Introduction: Fetal sinus bradycardia (FSB) is usually a benign antenatal finding but could be a marker of an underlying serious condition in later life. Aim: To evaluate the antenatal course and postnatal outcome of FSB. Method: A retrospective review of all cases of FSB (defined as fetal heart rate (FHR) < 3rd percentile for gestational age (GA) with 1:1 atrioventricular conduction between January 2014 and December 2024. Cases of isomerism were excluded but those with congenital heart disease (CHD) with normal situs were included. Antenatal data included GA at diagnosis, referral indication, family history, fetal echocardiogram findings and sequential FHR. Postnatal data included 12-lead ECG, echocardiogram, 24-hour Holter and genetic testing. Results: The final cohort of 34 cases of FSB resulted in 33 live births with one termination of pregnancy for multiple extracardiac anomalies. Referral indications included fetal bradycardia in 20, suspected CHD in five, maternal anti-Ro antibodies in one and family history of long QT syndrome (LQTS) in five, of cardiomyopathy (CMP) in two and of CHD in one. Associated cardiac abnormalities were present in seven fetuses (three cases of hypertrophic cardiomyopathy and one each of hypoplastic left heart syndrome, bilateral superior vena cava, left ventricular non-compaction (LVNC) and small ventricular septal defect. Postnatal diagnosis included LQTS in 10, sinus node dysfunction (SND) in six, two each of LVNC and Albright’s hereditary osteodystrophy with hypothyroidism, one each of histiocytic CMP, catecholaminergic polymorphic ventricular tachycardia and myotonic muscular dystrophy. The remaining 11 cases were normal. Genetic reports were available in 22 patients, being positive for mutations in KCNQ1 in seven, KCNH2 in three, GNAS in two, one each of NDUFB11, RYR2, CDH7 and DMPK. One had a variant of uncertain significance and five were normal. Cascade testing detected affected family members in two of the four de novo cases of LQTS and in the one case of CPVT. Only one baby with SND (anti-Ro related) required pacemaker at four years of age. Conclusion: FSB could be the first manifestation of serious underlying conditions including inherited arrhythmia syndromes, CMP or antibody mediated SND, and needs careful antenatal and postnatal evaluation. Cascade testing allows detection of potentially at risk first-degree relatives which in turns leads to prompt intervention and appropriate management.
Nair et al. (Tue,) studied this question.