Patent Ductus Arteriosus
|Reviewed by David Knight and Carl Kuschel|
|Presence and Size of the Duct||Left Atrial Size||Left Ventricular Size|
|Diastolic Descending Aortic Flow||LPA Flow||Flow in Other Organs|
Echocardiography is the best way to determine
In practice, there are several things to evaluate:
The presence of a duct can best be determined by the demonstration of flow between aorta and main pulmonary artery (MPA), and by a pattern of disturbed diastolic flow in the MPA.
The duct is most easily seen in the parasternal short axis and the so-called "ductal" views. Absolute quantification of its diameter is the best way to determine its presence or absence. In general, the duct is measured at its narrowest point. The duct is most easily seen with colour Doppler and this is the mode in which the measurement is taken, although it tends to overestimate ductal diameter.
|Click on the image on the left to see a larger image of the duct from the parasternal short axis view|
Click on the images on the left to see
a larger image of the "ductal" view in both 2D (black and
white) and with colour Doppler.
The duct measures 2.8mm on colour flow.
Sometimes, the views are difficult - even with colour. In this case, placing a Doppler probe on the main pulmonary artery helps. If there is a duct with a significant left-to-right shunt, there will be disturbance of diastolic flow in the main pulmonary artery. This is often useful to exclude a significant duct, rather than quantify the size of any shunt.
Ductal size also helps to evaluate haemodynamic significance. As diameter increases, so too does the amount of flow that occurs. In general, ducts more than 2mm in diameter on colour Doppler are haemodynamically significant.
|Click on the image on the left to see a larger image of disturbed flow in the MPA with the presence of a PDA.|
Left atrial (LA) enlargement signifies increased pulmonary venous return because of left-to-right ductal shunting. The reference measure is the ratio of the LA to aorta at the level of the aortic valve (the LA:Ao ratio). The aortic does not enlarge with even extremely large PDAs so it is a useful measurement that allows for different sized babies. In general, a LA:Ao ratio >1.4:1 indicates a moderate shunt but is dependent on the operator and views. NWH experience suggests that the ratio needs to be greater than 2:1 to support the finding of a significant shunt.
|Click on the image on the left to see a larger image of the LA:Ao ratio|
This will enlarge as cardiac output increases with both increased pulmonary venous return and with increased diastolic run-off from the systemic circulation. There are subjective measures of this (the "paired eyeball test", the presence of mitral regurgitation as the mitral valve ring dilates) and objective measurements (the left-ventricular end-diastolic dimension (LVEDD) :Ao ratio).
The presence of a significant ductal shunt results in diastolic run-off to the pulmonary circulation. This will result in flow that is retrograde in the descending thoracic aorta beyond the duct during diastole. In practice, this can be a difficult view to obtain.
|Click on the image on the left to see a larger image of flow patterns in the descending aorta.|
This is higher with large left-to-right shunts. Values less than 15cm/sec are seen when the duct is closed. Values greater than 40cm/sec are seen in babies with (so-called) symptomatic PDAs.
Disturbed flow patterns may be seen in brain, kidney, and gut vessels as an effect of a significant duct.
|Click on the image on the left to see a larger image of reversed flow in a renal artery|
None of these measures stands alone in determining which ducts require treatment. Other factors that influence the decision include
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|Skinner J. Diagnosis of patent ductus arteriosus. Seminars in Neonatology 2001;6:49-61.|
|3||Suzumura H, Nitta A et al. Diastolic velocity of the left pulmonary artery of patent ductus arteriosus in preterm infants. Pediatrics International 2001;43:146-51.|
|4||Knight DB. Yu VY. Contrast echocardiographic assessment of the neonatal ductus arteriosus. Arch Dis Child 1986;61:484-8.|