Introduction

• Cause: myxomatous degeneration (valvular endocardiosis) of mitral valve and chordae tendinae.
• Signs: acute onset dyspnea due to sudden pulmonary edema. New or changed character of mitral regurgitation murmur.
• Diagnosis: radiography, ultrasonography.
• Treatment: emergency → stabilize patient. Once stable, manage as for severe mitral endocardiosis.
• Prognosis: high mortality. Poor for medium-term survival with fair quality of life.

Pathogenesis

Etiology

• Degenerative process of collagen and glycosaminoglycans in valve leaflets and chordae tendinae.

Predisposing factors

• Breed.
• Age.
• Sex.
• Size? (Larger dogs).

Specific

• Concurrent endocardiosis Endocardiosis: tricuspid valve (does not have to be severe).

• Sudden exertion.
• Trauma?

Pathophysiology

• Myxomatous degeneration of mitral valve leaflets and associated chordae tendinae
• Mitral regurgitation and mitral prolapse usually present as a result of mitral endocardiosis before ruptured chordae tendinae.
• Increased systolic pressure gradient across incompetent mitral valve may be exacerbated by exertion or perhaps thoracic trauma.
• One of the chordae tendinae may rupture → dramatic increase in severity of mitral regurgitation (and altered character of heart murmur ).
• Sudden increase in left atrial/left ventricular volume overload cannot be accommodated by dilatation of the left atrium and left ventricle in the acute setting → sudden increase in left atrial and left ventricular end-diastolic pressures.
• Increased left atrial pressure → increased pulmonary venous pressure → increased pulmonary capillary (wedge) pressure → extravasation of fluid from capillaries.
• Pulmonary edema often alveolar in acute setting → expectorated with pulmonary surfactant (pink-white froth).
• Alveolar flooding and interstitial oedema and resulting decreased lung compliance → dyspnea.
• Sudden increase in left ventricular end-diastolic pressure causes increased wall stress (by La Place relationship ) → may result in ventricular arrhythmias.
• Sudden increase in left atrial pressure causes left atrial stretch → may result in supraventricular arrhythmias.
• Severity of signs depends on whether a primary chordal rupture (may result in sudden death) or a secondary or tertiary chordal rupture (less severe pulmonary edema - may present as just mitral endocardiosis).

Timecourse

• Even if patient can be stabilized in the short-term, usually dies within 6 months maximum.

Diagnosis

Treatment

Outcomes