<Case
report>
An 18-year-old Chinese woman was
evaluated for an episode of sudden collapse. The episode
happened during a trip of outdoor teaching. She lost her
consciousness suddenly when bending down to wear her shoes.
She was resuscitated by local medical personnel in an
ambulance and was sent to emergence service immediately. The
ambulatory electrocardiogram (ECG) recorded by automatic
external defibrillator revealed polymorphic and bidirectional
VT (figure 1
). She fully
recovered after the resuscitation.
She was healthy and had never experienced syncope or
exercise-induced dizziness before. There was no history of
heart disease, syncope, and sudden death in her family. Her
blood pressure was 132/68 mmHg and her respiratory rate was
22/min. There was no lymph node enlargement or jugular vein
engorgment on the neck. Her breath sounds were clear. The
heart sounds were regular without murmur. The abdomen was soft
with normoactive bowel sounds. The extremities were freely
movable without significant edema or cyanosis.
Laboratory tests including biochemical
profile and serum electrolytes were unremarkable (table 1).
The electrocardiogram (figure
2
), signal average electrocardiogram,
transthoracic echocardiography, and magnetic resonance imaging
were also within normal limit.
In order to evaluate the possibility
of exercise-induced arrhythmia, she underwent a treadmill
exercise test. After one minute of exercise, short runs of
bidirectional and polymorphic ventricular tachycardia
developed. Ventricular tachycardia became sustained and
bidirectional within next two minutes (figure
3
). Exercise was stopped and ventricular
tachycardia terminated 4 minutes later. She remained free of
symptoms and hemodynamically stable throughout the exercise
test.
Programmed electrical stimulation failed to induce
sustained or nonsustained ventricular tachycardia and so did
isoprotenolol infusion. The procainamide provocation test was
negative, so that Brugada syndrome was excluded. She was
diagnosed with catecholaminergic polymorphic ventricular
tachycardia (CPVT), and was placed on long-term treatment with
a β-blocker. Implantation of an automatic internal
cardioverter defibrillator was suggested, but she refused. She
was free of symptoms at six-month follow-up.
<Discussion>
Exercise-induced ventricular tachycardia in children and
young adult without structural heart disease are rare.
Generally, the prognosis is relative benign if the morphology
is monomorphic [1]. CPVT is a special entity with multiform
morphology carrying a worse prognosis [1,2]. Most cases of CPVT
are reported among Caucasian and Japanese. However, CPVT is
never reported among Taiwanese.
The definition of CPVT includes several factors. First,
more than two type of ventricular tachycardia morphology can
be induced by exercise or catecholamine infusion during more
than three consecutive beats. Second, there is absence of
electrolyte imbalance, drug treatment, or organic heart
disease. Finally, there is absence of primary electrical
disease such as long QT syndrome or Brugada syndrome [1]. The
morphology of CPVT is polymorphic, bidirectional, ventricular
fibrillation, or their combination [1,3]. Fourteen percent of
patients with CPVT had a positive family history [1]. Recent
studies suggest that familial CPVT is a genetic disorder. Both
autosomal dominant and autosomal recessive forms are found in
genetic inheritance. Lineage analysis reveal that a locus at
1q42-q43 is associated with CPVT with an autosomal dominant
inheritance [4]. Further analysis show that cardiac ryanodine
receptor gene (RyR2) is the disease causing gene [5]. In
patients with an autosomal recessive inheritance, the disease
locus is located at 1q31-21 and the responsible gene is
cardiac calsequestrin (CASQ2) [6]. Both pattern of mutation
are associated with increased calcium release from the
sarcoplasmic reticulum.
The prognosis of CPVT is poor. Mortality rate is around 30%
by the age of 30 [4,5]. β-blocker is effective in deceasing
the attacks. However, it completely controls CPVT in only
one-third of patients [1]. Implantation of an implantable
cardioverter defibrillator is indicated in patients who are at
high risk or have recurrent attacks even under β-blocker
therapy.
Table 1. Laboratory
data
[ CBC+PLT ]
|
WBC |
RBC |
Hct |
Hb |
MCV |
MCHC |
PLT |
Unit |
K/μL |
M/μL |
% |
g/dL |
fL |
g/dL |
K /μL |
Value |
7.86 |
4.39 |
38.4 |
12.9 |
87.5 |
33.6 |
467.0 | [ Biochemistry ]
|
T-bil |
Alb |
AST |
ALP |
BUN |
Cre |
Unit |
mg/dL |
g/dL |
U/L |
U/I |
mg/dL |
mg/dL |
Value |
0.29 |
4.37 |
35 |
204.0 |
9.0 |
0.5 |
|
Na |
K |
Ca |
Mg |
Unit |
mmol/l |
mmol/l |
mmol/l |
mmol/l |
Value |
140.3 |
4.3 |
2.39 |
0.87 | [ Coagulation
profile]
PT/PT, control |
13.2/12.4, INR:1.1 |
PTT/PTT control |
37.1/35.9 |
[ Serology ] C-reactive protein: 0.45 mg/dl
Legend of
figure
figure 1 : The long strip of the
electrocardiogram in a external defibrillator reveals
intermittently alternating bidirectional and polymorphic
ventricular tachycardia.
figure
2 : The resting
electrocardiogram is morphological normal and no QT
prolongation was noted.
figure
3 : The exercise
electrocardiogram in third minute of exertional time reveals
sustained bidirectional ventricular tachycardia.
<Reference >
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Nagashima M, et al. Catecholaminergic polymorphic ventricular
tachycardia: electrocardiographic characteristics and optimal
therapeutic strategies to prevent sudden death. Heart
2003;89:66-70.
2. Leenhardt A, Lucet V, Denjoy
I, Grau F, Ngoc DD, Coumel P. Catecholaminergic polymorphic
ventricular tachycardia in children: A 7-year follow-up of 21
patients. Circulation 1995;91:1512-1519.
3. Swan H, Piippo K, Viitasalo M,
et al. Arrhythmic disorder mapped to chromosome 1q42-q43
causes malignant polymorphic ventricular tachycardia in
structurally normal hearts. J Am Coll Cadiol 1999;34:2035-42.
4. Priori SG, Napolitano C, Memmi
M, et al. Clinical and molecular characterization of patients
with catecholaminergic polymorphic ventricular tachycardia.
Circulation 2002;106:69-74.
5. Laitinen P, Brown KM, Piipo K,
et al. Mutation of the cardiac ryanodine receptor (RyR2) gene
in familial polymorphic ventricular tachycardia. Circulation
2001;103:485-490.
6. Lahat H, Pras E, Olender T, et
al. A missense mutation in a highly conserved region of CASQ2
is associated with autosomal recessive catecholamine-induced
polymorphic ventricular tachycardia in Bedouin families from
Israel. Am J Hum Genet 2001;69:1378-1384.
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