MITRAL INSUFFICIENCY IN THE HORSE. 1 33 



degeneration, vegetations, aneurisms^ perforations, partial ruptures, or 

 adhesion between a flap and the ventricular wall. With the exception 

 of a case of rupture of the principal valve, of two others where a small 

 aneurismal depression existed, and of a few cases of rupture of one or 

 several of the chordae tendineae, I have never met with anything moie 

 than sclerotic changes — thickening, folding, and more or less pro- 

 nounced contraction of the valves of the auriculo-ventricular opening. 



But the anatomical peculiarities which mitral lesions exhibit are 

 not of great importance ; what dominates the after consequences, the 

 intensity of the symptoms, and the rapidity of their succession is the 

 degree of insufficiency. Once insufficiency is established, the cycle of 

 vascular troubles commences. What are these troubles ? 



The mitral valve incompletely closing the auriculo-ventricular 

 orifice during ventricular systole, the blood makes its exit from the left 

 ventricle by two orifices ; (i) by the normal aortic opening, and (2) by 

 the abnormal auriculo-ventricular opening, resulting from insufficiency 

 of the mitral valve. At each heart-beat a portion of the blood which 

 should pass into the aorta escapes by the auriculo-ventricular hiatus, 

 and enters the left auricle. The first effect of this reflux of blood 

 under pressure is to dilate the affected auricle, which, in order to 

 overcome the distension, becomes hypertrophied. During a period 

 of variable duration, termed the compensation stage, matters rest 

 thus, and the primary lesion produces no functional disturbance 

 likely to attract attention. At the autopsy of horses dead of accidents 

 or internal disease, lesions of the mitral valve, sufficiently developed to 

 cause insufficiency, are sometimes found, without during life having 

 attracted any attention whatever. Up to the last moment the animals 

 have been able to perform ordinary work. 



Here is a case of compensated mitral insufficiency seen in a horse 

 which died from rupture of the stomach. 



A ten-year-old Percheron horse, which had worked very hard for 

 some years, but the general condition of which had always been satis- 

 factory and the health good, was brought to the College on account of 

 impaction of the stomach, from which it finally died. At the post-inorteni 

 examination we found, in addition to ruptured stomach, an enlarged 

 heart. The left auricle was greatly dilated and its walls thickened. 

 On opening the left ventricle we detected old-standing mitral lesions. 

 The anterior and the left valves were little changed, but the principal 

 flap was thickened and contracted, and exhibited at its right extremity 

 an irregular fibrous vegetation; the right valve was shrivelled, and 

 showed near its free borders a large hardened area. The right heart 

 was normal. These mitral lesions certainly caused insufficiency. 



