- Definition
- Pathophysiology
- Systems Affected
- Genetics
- Incidence/Prevalence
- Signalment
- Signs
- Causes
- Risk Factors
BASICS
- The term complex congenital cardiac disease encompasses numerous defects or anomalies of the heart, which form during embryogenesis and are therefore present from birth
- Congenital cardiac defects can be classified as hypoplasia, obstruction defects, septal defects, and cyanotic defects
- To be described as complex, more than 1 specific defect is present, although frequently these include patent ductus arteriosus and/or ventricular or atrial septal defect, which can also occur singly (see chapters Atrial septal defect and Ventricular septal defect (VSD))
- In the embryo, formation of the heart begins with a straight tube of mesenchymal cells. This forms segments (atria, primitive ventricle, bulbus cordis, conus, and truncus) and then, through cardiac looping, the bulbus cordis migrates relative to the ventricle to take up positions that enable the formation of the right and left ventricles
- Septation of the right and left atria involves ingrowths of the septum and the septum secundum. Simultaneously, the atrioventricular canals remodel to align with their respective ventricles and ventricular septation begins. Failure at this stage can lead to a common ventricle or, more commonly, a range of ventricular septal defects
- The formation of the aortic and pulmonary trunks is achieved by truncoconal septation and spiraling of the conus. Abnormalities at this stage can lead to a wide range of malformations, of which the most commonly reported in the horse is tetralogy of Fallot
- Hypoplasia results in failure of formation of 1 of the ventricles
- Obstruction defects occur when heart valves, arteries, or veins are blocked; pulmonic stenosis is the most commonly reported form in horses
- Septal defects can involve the atrial and/or the ventricular septum
- Cyanotic defects arise when the defects lead to right-to-left shunting of blood such than unoxygenated blood reaches the systemic circulation. Examples include tetralogy of Fallot, tricuspid atresia, persistent truncus arteriosus, and transposition of the great vessels
- Not yet determined in horses
- Complex congenital cardiac diseases are heritable in other species
Congenital cardiac defects accounted for 3.5% of all congenital defects in 1 pathologic survey, and 1 report estimated that they occur in around 1–5 in 1000 births.
- Arabian horses appear to be predisposed to complex congenital cardiac defects
- Murmurs usually are detectable at birth
- Diagnosed most frequently in neonates, foals, and young horses but can be found at any age
Complex cardiac disease is more likely to present with signs of severe cardiac compromise than single (or simple) defects.
Depending on the specific defect and its severity, affected foals will present with lethargy, exercise intolerance, and failure to grow at expected rates.
- Cardiac murmurs are generally loud (grade ≥4/6), and often have a precordial thrill. The point(s) of maximal intensity will depend on the specific defect and the structures involved
- Tetralogy of Fallot produces murmurs on both sides of the chest but typically the loudest murmur is over the pulmonic valve on the left side
- Tricuspid atresia creates its loudest murmur over the tricuspid valve area on the right side
- Many complex cardiac defects are associated with cyanosis and affected foals have bluish mucous membranes
Failure of development at 1 or more stages of cardiac embryogenesis. In humans, both genetic and environmental factors (e.g. maternal illness, infection, and drugs) are associated with congenital cardiac defects but these factors have not been identified in horses.
DIAGNOSIS
TREATMENT
MEDICATIONS
FOLLOW-UP
MISCELLANEOUS