Seminars in Fetal & Neonatal Medicine (2005) 10, 504e514

www.elsevierhealth.com/journals/siny

Fetal brady- and tachyarrhythmias: New andaccepted diagnostic and treatment methods

Edgar T. Jaeggi*, Masaki Nii

Fetal Cardiac Program, The Hospital for Sick Children, University of Toronto, 555 University Avenue,Toronto, Ontario M5G 1X8, Canada

KEYWORDSFetal;Arrhythmia;Diagnosis;Complete AV block;Atrial flutter;Supraventriculartachycardia

Summary Sustained bradyarrhythmias are typically the result of symptomaticsinus bradycardia, atrial bigeminy or complete atrioventricular (AV) block. Fetal ta-chyarrhythmias relate to sinus tachycardia, atrial flutter and supraventriculartachycardia as the main aetiology. Ultrasound is essential to understand the under-lying arrhythmia mechanism, to study the impact on cardiac function, to excludecardiac defects or tumours, and to survey the fetal heart rate and well-being,e.g. during anti-arrhythmic treatment. Based on retrospective studies, severalmore or less safe, effective and well-tolerated anti-arrhythmic agents are currentlyavailable for the treatment of atrial and supraventricular tachycardia. Isolatedcongenital complete AV block is mainly related to maternal anti-Ro/La auto-antibodies. The rationale to treat a fetus at this irreversible stage of AV nodaldamage is primarily to mitigate or prevent concomitant myocardial inflammationand to augment cardiac output. A recently published study demonstrated a signifi-cant improved outcome with transmaternal dexamethasone and b-stimulation.ª 2005 Elsevier Ltd. All rights reserved.

Introduction

Depending on gestational age and degree of fetalactivity, the normal fetal cardiac rhythm is charac-terized by a regular heart rate ranging between 100and 180 beats/min (bpm) with a normal 1:1 atrio-ventricular (AV) electromechanical relationshipduring each cardiac cycle. Accordingly, fetal cardiacarrhythmias may present as an irregular heart

* Corresponding author. Tel.: C1 416 813 7466; fax: C1 416813 7547.

E-mail address: edgar.jaeggi@sickkids.ca (E.T. Jaeggi).

1744-165X/$ - see front matter ª 2005 Elsevier Ltd. All rights resedoi:10.1016/j.siny.2005.08.003

rate, as an abnormally slow or fast heart rate, oras a combination of irregular rhythm and an abnor-mal heart rate. Such fetal rhythm disturbances,which are diagnosed in at least 2% of pregnanciesduring routine ultrasound scanning, are commonreasons for referral to a fetal cardiologist.1 Inmore than 90% of cases, arrhythmias are brief andisolated events of little clinical relevance. Of moreconcern are the prolonged or incessant episodes ofheart rates that are too fast (O180 bpm) or tooslow (!100 bpm). This includes supraventriculartachycardia (SVT), atrial flutter and complete AVblock as the major fetal arrhythmia mechanisms.

rved.

Fetal brady- and tachyarrhythmias: New and accepted diagnostic and treatment methods 505

Major arrhythmias are not common. Even at theauthors’ large tertiary care centre, only a handfulof fetal cases are seen every year, as illustrated inFig. 1. The outcome of affected fetuses is influ-enced by numerous variables including arrhythmiacharacteristics, age at diagnosis, cardiac defectsand choice of treatment. Thus, the primary objec-tive of every newly detected fetal rhythm disordermust be: (1) to understand the underlying arrhyth-mia mechanism; (2) to clarify its impact on thefetal circulation; and (3) to conclude on the needfor treatment.

Figure 1 Distribution of major fetal bradyarrhythmias(n Z 28) and tachyarrhythmias (n Z 38) seen at the Hos-pital for Sick Children during the last 5 years (2000e2004). SVT, supraventr icular tachycardia; AV,atrioventricular.

Fetal rhythm assessment

Echocardiography

As in extra-uterine life, the classification of fetalrhythm and conduction anomalies is based primar-ily on the chronology of electrophysiologicalevents. However, assessment of the fetal cardiacrhythm is more challenging as conventional real-time electrocardiograms cannot be obtained.M-mode, pulse-wave and tissue Doppler echocar-diography have been used as surrogates as theyenable study of the chronology of atrial andventricular electrical events indirectly by theirrespective mechanical consequences.2e4 Guidedby two-dimensional echocardiography, the M-mode ultrasound beam is aligned simultaneouslythrough the atrial and ventricular walls and the se-quence of their systolic wall motions is studied(Fig. 2). A limitation of M-mode recordings is thatthe onset and maximum of the atrial and ventricu-lar contraction is often not clearly defined, andtherefore precise measurement of AV time inter-vals is not possible. Recording of blood flow veloc-ities that represent atrial and ventricular events ismore accurate in this regard as flow signals aremore readily recognized. Simultaneous pulse-wave Doppler interrogation of the superior venacava and the ascending aorta, two vessels thatare in close anatomical relation to each other,

Figure 2 M-mode tracing using a four-chamber view to demonstrate atrial (A) and ventricular (V) wall motions. TheM-mode is directed simultaneously through the left ventricle (LV) and right atrium (RA). There is atrial flutter with anatrial rate of 414 beats/min (bpm), functional 2:1 atrioventricular block, and a regular ventricular rate of 207 bpm.

506 E.T. Jaeggi, M. Nii

Figure 3 Pulsed Doppler flow modalities. (A) Simultaneous ascending aorta (V) and superior vena cava (A). Dopplerflow recording at 20 weeks of gestation showing sinus bradycardia with normal 1:1 atrioventricular conduction. (B)Simultaneous inflow/outflow Doppler of a 19-week fetus with long ventriculo-atrial tachycardia of 190 beats/mindue to fetal thyrotoxicosis. The mother had a medical history of Graves’ disease for which she had been treatedwith propylthiouracil and radioactive iodine.

uses this concept (Fig. 3A). The beginning of retro-grade flow in the superior vena cava indicates thebeginning of atrial systole, whereas the onset ofaortic forward flow marks the beginning of ventric-ular systole. Alternatively, simultaneous Dopplerrecording of mitral valvar inflow and ascendingaorta flow waves may be used; the beginning ofA-wave inflow marks the onset of active atrial con-traction (Fig. 3B). Colour-coded tissue velocity im-aging (TVI) allows offline quantification ofsegmental wall motion in any area of the heartduring the same cardiac cycle (Fig. 4). A typicalTVI curve from the basis of the heart is composedof two diastolic wave curves that are produced bylongitudinal tissue motion away from the apex dur-ing the early diastolic filling phase and during atrialcontraction. During ventricular contraction, theventricles move towards the apex; as a result, athird wave occurs in the opposite direction. Atrial(A) systolic velocities may also be recorded butare much smaller and point in the opposite direc-tion when compared with Aa in ventricular sam-pling. TVI recordings have an excellent temporalresolution but need to be analysed offline usingspecial software.

All ultrasound modalities are useful in assessingthe integrity of electrical AV conduction. However,it is important to realize that normal conduction

time values differ among modalities and prolongwith gestational age. Normal AV conduction timesare 190 G 36 ms by M-mode, 120 G 11 ms by leftventricular inflow/outflowDoppler, and 111G 17 msby superior vena cava/aorta Doppler sampling.3

To assess fetal arrhythmias, M-mode and simulta-neous Doppler of the superior vena cava andascending aorta are particularly user friendly asthey allow fast, reproducible and accurate onlineanalysis in most cases.2,5,6

Electrocardiogram (ECG) andmagnetocardiogram (MCG)

Transabdominal fetal ECG and MCG have recentlybecome commercially available and they are nowused by a few centres.7,8 Fetal ECG is based on sig-nal averaging of electrocardiographic complexesand does not allow beat-to-beat analysis. As a con-sequence, ECG is not helpful in diagnosing fetalrhythm and conduction anomalies with irregularheart rates. Fetal MCG provides better signal qual-ity than ECG because of more favourable transmis-sion properties of magnetic signals. The use of themagnetic analogue of ECG requires a magneticallyshielded room. Both MCG and ECG may provide

Fetal brady- and tachyarrhythmias: New and accepted diagnostic and treatment methods 507

Figure 4 Normal tissue Doppler imaging from the right atrioventricular (AV) groove and the right atrial wall. Sequen-tial analysis of regional tissue motion at the AV groove results in two diastolic [early diastolic filling phase (Ea) andatrial contraction (Aa)] waves and one systolic (Sa) wave.

useful information on cardiac time intervals suchas the QRS and QT duration.

Fetal bradycardia

Brief episodes of sinus bradycardia that last lessthan 1e2 min are frequent and benign findings,particularly during the first and second trimesters.No treatment is required. A prolonged or persis-tent decrease in heart rate !100 bpm may be ob-served during symptomatic sinus bradycardia,atrial bigeminy with blocked premature beats,and high-degree AV block. As the ventricular ratemay be comparable among these rhythm anoma-lies, ultrasound imaging is used for their diagnosticdifferentiation.

During sinus bradycardia, M-mode and Dopplerechocardiography show a normal 1:1 AV activationsequence (Fig. 3A). Causes of prolonged episodesinclude fetal distress secondary to conditions lead-ing to fetal hypoxia and acidosis, long QT syndromeand congenital sinus node dysfunction.9 Fetal ad-aptation to hypoxaemia is marked by changes inregional blood flow with an increased blood supplyfrom the venous duct to the brain and myocardium(brain and heart sparing). Runs of ventriculartachycardia and 2:1 AV block are additional find-ings that suggest fetal long QT syndrome. Carefulexamination and, in the absence of fetal MCG,

postnatal ECG are recommended in these childrenand their family members.

Persistent atrial bigeminy and trigeminy withblocked premature beats may lower the averageheart rate of the fetus to 70e100 bpm, which maybe confused with second- or third-degree AV block.Blocked premature beats and AV block are charac-terized by higher atrial than ventricular rates. InAV block, however, the time interval between con-secutive atrial impulses hardly varies while everysecond event occurs prematurely in atrial bigeminy(Fig. 5). This differentiation is essential as brady-cardia secondary to blocked premature beatsresolves spontaneously without treatment, whilecomplete AV block (CAVB) is an irreversible andpotentially life-threatening disorder.

AV block refers to a disturbance of electricalconduction within the AV node, the bundle of Hisor the bundle branches. First-degree AV block ischaracterized by a prolonged AV conduction timebut all impulses are conducted. Second-degree AVblock refers to a failure to conduct some, but notall, atrial impulses to the ventricles. Type I(Wenckebach) second-degree AV block denotesprogressive lengthening of the AV conductiontime, until an isolated impulse is blocked. Type II(Mobitz II) block is characterized by occasional orrepetitive sudden AV block without prior length-ening of the AV conduction time. In 2:1 AV block,only every second atrial beat is conducted to the

508 E.T. Jaeggi, M. Nii

Figure 5 M-mode echocardiography at 20 weeks showing significant fetal bradycardia (VeV: 67 beats/min) relatedto atrial bigeminy. There is atrial beat-to-beat variation with the premature atrial beats (AeA interval: 370 ms) beingblocked and the normal atrial impulses (450 ms) being conducted. A repeat echocardiogram showed normal cardiacrhythm 1 week later.

ventricles. In third-degree AV block or CAVB, theelectrical AV communication is completely inter-rupted and the atria and ventricles beat indepen-dently (Fig. 6). Significant bradycardia is only seenwith high-degree second- or third-degree AV block.The fetal heart compensates to the evolving heart

block by increasing its stroke volume. If the heartfails to adapt, fetal hydrops develops with a highrisk of fetal or neonatal death.10e13

CAVB accounts for nearly 40% of major fetalarrhythmias referred to the authors’ institution.In roughly half of the cases, CAVB is associated

Figure 6 Simultaneous Doppler of the aorta and superior vena cava showing complete atrioventricular block. Theatrial (AeA) rate was 138 beats/min (bpm) and the ventricular (VeV) rate was 54 bpm, with complete atrioventriculardissociation.

Fetal brady- and tachyarrhythmias: New and accepted diagnostic and treatment methods 509

with left isomerism and congenitally correctedtransposition.13 The outcome of fetal CAVB withmajor congenital heart disease is particularlypoor with less than 20% survival of the fetal andneonatal periods.13 In the absence of congenitalheart disease, CAVB is mainly associated with thetransplacental passage of maternal auto-antibod-ies to 48-kDa SSB/La, 52-kDa and/or 60-kDa SSA/Ro ribonucleioproteins.13 These antibodies are typ-ically found in Sjogren’s syndrome and systemic lu-pus erythematosus, but may also be demonstratedin 1e2% of pregnant women with no clinical evi-dence of auto-immune disease. Anti-Ro/La anti-bodies progressively enter the fetal circulation inthe second trimester and may elicit an immune-mediated tissue injury resulting in progressive de-struction of the AV node, myocardial inflammation,endocardial fibro-elastosis and dilated cardiomy-opathy in the susceptible offspring.12e14 FetalCAVB emerging between 20 and 24 weeks’ gesta-tion affects 1e2% of the cohort of antibody-positivemothers, while the other cardiac manifestationsare less common.15,16 The reported probability ofhaving a second child with immune-mediatedCAVB varies between 8% and 18%.12

So far, isolated CAVB has been associated witha significant mortality that ranges between 18%and 43%.10e13 Risk factors of adverse outcome in-cluded fetal hydrops, endocardial fibro-elastosis,premature delivery and fetal heart rate %55bpm.10e13 Of the survivors, most required pace-maker implantation during the first year of life.11

To improve the pregnancy outcome, numerouspreventive and therapeutic approaches havebeen used with variable success.17e30 Theoretical-ly, all mothers at risk of delivering a child with im-mune-mediated CAVB may be considered forpreventive treatment. In fact, this approach hasbeen chosen for a small number of pregnanciesby maternal plasma exchange and administrationof maternal immunoglobulin, steroid or azathio-prine.19,25,26 This approach aims primarily at re-ducing maternal auto-antibody titres, but mayresult in a state of severe antibody depletionthat renders both the mother and her offspringat an increased risk of infection. Considering thelow fetal CAVB risk, it is difficult to advocate pre-ventive treatment to mainly unaffected fetusesand mothers.

Unfortunately, there are no reliable markersthat predict which fetus of an anti-Ro/La-anti-body-positive woman will develop immune-medi-ated cardiac complications. Moreover, fetal CAVBseems to develop rapidly within a few days.6

Therefore, it is no surprise that most fetuses arediagnosed with established CAVB. The rationale to

treat a fetus at this irreversible stage of AV nodaldamage is primarily to mitigate or prevent con-comitant myocardial inflammation and to augmentfetal heart rate. Unlike prednisone, the fluorinat-ed steroid compounds dexamethasone and beta-methasone are only minimally metabolized bythe placenta, and become useful when anti-inflammatory fetal treatment is desired. Maternaldexamethasone administration has been shown toimprove fetal AV block, hydrops and myocardialdysfunction.17,18,20,27,29 Various b-stimulants havebeen used to increase the fetal heart rate andmyocardial contractility with variable suc-cess.23,28,30 However, an improved overall out-come was shown recently after introduction ofprenatal treatment guidelines (Fig. 7).30 Accordingto this protocol, maternal dexamethasone (4 mg/day) is initiated at diagnosis of immune-mediatedCAVB and, when possible, maintained for the dura-tion of the pregnancy. A b-sympathomimetic agent(oral salbutamol 3! 10 mg/day) is added if theaverage heart rate is below 55 bpm. The affectedpregnancy is closely surveyed, with elective deliv-ery being at around 37 weeks of gestation in un-complicated cases and neonatal care being in thecritical care unit. Since introduction of this ap-proach in 1997, the 1-year survival rate with iso-lated CAVB has increased from 47% to 95%(Fig. 8). Antenatal steroid treatment has its risksand future studies will need to address potentiallong-term effects, e.g. on brain development. Oli-gohydramnios did occur in 20% of cases afterchronic steroid treatment and resulted in prema-ture deliveries in some cases. Thus, the amnioticfluid volume needs to be carefully monitoredthroughout the pregnancy course, and a timely re-duction in dexamethasone dose to 2 mg/day maybe required. To stimulate the fetal heart rate,the authors prescribe salbutamol in high doses.This commonly results in unpleasant b-adrenergicmaternal side-effects including palpitations andtremor, but more serious adverse effects havenot been encountered. In the present state ofknowledge and with the obvious improvement inoutcome, there is no solid ground to deny the ben-efit of transplacental steroid treatment to fetuseswith immune-mediated CAVB.

Fetal tachycardia

Anomalies that lead to an intermittent or sus-tained increase in heart rate of R180 bpm accountfor 60% of the major fetal tachyarrhythmias seenat the authors’ centre. Echocardiography is againthe diagnostic cornerstone in establishing the

510 E.T. Jaeggi, M. Nii

Figure 7 Treatment protocol for the management of isolated fetal complete atrioventricular block at the Hospitalfor Sick Children. DXMT, dexamethasone; HR, heart rate. Reproduced with permission from Jaeggi ET, Fouron JC,Silverman ED, Ryan G, Smallhorn J, Hornberger LK. Circulation 2004;110:1542e8.30

arrhythmia mechanisms and haemodynamic conse-quences, and in detecting occasionally contribut-ing cardiac malformations and tumours. SVT,atrial flutter and sinus tachycardia are the pre-dominant fetal causes.31e33 Persistent tachyar-rhythmias may be well tolerated or, at the otherend of the spectrum, may lead to congestive heartfailure, dilated cardiomyopathy, neurological pa-thology and even death. Fetal hydrops has beenassociated with a mortality risk of up to 35%, com-pared with 0e4% in cases without significant heartfailure.33

Ventricular tachycardia is rarely detected inutero. Intermittent runs of ventricular rates be-tween 170 and 400 bpm exceed the atrial rate, andthere is complete dissociation between atrial andventricular events.9 If the AV node is able to con-duct retrograde to the atrium, a 1:1 AV relation-ship is possible. In the latter situation,ventricular tachycardia becomes difficult to differ-entiate from re-entrant SVT. Long QT syndromeshould be suspected when there is fetal bradycar-dia during sinus rhythm, intermittent or perma-nent complete heart block, or both.

Sinus tachycardia is characterized by atrial ratesof 180e200 bpm, 1:1 AV conduction, normal dura-tion of the AV interval and some variability of theheart rate. It is caused by a variety of fetal and ma-ternal conditions including fetal distress, anaemia,infections, maternal b-stimulation and fetal thyro-toxicosis secondary to thyroid-stimulatingmaternal

auto-antibodies (Fig. 3B). The importance of sinustachycardia is recognizing and treating the underly-ing cause without delay.

Atrial flutter is the result of an intra-atrialelectrical macro-re-entrant circuit around fixed orfunctional anatomical conduction barriers. Atrialflutter is mainly observed later in gestation as thepropagation of a sustained re-entrant circuit de-pends on a critical atrial size.30 Atrial rates rangebetween 300 and 550 bpm which is sufficientlyfast so that 1:1 AV conduction is not occurring.Typically only every second or third atrial beat isconducted, which results in better tolerated ven-tricular rates between 150 and 250 bpm (Fig. 2).Fetal atrial flutter may also be associated withre-entrant SVT.31,33,34

Management of atrial flutter aims to reverseatrial flutter to sinus rhythm or otherwise to impairthe AV conduction, thus reducing the ventricularresponse rate to a near-normal rate, allowingbetter ventricular filling and improved cardiacoutput. In terms of restoration to sinus rhythm,maternal administration of sotalol appears to bemore effective than digoxin.31,35 Once sinusrhythm has been established after birth, recur-rence of atrial flutter is uncommon in the absenceof structural heart disease and no anti-arrhythmiclong-term prophylaxis is usually required.31

The term ‘supraventricular tachycardia’ encom-passes tachycardias with three different mecha-nisms including: (1) AV re-entrant tachycardia

Fetal brady- and tachyarrhythmias: New and accepted diagnostic and treatment methods 511

(AVRT) related to retrograde fast accessory path-way conduction; (2) permanent junctional recip-rocating tachycardia (PJRT) related to retrogradeslow accessory pathway conduction; and (3) atrialectopic tachycardia (AET) due to enhanced focalautomaticity. SVT mechanisms may be quite accu-rately differentiated based on their arrhythmiapattern including the AV and ventriculo-atrial (VA)relationship.

AV re-entry is by far the most common mecha-nism of fetal SVT.2,36 During typical orthodromicAVRT, there is normal AV conduction through theAV node, while an accessory pathway conducts ret-rograde from the ventricles to the atria. As the ret-rograde atrial activation occurs shortly after theventricular activation, this yields a short VA timeinterval on Doppler or M-mode echocardiography(Fig. 9). Other features of short VA SVT include

Figure 8 Impact of transplacental fetal treatmentwith (Steroid) and without (No Steroid) dexamethasoneon outcome of isolated CAVB. The survival was bestwith a protocol-guided approach that was introducedin 1997 (Tx Protocol). Reproduced with permissionfrom Jaeggi ET, Fouron JC, Silverman ED, Ryan G, Small-horn J, Hornberger LK. Circulation 2004;110:1542e8.30

intermittent or sustained episodes of regular fastheart rates between 180 and 300 bpm and 1:1 AVconduction. The onset and termination of AVRT issudden. After birth, antegrade accessory pathwayconduction (Wolff-Parkinson-White syndrome) isfound in 10% of cases with fetal SVT.32,33

Long VA SVT is characterized by atrial contrac-tion that closely precedes the ventricular systole.Apart from sinus tachycardia, this pattern istypically caused by AET or PJRT. AET and PJRTare far less common but more resistant to treat-ment compared with short VA SVT.2 In PJRT, theretrograde (VA) conduction occurs through a slowconducting accessory pathway. This results in sus-tained long VA tachycardia of about 220 bpm witha 1:1 AV relationship. In AET, an atrial focus ex-ceeds the normal pacemaker activity of the sinusnode. AET is mainly sustained due to multipleruns of fast heart rates between 200 and250 bpm. The tachycardia may have a gradual on-set and offset, and variable second-degree AVblock may occur.

In theory, three management options are avail-able for fetal SVT and atrial flutter: (1) notreatment; (2) anti-arrhythmic drug therapy; and(3) delivery. Abstention of treatment with closepregnancy monitoring is a valid option if the fetuspresents with intermittent brief runs of tachycar-dia in the absence of haemodynamic impairment.More sustained tachyarrhythmia may significantlyaffect the fetal cardiovascular function due toimpaired ventricular filling, reduced cardiac con-tractility and venous congestion. In this situation,rapid and permanent conversion to sinus rhythm toprevent or resolve congestive heart failure isa primary task. Nevertheless, the choice of treat-ment is contentious as there are no controlleddata that document the superiority of any anti-arrhythmic drug treatment for fetal and paediatrictachyarrhythmia. There is, however, considerablenon-randomized experience in the transmaternaltreatment of fetal SVT with a number of anti-arrhythmic agents, including digoxin,2,5,33 procai-namide (class Ia),37 flecainide (class Ic),33,38,39

sotalol and amiodarone (class III).2,5,35,40e42 Directfetal administration of adenosine, digoxin and/oramiodarone, e.g. into the umbilical vein, has beenused for the acute treatment of incessant, poorlytolerated re-entrant SVT.43e45

Digoxin is still considered by many as drug ofchoice in treating fetal SVT. However, the likeli-hood of controlling arrhythmias within a reasonabletime frame is rather low,46,47 and digoxin is almostcertainly ineffective in long VA SVT.2 Moreover, inthe presence of fetal hydrops, maternal-fetal di-goxin transfer is poor and effective fetal drug

512 E.T. Jaeggi, M. Nii

Figure 9 Tissue velocity imaging of a short ventriculo-atrial tachyarrhythmia with a heart rate of 230 beats/min.Right atrial systole (A) occurs at the very end of ventricular systole (S). Atrioventricular re-entry as supraventriculartachycardia mechanism was confirmed by postnatal transoesophageal electrophysiological study.

levels may not even be obtained at near-toxic ma-ternal levels.47

The Hospital for Sick Children has used thefollowing approach for fetal SVT for some yearsnow (unpublished data). If a fetus presents withsignificant SVT after 35 weeks of gestation, expe-dited delivery followed by postnatal conversion isan option. At an earlier gestational age, the risksassociated with premature delivery probably out-weigh the potential hazards of fetal-maternalpharmacological treatment. Oral sotatol (80e160 mg bid) is used as the drug of choice if thereis sustained or incessant short VA SVT, long VASVTor atrial flutter. Sotalol is usually well toleratedand has little or no negative inotropic effect onthe fetal heart.48 Anti-arrhythmic treatment otherthanwith digoxin is always initiated in hospital afterthe maternal documentation of a normal 12-leadECG and normal serum electrolytes. The fetal andmaternal cardiac rhythm is intermittently moni-tored during the first 2 days of treatment, and noserious maternal adverse effects have occurred. Ifthe arrhythmia is not controlled within a few dayson the maximal sotalol doses, digoxin is usuallyadded (oral doses of 1 mg/day for 2 days, followedby maintenance doses). Using this approach,permanent suppression of SVT is achievable inmost (80%) cases. Oral flecainide (100 mg tid) isreserved for cases that are unresponsive to sotaloland digoxin. In situations of life-threatening

arrhythmia-related fetal compromise, direct fetaladministration of adenosine and amiodarone isused as a last resort. Transient neonatal hypothy-roidism has been reported after fetal amiodaroneexposure.42,49 Occasional reports of fetal deathshave raised concerns regarding the safety of anti-arrhythmic drugs such as flecainide and sotalol, al-though the demise could never be attributed withcertainty to the drug therapy.35,38 Although dataon the natural history of significant SVT are largelymissing, the benefit of anti-arrhythmic treatmentin reducing arrhythmia-related complications anddeath probably outweighs the low pro-arrhythmiarisk. Once the arrhythmia is under control, the suc-cessful anti-arrhythmic treatment is maintaineduntil delivery with weekly controls of the fetal car-diac rhythm. At the authors’ centre, newborns aretreated (usually with a b-blocker) for at least 6e12 months, if the SVT: (1) spontaneously recursearly after birth; or (2) is easily inducible by trans-oesophageal electrophysiological study.

Summary

Fetal echocardiography is essential in understand-ing arrhythmia mechanisms, to clarify the impacton the fetal circulation and to establish the needfor treatment. A large amount of experience onanti-arrhythmic therapy has been accumulated

Fetal brady- and tachyarrhythmias: New and accepted diagnostic and treatment methods 513

from retrospective analysis of paediatric and, lessimportantly, fetal data. Well-tolerated anti-ar-rhythmic drugs are available for the successfultreatment of most fetal tachyarrhythmias. Unfor-tunately, direct comparison of efficacy and safetybetween different studies is not feasible becausevariable criteria for therapy success are used, andinclusion criteria are vague in terms of underlyingarrhythmia mechanism. Preventive treatment ofpregnancies at risk of isolated CAVB appears to beunjustified based on a 1e2% fetal risk in womenwith anti-Ro/La antibodies. The outcome of iso-lated fetal CAVBmay be improved by transplacentaltreatment with dexamethasone and b-stimulationat heart rates !55 bpm. This and alternativetreatment approaches require further study.

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