congenital disease

• There are two types of septum that form during development…

  • Septum primum
  • Septum secundum
• 1. The dorsal and ventral endocardial cushions are formed which then fuse to separate the atria and ventricles
  2. the septum primum begins to form. This grows towards the endocardial cushions leaving a foramen (foramen primum) for continued R to L flow through the atria.
  3. the septum primum fenetrates forming the foramen secundum
  4. the septum secundum forms parallel to the septum primum. once formed it leaves the foramen ovale for continued right to left blood flow in the atria
  5. the septum primum regresses leaving a flap to close the foramen ovale after birth
• The clinical effect of atrial septal defects are unknown but can cause performance effects in adults
• There are 5 zones of the primitive tube…

  A) arterial trunk

  B) cordis

  C) ventricle

  D) atrium

  
• 1. The interventricular septum grows upwards from the base of the heart to the AV cushions. When it grows an interventricular foramen remains and the muscles become trabeculated.
  2. The AV valves develop and the muscular part of the ventricular septum grows and develops a membranous part of the interventricular septum. The septum is now divided into two parts.
  3. There is then further development of the AV values as well as the development of the chordae tendinae and papillary muscle
• VSD's are the most common congenital heart defect with some breed predisposition (Section A Welsh Mountain ponies, standardbreds and Arabians). It can be a standalone deflect or be a component of more complex congenital cardiac defects.
• Prognostic criteria include the…

  • Size of VSD
  • The horse with a small VSD (less than 2.5cm in diameter) has an excellent prognosis and should experience a normal performance life
  • Moderate defects are often well-tolerated at rest; although performance in high-intensity sports might be affected
  • Size of cardiac chambers
  • Maximal shunt velocity (proxy of VSD size)
  • The velocity is higher with the smaller shunt and hence a faster velocity indicates a better prognosis
  • Presence of significant Aortic or mitral regurgitation
  • PHT
  • Presence of CHF
• Scarborough Flyer is a 16 year old TB and ex-racehorse. He is now a teaching horse at SVMS. He has loud bilateral systolic murmur which is loudest on the right hand side, he is otherwise bright and well. what defect is present?

  VSD

  
• SUMMARY

  • The primitive heart tube divides into the common atria and ventricles
  • Atrial septation forms foetal pulmonary bypass
  • This is formed of two membranes which forms a one way valve
  • Atrial septal defects can occur with abnormalities in this process
  • Ventricular septation
  • Muscular and membranous portions are present
  • Ventricular septal defects can occur with abnormalities in this process