Endocardiosis

Synonyms

Myxomatous mitral valve disease, mitral insufficiency, mitral regurgitation, chronic valvular disease

Introduction

This condition tends to affect middle-aged and older dogs, with males being predisposed. Breeds with particular predisposition to the disease include smaller breeds such as Chiuahuas, Boston Terrirs, Poodles, Pomeraniams, Cavalier King Charles Spaniels and larger breeds such as the German Shepherd. It is the most common heart condition in dogs. In dogs over 9 years old 97% show lesions, of which approximatley 40% are clinically significant. The condition is often found at post mortem as an incidental age related change. The disease is rare in cats.

This is a valvular insufficiency The most commonly affected site is the mitral valve. The condition results in slowly developing heart failure as the valves become swollen and shortened/ misshapen, so as the heart cannot pump blood effectively to the circulation from the left ventricle.

Blood passes back into the left atrium, compromising the filling from the pulmonary vein, which leads to back pressure on the pulmonary capillaries. Resultant oedema forms in the lungs, and can be heard as moist sounds on auscultation. This reduces the oxygenation of blood leading to exercise intolerance. Failure of the left side eventually compromises the function of the right side.In right sided heart failure there is a pooling of blood in the venous system i.e. in the liver. In some cases a jet lesion can occur, where a small stream of blood passes back into the left atrium and contacts the atrial wall.

Clinical Signs

Signs depend on stage of disease, but may include coughing, syncope, weight loss, pale or cyanotic mucus membranes and prolonged capillary refill time. If left sided heart failure is present then signs will also include exercise intolerance, weakness, dyspnoea, inappetance and lethargy. If right sided heart failure is present then signs including hepatomegaly, jugular pulses & distension, pleural effusion, ascites and peripheral odema will occur.

Diagnosis

Clinical signs plus signalment of the dog are indicative of the disease. Upon physical examination a murmur over the left heart apex may be heard. Snaps, crackles, pops will also be heard if pulmonary edema is present. Muffled heart sounds in the presence of pleural/pericardial fluid will be auscultatable.

Upon radiography there will be visible signs of left sided heart enlargement. There will possibly be none, some or all of the following radiographic signs - left atrial enlargement (DV view appears at 2-3 o'clock position), left ventricular enlargement, dorsal displacement of trachea, bronchial compression, pulmonary venous congestion and/or edema and right-sided signs (distended caudal vena cava, ascites, pleural effusion, heptaomegaly).

Electrocardiography (ECG) may show a left atrial enlargement pattern, left ventricular enlargement pattern and rhythm disturbances (supraventricular arrhythmias: atrial premature complexes, atrial tachycardia, and ventricular rhythm disturbances). 

Echocardiography may detail irregularities of the valves affected (e.g. thickening, shortening, and/or prolapse of the valve leaflets), abnormal valve movements & valve regurgitation, left atrial enlargement (wide P wave) and left ventricular dilation (tall R wave, wide QRS complex). Dopper will demonstrate the presence of regurgitative flow. On M wave echography there may be a normal to increased fractional shortening of the myocardium in early stages of the disease and a decreased fractional shortening of the myocardium in later stages of the disease.

Treatment

If animal is presented in left-sided heart failure treatment is given at the onset of clinical signs. If the animal is presented in right-sided heart failure then treatment is also given at the onset of clinical signs. Such treatments include ACE inhibitors and diuretics and  If the disease is detected but the animal is not yet in heart failure then no treatment is required. Exercise must also be restricted and sodium reduced in the diet by specially formulated cardiac diets. Symptomatic treatments are also given if clinical signs persist while the animal is on heart failure medications.

Prognosis

Asymptomatic patients may live for many years. Once heart failure occurs, life expectancy is usually around one year although some patients remain stable for years on heart failure medications.

References

Ettinger, S.J. and Feldman, E. C. (2000) Textbook of Veterinary Internal Medicine Diseases of the Dog and Cat Volume 2 (Fifth Edition) W.B. Saunders Company
Ettinger, S.J, Feldman, E.C. (2005) Textbook of Veterinary Internal Medicine (6th edition, volume 2)W.B. Saunders Company
Fossum, T. W. et. al. (2007) Small Animal Surgery (Third Edition) Mosby Elsevier

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