SEVERE MITRAL REGURGITATION IN HORSES - CLINICAL, ECHOCARDIOGRAPHIC AND PATHOLOGICAL FINDINGS

Forty-three horses with mitral regurgitation (MR) and congestive heart failure were examined, using hi-mode, 2-dimensional real-time and Dop pler echocardiography, There was no breed or sex predisposition when c ompared to the general hospital population, The mean +/- s.d. age of a ffected horses was 7.6 +/- 8.1 years, Horses with MR and congestive he art failure had significant increases in mean values for left ventricu lar chamber size, left atrial size and heart rate and significant decr eases in interventricular septal and left ventricular free wall thickn ess, Significant increases in pulmonary artery diameter were detected compared to aortic diameter, Mean values for fractional shortening wer e not significantly different from normal. All horses had a Grade 3-6/ 6 holosystolic or pansystolic murmur with its point of maximal intensi ty in the mitral to aortic valve area, Atrial fibrillation was found a t presentation in 24 horses with MR and congestive heart failure. One horse presented with atrial tachycardia and subsequently developed atr ial fibrillation. Seven horses had ventricular premature contractions, Exercise intolerance (n = 34), respiratory signs (n = 31), and fever (n = 21) were the most common presenting signs, Thickening of the left atrioventricular valve leaflets, endocarditis, nail valve leaflets, r upture of a chorda tendineae, and mitral valve prolapse were detected echocardiographically. Doppler echocardiography confirmed the presence of a large systolic regurgitant jet in the left atrium in all horses in which it was used, and in many horses, concurrent tricuspid and pul monary regurgitation was detected, All horses died or were subjected t o euthanasia due to the severity of their MR and/or lack of response t o therapy. Post mortem examinations were performed in 35 horses and co nfirmed the echocardiographic findings, The echocardiographic detectio n of a nail mitral valve leaflet was significantly associated with the detection of a ruptured chorda tendineae at post mortem examination, There was a significant association between echocardiographic detectio n of a dilated pulmonary artery and its presence at post mortem examin ation. M-mode, 2-dimensional real-time, and Doppler echocardiography s hould be used to accurately characterise the valvular abnormalities an d assess the severity of mitral regurgitation. Pulmonary artery dilata tion, an echocardiographic indication of severe pulmonary hypertension , should be considered a grave prognostic indicator and may indicate i mpending pulmonary artery rupture.