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ASCENDING AORTA AORTIC ARCH DESCENDING AORTA |
ASCENDING AORTA |
- Exits the left ventricle
at an angle of 30-45 degrees.
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Exits
left ventricle at an angle of 30-45 degrees Does
not override the interventricular septum Flow
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- Crosses the pulmonary artery at right angles at the level of the heart.
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Transverse / Axial Plane |
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Short axis view |
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- The aortic valve can be easily visualized at its origin.
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- Normal size of the ascending aorta.
- The anterior portion of the aortic root is continuous with the interventricular septum.
- The posterior portion of the aortic root is continuous with the mitral valve.
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Left ventricular outflow tract
– gray-scale Video clip of
Aortic Outflow Tract – Color Doppler Video clip of Aortic Outflow Tract
– Gray-scale
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- Distal to the heart the pulmonary artery and transverse aortic arch become parallel to one another.
AORTIC ARCH |
- Can be seen with the fetus in the supine or spine up position.
- "Walking stick" or "Candy Cane" appearance.
- Not unusual to observe aliasing or disturbed flow at the junction of the aorta and ductus arteriosus.
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Video clip of the
Normal Aortic Arch – Sagittal view
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DESCENDING AORTA |
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- First trimester - As in the umbilical artery waveform, flow is characterized by absent end diastolic flow velocities.
- 12 - 13 weeks - End diastolic flow velocities gradually appear due to lower systemic vascular resistance. PI drops from 2.5 - 3.0 to 1.8 - 2.0.
- 17 - 18 weeks - No significant decrease in aortic PI with advancing age.
- Waveform
- Mid thoracic portion of the descending aorta about 1 - 2 cm above the aortic bifurcation.
- Waveform affected by:
- fetal heart rate.
- fetal breathing.
- fetal activity ( significantly lower PI in aorta during active sleep as compared to quiet sleep due to the reduction of systemic vascular resistance in the former sleep state).
- Angle of insonation = 45 degrees.
- Volume measurements - error = 20 - 25%.
- The pulsatility index decreases from the aortic arch to the distal descending aorta (1,2).
- At diaphragm = 1.96 ± 0.30.
- After renal arteries = 1.69 ± 0.28.
REFERENCES |
- Lingman G, Marsal K. Fetal central blood circulation in the third trimester of normal pregnancy: A longitudinal study: I. Aortic and umbilical blood flow. Early Hum Dev 1986;13:137-150.
- Marsal K, Perrson PH. Ultrasonic measurement of fetal blood velocity waveform as a second diagnostic test in screening for intrauterine growth retardation. J Clin Ultrasound 1988;16:239-244.