Atrial septal defects (ASD) are rarely diagnosed in dogs. Three types of defect have been identified: (1) a high sinus venosus atrial septal defects involves the atrial septum near the junction of the pulmonary vein and left atrium; (2) an ostium secundum atrial septal defects involves the middle portion of the atrial septum; (3) an ostium primum atrial septal defects involves the ventral atrial septum, with the ventral border of the atrial septal defects being formed by the ventricular septum or a trio ventricular valves.
An atrial septal defects usually creates a left to right shunt resulting in volume overload of the right atrium, right ventricle and pulmonary vessels. Severe dilation of the right ventricle occasionally leads to dysfunction of the tricuspid valve and tricuspid regurgitation. Occasionally an atrial septal defects occurs in combination with pulmonic stenosis.
The highest incidence of atrial septal defects occurs in Old English sheepdogs, boxers and samoyeds.
Dogs with small defects often show no clinical signs and have normal life expectancy. A more severe defect may be associated with signs of congestive heart failure (primarily respiratory signs because of the pulmonary overcirculation) and syncope. With large shunts a soft systolic murmur may be audible over the pulmonic valve region, with increased blood resulting in relative pulmonic stenosis and splitting of the second heart sound.
Electrocardiographs changes with atrial septal defects are nonspecific; signs of right ventricular enlargement are occasionally present with large shunts.
Radiographic evidence of right ventricular enlargement and pulmonary overcircularion occurs only with large shunts.
A suspect atrial septal defects should be imaged in several planes and Doppler echocardiography can be used to confirm the direction of blood flow through the shunt. A non-selective injection of contrast (for example an echocardiographic bubble study) may be used in cases when reversal of the shunt is suspected.
Atrial septal defect: Treatment
Most dogs with atrial septal defects do not require surgery. Surgical closure of an atrial septal defects is indicated if (1) there is progression of signs of congestive heart failure, (2) the defect is large and the Qp:Qs is greater than 2.5, or (3) there is evidence of increased pulmonary vascular resistance and / or a right to left shunt.
Persistent common atroientricuiar canal in cats
Persistent common atrioventricular canal is a common cardiac anomaly in the cat. A large ostium primum defect occurs in association with a high ventricular septal defect at the level of the coronary sinus, forming a common atrioventricular canal which is shared by all four chambers of the heart. Generalized cardiomegaly develops due to volume overload and signs of heart failure usually occur between 6 and 10 months of age. The condition is usually associated with malformation of the atrioventricular valves.