Main findings and interpretations:
Bradyarrhythmias and ectopies:
Bradyarrhythmias emerged as the predominant fetal arrhythmia (23/40) in our study, followed by irregular rhythms (9/40) and fetal tachyarrhythmias (8/40). This finding diverges from previous studies8-10 where fetal arrhythmias manifested commonly as irregular rhythms and were mostly deemed benign with minimal impact on fetal hemodynamics and often resolve spontaneously without intervention. However, among the cases of irregular rhythms also we found 5/9 cases associated with SHD, leading to adverse outcomes such as one IUD, one MTP for complex cardiac anomaly and one infant mortality. We also saw a case of PAC with a bigeminal pattern which progressed to SVT. This highlights the need for careful monitoring and proactive management of fetal cardiac rhythm abnormalities, even when irregular rhythms are present.
Our study reveals that only 26.1% (6/23) of fetal bradyarrhythmia cases were associated with structural cardiac anomalies, contrasting the literature reports11,12 where such associations were seen in approximately half of the cases. Moreover, both maternal SLE and anti-Ro/La antibody positivity was observed in 39.1% (9/23) of fetal bradyarrhythmia cases , emphasizing the need for heightened awareness of maternal health conditions impacting fetal cardiac rhythm and the importance of screening and early intervention in at-risk populations.
Management of fetal bradyarrhythmia poses unique challenges, especially in cases of CHB where an expectant approach is primarily employed, as there is no documented evidence of reversing an established third-degree block.5,16 Options like beta-adrenergic agents, immunoglobulin, and plasmapheresis are not preferred due to unclear efficacy and potential maternal risks.17-19,21,22 A study by Jaeggi et al.20suggested a survival rate above 90% for antibody-related CHB if maternal high-dose dexamethasone was initiated at the time of anomaly diagnosis and maintained throughout pregnancy. Another meta-analysis in 2018, including five different observational studies with second-degree immune-mediated CHB, concluded that the use of fluorinated glucocorticoids should not be discouraged unless more robust evidence is available.16 In our study, all cases with CHB (16/40) and AV block (4/40) received treatment with dexamethasone until delivery, and HCQ was added for cases with SLE. There were in total 14/20 live births among these cases, supporting existing literature that emphasizes the positive role of dexamethasone in improving outcomes in such cases. Similarly, in cases of isolated atrioventricular (AV) block, early initiation of treatment and close monitoring contribute to favorable outcomes, as illustrated by successful reversion to sinus rhythm in cases managed expectantly.
Tachyarrhythmias
Fetal tachyarrhythmias, occurring in 0.4 to 0.6% of pregnancies,23 can lead to severe complications if left untreated, including nonimmune hydrops, premature delivery, fetal demise, and perinatal morbidities. However, the requirement for therapeutic intervention in this condition remains a subject of ongoing debate, centered on the natural progression of the disease. Divergent opinions range from advocating non-intervention approach to aggressive pharmacotherapeutic intervention. Transplacental treatment by indirect drug administration to the mother appears to be the most preferred approach.23,24
SVT stands out as the most common contributor, accounting for 70-75% of cases, followed by atrial flutter, which contributes to 25-30%.25 Our study aligns with this pattern, with SVT being the predominant contributor (62.5%, 5/8). While fetal arrhythmias are typically isolated findings, around 5% of cases may also involve congenital heart diseases.26,27 In our study, all identified tachyarrhythmias were isolated without associated SHD or tumors.
The presence of hydrops also significantly influences management and outcomes, as it indicates an impact on the cardiovascular system, reducing ventricular filling and cardiac output.28 In this study, hydrops fetalis was observed in 50% (4/8) of fetal tachyarrhythmia cases. The primary goal of fetal therapy is to achieve the prevention or resolution of hydrops either through conversion to sinus rhythm or ventricular rate control.29,30Transplacental administration of antiarrhythmic drugs is a commonly employed and effective approach, with the primary aim of preventing or resolving hydrops.23,24 Although no standardized protocol exists for drug selection or doses, successful outcomes have been documented. However, the decision on in utero or postnatal treatment is challenging, with the effectiveness of both approaches well-established.31 While intrauterine treatment is highly effective, postnatal treatment remains a viable option particularly in cases when imminent delivery is crucial.
Digoxin is widely accepted as a first-line antiarrhythmic drug.24 Sotalol, flecainide, and amiodarone serve as secondary options when digoxin proves ineffective in achieving conversion to sinus rhythm.32 However, studies indicate that for fetuses with hydrops, digoxin’s limited placental transfer hampers its effectiveness.33 Therefore, for cases involving hydrops, especially in fetal treatment, it is recommended to initiate sotalol or flecainide, both of which exhibit good placental transfer abilities.31,34 In our study, the combination of digoxin and flecainide was introduced in the cases which had associated hydrops, encompassing three instances of SVT and one case of JET. All these cases reverted to sinus rhythm along with resolution of the hydrops, accounting for 50% of the case of fetal tachyarrhythmias. Digoxin monotherapy was initiated in two isolated cases of SVT and once case of atrial flutter. Successful reversion to sinus rhythm was achieved in the case of atrial flutter. However, in SVT cases, monotherapy with digoxin did not result in reversion, necessitating the addition of other antiarrhythmic agents in both instances.
Thus, the study underscores the prevalence of SVT in fetal tachyarrhythmias and the pivotal role of hydrops in treatment decisions. While much of the literature often compares digoxin versus flecainide and explores stepwise approaches to managing SVT, there are limited case studies delving into the initiation of combined digoxin and flecainide as a first line treatment, particularly in cases involving hydrops.35,36 The successful application of this combined therapy in our study suggests a potential shift in the treatment paradigm and proposes it as a viable first-line option for SVT with hydrops. However, further studies with larger sample sizes are necessary to validate the findings and it is crucial to exercise caution and make thoughtful selections of antiarrhythmics tailored to the unique characteristics of each case.
VT is a rare fetal arrhythmia, constituting only 1–2% of cases.25 Optimal therapy remains unclear due to its rarity. Current literature suggests maternal intravenous magnesium therapy as a first-line treatment for sustained VT.37Additional measures, such as intravenous lidocaine, oral propranolol, or oral mexiletine, are recommended alongside magnesium.32,37,38 In cases related to isoimmunization or myocarditis, dexamethasone and intravenous immunoglobulin infusion have been employed.39 In this study, we encountered one case of VT with prolonged QT, where treatment with IV magnesium sulphate followed by oral propranolol was initiated. While the rhythm was controlled with small recurring episodes, the baby succumbed to neurological complications 3 hours after birth. Hence, the study highlights the rarity of fetal VT, emphasizing the challenges in therapeutic strategies and the need for further research to establish standardized protocols. Beyond clinical aspects, the study suggests delving into the genetic and molecular factors associated with fetal VT, potentially leading to personalized management strategies based on identified markers. The impact of early VT diagnosis, evaluation of maternal and fetal risk factors, and a detailed analysis of neurological complications constitute key facets of this multifaceted approach.