Today we have a three-year-old female neutered Chihuahua thatÂ was presented to the Emergency service for further workup of polycythemia and episodes of collapse. What are your findings?
There is right-sided cardiomegaly visible on all projections, with increased sternal contact on the laterals and a reverse “D” shape on the d/v. The pulmonary vasculature appears normal, and there is an increased interstitial pulmonary pattern. On the d/v projection, there is a slight bulge in the left cranial mediasatinum, which could represent aorta of pulmonary artery.
congenital heart disease
- right-to-left patent ductus arteriosus
- pulmonic stenosis
Patent ductus arrteriosis with right-to-left shunting and Eisenmenger’s complex.
A bubble study was performed by injecting agitated saline into a peripheral vein. Bubbles were seen in the right heart and descending aorta.
The age of the dog and concentric heart enlargement point towards a congenital heart disease. Right heart enlargement can be caused by pressure overload, such as from a stenotic pulmonic valve or pulmonary hypertension. Patent ductus arteriosus is the most common congenital heart disease in dogs, and Chihuahuas are predisposed (along with Maltese, Pomeranian, Shetland sheepdog, Kerry blue terrier, Keeshond, Miniature and Toy Poodle, Bichon frise, Yorkshire terrier, English Springer Spaniel, Collie, Cocker Spaniel, German shepherd, and Irish Setter).
The lack of enlarged pulmonary arteries and an interstitial pattern suggest that there may be pulmonary hypertension contributing to the heart disease. The PDA usually causes left-to-right shunting as the pressure in the aorta is much greater than in the pulmonary artery. This increased blood flow to the lungs (or congential pulmonary hypertension) can cause fibrosis and increasedd pulmonary arterial pressure. If the pressure in the pulmonary arteries is greater than in the aorta, the shunt will flow from right to left. Deoxygenated blood then flows to the aorta causing hypoxia and a resulting increase in red blood cells (polycythemia).
The bubble study confirms a right-to-left shunt. If blood passed normally from the right heart through the lungs, the bubbles would be filtered by the lungs. Only if the blood bypasses the lungs are the bubbles seen in the descending aorta.
- Goodwin J-K, Holland M. Contrast Echoaortography as an aid in the diagnosis of right-to-left shunting patent ductus arteriosus. Veterinary Radiology & Ultrasound 1995;36:157-159.