Prenatal diagnosis and management of congenital complete heart block

Abstract

Congenital complete heart block (CCHB) is a life-threatening medical condition in the unborn fetus with insufficiently validated prenatal interventions. Maternal administration of medications aimed at decreasing the immune response in the fetus and beta-agonists intended to increase fetal cardiac output have shown only marginal benefits. Anti-inflammatory therapies cannot reverse CCHB, but may decrease myocarditis and improve heart function. Advances in prenatal diagnosis and use of strict surveillance protocols for delivery timing have demonstrated small improvements in morbidity and mortality. Ambulatory surveillance programs and wearable fetal heart rate monitors may afford early identification of evolving fetal heart block allowing for emergent treatment. There is also preliminary data suggesting a roll for prevention of CCHB with hydroxychloroquine, but the efficacy and safety is still being studied. To date, intrauterine fetal pacing has not been successful due to the high-risk invasive placement techniques and potential problems with lead dislodgement. The development of a fully implantable micropacemaker via a minimally invasive approach has the potential to pace fetal patients with CCHB and thus delay delivery and allow fetal hydrops to resolve. The challenge remains to establish accepted prenatal interventions capable of successfully managing CCHB in utero until postnatal pacemaker placement is successfully achieved.

Keywords: complete heart block; congenital heart block; electro-physiology; fetal cardiology; fetal echocardiography; fetal intervention; pacemakers; prenatal diagnosis.

Figure 1:

Congenital complete heart block is associated with congenital heart disease in ~14–42% of cases (Brucato et al., 2003). The rest are isolated congenital heart block. 91% of isolated congenital heart block cases are associated with autoimmune mediated fetal heart block (Brucato et al., 2011; Buyon et al., 1998).

Figure 2:

Maternal Anti-Ro/SSA and/or anti-La/SSB autoantibodies pass through the placenta . It is hypothesized that they A: bind to L-type Calcium Receptors on fetal cardiomyocytes preventing uptake of calcium possibly leading to cellular apoptosis. Alternatively, B: they may bind to internal target antigens released during physiologic apoptosis which are then opsonized by maternal circulating antibodies. This leads to activation of the TLR 7/8 cascade. Both hypotheses result in inflammation, fibrosis and eventual calcification of the cardiac system resulting in CHB.

Figure 3:

Prenatal evaluation for CCHB A: Pulsed Wave Doppler. B: M- mode C: Color Doppler M-mode. D: Tissue Doppler Imaging. A, atrial; V, ventricular.

Figure 4:

Fetal micropacemaker and its implantation system. (a): Implantation cannula (4.5 mm o.d. × 3.8 mm i.d.) with sharpened tip of the trocar protruding from the tip. (b): Configuration during implantation with the micropacemaker inside a polyimide plastic sheath that slides through the cannula. The friction disk is wedged into the end of the sheath, allowing the protruding Ir electrode to be turned into the myocardium (pre-deployment). The pacemaker is deployed from the sheath by a pushrod after confirming ventricular capture by ultrasound. (c): The fetal pacemaker as deployed. Features from left to right: battery case of lithium cell, which functions as return electrode; glass sleeve for epoxy encapsulation; printed circuit board with discrete surface-mount circuitry and RF coil for inductive recharging; flexible lead (75 μm Pt-30Ir with Parylene-C insulation; epoxy friction disk over welded joint, corkscrew electrode (254 μm Ir with Parylene-C insulation).