a fibrofatty infiltration in the RV in
November 2008. Electrocardiogram (Figure 1) showed
epsilon wave. The patient underwent single-lead
ICD implantation, with the ICD programmed for
VVI pacing at a rate of 50 bpm and with
antitachycardia pacing as the first option, low-energy
cardioversion as the second, and highenergy
cardioversion as a subsequent intervention
in case of failure of the previous options. The
patient, however, experienced frequent ICD shocks
and hospitalization since the ICD was implanted.
He was admitted to replace the ICD battery and
receive a new atrial lead to better discriminate
between supraventricular tachycardia (SVT) and VT
in July 2011. He was admitted to receive RF ablation
to eliminate VT, which causes ICD shock.
Electrocardiogram during VT (Figure 2) showed
two different QRS morphologies with the same
axis. A left bundle branch block-like configuration
in lead V1 indicated an exit in the RV or
interventricular septum. A dominant R-wave in V1
indicated an exit in the LV. According to the
morphology of VT, the exit site may have been the
peritricuspid valve area.
Substrate mapping delineates the likely
arrhythmogenic substrate during a stable sinus or
paced rhythm. This method often allow the identification of exits and channels without
mapping during VT, facilitating ablation in patients
with multiple, unstable VTs.3,6 Substrate mapping
usually can be performed by 3-dimensional
mapping system (Figure 3). Both endocardial
mapping and epicardial mapping should be done
because ARVD progresses from epicardium to
endocardium. Isolated potentials after the QRS
complex during sinus or paced rhythm may be an isthmus.7
Two VTs were induced with programmed
electrical stimulation. During slow VT induction,
vital signs were stable, pace mapping and
entrainment mapping (C, D in Figure 4) were done.
After ablation, the patient no longer experienced
ICD shock. Nonsustained VT was often noted, but it
was terminated by antitachycardia pacing.
Discussion
Scar-related RV tachycardias occur in ARVD
patients and reentry circuits are often adjacent to
the scar. The most commonly affected areas are the
infundibulum, apex, and the inferoposterior
subtricuspid areas. Patients with ARVD have
exhibited a good acute success rate, but the
recurrence rate is >70% during follow-up exceeding
1 year, suggesting disease progression.8 Catheter
ablation of VT plays an important role in reducing
VT episodes in patients with ICDs and controlling
incessant VT and electrical storms.9 Techniques for
epicardial mapping and ablation have improved
outcomes for patients with arrhythmias that are
not endocardial in origin (Figure 4).9
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