Tetralogy of Fallot
A number of variants forms of this congenital anomaly have been reported, including:
- Trilogy of Fallot - pulmonic stenosis, right ventricular enlargement, atrial septal defect
- Tetralogy of Fallot - pulmonic stenosis, right ventricular outflow stenosis, ventricular septal defect, dextropositioning of the aorta
- Pentalogy of Fallot - pulmonic stenosis, right ventricular outflow stenosis, ventricular septal defect , dextropositioning of the aorta, atrial septal defect.
- Conotruncal malformation - pulmonic stenosis, dextropositioning of the aorta, ventricular septal defect - Keeshond only
This disease has been reported in the Keeshond, English Bulldog, Miniature Poodle, Miniature Schnauzer, Dachshund, Japanese Shiba, Japanese tosa, Bernese Mountain Dog, Beagle, Airedale Terrier, Havanese and Wirehaired Fox Terrier.
In the Keeshond, conotruncal malformation is frequently observed in closely related dogs as a multifactorial autosomal-dominant disease, resulting in type I (subarterial) ventricular septal defects due to failure of fusion of the conal cushions.
Clinical signs are normally seen in young dogs (under 6 months of age) and usually present with exercise intolerance, dyspnea, cyanosis and a detectable murmur.
Blood tests are usually unrewarding, although polycythemia may be evident in some cases.
A tentative diagnosis can be established by auscultation of a high thrill murmur at the right cardiac apex.
Routine ECG shows deep S waves and right axis shift characteristic of right ventricular enlargement and bundle branch block. Arrhythmias are infrequent.
Radiographs often show right cardiomegaly and undersized pulmonary vessels.
Echocardiography is usually required for a definitive diagnosis, usually revealing rightward displacement of the aortic root, right ventricular hypertrophy, and a ventricular septal defect. The left-sided chambers may be small as a result of decreased pulmonary venous return. Routine contrast echocardiography demonstrates shunting from right to left at the level of the ventricular septal defect. Flow through the defect can also be detected by Doppler echocardiography.
A differential diagnosis would include subaortic stenosis, ventricular septal defect, double-chambered right ventricle, hyperthyroidism, cardiomyopathy, Duchenne muscular dystrophy, endocarditis, pulmonic stenosis, mitral valve endocardiosis and infections with Dirofilaria spp.
Corrective surgery, using surgical valvuloplasty, balloon valvuloplasty, or open heart surgery involving transannular pericardial patch graft or a modified Blalock-Taussig shunt procedure are options that are available.
The prognosis is guarded, but animals with mild to moderate shunting may reach adulthood.
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