Congenital anomalies of the cardiovascular system are defects that are present at birth and can occur as a result of genetic, environmental, infectious, toxicologic, pharmaceutical, nutritional, or other factors or a combination of factors. For several defects, an inherited basis is suspected based on breed predilections and breeding studies. Congenital heart defects are significant not only for the effects they produce but also for their potential to be transmitted to offspring through breeding and thus affect an entire breeding population. In addition to congenital heart defects, many other cardiovascular disorders have been shown, or are suspected, to have a genetic basis. Diseases such as hypertrophic cardiomyopathy, dilated cardiomyopathy, and degenerative valvular disease of small breeds of dogs may have a significant heritable component.
In dogs, the prevalence of congenital heart disease is estimated at <1%. In multiple large studies of congenital heart disease in dogs, the three most common defects are aortic stenosis Aortic Stenosis in Animals Aortic stenosis, typically caused by a ridge or ring of fibrotic tissue in the subaortic region (subaortic stenosis), is a common congenital defect of large breed dogs. The condition is typically... read more , pulmonic stenosis Pulmonic Stenosis in Animals Pulmonic stenosis is a common congenital defect of dogs, and it most commonly involves fusion or dysplasia of the pulmonic valve leaflets (valvar or valvular). This condition affects a variety... read more , and patent ductus arteriosus Patent ductus arteriosus Patent ductus arteriosus (PDA) is a common congenital defect of dogs, and it occurs less commonly in cats. Persistent flow through the ductus leads to excess blood flow (volume overload) to... read more (PDA). Less common defects include ventricular septal defect Ventricular Septal Defects in Animals Ventricular septal defect is a common congenital defect of cats and also occurs in dogs and can vary in location and size. Most defects are small enough to restrict significant shunting between... read more , atrial septal defect Atrial Septal Defects in Animals Atrial septal defect is an uncommon congenital defect of dogs and cats. The mid-septal location (secundum-type) is most common. Small defects may be hemodynamically insignificant and require... read more , mitral valve dysplasia Mitral Valve Dysplasia in Animals Mitral valve dysplasia is a congenital malformation of the mitral valve leaflets or any other component(s) of the mitral valve complex. This condition occurs in dogs and is a common defect of... read more , tricuspid valve dysplasia Tricuspid Valve Dysplasia in Animals Tricuspid valve dysplasia is a congenital malformation of the tricuspid valve leaflets or any other component(s) of the tricuspid valve complex. This condition occurs in dogs (such as Labrador... read more , tetralogy of Fallot Tetralogy of Fallot in Animals Tetralogy of Fallot is an uncommon but complex congenital defect comprised of pulmonic stenosis, ventricular septal defect, right ventricular hypertrophy, and overriding aorta. Clinical signs... read more , cor triatriatum Peritoneopericardial diaphragmatic hernia is the most common congenital pericardial disease in dogs and cats. It results from abnormal development of the dorsolateral septum transversum or from... read more , and persistent right aortic arch Persistent Right Aortic Arch in Animals Persistent right aortic arch is the most common vascular ring anomaly in dogs (German Shepherds in particular) and has also been reported in cattle, horses, and cats. The right aortic arch fails... read more . However, because of regional differences, the most common congenital cardiac defects in dogs in the USA vary from those reported in the UK and may likely differ from those in Europe and other regions.
In cats, the prevalence of congenital heart disease has been estimated to be 0.2%–1% and includes atrioventricular (AV) septal defects (including ventricular septal defect, atrial septal defect, and endocardial cushion defects), AV valve dysplasia, endocardial fibroelastosis, PDA, aortic stenosis, and tetralogy of Fallot.
Among horses, Arabians have a relatively higher incidence of congenital defects than other breeds; a variety of defects have been reported for this breed.
The early detection of a congenital heart defect is critical for several reasons. Certain defects are correctable with interventional or surgical treatments, and treatment is ideal before the onset of congestive heart failure (CHF) or irreversible cardiac damage; recently purchased animals may be returned to avoid economic loss; pets with congenital heart defects are likely to die prematurely, causing emotional distress; and animals purchased for performance have limited potential and will likely be unsatisfactory. Early detection also minimizes incorporation of genetic defects into breeding lines.
The evaluation of most animals with a congenital cardiac defect usually consists of a physical examination, electrocardiography, radiography, and echocardiography. This allows for a definitive diagnosis and an assessment of the severity of the defect. The use of Doppler echocardiography has supplanted the use of invasive cardiac catheterization studies in the evaluation of most cardiac defects. Once the diagnosis has been made and severity determined, treatment options can be developed and a prognosis given.
The clinical significance of congenital heart disease depends on the particular defect and its severity. Mildly affected animals may exhibit no ill effects and live a normal life span. Defects causing significant circulatory derangement will likely cause neonatal death. Such defects, many incompatible with life, can cause fetal death and reduced litter size. Medical, interventional, or surgical management is most likely to benefit animals with congenital cardiac defects of moderate or greater severity. Left-to-right shunting PDA is one notable exception in which surgical correction is indicated in nearly all affected animals.
Congenital heart defects produce signs of cardiac failure through a variety of pathophysiologic mechanisms.
Defects causing pressure overload and concentric hypertrophy: Stenotic defects that cause obstruction to normal outflow of blood from the heart, such as pulmonic stenosis and subaortic stenosis, may result in right- and left-side failure, respectively. Outflow obstruction leads to concentric hypertrophy of the respective ventricle, increasing the risk of ischemia-induced arrhythmias and sudden death.
Defects causing volume overload and eccentric hypertrophy: Cardiac shunts such as PDA and septal defects are examples of abnormal communications between the systemic and pulmonary circulatory systems or heart chambers, respectively. The direction of shunting is typically left-to-right, based on the pressure gradient between communicating structures. . The recirculation of blood through the pulmonary circulation and into the left heart chambers can precipitate signs of left-side CHF (eg, pulmonary edema, dyspnea, cough, fatigue). Larger defects typically result in a greater degree of volume overcirculation to the left heart chambers. Large defects with significant left-to-right shunting can result in pulmonary hypertension and reversal of shunting, such as reversed (right-to-left) PDA. Animals with right-to-left shunting defects Right-to-Left Shunts (Cyanotic Heart Disease) in Animals Right-to-left shunts include Tetralogy of Fallot and truncus arteriosus. read more (tetralogy of Fallot, reversed PDA) may develop right heart failure but more often have clinical signs associated with polycythemia Erythrocytosis and Polycythemia read more , which develops subsequent to renal perfusion with deoxygenated blood. This results in an increase in erythropoietin production by the kidneys and consequent polycythemia.
The presence of a heart murmur in a young animal is not pathognomonic for a congenital heart defect. Many young animals will have a low-grade systolic murmur (often grade II/VI or less) that is "innocent" and caused by mild turbulence that is not associated with a congenital heart defect. These murmurs usually disappear by 6 months of age in dogs and cats. Innocent murmurs are heard in the absence of any other demonstrable evidence of cardiovascular disease. High-grade systolic murmurs (grade III/VI or greater), continuous murmurs, and diastolic murmurs are indicative of cardiac disease and warrant further investigation.
The most common congenital defects of dogs are patent ductus arteriosus, pulmonic stenosis, and aortic stenosis.
The most common congenital defects of cats are atrioventricular septal defects and atrioventricular valve dysplasia.
The presence of a loud systolic murmur, or any diastolic or continuous murmur. is supportive of congenital heart disease and warrants further investigation. Congenital heart defects range in severity and complexity, and early detection and treatment may improve the outcome with certain conditions.
Also see pet health content regarding congenital and inherited anomalies of the cardiovascular system in dogs Congenital and Inherited Disorders of the Cardiovascular System in Dogs Congenital abnormalities of the cardiovascular system are defects that are present at birth. They can occur as a result of genetic defects, environmental conditions, infections, poisoning, medication... read more , cats Congenital and Inherited Disorders of the Cardiovascular System of Cats Congenital abnormalities of the cardiovascular system are defects that are present at birth. They can occur as a result of genetic defects, environmental conditions, infections, poisoning, medication... read more , and horses Congenital and Inherited Disorders of the Cardiovascular System in Horses Congenital abnormalities of the cardiovascular system are defects that are present at birth. They can occur as a result of genetic defects, environmental conditions, infections, poisoning, medication... read more .