is patent ductus arteriosus (PDA)?
birth, mammals must adapt from living in a fluid environment
(the amniotic fluid) and acquiring oxygen through the mother's
blood, to breathing air and acquiring oxygen through their own
lungs. The ductus arteriosus is very important in the adaptation
process. This is a small communicating blood vessel between the
pulmonary artery (which carries blood to the lungs), and the
aorta (which carries blood to the rest of the body). Before
birth, most of the blood from the fetal heart bypasses the fetal
lungs via the ductus arteriosus. The lungs gradually become
functional fairly late in fetal development. At birth, the blood
supply from the mother is of course cut off, the dog (or other
mammal) begins breathing on its own, and blood flow through the
ductus arteriosus decreases dramatically. Within a few days, the
ductus closes off completely.
the ductus does not close, the dog is left with a patent ductus
arteriosus (PDA). The extent to which this affects the dog
depends on the degree of patency, or opening, of the ductus.
is patent ductus arteriosus inherited?
breeds are affected by patent ductus arteriosus?
is the most commonly diagnosed congenital heart defect in dogs.
It occurs in many breeds and is seen more often in females.
The breeds at most risk for this disorder are the Maltese,
Pomeranian, Shetland sheepdog, and Kerry blue terrier. Other
breeds with an increased risk are the Keeshond, miniature and
toy poodle, Bichon frise, Yorkshire terrier, English springer
spaniel, collie, cocker spaniel, German shepherd, Irish setter
many breeds and many disorders, the studies to determine the
mode of inheritance or the frequency in the breed have not been
carried out, or are inconclusive. We have only listed breeds for
which there is a strong consensus among practitioners that the
condition is significant in this breed.
does patent ductus arteriosus mean to your dog & you?
degree to which your dog is affected depends on the magnitude of
the defect. This can range anywhere from a small blind pocket
off the aorta which doesn't cause any problems, to varying
degrees of abnormal blood flow through the ductus between the
aorta and the pulmonary artery. Most commonly there is a shunt
from the left to the right side of the heart , with blood from
the higher pressure aorta continuously shunted to the main
pulmonary artery. This means an increased volume of blood to the
lungs which results in fluid build-up (pulmonary edema) and
volume overload to the left heart. You may see coughing, reduced
tolerance of exercise, loss of weight, and eventually,
congestive heart failure. Without surgery, premature death is
Less commonly, there is a right-to-left shunt. This may be
the case from birth or, it may develop because the PDA is so
large that the pressure in the lungs, and resultant resistance
to this pressure, markedly increase. In effect, the circulation
is the same as when the dog was a fetus - that is, some of the
blood leaving the right side of the heart bypasses the lungs
entirely. This results in circulation of poorly oxygenated
blood. Your dog may have shortness of breath and weakness or
collapse in the hind limbs.
is patent ductus arteriosus diagnosed?
a PDA is first suspected when the veterinarian hears the
characteristic continuous "machinery" heart murmur
when your dog is examined at the time of vaccination. There are
radiographic and electrocardiographic signs to confirm the
diagnosis. At this point your puppy will not likely show any
clinical signs relating to the PDA.
continuous "machinery" murmur - (disappears with
left atrial enlargement, left ventricular dilation and
hypertrophy, (right ventricular hypertrophy with right-to-left
pulmonary over-circulation, left atrial and ventricular
enlargement, possibly dilation of the descending aorta and main
pulmonary artery (right ventricular hypertrophy with
left sided cardiac enlargement and dilation of aorta and
pulmonary artery (right ventricular hypertrophy with
of pulmonary edema and left-sided heart failure. In a
right-to-left shunt, unoxygenated blood directly from the
pulmonary artery mixes with blood from the lungs in the
descending aorta causing differential weakness and cyanosis in
the hind end. Desaturated arterial blood also goes to the
kidneys, causing hypoxemia, polycythemia, and hyperviscosity.
The PCV often exceeds 65 per cent.
is patent ductus arteriosus treated?
is recommended in all dogs less than 2 years of age in which a
left-to-right shunting PDA has been diagnosed. Surgical
treatment consists of tying off the patent ductus and is quite
successful. Surgery should be performed as soon as possible - as
early as 8 to 16 weeks of age - before changes have occurred as
the heart tries to compensate for the defect. The prognosis for
a normal life with early surgery is usually very good. Where
there are signs of heart disease, there are increased risks
associated with surgery and your veterinarian will recommend
medical stabilization before surgery.
problems associated with the less common right-to-left shunt are
managed medically rather than surgically. Treatment includes
rest, exercise restriction, and avoidance of stress. Your
veterinarian will monitor and work with you to manage the
changes which occur due to the circulation of poorly oxygenated
in whom PDA has been diagnosed, with or without surgical
correction, should not be used for breeding. Their parents
should not be bred either, and siblings should only be used
after careful screening. If any affected offspring are born,
breeding of the parents should be discontinued.
More Information about this Disorder, Please See Your
J.D. and Darke,
P.G.G. 1995. Congenital heart disease. In S.J. Ettinger and E.C.
Feldman (eds.)Textbook of Veterinary Internal Medicine, p.
892-943. W.B. Saunders,
1989. Hereditary congenital heart defects in dogs. Journal of
Small Animal Practice 30:153-165. Information on inheritance.
1996. The genetics of canine congenital heart disease. ACVIM -
Proceedings of the 14th Annual Veterinary Medical Forum:
225-226. This reference has good information for breeders and
veterinarians regarding screening and genetic counselling for
congenital heart defects.