Mitral valve disease in small animals

Mitral valve disease is the most frequent cardiac disorder in small animal medicine. It is a chronic disease in which the mitral valve suffers a degenerative process which leads to a failure of this valve. It has high incidence in toy breeds (miniature poodle, daschsunds, chihuahua) and patients with 8-11 years of age. This disease is characterized by a degeneration of the mitral valve structures which produces a failure in the closure of the valve. This generates a regurgitation to the left atrium, when the left ventricle contracts. This, in turn, produces an increase in volume and pressure in the left atrium. Besides, a decrease in stroke volume and arterial pressure occurs. These changes produce the activation of compensatory mechanisms (rise in hearth rate, elevation of the inotropism and peripheral constriction of the vasculature).

Diagnosis: The main clinical sign in patients with mitral valve disease is a systolic heart murmur. This can be heard in the mitral area on the left side of the thorax. At the beginning of the disease, the heart murmur usually has low intensity. When the process evolves, a cough could appear. This sign is produced by two mechanisms: in the first place, the increase in the dimension of the left atrium produces a mechanic compression of the trachea and bronchi. On the other hand, in advanced stages of the disease, pulmonary edema could appear. Different kinds of complementary diagnosis methods could be used to diagnose mitral valve disease. These different studies give information about heart and circulatory state. Radiology gives information about heart size and pulmonary condition. However, this method does not provide information about valve damage. The utility of ECG is relative. Information about increase in atrium size could be found as a longer P wave. However it is not always possible to find alterations in ECG. The main applicability of this study in mitral valve disease is the detection of secondary arrhythmia (for example atrial fibrilation). Echocardiography is the diagnosis method that gives us the most information about structural alterations. Increase in atrium dimensions and changes in echogenicity in valve structures are the most common findings. In advanced stages, dilatation of the left ventricle can be observed.

Treatment: The treatment in mitral valve disease depends on the severity of presentation. Generally the object of the treatment is to reduce vascular resistance, and improve venous returns. The implementation of diuretic therapy and antiarrhythmic therapy could be necessary if edema or arrhythmia appear.

References

• Kittelson, M.D., Kienle, R.D. (Eds.), Small Animal Cardiovascular Medicine Textbook. Mosby, St. Louis.

• Boon, J.A. (Ed.), Manual of Veterinary Echocardiography. Williams and Wilkins, Media.