Peritoneopericardial diaphragmatic hernia is the most common congenital pericardial disease in dogs and cats. It results from abnormal development of the dorsolateral septum transversum or from failure of the lateral pleuroperitoneal folds and the ventromedial pars sternalis to unite. The result is herniation of abdominal viscera into the pericardial sac. The liver is the most commonly herniated organ, followed by the small intestine, spleen, and stomach.
Clinical signs are highly variable, with many animals remaining asymptomatic and the defect being discovered on postmortem examination. Thoracic radiographs can demonstrate enlargement of the cardiac silhouette (perceived as cardiomegaly), lack of a visible diaphragmatic border and small-intestinal loops or liver crossing the diaphragm into the pericardial sac.
The suspicion of peritoneopericardial diaphragmatic hernia is heightened when abdominal organs are seen adjacent to the heart on echocardiogram. A contrast radiographic examination using oral barium may also identify small-intestinal loops or stomach in the pericardial sac. CT can usually confirm the diagnosis before surgery. In animals with respiratory signs or signs relatable to organ entrapment, the hernia should be surgically reduced.
Cor triatriatum sinister and dexter result from a fibrous membrane dividing the left or right atrium, respectively.
Cor triatriatum sinister is a rare defect of cats. It occurs when the common pulmonary vein fails to regress normally; as a result, a fibrous membrane persists within the left atrium, dividing the left atrium into two subchambers. There are commonly one or more perforations in the separating membrane, allowing communication between the two portions of the atrium. The proximal, high-pressure subchamber receives pulmonary venous return, while the distal, low-pressure subchamber is adjacent to the mitral valve and contains the left auricular appendage. Affected cats can present in left heart failure, with pulmonary edema, pleural effusion, or both. Surgical resection and balloon dilation of the membrane using a surgical approach have been reported.
Cor triatriatum dexter is a rare defect mostly of dogs. It is caused by persistence of the right valve of the sinus venosus. The remaining fibrous membrane partitions the right atrium into two subchambers; the cranial vena cava and tricuspid valve are associated with the low-pressure subchamber (true right atrium), whereas the caudal vena cava and coronary sinus are typically associated with the high-pressure subchamber. The membrane may contain one or more perforations, or be imperforate. The degree of blood flow between the subchambers determines the severity of disease. Dogs with more severe septation often present with right heart failure (typically ascites). Surgical resection, transcatheter balloon dilation, and stenting of the membrane are treatment options. CHF should be medically managed before surgery.
Double chamber right ventricle is an uncommon defect in which an anomalous muscle bundle divides the right ventricle into two subchambers. The muscle bundle leads to obstruction of the right ventricular outflow tract, creating a high-pressure proximal subchamber (receiving inflow through the tricuspid valve) and a low-pressure distal subchamber distal to the obstruction. Increased pressure in the proximal subchamber leads to right atrial dilatation and possible right heart failure. A systolic ejection murmur is often evident on auscultation. Definitive therapy requires open-heart surgery to resect the muscle bundles, which requires cardiopulmonary bypass. Balloon valvuloplasty has not proved to be a successful treatment option.
Anomalous pulmonary venous connection is a congenital abnormality in which varying numbers of pulmonary veins (from one to all) attach to the right atrium or a systemic vein.
Endocardial cushion defects (AV canal defects, persistent AV ostium, AV septal defects) involve abnormalities of endocardial cushion development and can produce septum primum defects, AV valve abnormalities, and ventricular septal defects.
Dextrocardia, positioning of the heart in the right hemithorax, can be seen as a congenital cardiac defect and by itself is typically benign. It can also be seen in combination with situs inversus (reversed or mirror-image orientation of the internal organs). The combination has been associated with ciliary dyskinesis (Kartagener syndrome) and clinical signs related to abnormal mucociliary clearance (eg, respiratory infection, infertility).