Congenital Heart Disease

9 Congenital Heart Disease

3. What is the evidence for a genetic cause for CHD?

CHD is most common in purebred dogs and many specific malformations have an obvious familial distribution. In some cases, breeding experiments have demonstrated that the malformation is genetically transmitted; on the basis of these studies, the mode of inheritance is known or suspected for some forms of CHD.

Interpretation of breed predisposition data must be undertaken with care. In some cases, apparent breed predispositions that do not take into account breed popularity have been reported in the literature. For example, German Shepherds have occasionally been reported to be at increased risk for patent ductus arteriosus (PDA) because they have been “overrepresented” in case series of dogs with PDA. However, the relatively high frequency with which PDA is diagnosed in German Shepherds, is partly due to the popularity of the breed. One way of overcoming the confounding influence of breed popularity is use of a statistic known as the odds ratio. Buchanan (see Bibliography), has reported odds ratios for heart disease in various breeds of dogs.

In a few cases, breeding experiments have demonstrated heritability of specific lesions. This is the case for subaortic stenosis in the Newfoundland, for PDA in Miniature Poodles, for pulmonic stenosis in Beagles, and for a spectrum of conotruncal defects in Keeshonden. In this last breed, it has recently been shown that conotruncal defects—meaning developmental abnormalities of ventricular outflow and the great vessels that include tetralogy of Fallot—are associated with a single genetic mutation.

18. What echocardiographic findings are associated with a PDA?

In animals with moderate or large PDAs (left-to-right shunts), dilation and hypertrophy of the left ventricle is evident echocardiographically (Fig. 9-1). Echocardiographic examination also demonstrates left atrial enlargement. Myocardial dysfunction, reflected in a large end-systolic ventricular dimension and often a low fractional shortening index, is sometimes evident. Direct visualization of the PDA is usually possible when the study is performed by an experienced echocardiographer. The PDA extends from the descending aorta to the bifurcation of the main pulmonary artery. It is best demonstrated by a cranial left parasternal image of the pulmonary artery bifurcation.

Doppler flow studies are used to confirm that blood from a PDA flows into the main pulmonary artery. In animals with a PDA, this will be evident on color-flow Doppler studies as a diastolic color mosaic that originates near the pulmonary artery bifurcation and extends retrograde toward the pulmonic valve. In many cases, the jet extends beyond the pulmonic valve and results in mild pulmonic regurgitation. On spectral Doppler studies, continuously disturbed flow will be evident within the pulmonary artery (Fig. 9-2).

Additional findings detected by Doppler studies in a dog with a PDA include mitral valve regurgitation. When a substantial shunt is present, aortic flow velocities are often higher than normal. This does not necessarily reflect aortic obstruction but rather a larger left ventricular stroke volume.

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Jul 31, 2016 | Posted by in INTERNAL MEDICINE | Comments Off on Congenital Heart Disease

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