Patent
ductus arteriosus
The patiency of the ductus arteriosus, a small tube connecting the
pulmonary artery to the aorta, is necessary during fetal life. Soon
after birth, however, this connection spontaneously closes in most
infants. If it does not close, and pulmonary pressures fall in the
antenatal period, shunting between the aorta and the pulmonary artery
occurs. In this setting, the shunting occurs through a patent ductus
arteriosus.
Identification of the ductus arteriosus is an important part of
pediatric echocardiography. The ductus is encountered in a number
of clinical conditions, commonly in premature infants or full term
infants with other forms of congenital heart disease.
It is possible to identify a large patent ductus arteriosus by two-dimensional
echocardiography. A moderate-size ductus arteriosus is very difficult
to identify with imaging alone except in the most skilled hands.
Currently, the method of choice involves the adjunct use of conventional
Doppler and/or Doppler color flow methods.
Without Doppler, only indirect signs of a patent ductus arteriosus
are evident. With marked increase in pulmonary blood flow, the left
atrium dilates significantly, together with an increase in left
ventricular end-diastolic dimension. In the normal infant, the ratio
of maximal left atrial dimension to aortic root dimension is less
than 0.9:1. An increase in this ratio to greater than 1.1:1, combined
with an abnormal increase in left ventricular end- diastolic dimension,
is strongly suggestive of a patent ductus. Such findings, however,
lack specificity as identical echocardiographic findings are also
associated with both mitral incompetence and ventricular septal
defect. Also, the left atrial enlargement associated with a persistent
ductus is dependent on an intact atrial septum. Such indirect indices
are not reliable in the hypovolemic neonate. Furthermore, a ductus
associated with complex congenital heart disease cannot be excluded
on the basis of normal left dimensions.
2004