Cardiology Canine Conditions

Myxomatous Mitral Valve Degeneration and Regurgitation

The mitral valve is the most common heart valve to undergo degeneration with age such that the valve becomes thickened and does not close properly. This lack of proper closure results in blood leaking backwards, and this leak (regurgitation) causes the heart to work harder. Many compensatory mechanisms are initiated to counteract this leak, including retention of salt and water. Over time, the heart enlarges and fluid retention can lead to congestive heart failure. The mitral valve is the most commonly affected by degenerative changes, however other valves can also be affected. This condition is most common in older, small breed dogs.

Echocardiogram from a dog with mitral regurgitation. The mosaic, multicolored jet is the leak in the mitral valve (regurgitation).	Echocardiogram showing mitral regurgitation. LA = left atrium, LV = left ventricle. The mosaic multicolored area is the jet of mitral regurgitation.	Echocardiogram showing mitral valve prolapse (arrow) due to degenerative valve disease. LV = left ventricle, LA = left atrium.
Xray from a dog with mitral regurgitation and congestive heart failure		2nd view

Dilated Cardiomyopathy

Dilated cardiomyopathy is a disease whereby the heart muscle becomes weak, causing poor contractions and poor heart function. The heart enlargement that ensues in conjunction with compensatory salt and water retention can eventually lead to congestive heart failure. Some dogs have serious arrhythmias (irregular heart rhythms) that can predispose them to sudden death. This disease mostly affects large breed dogs.

Echocardiogram from a dog with dilated cardiomyopathy. The heart shows very weak contractions.

X-rays of the chest of a dog with dilated cardiomyopathy and congestive heart failure.

2nd View

Arrhythmias (abnormal heart rhythms)

Ventricular and atrial arrhythmias can be associated with underlying heart disease or can be secondary to other diseases. Arrhythmogenic Right Ventricular Cardiomyopathy of Boxers is one example of a disease characterized primarily by arrhythmias. It is unique to and inherited in the Boxer breed. It is characterized by severe ventricular arrhythmias (abnormal heart rhythms) and sometimes poor heart function.

CLICK TO ENLARGE ECG showing ventricular tachycardia (area in parentheses).

CLICK TO ENLARGE        ECG showing atrial fibrillation.

CLICK TO ENLARGE   ECG showing supraventricular     tachycardia.

Pericardial Effusion

Fluid that builds up in the sac around the heart is called pericardial effusion. This can be due to a tumor in or around the heart or may be idiopathic (unknown cause). Occasionally it is due to other rare conditions. Pericardial effusion causes weakness and often visible distention (swelling) of the abdomen. This condition tends to occur most commonly in middle-aged to older large breed dogs.

Echocardiogram from a dog with pericardial effusion (fluid in the sac around the heart).

Echocardiogram showing pericardial effusion (PE) that is caused by a tumor (arrow). RA = right atrium, RV = right ventricle, LV = left ventricle.

Recording of a continuous murmur from a dog with a patent ductus arteriosus.

Congenital Defects

Heart defects that are present at birth are called congenital defects and the most common ones in dogs are patent ductus arteriosus (PDA), pulmonic stenosis (PS) and ventricular septal defects (VSD). Subaortic stenosis (SAS) is not truly congenital (it is not present at birth) but rather is a developmental defect, meaning that the abnormality develops within the first year of life. When severe, SAS carries a high risk of sudden death. Other less common congenital defects include atrial septal defects (a hole in the wall that separates the left and right atrium), tricuspid dysplasia (malformation of the tricuspid valve) and mitral dysplasia (malformation of the mitral valve).

Echocardiogram from a dog with a patent ductus arteriosus (PDA) which is a communication between the aorta and pulmonary artery (PA).	Angiogram from a dog with a patent ductus arteriosus (PDA). Contrast is outlining the PDA (arrow).	Echocardiogram from a dog with pulmonic stenosis. RV = right ventricle, PA = pulmonary artery, arrow = stenosed (narrowed) pulmonary valve.
Echocardiogram from a dog with pulmonic stenosis. The green jet is turbulent blood flow that occurs because of the malformed pulmonary valve.	Echocardiograms from a dog with a ventricular septal defect (VSD). The picture on the left shows the defect (arrow) which is a hole between the left ventricle (LV) and right ventricle (RV). The picture on the right shows color flow Doppler superimposed showing a turbulent jet of blood going across the VSD (the yellow and blue mosaic area).	Echocardiogram from a dog with subaortic stenosis (SAS). The arrow points to a narrowed area just below the aortic valve. LV = left ventricle, Ao = aorta.
Echocardiogram from a dog with subaortic stenosis. The multicolored area is turbulent blood flow because of a narrowing below the aortic valve. LV = left ventricle, Ao = aorta	Echocardiogram showing an atrial septal defect as a communication between the left atrium (LA) and the right atrium (RA) (note arrow).	Echocardiogram from a dog with tricuspid valve dysplasia. The mosaic, multicolored area is a jet of tricuspid regurgitation originating from a malformed valve. RA = right atrium. RV = right ventricle.
	Echocardiogram from a dog with mitral valve dysplasia. The mitral valve leaflets are thickened and curled (arrow). LA = left atrium, LV = left ventricle