Fetal Long QT Syndrome - Challenges in Perinatal Management: A Review and Case Report. Induction of Labor and Vaginal Birth Under Continuous Magnesium Therapy.

Congenital LQTS is an often undetected inherited cardiac channel dysfunction and can be a reason for intrauterine fetal demise. It can present in utero as CTG and ultrasound abnormalities, i. e., bradycardia, ventricular tachycardia, or fetal hydrops. Diagnosis is made by CTG, echocardiography, or fMCG. Intrauterine therapy with a ß blocker and i. v. magnesium should be started. Our objective was to examine the current knowledge about diagnosis and treatment of LQTS and in particular to highlight the opportunity of vaginal birth under continuous intravenous magnesium therapy. Therefore, a thorough MEDLINE and Google Scholar search was conducted. Randomized controlled trials, meta-analyses, prospective and retrospective cohort trials, and case reports were considered. We showed the possibility of vaginal delivery under continuous magnesium therapy in a case of suspected fetal LQTS. A stepwise concept for diagnosis, monitoring, and peripartum management in low, intermediate, and high risk cases of fetal LQTS is presented. If risk is low or intermediate, a vaginal delivery under continuous monitoring is reasonable. Induction of labor at term should be evaluated.

Refractory supraventricular fetal tachycardia as a cause of non-immune hydrops: management conundrum.

Supraventricular tachyarrhythmia (SVT) is the most common form of fetal tachyarrhythmias. The presentation can vary from ill-defined, non-sustained episodes of tachyarrhythmia to frank non-immune hydrops. The standard of care is transplacental therapy by treating the mother with oral antiarrhythmic drugs, followed by direct fetal therapy in refractory cases. We report a case of primigravida in her late 20s, who presented at 28.1 weeks of gestation with fetal hydrops and SVT. She was initially managed with oral digoxin and flecainide, but due to worsening hydrops, risk of fetal demise and extreme prematurity, further management by direct fetal therapy was given in terms of intramuscular digoxin and intraperitoneal flecainide. Following which, the fetus had a favourable outcome. This case highlights the possible role of direct fetal therapy in refractory cases of SVT.

Intrauterine management and outcomes of persistent fetal atrial flutter: A case report.

BACKGROUND: Fetal atrial flutter (AF), accounting for 30% of all fetal tachyarrhythmias, predominantly (over 80%) manifests as a 2:1 atrioventricular conduction. Swift referral and timely intervention become imperative in instances of severe persistent arrhythmia. CASE PRESENTATION: We discuss the case of a 32-year-old multiparous Chinese woman, at 30+2 weeks of gestation, wherein an ultrasonographic examination revealed persistent fetal AF (atrial rate ranging from 219 to 445 beats/min and ventricular rate from 219 to 228 beats/min, with a 2:1 or 1:1 down transmission) and minor ascites. Despite the maternal ingestion of digoxin and sotalol, the fetal heart rhythm remained uncorrected. Following this, at 32+3 weeks of gestation, an intramuscular injection of cedilanid, guided by ultrasound, was administered to the fetus. Postoperatively, the fetal ventricular rate demonstrated a decline after 6 days, and the ascites resolved. Subsequently, at 33+3 weeks, a cesarean section was necessitated due to maternal intolerance to the medication, resulting in the delivery of the infant. Remarkably, the infant's cardiac rhythm spontaneously converted to sinus rhythm within 5 min of birth. A follow-up conducted 1 year postpartum revealed no recurrence of AF. CONCLUSIONS: This case illustrates that in the event of transplacental drug treatment failure, intrauterine therapeutic intervention should be considered. Moreover, it highlights the encouraging prognosis associated with fetal AF, as the cardiac rhythm spontaneously reverted to sinus rhythm postbirth in this instance.

Successful intra-amniotic levothyroxine treatment for fetal goitrous hypothyroidism in a triplet pregnancy.

We report an extremely challenging case of fetal goitrous hypothyroidism involving all three fetuses of a triplet pregnancy in which successful fetal treatment led to a favorable pregnancy outcome. The patient had a trichorionic, triamniotic triplet pregnancy and was referred to us at 24 weeks gestation after goiters affecting all three fetuses and polyhydramnios involving two fetuses were noted. Immediately before the conception, she underwent hysterosalpingography with an oil-soluble iodinated contrast medium. After the diagnosis of fetal hypothyroidism was made, intra-amniotic injection of levothyroxine was performed for two fetuses with polyhydramnios 3 times between 28 and 31 weeks gestation. The goiters shrunk and the polyhydramnios improved in response to the in utero treatment. No complications occurred. Cesarean section was performed at 33 weeks gestation. None of the three neonates developed respiratory insufficiency. Our experience suggested that successful intrauterine treatment is possible for fetal goitrous hypothyroidism, even in a triplet pregnancy. The indication, treatment timing, and diagnostic and assessment strategies should be carefully discussed to minimize puncture-related complications.

Fetal Arrhythmia Diagnosis and Pharmacologic Management.

One of the most successful achievements of fetal intervention is the pharmacologic management of fetal arrhythmias. This management usually takes place during the second or third trimester. While most arrhythmias in the fetus are benign, both tachy- and bradyarrhythmias can lead to fetal hydrops or cardiac dysfunction and require treatment under certain conditions. This review will highlight precise diagnosis by fetal echocardiography and magnetocardiography, the 2 primary means of diagnosing fetuses with arrhythmia. Additionally, transient or hidden arrhythmias such as bundle branch block, QT prolongation, and torsades de pointes, which can lead to cardiomyopathy and sudden unexplained death in the fetus, may also need pharmacologic treatment. The review will address the types of drug therapies; current knowledge of drug usage, efficacy, and precautions; and the transition to neonatal treatments when indicated. Finally, we will highlight new assessments, including the role of the nurse in the care of fetal arrhythmias. The prognosis for the human fetus with arrhythmias continues to improve as we expand our ability to provide intensive care unit-like monitoring, to better understand drug treatments, to optimize subsequent pregnancy monitoring, to effectively predict timing for delivery, and to follow up these conditions into the neonatal period and into childhood. Coordinated initiatives that facilitate clinical fetal research are needed to address gaps in knowledge and to facilitate fetal drug and device development.

Oral diazoxide versus placebo for severe or recurrent neonatal hypoglycaemia: Neonatal Glucose Care Optimisation (NeoGluCO) study - a randomised controlled trial.

INTRODUCTION: Infants with severe or recurrent transitional hypoglycaemia continue to have high rates of adverse neurological outcomes and new treatment approaches are needed that target the underlying pathophysiology. Diazoxide is one such treatment that acts on the pancreatic ß-cell in a dose-dependent manner to decrease insulin secretion. METHODS AND ANALYSIS: Phase IIB, double-blind, two-arm, parallel, randomised trial of diazoxide versus placebo in neonates ≥35 weeks' gestation for treatment of severe (blood glucose concentration (BGC)<1.2 mmol/L or BGC 1.2 to <2.0 mmol/L despite two doses of buccal dextrose gel and feeding in a single episode) or recurrent (≥3 episodes <2.6 mmol/L in 48 hours) transitional hypoglycaemia. Infants are loaded with diazoxide 5 mg/kg orally and then commenced on a maintenance dose of 1.5 mg/kg every 12 hours, or an equal volume of placebo. The intervention is titrated from the third maintenance dose by protocol to target BGC in the range of 2.6-5.4 mmol/L. The primary outcome is time to resolution of hypoglycaemia, defined as the first point at which the following criteria are met concurrently for ≥24 hours: no intravenous fluids, enteral bolus feeding and normoglycaemia. Groups will be compared for the primary outcome using Cox's proportional hazard regression analysis, expressed as adjusted HR with a 95% CI. ETHICS AND DISSEMINATION: This trial has been approved by the Health and Disability Ethics Committees of New Zealand (19CEN189). Findings will be disseminated in peer-reviewed journals, to clinicians and researchers at local and international conferences and to the public. TRIAL REGISTRATION NUMBER: ACTRN12620000129987.

Treatment of Severe Fetal Ebstein's Anomaly with Prenatal Nonsteroidal Anti-Inflammatory Therapy.

INTRODUCTION: Prenatally diagnosed Ebstein's anomaly with tricuspid valve dysplasia (EA/TVD) is a rare and high-risk congenital heart malformation with limited effective treatments. We report a case of severe fetal EA with hydrops treated with modest doses of nonsteroidal anti-inflammatory drug (NSAID) therapy, resulting in reversal of hydrops and a favorable fetal outcome. CASE PRESENTATION: Fetal heart defects included an inferiorly displaced tricuspid valve, severe tricuspid regurgitation, significantly dilated right atrium, and hypoplastic pulmonary valve with moderate regurgitation resulting in a circular shunt across the ductus arteriosus. Maternal indomethacin therapy was initiated at 31+5 weeks gestation due to the development of fetal hydrops as demonstrated by the presence of a pericardial effusion and ascites. Indomethacin therapy resulted in the desired restriction of the ductus arteriosus and resolution of fetal hydrops. Maternal therapy was transitioned to ibuprofen and serial fetal echocardiograms ensured continued ductal restriction. Delivery occurred via cesarean at 36+3 weeks. The neonate did not require immediate cardiac surgical intervention and was discharged home with close follow-up. DISCUSSION/CONCLUSION: A lower dose of prenatal NSAID therapy effected successful ductal restriction and hemodynamic mitigation of the circular shunt, resulting in reversal of hydrops and avoidance of postnatal cardiac surgical intervention.

Interferon Lambda Signals in Maternal Tissues to Exert Protective and Pathogenic Effects in a Gestational Stage-Dependent Manner.

Interferon lambda (IFN-λ) (type III IFN) is constitutively secreted from human placental cells in culture and reduces Zika virus (ZIKV) transplacental transmission in mice. However, the roles of IFN-λ during healthy pregnancy and in restricting congenital infection remain unclear. Here, we used mice lacking the IFN-λ receptor (Ifnlr1-/-) to generate pregnancies lacking either maternal or fetal IFN-λ responsiveness and found that the antiviral effect of IFN-λ resulted from signaling exclusively in maternal tissues. This protective effect depended on gestational stage, as infection earlier in pregnancy (E7 rather than E9) resulted in enhanced transplacental transmission of ZIKV. In Ifnar1-/- dams, which sustain robust ZIKV infection, maternal IFN-λ signaling caused fetal resorption and intrauterine growth restriction. Pregnancy pathology elicited by poly(I·C) treatment also was mediated by maternal IFN-λ signaling, specifically in maternal leukocytes, and also occurred in a gestational stage-dependent manner. These findings identify an unexpected effect of IFN-λ signaling, specifically in maternal (rather than placental or fetal) tissues, which is distinct from the pathogenic effects of IFN-αß (type I IFN) during pregnancy. These results highlight the complexity of immune signaling at the maternal-fetal interface, where disparate outcomes can result from signaling at different gestational stages. IMPORTANCE Pregnancy is an immunologically complex situation, which must balance protecting the fetus from maternal pathogens with preventing maternal immune rejection of non-self fetal and placental tissue. Cytokines, such as interferon lambda (IFN-λ), contribute to antiviral immunity at the maternal-fetal interface. We found in a mouse model of congenital Zika virus infection that IFN-λ can have either a protective antiviral effect or cause immune-mediated pathology, depending on the stage of gestation when IFN-λ signaling occurs. Remarkably, both the protective and pathogenic effects of IFN-λ occurred through signaling exclusively in maternal immune cells rather than in fetal or placental tissues or in other maternal cell types, identifying a new role for IFN-λ at the maternal-fetal interface.

Outcome of Antibody-Mediated Fetal Heart Disease With Standardized Anti-Inflammatory Transplacental Treatment.

Background Transplacental fetal treatment of immune-mediated fetal heart disease, including third-degree atrioventricular block (AVB III) and endocardial fibroelastosis, is controversial. Methods and Results To study the impact of routine transplacental fetal treatment, we reviewed 130 consecutive cases, including 108 with AVB III and 22 with other diagnoses (first-degree/second-degree atrioventricular block [n=10]; isolated endocardial fibroelastosis [n=9]; atrial bradycardia [n=3]). Dexamethasone was started at a median of 22.4 gestational weeks. Additional treatment for AVB III included the use of a ß-agonist (n=47) and intravenous immune globulin (n=34). Fetal, neonatal, and 1-year survival rates with AVB III were 95%, 93%, and 89%, respectively. Variables present at diagnosis that were associated with perinatal death included an atrial rate <90 beats per minute (odds ratio [OR], 258.4; 95% CI, 11.5-5798.9; P<0.001), endocardial fibroelastosis (OR, 28.9; 95% CI, 1.6-521.7; P<0.001), fetal hydrops (OR, 25.5; 95% CI, 4.4-145.3; P<0.001), ventricular dysfunction (OR, 7.6; 95% CI, 1.5-39.4; P=0.03), and a ventricular rate <45 beats per minute (OR, 12.9; 95% CI, 1.75-95.8; P=0.034). At a median follow-up of 5.9 years, 85 of 100 neonatal survivors were paced, and 1 required a heart transplant for dilated cardiomyopathy. Cotreatment with intravenous immune globulin was used in 16 of 22 fetuses with diagnoses other than AVB III. Neonatal and 1-year survival rates of this cohort were 100% and 95%, respectively. At a median age of 3.1 years, 5 of 21 children were paced, and all had normal ventricular function. Conclusions Our findings reveal a low risk of perinatal mortality and postnatal cardiomyopathy in fetuses that received transplacental dexamethasone±other treatment from the time of a new diagnosis of immune-mediated heart disease.

Favourable outcome for hydrops or cardiac failure associated with fetal tachyarrhythmia: a 20-year review.

BACKGROUND: Prognosis of fetuses with hydrops and tachyarrhythmia has been portrayed as poor in most published reports. This might lead to biased counselling, unnecessary caesarean section, preterm delivery, and even termination of pregnancy. AIMS: To evaluate contemporary fetal and postnatal outcomes of hydropic fetuses with fetal tachyarrhythmia when it is treated effectively and monitored systematically. METHODS: This is a retrospective review of a single centre experience at the University Hospital of Wales over a 20-year period. All fetuses received high doses of flecainide and digoxin combination treatment. Tachycardia response rate, time to arrhythmia and hydrops resolution, fetal and postnatal morbidity, and mortality rates were analysed. RESULTS: Twenty fetuses were diagnosed with hydrops fetalis and received treatment. The mechanism of fetal tachyarrhythmia was supraventricular tachycardia in thirteen and atrial flutter in eight cases. Among the 20 fetuses treated, the overall tachycardia response rate was 90% (18/20) with the restoration of sinus rhythm in 85% (17/20) of the cases. The median time to restore sinus rhythm or to rate control of the arrhythmia was 1.5 days (range 12 hours to 13 days). Hydrops resolved in 17 of the 20 fetuses, with a median time of 12 days (range 3-21 days). Four fetuses went into spontaneous preterm birth and one fetus was delivered early due to worsening hydrops. No significant neurological morbidity was observed in surviving neonates and infants on clinical examination. There was one postnatal death due to respiratory complications of prematurity in the non-responsive supraventricular tachycardia case. CONCLUSIONS: High-dose flecainide and digoxin combination offers effective treatment strategy in fetuses with hydrops and tachyarrhythmia with favourable outcomes. This study may guide more realistic counselling for pregnancies complicated by tachyarrhythmia and hydrops.

Fetal Supraventricular Tachycardia: What the Adult Cardiologist Needs to Know.

Fetal supraventricular tachycardia management is challenging, with consequences for both the fetus and the mother. If left untreated, fetal hydrops may ensue, at which point delivery and treatment of the arrhythmia is preferred. However, if the fetus is not at term nor near-term, significant doses of antiarrhythmics may be needed to achieve adequate transplacental bioavailability. Although digoxin has classically been the mainstay of treatment, the use of flecainide or sotalol as monotherapy or in combination with digoxin is being studied. Interdisciplinary team management and shared decision-making between the physician and patient are key to achieving successful outcomes. Adult cardiologists, particularly inpatient consultation services or through burgeoning cardio-obstetrics programs, may, in some practice settings, be asked to evaluate or comanage pregnant women with fetal arrhythmia.

Management of Fetal Supraventricular Tachycardia: Case Series from a Tertiary Perinatal Cardiac Center.

BACKGROUND: Fetal supraventricular tachycardia is a relatively uncommon cardiac rhythm abnormality which is often associated with adverse perinatal outcomes if untreated. Although there are several treatment modalities and protocols in use globally, there is no consensus as to the most effective antiarrhythmic to manage this condition. AIM: This study aimed to evaluate perinatal outcomes following prenatal maternal therapy for fetal supraventricular tachycardia. MATERIALS AND METHODS: This was a 20-year retrospective cohort study. Institutional records were reviewed for antenatal therapy choice and maternal and fetal outcomes. RESULTS: Sixty-nine cases met diagnostic criteria for fetal SVT, of which 56 (81%) received maternal antiarrhythmic therapy. Digoxin was the most common, but least effective, first-line therapy in 28 patients, achieving successful rate reversion in 35.7%. Thirty-one patients (55%) required second-line therapy, and this was most successful with digoxin and flecainide polytherapy achieving rate reversion in 17 of 18 cases (94.5%) at a median of 3 days (1.5-7). Hydrops was present in 23 (33%) cases at initial presentation, 16 of which achieved rate reversion. There was minimal difference in treatment efficacy comparing single- or multiple-agent treatment in the setting of hydrops (50% vs. 42.8%). Side effects occurred in 14/56 treated patients (25%) but were severe in only 8 (14.3%) women, most commonly with digoxin and flecainide polytherapy (6 of 8 cases). There were 3 (4%) fetal deaths amongst the study cohort. CONCLUSIONS: Digoxin and flecainide polytherapy were well tolerated and successfully achieved rhythm and rate control in fetuses with prenatally diagnosed supraventricular tachycardia. The presence of hydrops was a poor prognostic feature.

Prenatal Sirolimus Treatment for Rhabdomyomas in Tuberous Sclerosis.

BACKGROUND: In tuberous sclerosis, most cardiac rhabdomyomas regress spontaneously. In some cases, the tumors can cause life-threatening hemodynamic compromise requiring subsequent surgical resection. The mechanistic target of rapamycin inhibitors everolimus and sirolimus have shown to be effective treatments for multiple conditions. There are four reports of off-label treatment with transplacental sirolimus for fetal rhabdomyomas due to tuberous sclerosis complex. The optimal dosing regimen is unknown. METHODS: We reviewed the medical records of all patients treated prenatally with sirolimus for rhabdomyomas. All fetuses had a clinical and molecular diagnosis of tuberous sclerosis complex (2012 Consensus Diagnostic Criteria, including a positive genetic test). Clinical history, mechanistic target of rapamycin inhibitor dosing and levels, outcome, and adverse events were reviewed after initiation of sirolimus treatment. RESULTS: Three fetuses were treated with maternal sirolimus. Dosing regimens and subsequent trough levels differed from 1 mg/day to 6 mg/day and <1.0 ng/mL to 12.2 ng/mL. Cardiac rhabdomyomas gradually shrank in all patients. Growth restriction was noted in one patient. No severe adverse events occurred during the treatment period. CONCLUSIONS: Maternal sirolimus appears to be a safe treatment option in prenatally detected rhabdomyomas with possible need for intervention. Follow-up visits with fetal ultrasound, echocardiography, and laboratory work should be performed weekly during the treatment period. The optimal dosing and trough level timepoints remain unclear. Based on our results, we recommend a sirolimus starting dose of at least 2 mg/m2/day, preferably 3-3.5 mg/m2/day to achieve a target trough level of 10-12 ng/mL.

Association of Fetal Atrial Flutter with Neonatal Atrioventricular Re-entry Tachycardia Involving Accessory Pathway: A Link to be Remembered.

To investigate prenatal and postnatal outcomes of atrial flutter and its association with the development of a second tachycardia, following restoration of sinus rhythm, in the fetus or newborn. This study is a retrospective review of all fetuses that presented with atrial flutter from January 2001 to December 2019 at the University Hospital of Wales, Cardiff, UK. The specific type of arrhythmia, its time of appearance and clinical characteristics, echocardiographic findings, medical management, and postnatal outcomes were evaluated. Sixteen fetuses were diagnosed with atrial flutter (AFL). Thirteen fetuses had persistent AFL and three fetuses had intermittent AFL. Seven patients had hydrops, of which one had Ebstein's anomaly and the other six had normal hearts. Three of the fetuses that presented with AFL were diagnosed at 20, 21, and 23 weeks' gestation and the remainder were diagnosed in the third trimester. Thirteen patients with AFL received antiarrhythmic drugs and three were delivered without any treatment. Five fetuses with AFL developed atrioventricular reciprocating tachycardia following DC cardioversion after birth, and four of them exhibited pre-excitation on the ECG. These five patients (31.3%) required postnatal antiarrhythmic treatment for up to 2 years. Pre-excitation disappeared in two patients during follow-up and two asymptomatic patients with neonatal pre-excitation required accessory pathway ablation. Fetal atrial flutter has a strong association with atrioventricular reciprocating tachycardia and ventricular pre-excitation in the neonatal period. Therefore, electrocardiograms should be carefully reviewed in newborns following the initial resolution of atrial flutter.

Challenge of managing opposing rhythms in a mother and fetus.

INTRODUCTION: We report a case of a fetus with complex congenital heart disease and supraventricular tachycardia in the setting of maternal high grade atrioventricular block at 26 weeks' gestation. METHODS AND RESULTS: Electroanatomic mapping allowed successful implantation of a permanent pacemaker to provide adequate back-up pacing in the mother with zero radiation exposure, thus allowing safe delivery of transplacental anti-arrhythmic medications to reduce the fetal arrhythmia burden and optimize the fetal ventricular rate. CONCLUSION: This is the first reported case of using electroanatomic mapping, with zero fluoroscopy use, for pacemaker lead placement and for a novel indication.

Fetal ventricular tachycardia: betablockers should be the first line treatment.

Ventricular tachycardia (VT) is a rare cause of tachycardia during the fetal life. Coexistence of VT with sinus bradycardia or second-degree heart block strongly suggests long QT syndrome (LQTS) [1-3] and needs to administrate to the mother beta-blockers and in some cases magnesium sulfate [1,2,4]. When there is no argument for a LQTS several drugs have been proposed, most of them contraindicated in LQTS. We present a case of fetal LQTS with fetal VT and cardiac insufficiency with no antenatal clue for LQTS, successfully managed with propranolol. Thus, we suggest that in case of isolated fetal VT (i.e. without tumor or cardiomyopathy) beta blockers (excluding sotalol) should be the first line treatment since LQTS can be a possible cause for the dysrhythmia.

Immune-Mediated Fetal Complete Atrioventricular Block: Can Dexamethasone Therapy Revert the Process?

BACKGROUND: Fetal complete atrioventricular block (CAVB) is usually autoimmune mediated. The risk of developing CAVB is 2% to 3% in anti-Ro/SS-A seropositive pregnancies and it increases 10 times after previous CAVB in siblings. Despite being a rare complication, CAVB carries a 20% mortality rate and substantial morbidity, as about 65% of newborns will eventually need life-long pacing. Once found, fetal CAVB is almost always irreversible, despite aggressive immunotherapy. This poor outcome prompted some research groups to address this situation. All groups followed anti-Ro/SS-A seropositive pregnancies on a weekly basis during the second trimester of pregnancy and tried to detect first degree atrioventricular block (AVB) using accurate echocardiographic tools, assuming they may characterize the initiation of the immune damage to the A-V conduction system, at which point the process might still be reversible. Some of the groups treated fetuses with first degree AVB with maternal oral fluorinated steroids. We summarized the results of all groups, including our group. We describe a case of a fetus that developed CAVB 6 days after normal sinus rhythm (NSR), who under aggressive dexamethasone therapy gradually reverted to NSR. This fetus had a previous sibling with CAVB. We assumed the immune damage to the conduction system in this small group of fetuses with a previous CAVB sibling may have occurred more quickly than usual. We therefore recommend a twice-weekly follow-up with these fetuses.

Prenatal Treatment of Congenital Cytomegalovirus With Valganciclovir: A Case Report.

Cytomegalovirus (CMV) is the most common congenital infection and infectious cause of fetal anomaly and neurologic injury. However, treatment strategies for congenital CMV (cCMV) infection during pregnancy remain elusive. We report a case of hydrops fetalis secondary to cCMV infection with minimal sequelae after maternal and subsequent neonatal treatment with valganciclovir.

Fetal arrhythmias: prenatal evaluation and intrauterine therapeutics.

INTRODUCTION: Fetal arrhythmias are a common phenomenon with rather complicated etiologies. Debates remain regarding prenatal diagnosis and treatment of fetal arrhythmias. METHODS: The literature reporting on prenatal diagnosis and treatment of fetal arrhythmias published in the recent two decades were retrieved, collected and analyzed. RESULTS: Both fetal magnetocardiogram and electrocardiogram provide information of cardiac time intervals, including the QRS and QT durations. M-mode ultrasound detects the AV and VA intervals, fetal heart rate, and AV conduction. By using Doppler ultrasound, simultaneous recording of the atrial and ventricular waves can be obtained. Benign fetal arrhythmias, including premature contractions and sinus tachycardia, do not need any treatment before and after birth. Sustained fetal arrhythmias that predispose to the occurrence of hydrops fetalis, cardiac dysfunction or eventual fetal demise require active treatments. Intrauterine therapy of fetal tachyarrhythmias has been carried out by the transplacental route. If maternal transplacental treatment fails, intraumbilical, intraperitoneal, or direct fetal intramuscular injection of antiarrhythmic agents can be attempted. CONCLUSIONS: The outcomes of intrauterine therapy of fetal tachyarrhythmias depend on the types or etiology of fetal arrhythmias and fetal conditions. Most are curable to a transplacental treatment by the first-line antiarrhythmic agents. Fetal cardiac pacings are effective methods to restore sinus rhythm in drug-resistant or hemodynamically compromised cases. Immediate postnatal pacemaker implantation is warranted in refractory cases.