Chapter 5
Chapter 5

Congenital Heart Disease

The incidence of different types of congenital heart disease (CHD) varies markedly between species. Congenital heart disease is relatively uncommon in the horse compared with dogs or cattle. Many veterinary students will be exposed to a large number of dogs with CHD during their training and will be familiar with patent ductus arteriosus, aortic stenosis and pulmonary stenosis, the most common forms of CHD in the dog. These defects are, however, very rare in the horse. Some congenital abnormalities have been reported more often in certain breeds. Standardbred horses are reported to have an increased inciof CHD compared with Thoroughbreds, and complex CHD has been reported most frequently in the Arabian breed, but CHD is uncommon in horses compared with other domestic species.

The severity of CHD varies enormously and may cause a range of clinical signs. CHD may be recognised at post-mortem examination following fetal or early neonatal death, but usually the condition is detected when the animal is presented to the veterinarian as a foal, or at the beginning of its athletic career if it results in poor athletic performance. In some animals the disease may not be noticed until well into adult life, or it may be an incidental finding in an apparently normal foal or a horse with normal athletic performance. An accurate diagnosis must be made to aid prognostication.

Some congenital cardiac malformations have been shown to be heritable in certain domestic species and in man, although not as yet in the horse. In other instances, CHD may result from teratogens, usually unknown, during early gestation. However, it must be assumed that CHD may be heritable and, once diagnosed, appropriate advice must be given with regard to breeding. The mare/ stallion pairing which is responsible should not be repeated and an animal affected by CHD should not be used for breeding.

In evaluating an animal with suspected CHD, it is important to:

·establish that the primary problem is cardiac.;
·distinguish congenital from acquired heart disease;
·make a specific diagnosis of the form of CHD;
·assess the cardiovascular effects of the condition and establish a prognosis for survival and athletic performance in that individual;
·investigate the animal for evidence of other conditions such as respiratory disease which may complicate treatment and management;
·advise about future breeding programmes.

Topics

5.1 The fetal circulation

5.2 Changes in the fetal circulation at birth

5.3 Clinical diagnosis of congenital heart disease

5.4 Investigative aids to diagnosis of CHD

5.5 Ventricular septal defect

5.6 Tetralogy of Fallot

5.7 Atrial septal defect

5.8 Tricuspid atresia

5.9 Pulmonary stenosis

5.10 Patent ductus arterious

5.11 Endocardial cushion defect

5.12 Other defects

5.13 Arrhythmias in the neonate

5.14 Detection of cardiovascular compromise in the fetus