23 Congenital Complete Heart Block

Rima S. Bader, James C. Huhta

I. CASE

A 35-year-old white woman, gravida 4, para 2, was referred at 22 weeks’ gestation by the obstetrician for fetal bradycardia. The mother has systemic lupus erythematosus (SLE) with a high titer of anti-Ro (SSA) antibodies. Her cardiac evaluation showed unifocal premature ventricular contractions (PVCs) but no evidence of myocardial dysfunction or pericarditis.

A. Fetal echocardiography findings

1. The fetal echo reveals situs solitus of the atria, levocardia, and left aortic arch.

2. The ventricular rate is 58 bpm and the atrial rate is 150 to 160 bpm, showing complete atrioventricular (AV) dissociation (congenital complete heart block [CCHB]).

3. The intracardiac anatomy is normal, with normal cardiac axis and position and equal-sized ventricles but mildly increased heart size (cardiothoracic ratio = 0.37).

4. There is no evidence of endocardial fibroelastosis (echogenic walls of one or more of the cardiac chambers).

5. The ductal and aortic arches are of similar size, and both arches have antegrade flow.

6. The pulmonary venous flow pattern is normal.

7. M-mode echocardiography confirmed the presence of atrial contractions that are at a normal rate and unrelated to a much slower ventricular rate (Fig. 23-1).

8. There is no evidence of valvar regurgitation (AV or semilunar). However, there is occasional intermittent tricuspid valve regurgitation related to the AV sequence. There is also a very low velocity diastolic regurgitation, which is normal in complete heart block (CHB).

9. The right ventricle (RV) and left ventricle (LV) Tei indices (myocardial performance index) are normal.

10. There is no evidence of heart failure.

11. The pulsatility index on the umbilical arterial Doppler (1.3) and middle cerebral artery Doppler (1.9) are normal.

Fig. 23-1 Fetal complete heart block confirmed by M-mode tracing through the ventricular and atrial walls. A, Note the atrial rate independent of the ventricular rate. B, The ventricular rate is measured.

B. Cardiovascular profile score

1. The cardiovascular profile score is 9/10 (1 off for cardiac size).

2. There are no other signs of heart failure.

3. The umbilical artery and vein flow patterns are normal.

C. Associated syndromes and extracardiac anomalies

None.

D. Fetal management and counseling

1. Amniocentesis is not offered because the risk from amniocentesis is higher than the risk of abnormal karyotype in isolated CCHB.

2. Fetal management of CHB.

a. Fetal drug therapy has been mainly directed toward three different features of the disease entity.

    (1) Autoimmune-mediated AV block.

       (a) Glucocorticoids that cross the placenta (e.g., dexamethasone) have been used to treat the autoimmune inflammatory process that eventually can lead to disruption of the fetal conduction system.

       (b) Several case reports have documented resolution of pleural and pericardial effusions in maternal autoantibody-mediated AV block, despite the etiology of heart block.

       (c) Glucocorticosteroids have not been shown to significantly affect the incidence or severity of AV block among affected pregnancies.

       (c) With steroid treatments, the possible adverse effects in the mother (e.g., gestational diabetes) and in the fetus (adrenal suppression) or the newborn (e.g., adrenal suppression) must be considered.

       (d) Oligohydramnios in the third trimester has also been observed in some treated pregnancies.

    (2) Slow heart rate.

       (a) Several studies have shown that ventricular rates less than 50 to 55 bpm are related to a worse outcome.

       (b) Based on this observation, administration of sympathomimetic drugs has been advocated for the treatment of CCHB to increase the fetal ventricular rate.

       (c) Terbutaline and salbutamol appear to cross the placental barrier well and increase fetal ventricular rate by only 15%, but improve cardiac output.

    (3) Heart failure.

       (a) For maternal autoantibody-induced AV block associated with heart failure or evolution of fetal hydrops, glucocorticosteroids have been advocated as well as β-sympathomimetics to increase the ventricular rate and even provide inotropic support.

       (b) Heart failure in maternal autoantibody-induced AV block often results from the associated diffuse myocardial disease with endocardial fibroelastosis.

       (c) Some have advocated the use of intraumbilical pulsed steroids and γ-globulin in such severe cases, given the high likelihood of intrauterine or neonatal demise.

       (d) The true efficacy of these measures has not been fully delineated. Isolated case reports have documented the use of maternally administered digoxin and rarely furosemide with variable success.

b. Premature delivery.

    (1) Premature delivery of the hydropic fetus is a high-risk strategy, because the fetus invariably suffers all the disorders of prematurity including respiratory distress syndrome and infections. Nevertheless, in the face of evolving hydrops there is little alternative.

    (2) After delivery, good results have been achieved with the early institution of permanent epicardial pacing.

c. Fetal ventricular pacing.

    (1) Experimental data from fetal lamb studies have shown that pacing is feasible using either a transvenous or an epicardial approach; chronic ventricular pacing was well tolerated and did not affect ventricular performance.

    (2) Substantial increases in cardiac output have also been shown with fetal ventricular pacing in experimentally induced CHB.

    (3) Current technology does not allow safe in utero pacing; however, two such cases have been reported.

    (4) Open pacemaker implantation has been attempted once in the human fetus but was unsuccessful.

3. Follow-up included serial antenatal studies at 1- to 2-week intervals.

a. Mother’s follow-up.

    (1) Depends on the etiology.

       (a) Check maternal autoantibodies. Isolated fetal AV block is associated with maternal autoantibodies (anti-Ro and anti-La) in 95% of cases. Most mothers of fetuses with autoantibody-mediated fetal AV block (70%-80%) have no clinical autoimmune disease; however, some might have such autoimmune entities as Sjögren’s or systemic lupus erythematosus.

       (b) In 5% there may be a genetic etiology or infectious etiology, so TORCH (toxoplasmosis, other infections, rubella, cytomegalovirus, herpes simplex virus) screen is advisable in such cases. However, in some cases there is no definite etiology.

    (2) ECG should be monitored for arrhythmia during sympathomimetic therapy. Terbutaline has been associated with development of pulmonary edema in the mother, requiring discontinuation.

b. Fetus’s follow-up: A fetal ECG and general fetal surveillance should be provided every 1 to 2 weeks. The following should be serially evaluated:

    (1) Heart rate.

       (a) Studies have shown that ventricular rates greater than 50 to 55 bpm are related to a better outcome, with possible implementation of b-sympathomimetic therapy for ventricular rates of less than 55 bpm or if there is evidence of evolving hydrops.

       (b) Terbutaline may be given 2.5–5.0 mg every 4–6 hours with subsequent dose adjustment.

    (2) Heart size and ventricular function.

       (a) Systolic function can be assessed. In most affected fetuses, the systolic function is hyperdynamic. The heart must produce a much larger stroke volume with every beat in order to maintain the equivalent of a normal biventricular output. The heart is larger as a result of a greater preload.

       (b) If the heart muscle is echogenic, one should suspect evolving endocardial fibroelastosis, which could compromise the heart function and ultimately lead to heart failure and demise.

    (3) Evidence of hydrops fetalis, including pericardial effusion, ascites, and skin edema.

    (4) AV valve regurgitation.

    (5) Semilunar valve regurgitation.

    (6) Abnormal venous Doppler flow, such as atrial wave reversal in the ductus venosus or cord.

    (7) Arrhythmia.

       (a) Monitor for medication-induced arrhythmias or spontaneous ventricular ectopies.

       (b) There may be spontaneous ventricular ectopy in the absence of β-sympathomimetics.

E. Delivery

1. In isolated CHB, delivery should be near term (36 to 38 weeks) in a tertiary care center given the risk of hydrops fetalis and fetal demise from more severe bradycardia.

2. Premature delivery should normally be planned (for maternal or fetal indications) so that preparations can be made for care of the baby and mother.

F. Follow-up

1. Before the widespread application of pacemakers, infant mortality in isolated CCHB was estimated to be 8% to 16%.

2. The majority of newborns with isolated CCHB are hemodynamically stable.

3. Permanent pacing is required in a minority because of:

a. Heart failure.

b. Failure to thrive.

c. Mean heart rate less than 55 bpm.

d. LV dilation and mitral regurgitation.

e. Long QTc syndrome.

2. Many asymptomatic patients reach adult life without pacing, but the risk of sudden death is 5% during adult life. For this reason, dual-chamber pacemaker implantation is increasingly advocated routinely in adolescence.

3. Following pacemaker implantation, the prognosis is good, with almost normal exercise tolerance in the majority.

4. Immune-positive patients can develop cardiomyopathy, requiring transplantation.

5. Rarely, LV function deteriorates in spite of adequate pacing. This could be explained by an accompanying myocarditis from the original insult, leading to cardiac dysfunction.

6. Pacemaker checks should be every 6 months in the first year and yearly thereafter.

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