Download Transient Prolongation of QT Interval in a Neonate

Transient Prolongation of QT Interval in a Neonate
Shu-Chi Mu, Tseng-Chen Sung, and Ming-I Lin
There is limited information in the literature about sudden infant death syndrome (SIDS) and apparent lifethreatening events (ALTEs) in mature neonates during the first 2 weeks of life. Lethal arrhythmias may occur
in infants with QT interval prolongation due to temporary cardiac sympathetic innervation imbalance.
We report on a male neonate with a prolonged QT interval (the corrected QT interval was 0.53 seconds)
who presented with ALTEs. He had frequent episodes of apnea and cyanosis with continuous bradycardia at
the age of 3 days and was resuscitated. Three days later, the QTc was 0.48 seconds and the heart beat had
increased spontaneously. At the age of three months, the baby was well with a normal QTc (the QTc was
0.41 seconds). The baby’s father had an apparent life-threatening event at the age of three days without any
significant sequelae later. No more detail information could contribute to our etiological consideration.
It is wise to be suspicious of any infant or child with a QTc (corrected QT interval) greater than 0.44 seconds, but this finding should not be used in isolation. When discovered in a newborn, a long QT interval may
be the marker of a true long QT syndrome with its attendant risk of sudden death, or simply a transient electrocardiographic abnormality.
Key words: prolonged QT interval, sudden infant death syndrome (SIDS), apparent life-threatening events (ALTEs)
Sudden infant death syndrome (SIDS) and apparent lifethreatening events (ALTEs) in mature neonates during
the first 2 weeks of life are uncommon with an incidence
of 1% to 3% [1]. ALTEs do occur in the early newborn
period in a presumably low-risk term group [2]. Attempts
to explain SIDS have taken into account two possible
pathogenetic mechanisms. The first hypothesis suggests
that newborns die of apnea which occurs during sleep.
Both central and obstructive apnea have been implicated
[3,4]. The second hypothesis suggests that babies die
suddenly of cardiac arrhythmia. Lethal arrhythmias may
occur in infants with QT interval prolongation, due to
temporary cardiac arrhythmia [5-7]. We report on a neonate with a prolonged QT interval who presented with
ALTEs in the first two weeks of life.
Case Report
A male neonate with a birthweight of 3,500g was born at
full gestation to a 31-year-old primigravida via vaginal
delivery in a community hospital. He had frequent apnea
and cyanosis in the nursery at the age of 3 days. He was
resuscitated and intubated. Due to persistent apnea and
Department of Pediatrics, Shin Kong Wu Ho-Su Memorial Hospital, Taipei, Taiwan, R.O.C.
Received: June 18, 1998
Accepted: September 8, 1998
Clinical Neonatology 1998 Vol.5 No.2
bradycardia (around 60 to 70 beats per minute) and failure to wean from the ventilator, he was transferred to our
neonatal intensive care unit. After admission, he had one
episode of apnea, hypoventilation and continuous bradycardia around 70 to 85 beats per minute with a prolonged
QT interval (the corrected QT interval was 0.53 seconds;
Fig. 1). There was no family history of arrhythmia. Three
days later, the QTc was 0.48 seconds (Fig. 2). At that
time, the heart beat had increased to 110 beats per minute.
The hemogram, brain echography, echocardiography,
EEG and auditory brain stem response were within normal limits. Arterial blood gases were PH 7.447, PaCO2
20.0 mmHg, PaO2 75.7 mmHg, base excess *7.0 mmol/L
and bicarbonate 13.9 mmol/L. Electrolytes levels were
normal (sodium 138 mEq/L, potassium 5.0 mEq/L, chloride 110 mEq/L and ionized calcium 5.05 mg/dl). Creatine kinase was 220 u/L with CK-MB 23u/L. The parent’s
EKG studies were normal with 0.41 seconds and 0.42
seconds of corrected QT interval. According to the
baby’s grandmother, the father had an apparent lifethreatening event at the age of three days. After the resuscitations of intubation and oxygen supplement, he was
extubated one week later without significant sequelae.
His heart beat was 130 beats per minute and his corrected
Reprint requests to: Dr. Shu-Chi Mu, Department of
Pediatrics, Shin Kong Wu Ho-Su Memorial Hospiatl,
No. 95, Wen Chang Road, Shih Lin District, 110,
Taipei, Taiwan, R.O.C.
27
SC Mu, TC Sung, MI Lin
QT
interval
was 0.44 seconds. at
The
baby of
was
discharged
Figure
1. Electrocardiogram
6 days
age.
QT proin good health
without
any
medications
two weeks
longation
was
noted
with a QTc
of 0.53later.
secAt the age onds.
of three months, he had a normal QTc (QTc
was 0.41 seconds).
Figure 2. Electrocardiogram at 10 days of age. QTc was
Discussion
0.48 seconds.
QT interval was 0.44 seconds. The baby was discharged
in good health without any medications two weeks later.
At the age of three months, he had a normal QTc (QTc
was 0.41 seconds).
Discussion
According to Bazett's formula, the QTc should not exceed 0.425 seconds except in infants. A QTc up to 0.49
seconds may be normal in the first 6 months of life. It is
wise to be suspicious of any infant or child with a QTc
greater than 0.44 seconds, but this finding should not be
used in isolation. QT prolongation could be due to hypocalcemia, hypothermia, hypothyroidism, cerebral vascular accident, antiarrhythmia drugs, myocardial damage
and native long QT syndrome. A QTc over 0.60 seconds
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is frequently associated with severe ventricular arrhythmias and second-degree AV block. Special attention
should be given to infants who have a very long QT interval and major ST segment change; the risk of sudden
death in these infants is high, especially in the first week
of life [7]. In our case, the QTc interval was 0.53 seconds
with persistent bradycardia and hypoventilation. Cases of
temporary prolongation of the QT interval have been
reported, sometimes with documented life-threatening
arrhythmias [7]. They can be transient, benign or have a
high correlation with lethal arrhythmias. The QT interval
might return to normal within the first month. Prolongation of the QT interval in neonates may be transient or
may present as an early form of the long QT syndrome.
The length of the QT interval may indicate prognosis. In
one study, patients with a QTc less than 0.50 seconds
eventually recovered with a normal QTc; those with a
QTc greater than 0.60 seconds had severe arrhythmias
[7].
The QT prolongation may be secondary to a variety of
medications, metabolic disorders, and other medical conditions [8]. The ischemic changes of myocarditis and
cardiomyopathy can cause a similar clinical picture of
long QT syndrome. Our patient had a normal heart structure and cardiac function. Symptoms include sudden
death, seizures and syncope [9]. Schwartz hypothesized
that one or more of the following is true: (1) the long QT
syndrome is hereditary; (2) birth defects occur in the
brain, spinal cord, thoracic sympathetic ganglia, or
adrenergic terminals in the myocardium; (3) right-sided
sympathetic activity is decreased; or (4) there are developmental delays in right-sided sympathetic activity [5].
Schwartz favors the latter hypothesis. Prolongation of the
QT interval, at some time of life, may be a marker of
sympathetic imbalance and would allow early identification of some babies at risk. The genesis of SIDS may be
considered multifactorial. Different causes and mechanisms are involved. It is likely that the majority of the
proposed hypotheses account for a few cases. Respiratory
death is slow and allows a few minutes to observe apnea,
cyanosis, and struggle, whereas arrhythmic death is instantaneous and silent [10]. Prolongation of the QT interval in the first week of life is strongly associated with
SIDS. Neonatal electrocardiographic screening may permit the early identification of a substantial percentage of
infants at risk for SIDS, and preventive measures can be
taken [11]. In considering the cause and effect of SIDS
and prolonged QT interval, it was difficult to differentiate what was the primary cause in our case. We couldn’t
exclude the possibility of postresuscitational effect. The
father had an ALTE as a newborn and we could not find
any significant cause of the ALTE. We more favor the
prolongation of QT interval as primary pathogenesis.
Clinical Neonatology 1998 Vol.5 No.2
Prolonged QT Interval in the Neonate
In one study, a neonate who had presented with a sustained irregular heart rate during labor was found to have
QT prolongation and repetitive polymorphic ventricular
arrhythmias [12]. Sinus bradycardia in an otherwise normal fetus may be a symptom of long QT syndrome. With
prolonged QT syndrome, early diagnosis and therapy are
crucial. The β-blocking agents (e.g., propranolol) alone
or in combination with left cardiac sympathetic denervation or permanent cardiac pacing are known to diminish
the risk for sudden death [13]. As neonates are particularly at risk of sudden death, early introduction of permanent cardiac pacing should be considered when propranolol failure is suspected [8,10].
We feel there is a high correlation between prolonged
QT interval and ALTEs. It’s uncommon to observe that
the prolonged QT interval on the electrocardiogram in
certain individuals is associated with an increased incidence of life-threatening arrhythmias and sudden death.
When discovered in a newborn, a long QT interval may
be the marker of a true long QT syndrome with the risk
of sudden death, or simply a transient, benign electrocardiographic abnormality. The relationship between long
QT syndrome, various conduction disturbances and late
potentials will require further scrutiny.
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