Chronic valve disease (myxomatous degeneration, endocardiosis) is the most common form of heart disease in dogs. It is characterized by mucoid degeneration of both mitral and tricuspid atrioventricular valves and proximal chordae tendineae. The mitral apparatus usually is more severely affected. Pathologic changes include valve thickening and prolapse, chordae tendineae lengthening and/or rupture and dilation of the valve annulus. The changes, individually or in combination, allow backward flow of blood from the left ventricle to the left atrium (mitral regurgitation) during ventricular contraction.

abmitvalve

LA = Left Atrium
LV = Left Ventricle
M = Mitral Valve
A = Mitral Annulus
C = Chordae Tendineae

Mitral regurgitation (a.k.a. mitral insufficiency) can vary from a mild systolic leak to a major leak often in combination with annular dilation and one or more ruptured chordae tendineae. This results in enlargement of the atrium and ventricle which compound the degree of regurgitation. (“Mitral regurgitation begets mitral regurgitation”)

leakphotos

A left ventricular injection angiocardiogram demonstrates contrast material passing backwards through the mitral valve (M) from the left ventricle (LV) to an enlarged left atrium (LA). Significant mitral regurgitation (arrow) causes left atrial and left ventricular enlargement, arrhythmias and ultimately may cause congestive heart failure.

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A two dimensional, short axis echocardiogram demonstrates a large left atrium and increased left atrium:aorta diameter ratio ( 2.5:1). Normally it is <1.5:1.

LAAO-Nolan

Color Doppler echocardiography reveals turbulent, regurgitant blood flow through the mitral valve.

A spectral Doppler echocardiogram in a dog with significant mitral regurgitation reveals systolic, turbulent, retrograde flow from the left ventricle to the left atrium. There is reduced ejection time and a characteristic v-wave “cutoff” pattern. The v-wave effect is explained on the next screen.

mrspectral

Systolic left ventricular and left atrial pressure recordings before and after mitral valve replacement in a patient with severe mitral regurgitation. Before valve replacement, LV pressure is reduced in late systole because of loss of ventricular volume into the left atrium. Regurgitant flow raises LA pressure (elevated V-wave) which further reduces the transmitral pressure gradient and the velocity of regurgitant blood flow. After valve replacement, LV pressure is sustained throughout systole and LA pressure is normal.

v-wave-effect

Auscultation in a dog with mitral regurgitation reveals a characteristic blowing, holosystolic murmur over the cardiac apex (M) on the left side. 

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M = Mitral Valve Area
A = Aortic Valve Area
P = Pulmonary Valve Area

A phonocardiogram records a systolic murmur between the first (S1) and second (S2) heart sounds.

phono