Canine Cardiac Conditions

[This information is extracted form “The Genetic Connection” and may not be used elsewhere without the express written consent of the author].

HEART CONDITIONS

AORTIC STENOSIS

Subaortic stenosis (SAS) is a congenital heart disease involving a narrowing or stricture just below the aortic valve. The stricture is usually an abnormal fibrous ring of tissue that results in a reduction of blood flow pumped from the heart. This condition causes the cardiac muscle to overwork, and thereby increases the oxygen needs of the heart itself. The result can be arrhythmias and, potentially, sudden death.

ATRIAL SEPTAL DEFECT

Atrial septal defect is a congenital cardiac anomaly resulting in communication through the interatrial septum. Currently, a genetic basis for the disorder has not been documented. Clinical signs may be absent with small defects, or may include exercise intolerance, dyspnea, and syncope. Severely affected animals develop and are treated for congestive heart failure.

CARDIOMYOPATHY

Dilated cardiomyopathy (DCM) refers to a defect of the heart muscle in which the heart muscle becomes thin and stretched, much like a balloon. In this condition, the heart is not an effective pump, and eventually affected dogs succumb to heart failure.

CHRONIC MITRAL VALVULAR DISEASE (ENDOCARDIOSIS)

Chronic mitral valvular disease is the most common acquired cardiac abnormality of dogs. It is a degenerative process, most typically involving the atrioventricular valves and resulting in mitral regurgitation, rupture of the corda tendinea, and potentially, left-sided heart failure. There is some similarity to mitral valve prolapse in humans. An underlying connective tissue defect is postulated. There is thought to be a genetic tendency to experience degeneration of the collagen in the heart valves. The insufficiency increases in frequency and severity with advancing age, and chronic mitral valve insufficiency is estimated to be present in more than half of dogs 9 years of age and older.

FEMORAL ARTERY OCCLUSION

Thrombosis of the femoral arteries in the Cavalier King Charles spaniel is considered a primary form of vascular disease rather than just an extension of thromboembolism. The condition seems to be familial but with no clear mode of inheritance determined to date. Affected dogs should not be bred, but there is insufficient information to make breeding recommendations for other family members.

HYPERTENSION

High blood pressure, or hypertension, has been reported in dogs. Although the primary form, essential hypertension, accounts for more than 90% of human cases, secondary hypertension is much more common in dogs. Still, essential hypertension in the dog is believed to have a polygenic mode of inheritance.

PATENT DUCTUS ARTERIOSUS (PDA)

Patent ductus arteriosus (PDA) is the most common congenital heart defect in dogs. It is inherited as a polygenic threshold trait with a high rate of heritability in some breeds. This means that the trait is controlled by a number of different genes and has a threshold, although the degree of patency can vary from a large patent ductus to a blind-ended diverticulum.

This defect occurs when normal fetal communication between the nonfunctional lungs and the aorta fails to close after birth. This results in blood being shunted into the pulmonary artery and overperfusing the lungs. At the same time, the rest of the body is not getting adequate circulation.

PULMONIC STENOSIS

Pulmonic stenosis (PS) refers a stricture or incomplete opening through the pulmonic valve within the heart. In most cases, the underlying defect is pulmonic valve dysplasia (G012). The valve is located between the right ventricle and the pulmonary artery, which delivers the blood from the heart to the lungs. Many dogs with pulmonic stenosis are asymptomatic but do have a heart murmur. As they get older or if the condition is severe, they show evidence of exercise intolerance, fainting (syncope), coughing (rarely), or fluid accumulation within the body.

SICK SINUS SYNDROME

Sick sinus syndrome is a clinical syndrome associated with irregular discharge of the sinoatrial node, causing severe bradycardia. An underlying genetic susceptibility is suspected but undocumented. It is characterized by periods of sinus arrest, which may be clinically apparent or may result in dizziness or syncope. Animals recover soon after the attack. Sudden death is a rare sequel.

TETRALOGY OF FALLOT

Tetralogy of Fallot, the most common cause of cyanosis in the dog, has four components: ventricular septal defect; overriding of the interventricular septum by the aorta; pulmonic stenosis; and right ventricular hypertrophy. Affected dogs have right-to-left shunting of blood and develop chronic hypoxia, cyanosis, and exercise intolerance.

TRICUSPID VALVE DYSPLASIA

Tricuspid dysplasia is a congenital abnormality of the right atrioventricular valve, characterized by anomalies of the chordae tendinae, papillary muscles, and valvular tissue. Clinically, a murmur (systolic regurgitant murmur over tricuspid valve area) is apparent, but an electrocardiogram might not show classic evidence of right-sided heart enlargement. Affected dogs are eventually treated for cardiac insufficiency and arrhythmias.

VASCULAR RING ANOMALIES

Vascular ring anomalies include persistent right aortic arch (which accounts for 95% of cases), aberrant right subclavian artery, aberrant left subclavian artery, double aortic arch, persistent right ductus arteriosus with normal aortic arch, aberrant intercostal arteries, and persistent right dorsal aorta. Persistent right aortic arch is a developmental anomaly in which the aorta is formed by the right fourth aortic arch instead of the left fourth aortic arch. In about 40% of cases, a retroesophageal left subclavian artery is also present. In this anomaly, the esophagus and trachea are encircled by a vascular ring consisting of the aorta on the right, the pulmonary trunk and base of the heart ventrally, and the ligamentum arteriosum on the left. It is actually more of a gastrointestinal disorder than a heart disease because it often results in regurgitation and aspiration pneumonia rather than cardiac dysfunction.

VENTRICULAR ECTOPY

Ventricular ectopy includes premature ventricular complexes, ventricular bigeminal or trigeminal rhythms, ventricular couplets, and ventricular tachycardia. Affected dogs develop arrhythmias by 12 months of age and typically die suddenly during this period.

VENTRICULAR SEPTAL DEFECT

Ventricular septal defect (VSD), a common cardiac abnormality, refers to an abnormal opening or hole in the wall between the left and right ventricles of the heart. This creates a communication between the two ventricles. Affected animals have a pronounced heart murmur, but if the opening is small, the animal may be completely asymptomatic. If the hole is large, clinical signs usually develop by 1 year of age and include a cough, exercise intolerance, and poor growth.