Perspectives on Fetal Pacing

Abstract

Congenital complete heart block (CHB) is now usually diagnosed in utero. It can be isolated, i.e. with a structurally normal heart or associated with structural heart disease in the fetus (left atrial isomerism, AV septal defect or AV discordance). Isolated congenital CHB is thought to result from the trans-placental passage of maternal antibodies, anti-Rho and anti-La. Although fetal heart block may generate a slow heart rate of 30 to 50 % of normal fetal rate, the majority of the fetuses with CHB does well and progress to term and can be delivered normally. However, a small part of the cases develops in utero heart failure, which manifests as fetal hydrops. This morbid association of diseases presents uniform fatal outcome, regardless of the presence or absence of an associated structural heart defect. If low-output failure and/or fetal heart rate cannot be reversed by medical treatment with positive chronotropic drugs or steroids, fetal ventricular pacing seems to be the next logical form of treatment. The arguments for trying to attempt fetal pacing are compelling. This therapeutic alternative offers some advantages. Firstly, definitive treatment can be introduced immediately after the first signs of fetal hydrops. This would allow the pregnancy to continue normally with recovery from congestive heart failure and normal fetal development until term, with stable respiratory and cardiovascular functions at delivery. This chapter describes different fetal pacing proposals to establish effective treatment for fetuses with complete heart block who are in heart failure – apart from premature delivery. The development of a purpose built pacing lead and the available expertise of a Fetal Medicine Specialist, Fetal Cardiologist, Pediatric Cardiac Surgeon and Electrophysiologist that can work together will optimize all and every chance of this procedure becoming a feasible alternative to treat these high-risk fetuses.