Prenatal diagnosis of sustained bradycardia with 1 : 1 atrioventricular conduction

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1 Ultrasound Obstet Gynecol 2003; 21: Published online in Wiley InterScience ( DOI: /uog.71 Prenatal of sustained bradycardia with 1 : 1 atrioventricular conduction Y. MAENO*, N. RIKITAKE*, O. TOYODA*, Y. KIYOMATSU*, T. MIYAKE*, W. HIMENO*, A. HIROSE*, D. HORI, T. KAMURA* and H. KATO* *Department of Pediatrics and Child Health and Department of Obstetrics and Gynecology, Kurume University, Kurume, Japan KEYWORDS: fetal bradycardia; fetal echocardiography; prenatal ; sinus bradycardia ABSTRACT Objectives The aims of this study were to elucidate the clinical course of fetal bradycardia with 1 : 1 atrioventricular conduction, and to discuss the optimal management of affected fetuses in the second and third trimesters of pregnancy. Methods The hospital records of five fetuses with the of bradycardia (100 bpm) with 1 : 1 atrioventricular conduction between 1981 and 2000 in our institution were reviewed. Atrioventricular conduction was evaluated by simultaneous M-mode echocardiographic tracing of the atria and the ventricles. Results The gestational ages at referral ranged from 19 to 36 (median, 25) weeks, and fetal heart rates ranged from 60 to 80 (median, 80) bpm. Postnatal electrocardiography revealed sinus bradycardia in four (two of which were siblings) of the five cases, and junctional rhythm in the remaining case. Two fetuses with congenital heart defects (CHDs) were delivered by Cesarean section but died postnatally. The three fetuses without CHDs were delivered vaginally and have survived to date for 6, 8 and 15 years. Conclusions Fetal bradycardia with 1 : 1 atrioventricular conduction caused by sustained sinus bradycardia or wandering pacemaker is an important type of fetal arrhythmia. Further investigations with a larger number of cases are required to determine the risk factors for predicting the outcome of affected fetuses. Copyright 2003 ISUOG. Published by John Wiley & Sons, Ltd. INTRODUCTION Fetal arrhythmia is easily detected by the routine use of fetal heart rate (FHR) monitoring and prenatal ultrasound 1 3. Prenatal is important for appropriate perinatal management to improve the prognosis of the affected fetus. Fetal bradycardia with a heart rate of less than 100 bpm is a well-known form of arrhythmia 1,2,4,5, which may be associated with fetal hydrops or intrauterine death. The most common cause of fetal bradycardia is congenital heart block 1,2,4 7,and the etiology 6 9, natural course, and prognosis of this fetal complete heart block have been thoroughly investigated 10. In contrast, fetal bradycardia with 1 : 1 atrioventricular conduction, such as sustained sinus bradycardia, has rarely been documented 4,5, There have been few reports investigating the natural course of sustained sinus bradycardia in the fetus 4,5. Conversely, transient sinus bradycardia, which is often seen during fetal echocardiographic examination by compression of the umbilical cord, has been well documented 1,2. Sinus bradycardia due to fetal distress is also a well-known phenomenon. However, sustained sinus bradycardia due to sinus dysfunction has rarely been documented 12,13. Evidence from sinus bradycardia in infants and children 14 suggests that sustained sinus dysfunction may also be one of the important causes of bradycardia in the fetus. In addition, management of the fetus with sinus bradycardia might be different from that of fetuses with other forms of fetal bradycardia, such as fetal complete heart block 12. The aims of this study were to elucidate the clinical course of fetal bradycardia with 1 : 1 atrioventricular conduction, and to discuss optimal management of affected fetuses in the second and third trimesters of pregnancy. METHODS The prenatal echocardiographic database of our institution was reviewed, and from the period 1981 to 2000 all Correspondence to: Dr Y. Maeno, Department of Pediatrics and Child Health, Kurume University, 67 Asahi-machi, Kurume, Japan ( yasukim@med.kurume-u.ac.jp) Accepted: 9 December 2002 Copyright 2003 ISUOG. Published by John Wiley & Sons, Ltd. ORIGINAL PAPER

2 Fetal bradycardia with 1 : 1 AV conduction 235 fetuses with sustained fetal bradycardia with 1 : 1 atrioventricular conduction were included in the study. Prenatal history, prenatal echocardiographic findings including presence or absence of associated structural abnormalities, perinatal course, and postnatal outcome were reviewed. In addition, these clinical features and perinatal courses were compared with those cases at our institution with congenital heart block. The ultrasound devices used for prenatal echocardiography were the Aloka 650, SSD-730, and SSD 550 (Aloka, Tokyo, Japan) equipped with a or 3.5-MHz transducer. An M-mode cursor was positioned through one of the atria and one of the ventricles. This simultaneous M- mode trace of atrial and ventricular contraction was used to demonstrate the timing of contraction in each chamber, and to distinguish fetal bradycardia with 1 : 1 atrioventricular conduction from atrioventricular block 1,2. The inflow pattern to the ventricle, as demonstrated by pulsed-wave Doppler, was also used to assess the timing of contraction in each chamber. The FHR was calculated from the beat-to-beat interval of this M-mode trace combined with the pulsed-wave Doppler flow trace of either the aortic or pulmonary artery 3. Bradycardia was diagnosed if the FHR, in stable condition, was less than 100 bpm (i.e. the beat-to-beat interval was longer than 0.6 s). Transitional bradycardia due to compression by the probe or due to contraction of the uterus was excluded from this heart rate measurement. sustained sinus bradycardia by prenatal echocardiography (Figures 1 and 2). The gestational ages at referral ranged from 19 to 36 (median, 25) weeks. The reason for referral was fetal bradycardia in all but one case (Case 5), with a previous maternal history of fetus with sinus bradycardia. In Cases 1 3 there was no family history of arrhythmia or CHD. The mother of the sibling cases (Cases 4 and 5) had a history of atrial fibrillation. FHRs at the time of referral ranged from 60 to 80 (median, 80) bpm. Two cases had associated CHDs. Clinical course None of the five fetuses showed any sign of fetal hydrops during the prenatal period. All five cases continued to have a slow heart rate throughout gestation. However, the heart rate of Case 2 occasionally increased to about bpm during stress. RESULTS According to our institutional database, 20 fetuses were diagnosed with fetal bradycardia during the time period investigated. Of these 20, six were recorded as having fetal bradycardia with 1 : 1 atrioventricular conduction. Of these six, one with tetralogy of Fallot and fetal hydrops was excluded, because this case was suspected of having fetal asphyxia and it died in utero on the day of fetal echocardiography. Therefore, five cases were included in the study (Table 1), two of which (Cases 4 and 5) were siblings. Of the five fetuses with fetal bradycardia with 1 : 1 atrioventricular conduction, all had been diagnosed as Figure 1 Fetal echocardiogram in Case 4 at 37 weeks of gestation. M-mode echocardiography revealed 1 : 1 atrioventricular conduction with a slow ventricular contraction rate of about 70 bpm. LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle. Table 1 Fetal bradycardia with 1 : 1 atrioventricular conduction Case GA at referral (weeks) Prenatal HR at (bpm) CHDs GA at birth (weeks) Delivery method Postnatal Postnatal HR (bpm) Outcome 1 31 SB 80 LAI 38 CS SB 80 Died at 9 months of CHF 2 20 SB Vaginal Wandering pacemaker 68 Alive, 15 years 3 36 SB 80 AVSD/CoA 36 CS SB 80 Died at 3 days (perioperative death) 4 19 SB Vaginal SB 70 Alive, 8 years. af at 8years 5 25 SB Vaginal SB 50 Alive, 6 years af, atrial fibrillation; AVSD, atrioventricular septal defect; CHDs, congenital heart defects; CHF, congestive heart failure; CoA, coarctation of the aorta; CS, Cesarean section; GA, gestational age; HR, heart rate; LAI, left atrial isomerism; SB, sinus bradycardia.

3 236 Maeno et al. I II Figure 2 Fetal echocardiogram in Case 5 at 35 weeks of gestation. Pulsed Doppler waveform at the tricuspid valve revealed an unusual inflow pattern, which is a prolonged gap from the E wave (E) to the A wave (A). RA, right atrium; RV, right ventricle. The two cases with CHDs were delivered by Cesarean section. Neither had fetal distress; Cesarean section was performed because of a concern for the neonatal condition, based on the relatively complex form of the heart defects. The remaining three cases with normal cardiac structures were delivered vaginally. Variable FHR, which was increased heart rate in response to fetal or neonatal stress, was useful for fetal monitoring during labor, and allowed for vaginal delivery. There was no fetal or neonatal distress during the perinatal period. Postnatal electrocardiography revealed sinus bradycardia in 4/5 cases (Figure 3). The remaining case (Case 2) had a wandering pacemaker with bradycardia. None of the electrocardiograms showed a long QT interval. Postnatal outcomes are shown in Table 1. In the two cases with CHDs, the infants died postnatally. All three cases with a normal cardiac structure survived and continued to show bradycardia. No case underwent pacemaker implantation. The most recent heart rates of Cases 2, 4, and 5 were 45, 60, and 60 bpm at 15, 8, and 6 years after birth, respectively. At 8 years old, Case 4 developed atrial fibrillation, which could not be converted to sinus rhythm by medication or electronically (Figure 4). III Figure 3 Postnatal electrocardiogram in Case 4 revealed sinus bradycardia. I II DISCUSSION Sustained sinus bradycardia due to sinus dysfunction is an important type of bradycardia that has been well documented in infants, children, and adults 14. In contrast, sustained sinus bradycardia in the fetus has not attracted much attention 1,2,4,5. However, it is important to elucidate the clinical course of this arrhythmia in order to manage affected fetuses. In addition, other types of arrhythmia that reveal similar prenatal echocardiographic findings, namely bradycardia with 1 : 1 atrioventricular conduction, need to be clarified. We have described the clinical features of fetal bradycardia with 1 : 1 atrioventricular conduction. The most common cause of this type of fetal bradycardia is III Figure 4 Electrocardiogram in Case 4 at 8 years old revealed atrial fibrillation with a ventricular rate of bpm. sustained sinus bradycardia. Wandering pacemaker was another cause of this type of fetal bradycardia. Although we did not experience this in our study, a recent report showed that some neonates with long QT syndrome had

4 Fetal bradycardia with 1 : 1 AV conduction 237 had bradycardia with 1 : 1 atrioventricular conduction during the prenatal period 15,16. Incidence In our institution, 30% of all cases of fetal bradycardia revealed 1 : 1 atrioventricular conduction, and 4/5 of these cases had sinus bradycardia by postnatal electrocardiography. In other institutions, Crawford et al. and Wladimiroff et al. reported that 2/12 cases 4, and 3/17 cases 5 with fetal bradycardia had sinus bradycardia, respectively. However, sustained sinus bradycardia in utero has not been as widely reported as complete heart block. The relatively higher heart rate, and the more favorable prognosis in fetuses with isolated sinus bradycardia as compared with those with heart block, may partly explain the dearth of interest in the former. A larger study is required to clarify its incidence. Although some of the cases with fetal bradycardia with 1 : 1 atrioventricular conduction had associated CHDs, the incidence cannot be determined from our limited experience. There have been only sporadic reports of the association between sinus bradycardia and CHDs 14.One pathological study reported that the sinus node was absent in 9/12 cases with left isomerism 9. Outcome Fetal bradycardia with 1 : 1 atrioventricular conduction seems to have a good prenatal and postnatal prognosis when the cardiac structure is normal. This bradycardia may have several advantages compared with bradycardia with heart block. One-to-one synchronized atrioventricular contraction has a clear hemodynamic advantage over non-synchronized contraction with heart block (Figure 2). Variable FHR, which is increased heart rate in response to fetal or neonatal stress, may allow better blood and oxygen supply compared to non-variable ventricular rate in the fetus with heart block. Cardiac function seems to be normal, in contrast to that in some fetuses with heart block in which poor cardiac contraction is caused by autoimmune myocarditis 10. Hence, the fetuses with bradycardia with 1 : 1 atrioventricular contraction may have a better prognosis than those with heart block. Sibling case Although there have been several reports of familial sinus node dysfunction, to our knowledge this is the first report to describe a sibling case with sinus bradycardia starting in the fetal period. In Case 5, the fetus had been carefully followed since the pregnancy was diagnosed. Hence, the onset of fetal bradycardia at 25 weeks of gestation was clearly demonstrated even though Case 4 was diagnosed as having bradycardia at 19 weeks of gestation. Both siblings have had an uneventful postnatal course and normal exercise tolerance for 8 and 6 years, respectively. Electrophysiological examination has not yet been performed; the parents are reluctant to allow an invasive examination of their clinically healthy children. There are no other family members who have sinus bradycardia. It is interesting to note that Case 4 recently developed atrial fibrillation, which also affects her mother. There may be functional or anatomical problems in the sinus or atrial electrical function in this family. We will follow Case 5 very carefully to monitor for additional arrhythmia. Clinical management Once fetal bradycardia has been detected and 1 : 1 atrioventricular conduction is observed, detailed cardiac structural assessment is required to rule out associated cardiac defects. During the fetal period, serial fetal echocardiography may be required to detect early signs of fetal congestive heart failure, especially in cases with heart defects. 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