The Journal of Maternal-Fetal Medicine 1:202-205 (1992)

Prolonged QT Syndrome Presenting as Fetal Bradycardia

David W. Green, MD, Nee1 6. Ackerman, MD, Cregg Lund, DO, and Darnaris Wright, MD

Division of Neonatology, Presbyterian Hospital, Dallas, Texas

Abstract A case report of congenital prolongccl QT syndrome that presented with feral hrdycardia and subsequent fetal distress is presented. Perinatal hradycardia and congenital prolonged QT syndrome are reviewed. o 1492 wi lcy -~ i s s . Inc.

Key Words: QT-interval, Fetal arrhythmia, Perinatal hradycardia, Fetal heart rate decelerations

I NTRO D U CTI 0 N Fetal heart rate tracings during labor can provide

clinicians with important information about utero- placental sufficiency and fetal well-being [ 11. How- ever, fetal arrhythmias during labor may make the interpretation of fetal heart tracings and thus fetal status difficult 111. Congenital prolonged QT syn- drome is a rare disorder of cardiac ventricular repolar- ization, which can be associated with various signifi- cant arrhythmias [2]. We report a case of congenital prolonged QT syndrome that presented as fetal brady- cardia during labor.

CASE REPORT A 32 year old primigravid female received prenatal

care from approximately 20 weeks gestation. There were no significant problems during the pregnancy, and routine obstetrical evaluations including fetal heart rate examinations were unremarkable. The mother smoked 2 packages of cigarettes per day. There was no maternal history of collagen vascular disease. The maternal family history was remarkable for a sister with bradycardia and several uncles with unknown “heart conditions” which began in the fourth decade of life. There was no family history of congenital deaf- ness, recurrent syncope, or sudden death during child- hood or early adulthood.

When labor began at 40 weeks gestation, the base- line fetal heart rate was 90-100 beats per minute, with accelerations to 120-130 beats per minute, and good beat-to-beat variability. Artificial rupture of mem- branes revealed clear amniotic fluid, and oxytocin was begun. Shortly after the mother was given oxymor-

phone and promethazine, the fetal heart rate dropped acutely to approximately 60 beats per minute. There was no response to the discontinuation of oxytocin, maternal positioning, or oxygen therapy. A n emer- gent cesarean section was performed using general an- esthesia for presumed fetal distress.

A t delivery, the presentation was vertex and there was no evidence of cord entanglement or placental abnormality. The baby was initially cyanotic with fair tone and a wet cry. The heart rate was less than 100 beats per minute and there was no improvement with tactile stimulation. She became apneic and limp, and mask-bag ventilation with 100% oxygen was ineffec- tive in establishing either a heart rate greater than 100 beats per minute or an improvement in the cyancisis. The baby was intuhated and ventilated with 100% oxygen, whereupon her color and activity improved despite a persistent heart rate less than 100 beats per minute. The apgar scores were 1 and 7 a t 1 and 5 minutes, respectively. Results of a cord blood gas were a pH of 7.32, a pC0 , of 45 torr, a p 0 , of 36 torr, and a base deficit of -2.8.

Examination at 30 minutes of age revealed a pink, intuhated female with acrocyanosis, in no respiratory

Received August 23, 1991; revised April 8, 1992, accepted May 8,

Address reprint requests to Dr. David W. Green, Presbyterian Hospi- 1992.

tal, 8210 Walnut Hill Lane, Suite 604, Dallas, TX 75231.

0 1992 Wiley-Liss, Inc.

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PROLONGED QT SYNDROME PRESENTING AS FETAL DISTRESS 203

distress on the ventilator. Birthweight was 3,424 g which was appropriate for the gestational age. The heart rate was 96 beats per minute, and the blood pressure was 76/34 torr. Aside from the bradycardia, the physical examination was grossly normal.

Laboratory evaluation included an initial serum glu- cose of 26 mg%. A complete blood count, electro- lytes, calcium, and magnesium were normal. A n arte- rial blood gas at 1 hour of age had a pH of 7.55, a p o l of 375 torr, and a p C 0 , 23 torr, with a base excess of I . 1 on 60%) oxygen. A chest roentgenogram showed cardiomegaly with clear lung fields.

The baby was transferred to a level 111 neonatal intensive care unit. Physical examination of the baby on the ventilator at 4 hours of age was remarkable for a heart rate of 80 to 95 heats per minute. A 12-lead electrocardiogram (EKG) revealed sinus bradycardia with a rate of 79 beats per minute, right ventricular hypertrophy, abnormal T waves (inverted in leads I , V,, and V,) and a corrected QT-interval (QT,) of .45 seconds (normal <. 44 seconds) [I]. A n echocardio- gram of the heart revealed a slightly thickened septum and left ventricle, with normal function.

The baby was weaned off the ventilator by 24 hours of age. Neurologic examination remained normal. A diagnosis of prolonged QT syndrome was made on the basis of persistent sinus bradycardia ( the resting heart rate varied from 70 to 100 beats per minute), associ- ated with a prolonged QT-interval and abnormal T waves. Propranolol was started on the 4th day of life. A subsequent 24-hour Holter monitor evaluation re- vealed sinus rhythm with an average heart rate of 1 12 beats per minute and no significant arrhythmias. The baby was discharged on the 9th day of life on pro- pranolol. O n follow-up at 1 month, the baby was doing well, and a brainstem auditory evoked response examination was normal. Electrocardiograms ob- tained for the father, mother, and maternal aunt re- vealed normal, borderline normal, and prolonged QT,s o f . 38, .44, and .48 seconds, respectively.

DISCUSSION Bradycardia detected by fetal heart rate monitor is

defined as a sustained fetal heart rate (FHR) below 120 beats per minute, and can be due to fetal hypoxia, head compression, bradyarrhythmia, or mechanical (monitor) error [ 11. Therefore, management of fetal bradycardia varies from emergent delivery for fetal dis- tress to changing monitor leads. Significant hypoxia

due to various causes of iitero-placental insufficiency may cause prolonged late FHR ckcelerations [ I ] . Fetal head compression during uterine contractions may cause early FHR decelerations via a presumed vagal reflex [ 11. True fetal bradyarrhythniias such as blocked atrial bigeminy [3,4] and trigeminy [5], as well as atri- oventricular (AV) block 111, can present as fetal bradycardia during labor. Also, spurious monitor trac- ings may be misinterpreted as fetal bradycardia [5,6]. The prolonged QT syndrome has been diagnosed in utero associated with bradycardia due to 2: 1 AV block [7,8], as well as the tachyarrhythmia torsades de pointes [ 71. In utero prolonged QT syndrome associ- ated with sinus bradycardia and fetal distress in the perinatal period has not been previously reported.

In this case, the initial fetal heart rate was abnormal at 90-100 beats per minute, with accelerations to the 120 beats per minute range, and good beat-to-beat variability. W e speculate that this baseline fetal brady- cardia was due to the prolonged QT syndrome. Subse- quently, either a mechanical complication of labor and/or maternal medications (oxymorphonei promethazine) caused a more pronounced fetal brady- cardia (60 beats per minute). The maternal oxymor- phone HCUpromethazine were given in standard obstetrical intravenous dosages (0.5 and 6.25 mg re- spectively), and there were no untoward effects noted on the maternal condition. However, because these medications are known to rapidly enter the fetal circu- lation, it is possible that the fetus with prolonged QT syndrome is more sensitive to these drugs than the normal fetus. This could explain the severe fetal bradycardia seen 5 minutes after the medications were given.

After the baby was delivered, the baseline hradycar- dia persisted despite appropriate resuscitative efforts. In the newborn, sinus bradycardia is often due to hy- poxia; less common etiologies include hypothy- roidism, hypokalemia, medications (for example Beta- blockers), increased intracranial pressure, arrhythmia, or cardiac disease 191. In this case, history, physical examination, chest roentgenogram, laboratory stud- ies, and EKG were important in determining the etiol- ogy of the bradycardia.

The QT-interval of the EKG represents ventricular depolarization and electrical repolarization. Thus the QT-interval is measured from the onset of the QRS complex to the isoelectric finish of the T wave. The QT-interval must be corrected for the heart rate; the Bazett equation defines the corrected QT-interval as

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204 GREEN ET AL.

the measured QT-interval, divided by the square root of the preceding R-R interval, in seconds [2]. The upper limit of normal for the corrected QT-interval with a normal QRS interval is .44 seconds [2].

Prolonged QT syndrome may he congenital or ac- quired. Acquired causes include hypocalcemia, hypo- magnesemia, myocarditis, myocardial disease, ex- treme dieting, and medications (for example, antiarrhythmics) [ 101. The congenital prolonged QT syndrome is a rare abnormality in cardiac conduction which may be hereditary or occur sporadically. A syn- drome with autosomal recessive inheritance associated with hearing loss was initially described by Jervell and Lange-Nielsen [ 1 11. Subsequently, congenital pro- longed QT-interval with an autosomal dominant in- heritance associated with normal hearing was reported separately by Romano [12] and by Ward [13]. Our patient’s auditory brainstem evoked response was nor- mal. E1ectn)cardiography of family members revealed that the mother had a borderline QT-interval, and a maternal aunt had bradycardia and a prolonged QT- interval; these findings are consistent with a heredi- tary pattern.

Because the manifestations of the prolonged QT syndrome are variable, Schwartz proposed major and minor criteria for the diagnosis [ 141. Major criteria include a corrected QT-interval (Bazett’s formula) greater than .44 seconds, family members with pro- longed QT syndrome, and syncope related to emo- tional stress. Minor criteria include congenital deaf- ness, bradycardia, abnormal T waves, and T-wave alternans. In children, the diagnosis can be made on the basis of a prolonged QT-interval and one minor criterion [ 141.

The clinical course of congenital prolonged QT syndrome is variable. Patients may be asymptomatic, but more frequently present in childhood or adoles- cence with recurrent light-headedness or syncope [ 151. Sudden death due to malignant ventricular arrhyth- mias may follow these symptoms, at a rate of 1-5% per year [2]. Risk factors for morbidity and mortality in- clude the female gender, congenital deafness, prior episodes of syncope, and documented malignant ven- tricular arrhythmia [16].

Treatment is aimed at decreasing the sympathetic input to the heart. Beta-blockers, especially propran- 0101, are the first line of medical management for prolonged QT syndrome [ 15,171. Patients refractory to propranolol may require left-sided ganglionectomy

(again to decrease the sympathetic input) [2]. For persistent treatment failures, implantation of a pace- maker or an automatic defibrillator may be indi- cated [2].

W e have reported a case of congenital prolonged QT syndrome that presented as fetal bradycardia dur- ing labor. It is unclear whether the baseline fetal bradycardia contributed to the inability of the fetus to tolerate the stress of labor and/or maternal medica- tions. The initial presence of good beat-to-beat vari- ability and accelerations, the cord hlood gas, and the perinatal course all support the theory of an acute episode of fetal distress. This was likely due to a me- chanical complication of labor and/or maternal medi- cations, and resulted in the more severe bradycardia. This acute situation was managed with emergent ce- sarean delivery. However, the baseline bradycardia persisted in the newborn despite resuscitative mea- sures. W e conclude that in the perinatal period, bradyarrhythmia may mimic and/or complicate fetal and neonatal hypoxia, and thus present special prob- lems for obstetrical and neonatal management. None- theless, because hypoxia is the most serious cause of perinatal bradycardia, the appropriate resuscitative measures should not be delayed.

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