An infant boy was born at 36 weeks gestational age by induced vaginal delivery. Abnormal nonstress testing led to subsequent fetal echocardiography, which revealed a ventricular rate of approximately 200 beats per minute and an atrial rate of 450 beats per minute, as calculated by measuring the mechanical events of the cardiac cycle using mitral valve inflow Doppler. There were no signs of heart failure, hydrops fetalis, or abnormalities of cardiac anatomy at the time of imaging. The mother had no personal or family history of cardiovascular disease. Her antenatal serologies were negative, but Group B Streptococcus status was unknown. Prior to induction of labor, the mother was given a single dose of digoxin (only one dose was administered due to planned delivery), and three doses of penicillin G. The infant was delivered with APGAR (Activity, Pulse, Grimace, Appearance, Respiration) scores of 6 at 1 minute and 8 at 5 minutes, and did require administration of continuous positive airway pressure (CPAP). His birth weight was 3.705 kg. Initial physical examination was significant for a heart rate of 198 beats per minute, subcostal retractions, and a II/VI holosystolic murmur. Otherwise, pulses were equal throughout with good capillary refill, lungs were clear to auscultation, and the liver edge was 1 cm below the right costal margin. A blood culture was drawn, and the patient was started on empiric ampicillin and gentamicin. He was admitted to the neonatal intensive care unit (NICU) for management of his prematurity, tachycardia, and respiratory distress.
Diagnosis and NICU Course
Upon NICU admission, a 12-lead electrocardiogram (ECG) confirmed atrial flutter (AFL) with 2:1 atrioventricular (AV) conduction (Figure 1). Echocardiography on the day of birth showed a moderate patent foramen ovale with a left-to-right shunt, and patent ductus arteriosus with a bidirectional shunt. Both atria and the right ventricle (RV) were significantly dilated; the left ventricle (LV) size was within normal limits. RV pressure was elevated (38–40 mm Hg) and tricuspid regurgitation (3 m/s) was present. RV function was significantly depressed, and LV function was borderline. The decision was made to perform direct current cardioversion (DCC) on the day of birth due to significant acidosis and signs of early congestive heart failure. The patient was successfully cardioverted (0.5 J/kg) to normal sinus rhythm after one attempt (Figure 2), loaded with digoxin, and then started on a maintenance dose. The patient was also started on a dopamine intravenous infusion for poor ventricular function. By day 2, he had been weaned off of dopamine. Antibiotics were discontinued after the blood culture yielded no growth for 48 hours. The patient was weaned off of CPAP by day 3, and repeat echocardiogram on day 3 showed normal biventricular function while off of dopamine. However, both atria were still mildly dilated with half-systemic RV pressure. On days 5 and 6, the patient had episodes of tachycardia (190 beats per minute) at a fixed rate that were concerning for recurrent AFL, thus propranolol was started. After dose adjustment of digoxin to therapeutic levels (1.5–2 ng/mL) and maintenance of normal sinus rhythm confirmed by telemetry and ECG, the patient was discharged on day 11 with a maintenance antiarrhythmic regimen of propranolol and digoxin, as well as follow-up observation with a cardiologist.
An electrocardiogram showing atrial flutter with 2:1 atrioventricular conduction. The red arrows point to “saw tooth” flutter waves. Ventricular rate is approximately 185 beats per minute.
An electrocardiogram status-post direct current cardioversion (normal sinus rhythm). Ventricular rate is approximately 165 beats per minute.
Tachycardia in the fetus warrants prompt evaluation by a cardiologist, as lack of treatment results in up to a 20% mortality rate.1 The most common causes of both fetal and neonatal tachycardia are sinus tachycardia and supraventricular tachycardia (SVT). Sinus tachycardia originates from the sinoatrial node with a rate above the upper limit of normal for age, specifically, 166 beats per minute in the first week after birth. Common causes of sinus tachycardia include infection, anemia, hyperthyroidism, or medications such as beta-adrenergic agonists. Unlike sinus tachycardia, which usually presents with a rate of 160 to 200 beats per minute, SVT usually presents with a rate of 220 to 300 beats per minute and is typically, but not always, characterized by narrowed QRS complexes. SVT rhythms can originate at or above the AV node.
SVT in neonates is typically caused by re-entrant circuits; the most common type is atrioventricular re-entrant tachycardia (AVRT). AVRT is characterized by an accessory pathway outside the AV node. This pathway connects the atria and ventricles to form a re-entrant circuit. In neonates, the most common direction of conduction is antegrade (from the atria to the ventricles) through the AV node, and then retrograde (from the ventricles to the atria) through the accessory pathway. On an ECG, this manifests as a short PR interval and narrowed QRS complex; however, the presence of a widened QRS and delta wave (slurred upstroke of the QRS complex on resting ECG) is pathognomonic for Wolff-Parkinson-White syndrome, a subtype of AVRT.
AFL is a type of SVT with an automatic focus above the AV node, which causes an atrial rate of 240 to 360 beats per minute and a “saw tooth” appearance on ECG. It is important to note, however, that “saw tooth” waves may be difficult to observe in a patient with tachycardia. Although less common than AVRT, AFL accounts for up to one-third of clinically relevant fetal tachyarrhythmias.2 As shown in our illustrative case, 2:1 AV conduction is most common in fetal and neonatal AFL2–4; therefore, the ventricular rate is typically slower than that of AVRT. However, AV conduction can also be 1:1 or variable; the former is associated with higher mortality in-utero due to an increased incidence of hydrops,3,4 and the latter leads to an irregular ventricular rate. On the echocardiogram, bilateral atrial dilatation is the most common finding of AFL, followed by decreased ventricular function, and finally, AV valve regurgitation.4 AFL is usually associated with an anatomically normal heart, although an accessory AV pathway is occasionally implicated. In such an instance, coexisting AVRT is often identified.
In cases of fetal AFL, a decision for delivery is dependent on gestational age, fetal lung maturity, failure of medical treatment, and the presence of hydrops fetalis (defined as fluid accumulation in at least two fetal compartments). Fetal lungs mature around 35 weeks gestation and prematurity remains the most significant risk factor for postnatal AFL-associated mortality; therefore, AFL is often managed medically even in the presence of hydrops fetalis.1 Maternal digoxin therapy remains the most common treatment, although some literature suggests that sotalol may be preferred due to better placental transfer.3,5 However, a recent nonrandomized controlled trial demonstrated higher efficacy of transplacental digoxin or flecainide compared to sotalol.6 Medical management of fetal tachycardia can be up to 80% efficacious, even in hydrops fetalis cases.1
Postnatal AFL is most successfully managed with DCC. Whereas defibrillation involves a shock that is randomly delivered during the cardiac cycle, DCC is the delivery of energy that is synchronized with the QRS complex. The delivery of a shock to the excitable tissue of an accessory pathway leads to a refractory period that does not allow the electrical signal to propagate. According to the most recent Pediatric Advanced Life Support guidelines,7 the first dose should be administered at 0.5 J/kg, with subsequent doses given at 2 J/kg. The clinically stable patient, as in our case, should receive analgesia and sedation prior to cardioversion. Compared to DCC, transesophageal pacing appears to be less effective for the treatment of AFL and carries the risk of conversion to atrial fibrillation. However, it can be useful in cases refractory to DCC.4,8 Digoxin monotherapy has only an approximate 33% efficacy rate,4,9 and is also contraindicated in the setting of concomitant AVRT. If the patient displays signs or symptoms of congestive heart failure, DCC should be used as first-line therapy.
Generally, uncomplicated AFL rarely recurs after conversion to normal sinus rhythm, and long-term prognosis is excellent. The presence of an additional arrhythmia, most commonly AVRT, is a well-established risk factor for AFL recurrence as well as for medically refractory AFL. Most studies report an 8% to 30% incidence of coexisting AVRT,4,5 and in such cases patients will require long-term antiarrhythmic therapy, with the most common agents being propranolol, sotalol, and flecainide. The mean duration of therapy after discharge is usually around 9 months, a somewhat arbitrarily designated length of time.5 Otherwise, there is no indication for additional medical therapy for a patient with uncomplicated AFL who has undergone successful cardioversion and maintained a normal sinus rhythm.
After AVRT, AFL is the second most common tachyarrhythmia in the fetal and neonatal period. Fetal AFL can be treated medically to maximize gestational age, whereas neonatal AFL is most effectively treated with DCC. Relapse is rare after successful cardioversion, unless a concomitant arrhythmia is present.
- Van Engelen AD, Weijtens O, Brenner JI, et al. Management outcome and follow-up of fetal tachycardia. J Am Coll Cardiol. 1994;24(5):1371–1375. doi:10.1016/0735-1097(94)90122-8 [CrossRef]
- Jaeggi E, Fouron JC, Drblik SP. Fetal atrial flutter: diagnosis, clinical features, treatment and outcome. J Pediatr. 1998;132(2):335–339. doi:10.1016/S0022-3476(98)70455-X [CrossRef]
- Lisokowski LA, Verheijen PM, Benatar AA, et al. Atrial flutter in the perinatal age group: diagnosis, management and outcome. J Am Coll Cardiol. 2000;35(3):771–777. doi:10.1016/S0735-1097(99)00589-6 [CrossRef]
- Texter KM, Kertesz NJ, Friedman RA, Fenrich AL Jr, . Atrial flutter in infants. J Am Coll Cardiol. 2006;48(5):1040–1046. doi:10.1016/j.jacc.2006.04.091 [CrossRef]
- Moodley S, Sanatani S, Potts JE, Sandor GG. Postnatal outcome in patients with fetal tachycardia. Pediatr Cardiol. 2013;34(1):81–87. doi:10.1007/s00246-012-0392-7 [CrossRef]
- Jaeggi ET, Carvalho JS, De Groot E, et al. Comparison of transplacental treatment of fetal supraventricular tachyarrhythmias with digoxin, flecainide and sotalol: results of a nonrandomized multicenter study. Circulation. 2011;124(16):1747–1754. doi:10.1161/CIRCULATIONAHA.111.026120 [CrossRef]
- Kleinman ME, Chameides L, Schexnayder SM, et al. Part 14: pediatric advanced life support: 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2010;122(18 Suppl 3):S876–S908. doi:10.1161/CIRCULATIONAHA.110.971101 [CrossRef]
- Killen SAS, Fish FA. Fetal and neonatal arrhythmias. NeoReviews. 2008;9(6):242–252. doi:10.1542/neo.9-6-e242 [CrossRef]
- Casey FA, McCrindle BW, Hamilton RM, Gow RM. Neonatal atrial flutter: significant early morbidity and excellent long-term prognosis. Am Heart J. 1997;133(3):302–306. doi:10.1016/S0002-8703(97)70224-2 [CrossRef]