Keywords
pulmonary stenosis regurgitation - sick sinus syndrome - fetal echocardiography -
fetal bradyarrhythmia - congenital heart disease
Congenital sick sinus syndrome (SSS) is characterized by dysfunction of the sinoatrial
node which results in inappropriate sinus bradycardia, sinus arrest, or chronotropic
incompetence. Approximately 80% children with SSS have a history of cardiac surgery
for congenital heart disease (CHD),[1]
[2]
[3]
[4] and SSS is also observed in fetuses with CHD.[5] However, detailed mechanisms underlying the development of SSS are not fully understood.
Although the incidence of fetal SSS is not fully understood, it accounts for approximately
50% of cases of bradycardia with CHD and 9% of cases of bradycardia without CHD.[5] Tricuspid regurgitation might cause SSS, but there is no report about the relationship
between SSS and PSR during pregnancy, particularly in spontaneously resolved cases.
Here we report a case of fetal SSS caused by pulmonary stenosis regurgitation (PSR)
that spontaneously resolved during pregnancy.
Case Description
A 29-year-old woman, gravida 1, para 0, was referred to our hospital at 21 weeks of
gestation because of persistent fetal bradycardia. She did not have any history of
familial genetic disease. A detailed ultrasonographic examination (Voluson E8 GE Healthcare,
Milwaukee, WI) revealed sinus bradycardia (60–70 beats/minute [bpm]) with 1:1 atrioventricular
(AV) conduction ([Fig. 1A, b]). The four-chamber view showed ventricular septal defect (VSD; [Fig. 2]). The diameter of VSD was 4 mm. The size of ventricles and atria were proportionate
and did not show enlargement. The three-vessel view showed an enlarged main pulmonary
artery. The right outflow tract showed pulmonary valve stenosis with regurgitation
([Fig. 3A, B]). No blocked atrial extrasystoles or tachyarrhythmia was detected, and maternal
autoantibodies were negative; thus, congenital SSS owing to PSR was suspected. The
fetal status was good without any sign of hydrops. Examinations at 24 and 26 weeks
of gestation revealed sustained fetal bradycardia. However, fetal bradycardia spontaneously
resolved at 28 weeks of gestation without any fetal treatment, regardless of persistent
PSR ([Fig. 4]). The ventricular rate was approximately 120 bpm. Thereafter, although the degree
of PSR did not change in the fetus, SSS was absent throughout the pregnancy and there
were no signs of cardiac failure. A male neonate weighing 2,390 g was delivered via
Cesarean section at 38 weeks of gestation with an Apgar's score of 8 at both 1 and
5 minutes. Consequently, detailed echocardiography revealed PSR and VSD with regular
heart rhythm. The results of initial electrocardiography were normal. Thus, the postnatal
diagnosis was consistent with prenatal impressions obtained. The neonate was discharged
with an uneventful observation 27 days after birth. During the last hospital visit,
the 8-month-old infant had PSR without any signs of congestive heart failure and was
a relatively slow growth rate and 3-month developmental retardation. His heart rate
was approximately 110 bpm with regular heart rhythm.
Fig. 1 Prenatal diagnosis of sick sinus syndrome and pulmonary stenosis regurgitation. (A) Simultaneous pulsed Doppler interrogation of flow in the superior vena cava and ascending
aorta showed sustained fetal bradycardia with regular rhythm and 1:1 atrioventricular
conduction. (B) M-mode assessment with the cursor placed through the right atrium (RA) and left ventricle
(LV) showed 1:1 atrioventricular conduction. The ventricular rate was 68 bpm. Apical
four-chamber view showing ventricular septal defect. bpm, beats/minute.
Fig. 2 Apical four-chamber view showing ventricular septal defect.
Fig. 3 Image showing right ventricular outflow tract (RVOT). RVOT demonstrated pulmonary
valve stenosis (A) and pulmonary regurgitation (B).
Fig. 4 Simultaneous pulsed Doppler interrogation of flow in the superior vena cava and ascending
aorta at 28 weeks of gestation showed regular heart rhythm without fetal bradycardia.
The ventricular rate was 127 bpm. bpm, beats/minute.
Discussion
Fetal bradycardia is defined as a fetal heart rate with a baseline of < 110 bpm. The
major causes of bradycardia include congenital SSS, AV block, long-QT syndrome and
nonconducted atrial premature beats.[6] Sustained fetal bradycardia associated with regular and 1:1 AV conduction basically
suggests SSS. Fetal bradycardia may be present in fetuses with and without CHD. In
a fetus without CHD, antibodies, such as anti-Ro/Sjogren's syndrome A antibodies,
are often associated with fetal bradyarrhythmia owing to AV block.[7] Conversely, in a fetus with CHD, congenital bradyarrhythmia is believed to be caused
by the structural defect itself.[8] The discontinuity between the AV node and ventricular conduction tissues that is
often caused by heterotaxy and corrected transposition of the great arteries can result
in SSS. Additionally, SSS can be caused by hemodynamic stress and aging.[9]
[10] The severity of tricuspid regurgitation after the additive maze procedure during
mitral valve surgery has been reported to be associated with SSS development.[10] In the study, the late-onset SSS group had a higher mean age, suggesting that age
has an impact on the cumulative risk of developing SSS.[10] Noda et al reported that tachyarrhythmia spontaneously changed to SSS and finally
changed to complete heart block in patients with Ebstain's anomaly over a 16-year
period.[11] The author indicated that cell damage in the heart's conduction system and accessory
pathway may cause SSS even in a situation without hemodynamic stress because the patients
were young and had almost normal hemodynamics. Taken together, SSS can be caused by
not only hemodynamic stress but also age-related changes, such as apoptosis and fibrosis
in cardiac cells, suggesting that the dramatic development of fetal cardiac cell may
affect the condition of SSS.
Hemodynamic stress owing to pulmonary valve regurgitation of the sinoatrial node in
the absence of fetal heart maturity might have caused SSS in our case. However, SSS
was resolved by maturation of the fetal heart as pregnancy progressed despite persistent
PSR. Our report indicates the possibility of spontaneous disappearance of SSS caused
by CHD, particularly in the case of hemodynamic stress, such as regurgitation. It
is important to mention this when counseling the mother so that she is aware of the
actual fetal prognosis.
Conclusion
In conclusion, fetal PSR can cause SSS owing to fetal heart immaturity at an earlier
gestational age. Consequently, fetal SSS can be resolved spontaneously as pregnancy
progresses.
