Fetal heart rate tracing interpretation in cases of fetal heart block: A case series

Abstract Objective: To determine whether antepartum non-stress test (NST) and intrapartum FHR tracings in fetuses with heart block are reliable or not. Case series: This study describes three fetuses with second degree heart block (SHB) in the second half of pregnancy. They showed bradycardia (FHR: 65-80 bpm.) with reactive non-stress test (NST) and normal baseline variability. However, one subsequently developed complete heart block (CHB) and showed minimal FHR variability without accelerations in late gestation. The first two cases had intrapartum normal FHR variability with accelerations despite bradycardia. FHR tracings were readable and well-interpreted. They well tolerated labor and vaginal delivery, giving birth to the healthy babies with SHB. The third case with CHB showed intrapartum bradycardia with minimal FHR variability without acceleration, no response to acoustic stimulation. Because of difficulty in tracing interpretation, cesarean section in early labor at 37 weeks of gestation was performed, giving birth to a healthy newborn with CHB, though requiring pacemaker. Conclusion: FHR tracings of SHB fetuses still represent SA node function depending on sympathetic and parasympathetic tone, reflective of fetal hypoxic status. NST and intrapartum FHR tracings are reliable. On the contrary, FHR tracings of cases with CHB are independent from SA node impulses, representing solely ventricular rate, not reflective of SA node rate variability and CNS hypoxic status. Therefore, the interpretation in the fetuses with CHB is unreliable to determine fetal well-being.