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bases of her lungs bilaterally. A chest radiograph and ICD therapy that was instituted, the patient
demonstrated mild interstitial haziness at the bases. was given a list of drugs to avoid because of their
A diagnosis of community-acquired pneumonia was known QT-prolonging effects. A resource for pa-
made, and she was given a prescription for 10 days tients with LQTS including a comprehensive list of
of erythromycin. On the second day of therapy QT interval prolonging drugs can be found on the
while at home, she suddenly lost consciousness internet at www.SADS.org.
while preparing breakfast and developed convulsive
seizures on the floor. The emergency medical team
was called and found her unresponsive. No pulse
was detectable and the initial heart rhythm is shown
below. Cardiopulmonary resuscitation was initiated
and then DC cardioversion was performed with a
return to sinus rhythm. Lidocaine was administered
and she was transported to the local hospital. Her
presenting ECG is shown below. What is her diag-
nosis?
ANSWER: Long QT syndrome. LQTS is caused by an
abnormality in the function of specific ion channels
responsible for myocardial repolarization. This may
result from congenital mutations in the DNA en-
coding the ion channels (inherited form) or may be
acquired from pharmacological therapy or other ill-
ness (increased intracerebral pressure, for example).
In this patient s case, an abnormally long heart rate
corrected QT interval was present on her ECG, di-
agnostic of a cardiac repolarization abnormality.
After stopping the erythromycin, she was found to
have an underlying long QT interval that was exac-
erbated by the erythromycin. A detailed family his-
tory confirmed the diagnosis when it was revealed
that her mother had fainted on several occasions,
and her first cousin (maternal) drowned while
swimming in a lake 3 summers previously. Her
physicians began -blocker therapy and recom-
mended placing an implantable cardioverter
defibrillator. Several medications prolong cardiac
repolarization. The alteration in repolarization nor-
mally results from blockade of the rapid component
of the delayed rectifier potassium current. In sus-
ceptible patients, this may lead to a profound pro-
longation of the QT interval and place them at risk
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