Isolated Anti-Ro/La Antibody-Negative Fetal Complete Atrioventricular Block: A Case Report
Fetal complete atrioventricular block (CAVB) is a rare and serious form of bradycardia that can have significant implications for both fetal and neonatal health. This case report discusses a unique instance of isolated anti-Ro/La antibody-negative fetal CAVB, providing insights into its diagnosis, management, and long-term outcomes.
A 28-year-old woman, pregnant for the first time (P1G0), was referred to a diagnostic center at 30 weeks of gestation due to an irregular fetal cardiac rhythm. The patient had no notable risk factors, and tests for maternal auto-antibodies, including anti-Ro/La, anti-dsDNA, and anti-nuclear antibodies, were all negative. A comprehensive fetal systematic ultrasound examination revealed no abnormalities, and the fetal echocardiogram showed normal cardiac structure and function. There was no evidence of hydrops or any other malformations.
However, a detailed fetal echocardiogram, conducted by passing the sampling line sequentially through the right atrial wall, ventricular septum, and left ventricular wall, identified a complete atrioventricular block (CAVB). The atrial rate was regular and faster, ranging between 130 to 140 beats per minute (bpm), while the ventricular rate was significantly slower at 68 bpm.
The patient underwent a cesarean section at 38 weeks of gestation, delivering a healthy female baby. The amniotic fluid was contaminated (III degree), but there were no complications such as premature rupture of fetal membranes or nuchal cord. The newborn’s Apgar scores were 9 and 10 at the first and fifth minutes, respectively. An electrocardiogram (ECG) performed immediately after birth confirmed the diagnosis of CAVB, with atrial and ventricular rates of 136 and 68 bpm, respectively. A two-dimensional ultrasound reconfirmed the normal anatomical structure of the heart, with only the ductus arteriosus and the foramen ovale remaining open. Both the infant and her mother were discharged after three days of observation.
The child has since developed normally, engaging in typical play and achieving good academic performance. She has not required any medications or pacemaker implantation. At the age of 9, she revisited the diagnostic center for a follow-up. Echocardiography revealed a normally sized and structured heart, with a ventricular rate of 58 bpm. A 24-hour ambulatory ECG showed an average heart rate of 54 bpm, a total heart rate of 77,631 beats over 24 hours, a slowest heart rate of 43 bpm, and a fastest heart rate of 80 bpm.
Fetal CAVB is a condition with diverse etiologies. Approximately 50% of cases are associated with congenital heart disease (CHD), while nearly 40% are mediated by immune mechanisms. The remaining 10% of cases have no identifiable cause. In CHD patients, the prognosis of CAVB is closely linked to the type of CHD, with outcomes varying based on conditions such as isomerism, corrected transposition of the great arteries (cTGA), and critical pulmonary stenosis. Fetuses with cTGA often have a favorable prognosis, whereas those with left isomerism tend to have poorer outcomes. Pacemaker implantation is required in 89% of cases. Recent studies from Japan have indicated that a ventricular rate of less than 55 bpm can lead to significant fetal myocardial dysfunction and fetal hydrops, resulting in high mortality rates.
A retrospective, multi-center study involving 175 fetuses with isolated CAVB and maternal auto-antibodies identified several risk factors associated with death. These included a gestational age of less than 20 weeks, a ventricular rate of less than 50 bpm, fetal hydrops, and impaired left ventricular function at diagnosis. The presence of more than one of these variables was associated with a ten-fold increase in pre-birth mortality and a six-fold increase in neonatal mortality. Two-thirds of the survivors required pacemakers by the age of 1 year, and eight children developed cardiomyopathy.
Due to the low incidence of auto-antibody negative fetal CAVB, there are limited studies on this condition, and the natural prognosis and risk factors remain poorly understood. A multi-center study reported no significant difference in fetal and neonatal mortality between antibody-positive and antibody-negative pregnancies with known outcomes at 1 month of age. However, another multi-center study highlighted favorable long-term outcomes for congenital, non-immune, isolated atrioventricular (AV) block, with no patient deaths or cases of dilated cardiomyopathy, and few pacemaker-related complications.
In this case, the child with isolated, auto-antibody negative CAVB has thrived without any symptoms such as syncope, fatigue, or heart failure. She has not required any medication or pacemaker, and her heart rate has remained around 68 bpm at the last follow-up. The exact reason for this favorable outcome is unclear, but it may be related to the relatively higher ventricular rate (55 bpm or greater), which is thought to be associated with a high pacing site in the heart. An observational study of nine anti-Ro/La-negative cases found that three cases with a heart rate of less than 50 bpm died, despite timely pacemaker implantation. This suggests that in seronegative CAVB cases, a heart rate above 55 bpm may be indicative of a favorable prognosis.
In conclusion, this case report provides valuable insights into the diagnosis, management, and long-term outcomes of isolated anti-Ro/La antibody-negative fetal CAVB. Unlike previous studies focusing on pediatric auto-antibody positive cases, this report highlights a rare auto-antibody negative pediatric case with a relatively longer follow-up and a better outcome. Existing literature suggests that risk factors influencing the prognosis of isolated CAVB include a gestational age of less than 20 weeks, a ventricular rate lower than 50 bpm, fetal hydrops, and impaired left ventricular function. This case underscores the importance of heart rate as a key factor in determining the prognosis of fetal auto-antibody negative CAVB, likely related to the relatively high pacing site of the heart.
doi.org/10.1097/CM9.0000000000000581
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