Heart disease is common in dogs, perhaps as common as it is in humans. While some dogs are born with developmental heart problems, most develop their
problems during adulthood or old age. The heart is responsible for pumping the oxygen-carrying blood around the body, and when heart function is less than optimal,
body tissues do not receive as much oxygen as they need. When the heart is no longer capable of doing its job effectively, the condition is referred to as heart
failure.
There are now a great many ways of diagnosing heart disease. In addition to electrocardiograms (ECGs), cardiac ultrasound has made the diagnosis of heart disease
much easier to detect. Regular visits to your veterinarian often can mean the difference between life and premature death.
Dog owners may not realize that their pets are susceptible to many forms of heart disease. In most cases, heart disease can be successfully managed by early
detection and treatment. Of the dogs in the United States examined annually by veterinarians, approximately 3.2 million have some form of heart disease, and many
are in heart failure. Heart failure results from the heart's inability to pump blood at a rate required to meet the body's needs. While continuing to work harder to pump
blood, further damage can occur.
The most common congenital cardiovascular anomaly of dogs is patent ductus arteriosus, or PDA. When the duct doesn't close as it should, blood is pushed back
through the heart instead of throughout the body. This can cause such visual signs as exercise intolerance, increased breathing rate, and coughing or collapsing during
exercise. The best solution usually is surgery. In most cases surgery is successful and well-tolerated.
What is patent ductus arteriosus
(PDA)?
At 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.
Where 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.
How is patent
ductus arteriosus inherited?
Inheritance is complex.
What breeds are affected by patent ductus arteriosus?
PDA 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 and Chihuahua.
For 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.
What does patent
ductus arteriosus mean to your dog & you?
The 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 likely.
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.
How is patent
ductus arteriosus diagnosed?
Usually 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.
FOR THE VETERINARIAN:
- MURMUR: continuous "machinery" murmur - (disappears with
right-to-left shunt).
- ELECTROGARDIOGRAM: left atrial enlargement, left ventricular dilation
and hypertrophy, (right ventricular hypertrophy with right-to-left shunt).
- RADIOGRAPHS: pulmonary over-circulation, left atrial and ventricular
enlargement, possibly dilation of the descending aorta and main pulmonary artery
(right ventricular hypertrophy with right-to-left shunt).
- ECHOCARDIOGRAPHY: left sided cardiac enlargement and dilation of
aorta and pulmonary artery (right ventricular hypertrophy with right-to-left shunt).
- OTHER: signs 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.
How is patent
ductus arteriosus treated?
Surgery 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.
The 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 blood.
