COARCTATION OF THE AORTA

Coarctation is narrowing of the aortic lumen, usually at the ductus arteriosus. The severity of this defect ranges from slight narrowing of the distal end to severe hypoplasia of the entire arch. 

TYPES OF COARCTATION

 

Link to Types of Coarctation

 

CLASSIFICATION

 

Link to Classification

 

HEMODYNAMICS

No significant change because only about 10% of the cardiac output flows through the aortic isthmus. The descending aorta is mainly supplied via the ductus arteriosus. The hemodynamic effect may be greater if the aortic arch is hypoplastic.
 

ULTRASOUND

 

  1. Actual area of narrowing may be difficult to identify antenatally. This may be due to normal patency of the ductus arteriosus in utero. Prenatal diagnosis usually relies on the presence of ancillary findings.
  2. Large RV (with a ratio over the left ventricle greater than 1.3) (3,4). Right ventricular hypertrophy has been reported.
  3. Small LV is a useful sign (4,5), however some fetuses do not have ventricular size discrepancy and some fetuses with ventricular discrepancy do not have a cardiac lesion. It's sensitivity for the diagnosis of coarctation of the aorta is 50-60% (6,7).
    False positive (8,9) - Ventricular disproportion in the third trimester due to relative increase in the RV in comparison to the LV.

 

 

 

 

 

Video clip of Coarctation of Aorta - small left ventricle

Video clip of Coarctation of the Aorta – Sagittal views

Video clip of Coarctation of the Aorta – short axis

 

 
  1. Aortic arch - Hypoplasia of the aortic arch affects the proximal arch, most commonly between the left common carotid artery and the left subclavian artery or the isthmus, and may extend into the brachiocephalic vessels. Sonographically a small aorta at the level of the valve is present in most fetuses due to hypoplasia of the isthmus and transverse arch. Sagittal view of the arch may be normal. Hypoplasia of the transverse arch and isthmus may be detected in 80-100% of cases when adequate images of the distal arch can be obtained (14). 12/15 fetuses had a transverse arch diameter less the 3rd percentile. 10/10 fetuses had Isthmic hypoplasia with a diameter less than the third percentile. 15/18 fetuses with adequate visualization of the ascending aorta, the diameter was less than the third percentile for gestational age.
  2.  Normograms for aortic size have been reported.

 

 

      5.  Sagittal view.

Case 1

Case 2

  1. Echogenic contralateral (contraductal) shelf in the aortic lumen or generalized narrowing (3,4). This appears to be the least frequent finding that can be detected on antenatal scans. Hutchins (15) described it as an enfolded obstructive curtain in the posterior wall of the aorta, which could represent a branch point in the aorta, resulting from increased pulmonary artery and ductal flow relative to aortic flow in utero. Randolph et.al. (16) describe it as an exaggeration of a normal slight indentation in the posterior aortic wall from abnormal ductal flow diverted towards the posterior wall of the aorta.

 
  1. Color Doppler may demonstrate:
      1. Normal flow in the aorta with normal velocities.
      2. Increased or decreased velocities distal to the coarctation (3).
      3. Retrograde flow proximal to the coarctation (14).
      4. High velocity jet that is present within the narrowed segment or just proximal to it (17).
      5. Turbulent flow.

 

Velocity change across the coarctation on pulsed doppler

Reverse blood flow proximal to the coarctation

Reverse flow in the aortic arch

Normal flow in the aortic arch

  2. Color and pulsed doppler may demonstrate left to right flow through the foramen ovale (9).
  3. Increased flow across the tricuspid valve when compared to the mitral valve (3).
  4. Left axis deviation (>57°).
  5. Hornberger et.al. 1994 (14) studied prenatal scans on 20 fetuses with coarctation and 92 normal fetuses (gestational ages 18-36 wks):
    • Statistically significant difference between LV and RV diameters in 8/14 fetuses. Right to left ventricular diameter ratio was greater than 2SD above the normal ratio. RV to LV ratio was 1.69 ± 0.16 when a coarctation was present (Normally = 1.19 ± 0.08).
    • In 12 fetuses with coarctation the aorta was significantly smaller than the pulmonary artery. Pulmonary artery to ascending aorta ratio was 1.61 ± 0.35 when a coarctation was present (Normally = 1.18 ± 0.06). This suggests that aortic coarctation may be the result of diminished flow across the aortic isthmus. Arterial growth is thought to be related to blood flow, and distal arch hypoplasia occurs secondary to decreased aortic blood flow relative to flow through the pulmonary artery and ductus in utero. Decreased LV size and/or decreased LV function has been postulated to lead to reduction in LV stroke volume. This would reduce the amount of blood flow traversing the isthmus, resulting in further hypoplasia of the distal arch.
    • Ratio of internal diameter of left common carotid artery to transverse arch = 0.78 ± 0.13 (Normal ratio = 0.47 ± 0.07).

 

ASSOCIATED ANOMALIES
  • Abnormal aortic valve - bicuspid aortic valve (25-50%) or stenosed.
  • Mitral valve is abnormal in 25-50% of cases (10).
  • Complete heart block may coexist (11).
  • Other cardiac malformations.
    • PDA (33%).
    • VSD (15%), ASD.
    • Aortic stenosis or insufficiency.
    • Truncus arteriosus, double outlet right ventricle.
    • Single ventricle.
  • Turners Syndrome (13-15%).
  • Intracranial aneurysms.
  • Diaphragmatic hernia (12).
  • Situs anomalies, short umbilical cord, renal agenesis, polycystic disease of the kidney and tracheo-esophageal fistulae have been reported.

 

DIFFERENTIAL DIAGNOSIS
  • Small LV:
    • Relatively small LV.
    • Relatively large RV (pulmonary atresia, stenosis or regurgitation).
    • Interrupted aortic arch.
    • Anomalous pulmonary venous connection.
  • Severe IUGR (may have ventricular disproportion) (13).

 

REFERENCES
  1. Allan LD, Crawford DC, Tynan M. Evolution of coarctation of the aorta in intrauterine life. Br Heart J 1984;52:471-473.
  2. Ferencz C, Rubin JD, McCarter RJ et.al. Cardiac and non-cardiac malformations: Observations in a population based study. Tetralogy 1987;35:367-378.
  3. Allan LD, Chita SK, Anderson RH et.al. Coarctation of the aorta in prenatal life: an echocardiographic, anatomical and functional study. Br Heart J 1988;59:356-360.
  4. Benacerraf BR, Saltzman DH, Sanders SP. Sonographic sign suggesting the prenatal diagnosis of coarctation of the aorta. J Ultrasound Med 1989;8:65-69.
  5. Emerson D, Cartier M, DiSessa T et.al. Prenatal sonographic identification of coarctation of the aorta. J Ultrasound Med 1988;7:S271.
  6. Kirk JS, Comstock CH, Lee W et.al. Sonographic screening to detect fetal cardiac anomalies: A 5-year experience with 111 abnormal cases. Obstet Gynecol 1997;89:227-232.
  7. Brown DL. Sonographic assessment of fetal arrhythmias. AJR 1997;169:1029-1033.
  8. Brown DL, Durfee SM, Hornberger LK. Ventricular discrepancy as a sonographic sign of coarctation of the fetal aorta: How reliable is it? J Ultrasound Med 1997;16:95-99.
  9. Sharland GK, Chan K, Allan LD. Coarctation of the aorta: Difficulties in prenatal diagnosis. Br Heart J 1994;71:70-75.
  10. Becker AE, Becker MJ, Edwards JE. Anomalies associated with coarctation of the aorta. Circulation 1979;41:1067-1072.
  11. Machado MV, Tynan MJ, Curry PV et.al. Fetal complete heart block. Br Heart J 1988;60:512-515.
  12. Siebert JR, Hass JE, Beckwith JB. Left ventricular hypoplasia in congenital diaphragmatic hernia. J Pediatr Surg 1984;19:567-571.
  13. Siassi B. Normal and abnormal transitional circulation in the IUGR infant. Semin Perinatol 1988;12:80-83.
  14. Hornberger LK, Sahn DJ, Kleinman CS et.al. Antenatal diagnosis of coarctation of the aorta: A multicenter experience. J Am Coll Cardiol 1994;23(2):417-423.
  15. Hutchins GM. Coarctation of the aorta explained as a branch pint of the ductus arteriosus. Am J Pathol 1971;63:203-209.
  16. Rudolph AM, Heymann MA, Spitznas U. Hemodynamic considerations in the development of narrowing of the aorta. Am J Cardiol 1972;30:514-525.
  17. Snider RA,  Serwer GA. Abnormal vascular connections and structures: In: Snider RA, Serwer GA (eds): Echocardiography in pediatric heart disease. Chicago, Year Book Medical, 1980:pp289-293.