Mitral valve endocardiosis
Mitral valve endocardiosis (Myxomatous mitral valve disease; chronic mitral valve insufficiency) is a common heart disease of dogs accounting for up to 50% of canine heart disease and is characterized by mitral valve degeneration and congestive heart failure.
Mitral valve endocardiosis results from slowly increasing left atrioventricular valve regurgitation from the left ventricle into the atrium. This leads to compensatory increased left ventricular hypertrophy and stroke volume and heart rate. Over time, eccentric left ventricular hypertrophy and atrial enlargement occur, causing mitral valve prolapse and pulmonary edema. These degenerative changes have been shown to correlate with biochemical increases in transforming growth factor-β (TGF-β) and matrix metalloproteinases at the molecular level.
Clinically affected dogs may be asymptomatic for many years, but progressive deterioration of the valve leads to intermittent coughing, reduced exercise tolerance and generalized weakness.
A left apical systolic heart murmur may be evident on auscultation and ECG abnormalities are commonly observed such as P-wave dispersion, bundle branch block and sick sinus syndrome (bradycardia-tachycardia syndrome due to fatty infiltration of the sinoatrial node).
Radiographs often reveal cardiomegaly, pleural effusion and pulmonary edema.
Echocardiography is usually required for definitive diagnosis, especially use of M-mode Doppler echocardiograms, often showing fractional shortening, but requires specialist interpretation. However, prognostic assessment of eventual congestive heart failure is difficult on echocardiography alone.
Histolopathological examination of postmortem hearts usually reveals gross changes in the mitral valve complex with tissue swelling on the edge of valve leaflets, chordae tendineae, and the chordal-papillary muscle junction with myxomatous degeneration to fibrillar tissue.
A differential diagnosis would include Bartonella spp endocarditis, hyperthyroidism, cardiomyopathy, patent ductus arteriosus, Duchenne muscular dystrophy, endocarditis, ventricular septal defect and infections with Dirofilaria spp.
Treatment usually requires use of preload drugs such as pimobendan, the β-blocker carvedilol, or angiotensin-inhibitors such as enalapril or benazepril together with diuretics such as furosemide and in severe cases, digoxin.
Treatment of heart failure dogs with thyroid hormone or thyroid hormone analogues may improve cardiac performance.
- Louisiana State Uni
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