Fetal Tachyarrhythmia: A Tale of Two Presentations

Patient A is a 31-year-old gravida, 4 para 1-0-2-1 woman at 34 weeks and 2 days’ gestation transferred to our quaternary care center for suspected fetal arrhythmia. Her medical history was notable for chronic hypertension controlled on labetalol. Her fetal ultrasonography showed fetal growth restriction and a membranous ventricular septal defect. Fetal echocardiography showed an aneurysmal septum primum with normal valve function without evidence of hydrops. Of note, 3 brief episodes of tachycardia were appreciated during the fetal echocardiography, with a ventricular rate of 220 beats/min. Her obstetric history was unremarkable. She was admitted with a plan of continuous fetal monitoring for 24 hours to assess the duration of fetal tachycardia.Patient B was a 28-year-old gravida 2, para 1-0-1-1 woman at 28 weeks’ gestation who was also transferred to our quaternary center for fetal tachycardia. Her medical history was notable for chronic hypertension, which was controlled without medications, and gestational diabetes, which was controlled through diet. Scheduled ultrasonography for her chronic hypertension incidentally showed fetal tachycardia, with a ventricular rate of 257 beats/min. In addition, fetal ascites and polyhydramnios were noted, which was consistent with hydrops. She was given 1 dose of betamethasone before transfer to our quaternary care center. The plan was for continuous fetal monitoring for 24 hours.Upon arrival to triage, she was asymptomatic with normal vital signs and active fetal movement. Basic metabolic panel was within normal limits, and a maternal electrocardiogram (EKG) showed normal sinus rhythm. Betamethasone was initiated for fetal lung maturity given the concern for possible preterm delivery. A representative fetal heart rate tracing is demonstrated in Fig 1, which showed periods of normal fetal sinus rhythm with a baseline of 130 beats/min, moderate variability, and accelerations, as well as periods of tachycardia to 210 beats/min; this tachyarrhythmia is poorly traced.After 24 hours of monitoring, pediatric cardiology performed ultrasonography, which showed atrial flutter with 2:1 conduction (Fig 2) without ventricular dysfunction. Over the course of 24 hours, this tachyarrhythmia was present during ∼50% of fetal monitoring. Pediatric cardiology recommended against treatment, as the arrhythmia was not present during most of the monitoring period and as there was an absence of ventricular dysfunction and hydrops. After completion of the betamethasone course, the patient was discharged from the hospital with outpatient surveillance. Outpatient surveillance with weekly maternal ultrasonography and fetal echocardiography was reassuring, and there was no visualized recurrence of the atrial flutter.This patient was also asymptomatic with normal vital signs and active fetal movement. Maternal serum chemistries were within normal limits, and maternal EKG showed normal sinus rhythm. A representative fetal heart tracing is presented in Fig 3. Ultrasonography confirmed polyhydramnios and ascites (Fig 4). Fetal echocardiography demonstrated supraventricular tachycardia (SVT) with 1:1 conduction and moderate to severe biventricular systolic dysfunction.In this case, pediatric cardiology recommended treatment with flecainide given the concern for evolving hydrops and systolic dysfunction. Prolonged inpatient surveillance was indicated given the need to titrate antiarrhythmic medication. Over the course of several days, the maternal flecainide dose was increased, and a second antiarrhythmic agent, digoxin, was initiated. The betamethasone course was completed. She was monitored inpatient for 1 week, with ultimate resolution of fetal tachycardia (Fig 5). She was discharged from the hospital on flecainide 150 mg every 8 hours and digoxin 0.125 mg every 8 hours, with a plan for outpatient surveillance. The patient was able to tolerate flecainide and digoxin for the remainder of the pregnancy without maternal sequalae. Serial ultrasonography demonstrated interval resolution of the polyhydramnios and ascites. Outpatient surveillance with maternal ultrasonography weekly and fetal echocardiography every 2 weeks was reassuring, and the fetus remained in sinus rhythm.At 38 weeks’ gestation, she underwent induction of labor for chronic hypertension and fetal growth restriction. She had an uncomplicated spontaneous vaginal delivery. Intrapartum, the fetus remained in sinus rhythm, with a normal fetal heart rate on external fetal monitoring.At 38 weeks’ gestation, she presented for a scheduled induction of labor for chronic hypertension and gestational diabetes. She had a spontaneous vaginal delivery that was complicated by postpartum hemorrhage requiring multiple uterotonic medications. Her digoxin was discontinued upon delivery, and flecainide was tapered over 3 days by halving her doses.A female neonate was born weighing 2,335 g with an Apgar score of 7 and 9 at 1 and 5 minutes, respectively. An EKG on the first day after birth showed normal sinus rhythm and age-appropriate right axis deviation. Echocardiography demonstrated occasional ectopy, a moderate atrioventricular canal-type ventricular septal defect, and a small midcavity muscular ventricular septal defect with bidirectional ventricular septal defect flow. No atrial flutter was noted. The newborn had serial heart rate assessments and daily EKGs while in the hospital. After routine discharge, the newborn underwent Holter monitoring without evidence of an arrhythmia.A male neonate was born weighing 3,900 g with an Apgar score of 7 and 8 at 1 and 5 minutes, respectively. He was admitted to the NICU with respiratory distress requiring intubation. An EKG obtained on the day of birth showed normal sinus rhythm without abnormality. Echocardiography demonstrated a patent foramen ovale and patent ductus arteriosus. No arrhythmia was observed postnatally on telemetry. There was no pulmonary edema on chest radiography. He was discharged from the hospital 8 days after birth, with close cardiology follow-up.Fetal arrhythmias occur in 1% to 3% of all pregnancies, most of which are benign with no identifiable maternal symptoms. (1) Fetal arrhythmias can be characterized by premature atrial or ventricular contractions, bradyarrhythmia, or tachyarrhythmia. (2)(3) Bradyarrhythmias are defined as a sustained fetal heart rate under 110 beats/min, whereas tachyarrhythmias are defined as a sustained fetal heart rate above 160 beats/min. (4)Fetal arrhythmias are often first detected on routine fetal ultrasonography or during external fetal monitoring. (4) In our cases, both arrhythmias were detected incidentally during ultrasonographic surveillance of the pregnancy. Once identified, Doppler cardiac ultrasonography and echocardiography are performed to further categorize the fetal arrhythmia and evaluate for any underlying structural cardiac abnormality. (4) In addition, surveillance with fetal rhythm monitoring should be initiated if unconfirmed rhythm disturbances are detected, if there is suspected or known fetal arrhythmia, or if transplacental therapy is indicated. (3) Our discussion focuses on the diagnosis and management specifically of fetal tachyarrhythmias.Fetal tachyarrhythmias occur in less than 0.1% of all pregnancies. (5) Tachyarrhythmias can be further categorized as atrial flutter, SVT, sinus tachycardia, and ventricular tachycardia (VT) or junctional tachycardia. (6) It is estimated that atrial flutter accounts for ∼26% of fetal tachyarrhythmias, whereas SVT accounts for 73% of fetal tachyarrhythmias. (7) The prognosis ranges from benign to lethal, including the potential for progression to fetal heart failure and fetal hydrops. (5) Fetal SVT is more likely to be accompanied by hydrops than atrial flutter. (6) Due to the 50% mortality rate of hydropic fetuses with SVT, medical therapy is often recommended and initiated. Fortunately, in the treatment of the pregnant person with transplacental medications, cardioversion is seen in up to 95% of cases within the first 48 hours of initiation. (8) With cardioversion to sinus rhythm, the rate of mortality is low. (8) Even if complete cardioversion is not achieved antenatally, a slower ventricular rate is preferred as the risk of hydrops is lower with slower ventricular rates. (9)While intervention is not always necessary, the decision to initiate transplacental therapy often involves the gestational age at detection, the presence or absence of hydrops, the type of rhythm, and the expected responsiveness to treatment. The most commonly used agents given to the pregnant person for transplacental treatment include digoxin, flecainide, and sotalol. (5) These medications may be used individually or in combination. There is currently no standardized algorithm for medication management; however, multiple suggested protocols have been published. (5) Only 50% to 70% of fetal SVTs will require treatment postnatally. (1)The effects of medication on the pregnant person are an important aspect of intervention that requires careful counseling about the risks and benefits. For the 3 most commonly used agents, cardiac evaluation of the pregnant person is indicated, and adverse effects on the pregnant person should be discussed before initiation. Digoxin is often the first-line agent used for fetal SVT because of its overall safety profile, rapid absorption, and ability to monitor levels and response. (10) Adverse effects of digoxin on the pregnant person include vision changes, gastrointestinal disturbance (nausea, vomiting, abdominal pain), mental/cognitive symptoms (weakness, confusion, delirium), and abnormal cardiac conduction including premature atrial contractions and atrioventricular block. (11) Therefore, a baseline evaluation of the pregnant person that includes an EKG, electrolyte screening, and renal status is recommended to ensure that there is no underlying cardiac disease or propensity to cardiac conduction abnormalities. Electrolyte abnormalities such as hypomagnesemia or hypokalemia may promote digoxin-induced arrhythmias. In addition, impaired renal function may result in higher than anticipated serum drug levels. Typically, a loading period for digoxin includes serial digoxin levels and daily EKGs to monitor for PR wave prolongation and T wave abnormalities. Involvement of adult cardiac specialists may be necessary. The maintenance dosing depends on the adverse effects on the pregnant person and the fetal response to therapy. Once maintenance dosing is achieved, outpatient surveillance is a reasonable strategy for ongoing pregnancy management.Another antiarrhythmic medication that is used during pregnancy is flecainide. Flecainide affects sodium channels, and, as such, it can prolong depolarization and can slow conduction in the atrioventricular node and the His-Purkinje system. Adverse effects on the pregnant person include gastrointestinal symptoms, central nervous system effects (dizziness, headache, vision changes), palpitations, chest pain, dyspnea, and peripheral edema. (11) EKG changes in the pregnant person that need to be screened for during therapy include PR prolongation, increased QRS duration, first- and second-degree heart block, and T-wave changes. (12) If a pregnant person has preexisting sinus node disease, this medication can also cause profound sinus bradycardia. (12) Like digoxin, flecainide must be used with caution in patients with impaired renal function as clearance is limited and serum concentrations may accumulate quickly leading to drug toxicity. (13) Both the pregnant person and the fetus require inpatient monitoring during flecainide loading; once stability is achieved, outpatient monitoring is coordinated.Sotalol, like flecainide, is cleared by the kidney and can be proarrhythmic. There is a well-described risk of VT associated with QT interval prolongation; therefore, surveillance of the pregnant person via serial EKGs is necessary to screen for QT prolongation and QRS prolongation. (14)(15) Adverse effects of sotalol include nausea, vomiting, dizziness, and lightheadedness. (11)Our comparison of 2 cases highlights the importance of electronic fetal heart monitoring for the management of fetal tachyarrhythmia to better understand the frequency with which arrhythmia occurs. Both ultrasonography and fetal echocardiography are indicated to diagnose the specific type of arrhythmia and evaluate cardiac anatomy as it relates to the arrhythmia. If indicated, fetal treatment can be achieved via transplacental treatment to the pregnant patient. In these case presentations, 1 patient underwent transplacental medication treatment, whereas the other patient did not receive any therapy. Both maternal and neonatal outcomes were reassuring, with resolution of both fetal tachyarrhythmias antenatally. These cases highlight the importance of timely evaluation and collaborative communication with a multidisciplinary team including obstetricians, pediatric cardiology, and neonatology.