Left Atrial Isomerism

Published on 07/06/2015 by admin

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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

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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.

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:

       (a) Karyotyping.

2. Follow-up.

a. Prognosis.

b. Monitoring.

F. Neonatal management

1. Medical.

a. Isoprenaline infusion.

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.

c. Oxygen.

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.

2. Surgical.

a. Palliative.

b. Corrective.

c. Heart transplantation.

H. Risk of recurrence

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