Fetal Complete Congenital Heart Block

Case 1

One may appreciate the slow heart rate of the ventricles. We can also see that the atrial rate (right atrium) seems faster than the underlying ventricular rate.

4 chamber with colour to visualize the inflow, as well as output via the LVOT and RVOT.

There is some trivial tricuspid regurgitation. Inflammatory changes to the papillary muscles may occur in the context of the myocardial inflammation secondary to transplacental passage of maternal auto-antibodies (Anti-Ro, Anti-La). Significant atrio-ventricular valvular insufficiency may occur in this context.

Despite the low heart rate, there seem to be subjective appropriate biventricular contraction, as well as absence of clear endofibroelastosis, which may occur in the context of transplacental passage of Anti-Ro / Anti-La (SSa/SSb) antibodies in the context of maternal rheumatological conditions that may lead to congenital heart block by inflammatory changes / fibrosis of the fetal atrio-ventricular node and overall conductive system / myocardium.

Short axis demonstrating the slow bi-ventricular heart rate by B-mode

Sweep from the short-axis to the arch view.

Colour in arch view indicates that the blood flow corresponds to the ventricular rate.

These clips outline the contractions of the atriums at a faster rate than the ventricular contraction. The M-Mode (Ventricular-Atrial) will help characterize further the entity.

Ventricular rate of 53 bpm

M-mode outlining that the atrial rate is 161 bpm and the ventricular rate is 52 bpm.

Evaluation of the atrial and ventricular rates by M-Mode

Dopplers outlining the underlying ventricular rate

Case 2:

Views outlining the low ventricular rate. One may perceive the faster atrial contraction on the B-Mode. This will be better exemplified by the M-Mode (better temporal resolution), allowing for evaluation of atrial and ventricular rates and relationship.

M-Mode outlining that the ventricular rate is 66 bpm, while the atrial rate is 140. There is no clear relationship between the atrial and ventricular rates.

Doppler in the arch may be used to estimate the ventricular rate.

Dopplers in a fetus exposed to an Anti-Ro+ pregnancy but without any evidence of congenital heart block:

Normal atrivoentricular (AV) time interval (mitral-aortic) at 107 msec, (superior vena cava (SVC)-aorta) at 97 msec

Case of complete heart block with hydrops in fetal life provided by Dr Wadi Mawad, Pediatric Cardiologist at the Montreal Children's Hospital

Normal atrio-ventricular conduction on M-mode

Takes advantage of the Mital-Aortic continuity to sample both the inflow and outflow simultaneously and allows assessement of atrial, ventricular and atrio-ventricular conduction delays

SVC-Ao Doppler relies on the proximity of the superior vena cava and the ascending aorta, as well as the retrograde A wave in the SVC coinciding with atrial contraction (blood flow going back into the SVC during right atrial contraction).

This allows for evaluation of the atrial and ventricular rates as well as, the AV node conduction duration.

Functional AV block (blocked premature atrial contractions) or atrial bigeminy may be mistaken at times for complete heart block.

Presentation on Congenital Heart Block

Congenital Heart Block_web.pdf

Elements to consider in the care of fetuses with complete immune-mediated CHB (not exhaustive)

The management of these fetuses is still controversial. There are variations in practice due to the lack of trial-informed studies. These are elements to consider and adapt based on the practice at your institution and in consultation with your local experts. Ambulatory monitoring with Dopplers being performed by the pregnant patient may be considered, although the data does not seem to be convincing regarding the detection of first and second-degree heart block by the pregnant individual. A multi-centric study (STOP-BLOQ) is ongoing.

Prenatal:

Continue vigilant monitoring of fetal cardiac function and signs of hydrops. Adjust delivery timing based on maternal or fetal alterations in well-being.
Fetal cardiology to evaluate positive Anti-Ro or Anti-La pregnancy starting 16 weeks and up to 24 weeks with screening for fetal heart block
Review recent ultrasounds and fetal echocardiography conducted before the delivery.
Evaluate for presence of fetal heart block (quantification of mechanical AV interval), fetal cardiac performance, fetal endocardial fibroelastosis, hydrops, polyhydramnios, growth restriction, fetal umbilical and cerebral Dopplers, and presence/severity of atrio-ventricular valvular insufficiency. These are all factors of prognosis.
Consider prenatal treatment with maternal dexamethasone to reduce the risk of postnatal neonatal cardiomyopathy with those having fetal heart block. IVIG are reserved under certain circumstances (worsening CHB, signs of fetal cardiomyopathy). Please review section on fetal cardiac function.
Pregnant individuals with SSa (Anti-Ro) or SSb (Anti-La) circulating antibodies should be followed by rheumatology and maternal fetal medicine (and possibly obstetrical medicine). A titre value of the corresponding circulating antibody should be considered during pregnancy.
"The use of β-sympathomimetics such as terbutaline, salbutamol, and isoprenaline to augment fetal ventricular rates when <55 bpm has been reported. β-Sympathomimetics are reasonable to use in fetuses with heart rates <55 bpm or in fetuses with higher heart rates if there is underlying severe CHD or symptoms of fetal heart failure or hydrops. Terbutaline appears to be well tolerated, although maternal resting heart rates of 100 to 120 bpm and benign ectopy are commonly encountered. Unfortunately, although terbutaline may increase fetal rates and prolong pregnancy, no studies have shown survival benefit. Although there is merit to the notion, because of significant technical limitations, fetal pacing has not been shown to be successful in improving survival or prolonging gestation and therefore at present is experimental and not recommended as part of usual care." Reference.
After delivery - collaborate with pharmacy (adult) to devise a dexamethasone tapering strategy post-delivery in the mother exposed to prolonged dexamethasone therapy.

Delivery Room Management:

Plan a daytime and weekday C-section due to fetal bradycardia (inability to monitor fetal wellbeing during labour).
Ensure NICU and Cardiology team aware of delivery. NICU team presence at delivery and prompt notification when the mother arrives at the birthing center.
Evaluate the possibility of delayed cord clamping (DCC) at the discretion of the neonatologist and obstetrician, with immediate clamping if the baby lacks vigor and respiratory efforts.
Prepare for potential neonatal bradycardia, with readiness for respiratory support, intubation, line placement, and chest compression if needed.
The baby may be born with a heart rate lower than 60 (often ventricular rate can hover around 55-60 bpm during fetal echocardiography). Heart rate typically increases during the postnatal transition (adrenergic stimulation from delivery and transitional process increasing background ventricular rate) but it may be that the newborn will have a heart rate below 60 bpm with appropriate output to sustain transition without the need of significant resuscitation. These newborns will have had some adaptation in-utero to the low ventricular rate, if their cardiac performance was not impacted by myocardial inflammation (myocarditis) and if the AV valve have appropriate coaptation.
It could also be that these newborns experience significant need for support – respiratory support, and chest compression if significantly hypoperfused and dropping heart rate. Heart rate may not be an adequate indicator of efficiency of resuscitation measures. As such, the team should be ready to provide respiratory assistance and intubation, line placement and chest compression. The advancement to chest compression should only be after airway securement and adequate oxygenation/ventilation and if significant instability with no reactivity, poor perfusion (long refill, pale/blue, limp, weak pulses, mottled), poor pulses. Saturometer will often have a poor or no tracing due to the low perfusional status.
In the delivery room, a team member should be ready to install an umbilical venous line.
Isoproterenol should be prepared for an infusion and be available in the delivery room on a pump. The medication range is: 0.01 - 0.5 microgram/kg/minute (Maximum dose: 2 microgram/kg/ minute). This medication should be considered for initiation at 0.01 mcg/kg/min and up titration to effect (higher dosages such as 0.1 mcg/kg/min can be fairly pro-arrhythmic and vasodilating). It should only be started for hemodynamically instability rather than purely based on a heart rate value. Typically, it is initiated in babies with significant bradycardia hovering less than 50 bpm and with concomitant hemodynamics instability. This medication is used to accelerate the ventricular rhythm (not to increase atrio-ventricular conduction, since the AV node is often fibrosed in infants with complete congenital heart block). It may be titrated up if the response is not adequate (usually fast acting and titration can occur after 5-10 minutes of initiation or change in dose).
Transcutaneous pacing should be a last resort and may lead to significant skin burns. Ideally, it should be initiated only in consultation with cardiology, unless there is an extremely urgent situation and cardiology not available in the delivery room or at bedside. Skin needs to be dried and pads should not be touching each other (one pad on front and one pad on the back). Output should be initiated at 20 mA and rate at 90 bpm. Output may be increased by increment of 5 mA until there is QRS capture. The pacer machine should be set on “fixed” mode in the delivery room, and only be transitioned to “demand” mode once there is the possibility of connecting the ECG leads to the pacer machine.
Cardiac surgery and cardiology need to be aware of these cases in advance, in case there is a need for urgent pacemaker or epicardial pacemaker (if premature newborn / small weight).

Neonatal admission:

Newborn should be admitted to the NICU and UVL/UAL should be installed for administration of medication and monitoring. A double-lumen UVL should be placed for medications. In the case of pacing, analgesia may be required. Sedation/Analgesia may also be required to decrease cardiac work if the baby is unstable and with signs of heart failure.
Document liver edge on exam (presence of hepatomegaly and cm to coastal border).
NIRS is installed at our institution (cerebral and somatic) for monitoring.
Baby is kept NPO and TFI is at 65 mL/kg/day. Starter TPN and SMOF (lipids) may be considered to optimize nutrition.
Initial blood work include: gaz, crossmatch and Coombs, CBC, liver enzymes, albumin, creatinine, bilirubin (for cholestasis), baseline NT-proBNP, baseline troponin, baseline creatine kinase.
Blood gaz is then followed q 4-6 hours for the first day of life (to monitor glucose, calcium, pH, CO2, electrolytes and lactate)
Mg, PO4, Triglycerides (TPN labs) with liver enzymes (AST, ALT) and Bili at 24 hours of age to rule out autoimmune hepatitis, cholestasis and routine screening of neonatal jaundice
Chest and abdominal radiography, as well as abdominal shoot-through for line placement and cardio-thoracic silhouette
Consultation with cardiology with echocardiography and formal 12-lead ECG.
We obtain consent with parents for the admission, pasteurized human milk (if eventually needed), PICC line and transfusion.
Hydrocortisone initiated at 30 mg/m2/day (average newborn BSA is 0.25 m2) = 1 mg IV q8hr. This dose should be kept until clarification of the plan (i.e. need for pacemaker or not). It should then be tapered to 10 mg/m2/day and eventually an ACTH-stimulation test should be performed.
IVIG should only considered with approval of cardiology if there is a significant concern for carditis and cardiac dysfunction.
Newborn may also require inotropic support with epinephrine (or dobutamine) infusion (which also has chronotropic action) depending on the hemodynamic status / perfusion and cardiac evaluation. Dobutamine can be pro-arrhythmogenic, as such epinephrine may be a more optimal choice in the context of decreased cardiac function.
Will likely require a double-lumen PICC line during admission.
Follow CBC before discharge to rule out SLE-related thrombocytopenia, anemia and leucopenia
Consultation with social worker, lactation consultant.
Consultation pharmacy: may not be eligible to rotavirus (live) vaccine considering the prolong exposure to steroids during fetal life. As such, baby may not be eligible to live vaccines in first year of life.
The family may be eligible to Neonatal Follow-up.
Avoid sun light exposure to minimized risk of developing neonatal cutaneous lupus. Neonatal cutaneous lupus manifestation may occur in the first few days of life, but is typically appearing after sun exposure due to photosensitivity. It is transient and typically benign.