Left Atrial Isomerism

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20 Left Atrial Isomerism

I. CASE

A 40-year-old white woman, gravida 4, para 3+0, was referred by the obstetrician at 18 weeks’ gestation for slow fetal heart rate and a two-vessel cord. An ultrasound at 12 weeks revealed increased nuchal translucency, and normal fetal karyotype was documented by chorionic villous sampling (CVS). The woman has a 3 living children, none of whom have heart disease.

A. Fetal echocardiography findings

1. The findings suggest a picture of left atrial isomerism (LAI) or polysplenia syndrome (Table 30-1).

a. There is dextrocardia (cardiac axis = 60 degrees), and the stomach is on the right side of the fetal abdomen as well.

b. There is a midline liver and multilobed right-sided spleen.

c. The heart is mildly enlarged (cardiothoracic ratio = 0.47).

d. The inferior vena cava (IVC) is interrupted, with azygous continuation to a right superior vena cava (SVC) that connects directly to the right-sided atrium.

e. There is a left SVC to coronary sinus to right-sided atrium.

f. The four-chamber view reveals absence of the crux of the heart consistent with an atrioventricular septal defect (AVSD), with severe disproportion between the ventricles.

g. There is a dominant right-sided left ventricle (LV).

2. The outflow assessment reveals normally related great arteries with mild asymmetry. Aorta–to–pulmonary artery diameter ratio is 1:0.7.

3. The aortic valve is in continuity with the common atrioventricular (AV) valve and arises from the LV. The size is normal but the velocity through the aorta is increased (2 m/s). There is also mild aortic insufficiency.

4. The pulmonary artery arises from a small right ventricle (RV) that is composed largely of an outlet chamber. The pulmonary valve is bicuspid, with mild flow acceleration by Doppler (2 m/s).

5. The branch pulmonary arteries are a good size for gestational age (right pulmonary artery = 1.9 mm, left pulmonary artery = 2.2 mm).

6. The aortic arch is leftward, and the ductal and aortic arches have antegrade flow.

7. Interatrial flow is unrestricted through a primum atrial septal defect (ASD) with a bidirectional shunt.

8. The pulmonary veins connect via a confluence that joins the posterior wall of the left-sided atrium, and they exhibit a normal flow pattern.

9. The hepatic veins connect to the right-sided atrium via a common trunk.

10. There is fetal bradycardia with an atrial heart rate of 115 bpm and a ventricular heart rate of 68 bpm, and complete AV block is suspected.

11. The LV Tei index (myocardial performance index) is normal.

12. There was systolic a wave reversal at the atrial rate on each beat in the ductus venosus with intermittently larger a waves, suggesting cannon waves occurring during ventricular systole (Fig. 20-1).

13. There is no evidence of hydrops.

14. The peripheral arterial Doppler has a normal pulsatility index of 1.2, and the middle cerebral artery pulsatility index is 2.0.

TABLE 20-1 FEATURES CHARACTERIZING NORMAL ASYMMETRY

Adapted from Yoo SJ, Hornberger LK, Smallhorn J: Abnormal visceral and atrial situs and congenital heart disease. In Yagel S, Silverman NH, Gembruch U (eds): Fetal Cardiology: Embryology, Genetics, Physiology, Echocardiographic Evaluation, Diagnosis and Perinatal Management of Cardiac Diseases. London: Taylor & Francis Group, 2002.

Fig. 20-1 Pulsed Doppler in the ductus venosus in a fetus with complete heart block (CHB) and left atrial isomerism (LAI) showing atrial reversal at the atrial rate on each atrial contraction.

B. Cardiovascular profile score

1. The cardiovascular profile score is 7/10.

2. Points deducted were 1 for cardiac size, 1 for aortic insufficiency, and 1 for abnormal venous Doppler.

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

4. There are no signs of hydrops fetalis.

C. Associated syndromes and extracardiac anomalies

1. Two-vessel cord and history of increased nuchal translucency.

2. Female fetuses and newborns with LAI can have a Turner’s phenotype, and the web neck that is part of it is likely to have reflected increased nuchal translucency early on.

D. Fetal management and counseling

1. Amniocentesis.

a. Because the mother has already had chorionic villous sampling, there was no further discussion about fetal karyotype except that aneuploidy and 22q11.2 deletion are extremely rare in isomerism.

b. Diagnosis of tetralogy of Fallot (TOF) should prompt referral for the following:

(1) Thorough anatomic examination by ultrasound.

(2) Amniocentesis.

(a) Karyotyping.

(b) TORCH (toxoplasmosis, other infections, rubella, cytomegalovirus, herpes simplex virus) screen.

(c) Chromosomal anomalies including fluorescent in situ hybridization (FISH) screen for chromosome 22q11 microdeletion.

(1) In general, heart block in LAI, irrespective of the cardiac pathology, carries a poor prognosis, with a perinatal mortality that approaches 100%. This may in part be due to the very low ventricular rates associated with this condition.

(2) If the mother chooses to continue the pregnancy, serial antenatal studies should be done every week initially.

(1) Heart rate.

(a) Optimal ventricular rate greater than 55 bpm is achieved by giving the mother oral sympathomimetic medication (e.g., terbutaline) with subsequent dose adjustment.

(b) With increasing gestational age, increased doses of terbutaline may be needed to achieve the same effect.

(c) Tolerance to terbutaline can develop in the mother and or fetus.

(d) The maximum dosage of terbutaline is 5 mg PO every 4 hours.

(e) The mother must be monitored for the rare complication of pulmonary edema.

(f) Diabetes management can be altered by terbutaline.

(2) Heart size and ventricular function.

(3) Evidence of hydrops fetalis, such as pericardial effusion.

(4) AV valve regurgitation.

(5) Progressive aortic valve regurgitation could lead to heart failure.

(6) Progressive bilateral outflow tract obstruction is possible in this condition. Reassessment of the pulmonary outflow and direction of ductal and main pulmonary arterial flow is necessary.

E. Delivery

1. In LAI with complete heart block and complex congenital heart disease, delivery should be at term or as near as possible in a tertiary care center.

2. If the baby is developing fetal hydrops, earlier delivery may be necessary, as long as it is clearly possible to improve the hemodynamic condition of the fetus with delivery and intervention.

3. If delivery with postnatal intervention is not believed to be effective, aside from termination of pregnancy if desired by the patient, letting nature take its course with progressive hydrops may be the best option, with close follow-up of the mother to be certain there is no harmful consequence for her.

4. If there is no evolution of hydrops, cesarean section delivery may be considered given the difficulties with fetal monitoring in fetal bradycardia. Ideally, a planned cesarean section is performed at 36 to 38 weeks of gestation.

F. Neonatal management

a. Isoprenaline infusion.

(1) Isoprenaline infusion is the first step to increase the neonatal heart rate if the baby is clearly compromised hemodynamically.

(2) Indications include metabolic acidosis, hypotension, other evidence of low cardiac output, and ventricular (heart) rate less than 55 bpm.

b. Prostaglandin E₁ (PGE₁) infusion is indicated if there is evidence of critical pulmonary outflow tract obstruction with retrograde ductal flow in utero or unless the direction of ductal flow is not certain.

(1) Administration of oxygen can increase oxygen saturation by decreasing pulmonary valve regurgitation and increasing blood flow.

(2) Oxygen should be given only if the systemic saturations are very low (<70%), because oxygen delivery may be deleterious with single-ventricle physiology when it is given where there is too much pulmonary blood flow.

d. At times, volume and inotropic support may be indicated to improve ventricular function.

e. Assessment of heart rate in relation to the baby’s clinical condition.

(1) Indication for insertion of a temporary or permanent pacemaker (epicardial) is failure to respond to or need for ongoing medical therapy (isoproterenol).

(2) Immediate temporary pacing in the delivery room is indicated in the compromised hydropic neonate. This may be facilitated if the umbilical vein connects with the azygous because a pacing wire can be advanced in the umbilical vein to the azygous and might go directly down to the ventricle, thus providing a site for pacing that is guided by the baby’s unusual venous anatomy.

(1) If at birth the pulmonary stenosis is severe, and if the saturations are not adequate despite therapeutic measures such as volume replacement and oxygen supplementation, PGE₁ is added and an initial aortopulmonary shunt (modified Blalock–Taussig shunt) is performed in the first week of life. Surgical mortality is about 10% to 15%.

(2) If the pulmonary stenosis is considered mild to moderate, the baby should be observed until the ductus arteriosus has closed or is nearly closed so as to be absolutely certain that the pulmonary blood flow is sufficient before discharge.

(3) One should be certain that the desaturation is entirely related to the degree of pulmonary blood flow, because in a compromised baby with single-ventricle physiology the desaturation might also be caused by low mixed venous saturations.

(1) At 8 to 12 months of life, a right cavopulmonary shunt or bidirectional Glenn shunt should be performed.

(a) The timing is delayed in this type of infant because with an interrupted IVC, a much greater proportion of the systemic venous return goes to the SVC. Thus it is critical that the infant have a normal pulmonary vascular bed that is sufficiently matured to handle the bulk of the cardiac output.

(b) Flow through the hepatic veins is the only systemic venous flow that continues to return directly to the heart.

(2) At 2 to 5 years, a Fontan procedure is performed.

(a) Before surgery, cardiac catheterization must confirm the presence of normal cavopulmonary and pulmonary artery anatomy, low pulmonary vascular resistance, good ventricular systolic function, low-normal ventricular filling pressures, and no atrial septal restriction.

(b) In the Fontan procedure, the hepatic veins are connected via a conduit or intracardiac baffle to the pulmonary arteries, thereby bypassing the heart. Criteria for the Fontan should be fulfilled (see Chapter 12, Tricuspid Atresia).

(c) The course of this patient will continue to be complicated by the heart block and potential need for reintervention for pacemaker therapy.

c. Heart transplantation.

(1) With the potential for biventricular outflow tract obstruction, a common AV valve, and heart block, cardiac transplantation is another option and perhaps the best option for the family. Prenatal consultation with the transplant team is recommended.

(2) Transplantation is an option only for neonates who can be stabilized hemodynamically after birth for a period of 2 to 4 months while a suitable heart donor is sought.

(3) Survival at 10 years of age after neonatal transplantation when the heart is the primary pathology is 70% to 80%.

(4) After transplantation, lifelong antirejection medications are needed plus periodic surveillance for rejection by echocardiography and cardiac biopsy.

G. Follow-up

1. Subacute bacterial endocarditis (SBE) prophylaxis is required for life.

2. For residual hemodynamic abnormalities, anticongestive medications and some restriction of activities may be required.

3. The patient should have one or two outpatient follow-up visits each year, with 12-lead electrocardiogram (ECG) and echocardiogram.

4. If there is any history of unexplained palpitations or abnormal heart rhythm, a metabolic stress test with 24-hour Holter monitoring is recommended.

5. Pacemaker checks are necessary to detect lead or battery failure.

H. Risk of recurrence

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