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CARDIOVASCULAR JOURNAL OF AFRICA • Vol 24, No 2, March 2013
e6
AFRICA
channel blockers, cocaine, antidepressants and antihistamines
are known to facilitate a Brugada-type ECG by reducing the
inward current.
Hyperkalaemia, vagatonic agents and IKatp activators
augment the outward current, which is also transduced in
the ECG as the typical Brugada pattern.
8,9
The syndrome has
autosomal dominant transmission. Mutation of the SCN5A
gene, which encodes for cardiac sodium channels, causes loss of
cardiac sodium channel function,
10
resulting in a shortening of
the action potential duration in the right ventricular epicardium.
This causes a transmural voltage gradient, seen as ST elevation
and re-excitation on the ECG. This voltage gradient creates a
vulnerable window for extra-systoles or premature impulses to
initiate phase 2 re-entry, triggering VF.
Class IA (ajmaline, procainamide) and class IC (propafenone,
flecainide) anti-arrhythmia agents and heightened parasympa-
thetic tone increase ST-segment elevation and may precipitate
VF. Sympathetic activation, stress testing, isoproterenol and
dobutamine may decrease ST-segment elevation and result in
transient normalisation of the ECG.
11,12
The VF frequently seen
during sleep in patients with BS is probably due to a decrease in
sympathetic tone.
Our case underlines the ability of ajmaline to confirm an ECG
pattern compatible with BS in individuals in whom the disease is
suspected due to a positive family history of Brugada syndrome,
syncope or sudden cardiac death, previous syncope, documented
VT or a suspicious but non-diagnostic ECG.
11
Class IC and
IA anti-arrhythmia drugs (flecainide, propafenone, ajmaline,
disopryramide, procainamide) accentuate ST-segment elevation
and are capable of unmasking concealed forms of the disease.
10-14
Class IC anti-arrhythmia drugs tend to induce ST-segment
changes in BS more reliably than class IA drugs.
10,11
This was
considered to be caused by the differences in the strength of the
sodium channel blocking effect of class IA and IC drugs.
15
Ajmaline, which is available only for intravenous application
due to its poor oral bioavailability, seems to be the best drug to
unmask BS, possibly because of its kinetics and strength of rate-
dependent sodium channel-blocking effects. Additionally, a short
half-life and the brief duration of its electrophysiological effects
(minutes) render it superior to the other anti-arrhythmia drugs.
16
Mortality from BS is approximately 30% at two years following
diagnosis.
4
An ICD implant is the only effective treatment option
for prevention of sudden cardiac death in patients with BS.
Conclusion
Early recognition of BS may contribute to a decrease in the
frequency of VF. Therefore, patients who have a history of
syncope or sudden cardiac death in relatives, or a suspicious
but non-diagnostic ECG must be evaluated carefully. If the
provocation test, which is done with propafenone is negative, BS
should not be excluded. The challenge test should be repeated
with ajmaline.
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