March/April - West Virginia State Medical Association

| Scientific Article
Multiple types of LQTS have been
identified with over 300 underlying
gene mutations. LQTS subtypes
1-3 are the 3 major genotypes with
each type displaying characteristic
T-wave repolarization pattern on
ECG. Type 1 often displays a broad
based T-wave and Type 2 a biphasic
T-wave. Type 3 often has a prolonged
ST segment. Each genotype displays
unique associations: LQT1 genotype
displays cardiac events associated
with exercise; often swimming. LQT2
genotype has arrhythmic events
associated with exposure to sudden
loud noises (i.e. alarm clocks).
LQT3 genotype experience events
during sleep or at rest. 27 Medical
therapy aimed at prophylaxis of
cardiac events in LQTS has been
well established; it is more effective
in LQTS1 and LQTS2. 30 Despite
the risk reduction with use of betablockers
residual, cardiac events
can still occur; in a recent study,
in as many as 32% of patients with
LQTS3 on beta-blockers. 31 With this
in mind, ICD implantation is highly
effective in high-risk patients and
those who remain symptomatic
while on medical therapy. 32
Figure 3 shows the ECG of a 52
year old woman who presented
with syncope and a family history
of SCD. Her QT interval was 480
msec with a QTc of 520 msec. She
was started on beta-blocker therapy
and, given her significant history,
underwent implantation of an
ICD. Genetic testing subsequently
revealed a LQT3 genotype with
a mutation in the SCN5A gene.
ARVC first described in 1982, is
a genetically determined disorder
of cardiac myocytes in which RV
myocardium is replaced with
fibro-fatty tissue. 33 In the early
stages structural changes may be
localized to the RV; later they may
also involve the LV. 34 Three phases
have been described; first, an early
concealed phase followed by an
overt electrical phase and then a final
phase with diffuse disease involving
both ventricles leading to HF. 35
ARVC is a familial disease with
an autosomal dominant inheritance
pattern. Patients may present with
symptoms such as palpitations, dizzy
spells, and syncope. SCD is often
the first manifestation. 36 ARVC has
an estimated prevalence of 1/5000
and usually comes to attention when
a young patient with an otherwise
normal heart, presents with VT or VF
originating from the RV. The disease
affects desmosomes that constitute
the gap junctions between myocytes.
In most cases ECG abnormalities
precede histological changes
and ventricular dysfunction. 37
T‐wave inversions in leads V1‐V4
in individuals above 14 years of
age with an otherwise healthy
heart should increase suspicion. 38
The ECG, signal-averaged ECG,
echocardiogram, RV angiogram, and
MRI can be used very effectively
in accurately diagnosing ARVC.
Protocols for using such modalities
are available at www.arvd.org.
The differentiation between
ARVC and RVOT VT is very
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March/April 2011 | Vol. 107 35