The patient is coughing with no other signs, but now there is a murmur. What to do? I take radiographs and hope that they
guide me for the next test. Treatment for lung or heart disease, or advanced imaging, including echocardiography, video fluoroscopy
or CT? Cases discussed in this session will provide examples in the spectrum of intra-thoracic disease which can be significantly
guided by routine radiographs.
Coughing is caused by a wide spectrum of upper spectrum of upper and lower airway causes. The temptation when a dog has a
concurrent heart murmur is to assume a cause and effect relationship and treat for heart failure. After a year in private
practice, I concluded that there was only an infrequent relationship between the two clinical signs. My other observation
was that thoracic radiographs were not taken on each case, perhaps for other clinical or owner financial reasons. In addition,
veterinarians were interpreting the images with a biased eye toward heart failure. Perhaps even worse, many dogs with primary
tracheal and pulmonary apparently responded to furosemide therapy, even more firmly reinforcing the clinical diagnosis or
primary heart disease. Two specific cause and effect relationships are seen with heart enlargement and a cough; 1) left-sided
cardiac failure and cardiogenic pulmonary edema, and 2) moderate to severe left atrial enlargement and static left main stem
bronchial compression/collapse. Both of these conditions are based on left-sided cardiomegaly. Right-sided heart enlargement
or failure do not cause a cough. Alternatively, chronic lower airway disease (with clinical signs of a cough) or primary pulmonary
fibrosis may cause right heart failure. Some misused criteria of right-sided cardiomegaly include "reverse D" shape, which
is normal (gentle almond?) and sternal contact, which again is a normal finding.
The assessment of heart enlargement is both subjective and objective. True to form most radiologists depend on the their experience
for a subjective interpretation. More objective criteria include intercostal spaces and %width of the chest. These depend
on a normal full inspiratory effort, which is often inhibited by underlying pulmonary, pleural or chest wall diseases, pain
and obesity. The vertebral heart scale is a useful objective system of assessing dog and cat hearts. For cats I measure the
maximum width on the VD, which should not exceed 4 vertebra. For dogs the combined length and width on the lateral view should
not exceed 11 vertebrae. These criteria are most useful for overall cardiomegaly. For specific chamber or side of enlargement
the heart face analogy is very useful.
It is important to be able identify the left caudal mainstem bronchus on all projections. Elevation and compression of the
left caudal mainstem bronchus are important features of left atrial enlargement. The left atrium may be either elevated or
ventrally displaced by middle tracheobronchial adenopathy, but is always dorsally displaced by left atrial enlargement. Not
seeing left atrial enlargement significantly decreases the likelihood that lung disease is pulmonary edema.
In dogs, unlike cats, the pulmonary veins often become enlarged with moderate to severe pulmonary congestion. This is evidenced
by disparity between veins and arteries or when the veins exceed the width of the proximal 4th rib measured at the level where they cross this rib on the lateral projection or the 9th rib on the VD/DV view.