Congenital Heart Diseases
Congenital heart diseases are malformations of the heart and great vessels. It is important to identify them in newly acquired pets or those to be used for breeding.
Veterinarians should be encouraged to use their stethoscopes to routinely listen to the heart. With practice, subtle changes will become noticeable, allowing the vet to note abnormalities in the patient’s record.
Etiology
Causes of congenital heart disease include genetic, environmental, infectious, nutritional, and drug-related factors. More is understood of the genetic factors than the other causes.
Studies suggest the defects are polygenetic in nature and that they might be difficult to eliminate entirely from a specific breed.
Clinical Signs
Clinical signs of congenital heart diseases include failure to grow, dyspnea, weakness, syncope, cyanosis, seizures, and sudden death; however, many animals with congenital malformations may be asymptomatic.
Diagnosis
The diagnostic approach for congenital heart disease should include a detailed history, with special attention paid to the breed, sex, and age of the patient.
Most cases of congenital abnormalities are identified during the first visit to the veterinarian after the pet has been purchased. On examination, a loud murmur often accompanied by a precordial thrill (a vibration of the chest wall) may be heard.
With some defects, the vet may observe pulse abnormalities, cyanosis, jugular pulses, or abdominal distension.
Laboratory test results may all be normal. Radiography may suggest cardiac disease in some animals; however, echocardiography can provide an accurate diagnosis of the defect.
Congenital Heart Diseases of Animals
Various congenital heart diseases of animals are:
- Patent Ductus Arteriosus
- Atrial and Ventricular Septal Defects
- Stenotic Valves (Pulmonic and Aortic Stenosis)
- Subaortic Stenosis
- Tetralogy of Fallot
- Persistent Right Aortic Arch and Other Vascular Ring Anomalies
1. Patent Ductus Arteriosus
Patent ductus arteriosus is the failure of the ductus arteriosus to close after parturition results in blood shunting from the systemic circulation to the pulmonary artery.
Normally, the ductus carries blood from the pulmonary artery to the aorta during fetal development.
The increase in oxygen tension in the blood at birth results in closure of the path in the first 12 to 14 hours of life. If the ductus remains open, blood will hyperperfuse the lung, and the left side of the heart will become volume overloaded.
The resulting cardiac murmur is often referred to as a “machinery murmur”; this type of murmur is heard best over the main pulmonary artery high on the left base.
Surgical duct ligation before 2 years of age or coil or amplatz embolization can be done to treat patent ductus arteriosus in animals.
2. Atrial and Ventricular Septal Defects
During fetal development, the atria and the ventricles are joined as a common chamber. The atria are partitioned by two septa and a slitlike opening (the foramen ovale) that allows right to left shunting of blood in the fetus.
The ventricular septum is formed from several primordial areas. Eventually, the atrial septum and the ventricular septum join in the area of the endocardial cushions.
Defects in the structure of these septae result in patencies of the AV septum. This defect is fairly common in the cat. With atrial septal defects (ASDs), blood will typically shunt from left to right, overloading the right side of the heart.
In ventricular septal defects (VSDs), the left side of the heart is usually overloaded and enlarged.
Repair of these defects requires open-heart surgery or cardiopulmonary bypass. This is uncommon in animals. Affected animals will eventually experience development of CHF and require treatment.
3. Stenotic Valves (Pulmonic and Aortic Stenosis)
Pulmonic stenosis results when the pulmonic valves are dysplastic or malformed. The lesion results in a narrowing of the outflow tract from the right ventricle.
Obstruction to right ventricular outflow causes an increase in ventricular systolic pressure resulting in right ventricular hypertrophy. The right atrium also becomes enlarged.
Balloon valvuloplasty to relieve the obstruction. Valvulotomy or partial valvulectomy to open the outflow tract. Patch graph over the outflow tract to alleviate the obstruction and Medical management of CHF can be done in animals.
4. Subaortic Stenosis (SAS)
Subaortic stenosis (SAS) occurs predominantly in large breed dogs. The Newfoundland, Boxer, German Shepherd, Golden Retriever, and Bull Terrier are the most commonly affected. In the Newfoundland, support exists for a genetic basis most compatible with an autosomal dominant mechanism.
The lesion develops during the first 4 to 8 weeks of life. The lesion consists of thickening of the endocardial tissue just below the aortic valve.
The fibrous thickening results in obstruction to outflow producing left ventricular hypertrophy, left atrial hypertrophy, and dilation of the aorta. Coronary artery circulation may also be affected. Severe SAS may lead to left-sided CHF or sudden death.
Severe stenosis limits cardiac output during exercise. Animals should not be used for breeding. Most will experience development of left sided CHF.
5. Tetralogy of Fallot
Tetralogy of Fallot is a polygenic, genetically transmitted malformation of the heart.
Components include right ventricular outflow obstruction (pulmonic stenosis), secondary right ventricular hypertrophy, a subaortic VSD, and overriding aorta (Fig. 1.6). This condition is seen in the Keeshond and the English Bulldog and in cats.
It occasionally occurs in other breeds. Symptoms may vary with the severity of the defects.
The presence of these malformations results in increased right-sided resistance and pressure and a right-to-left shunt between the pulmonary and systemic circulations. Because of this pressure gradient, deoxygenated blood from the right ventricle shunts through the VSD to mix with oxygenated blood in the left ventricle. Blood flow to and from the pulmonary vasculature is minimal.
This shunting results in hypoxemia, cyanosis, and secondary polycythemia (increased numbers of red blood cells [RBCs]). Right ventricular hypertrophy occurs.
The murmur of pulmonic stenosis usually can be detected on the left hemithorax, and less often, the VSD murmur can be heard as well.
6. Persistent Right Aortic Arch and Other Vascular Ring Anomalies
Persistence of the right fourth aortic arch is a common malformation. The defect results in regurgitation of solid food in weanlings because of obstruction of the esophagus by the retained vascular arch.
It is a common defect in German Shepherds, Irish Setters, and Great Danes and is frequently seen in other large breeds.
