(USMLE topics, cardiology) Mitral (bicuspid) valve diseases: pathology, complications, diagnosis and treatment.
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The mitral valve serves to ensure ONE-WAY blood flow from the left atrium to the left ventricle of the heart. It OPENS during diastole when the left atrial pressure is higher than the left ventricular pressure, allowing blood to fill the left ventricle; and CLOSES during systole, when the pressure gradient is reversed, to prevent blood from flowing BACK to the atrium as the ventricles contract. The mitral valve has 2 flaps, known as anterior and posterior mitral leaflets, which are supported by a fibrous ring, called mitral annulus. During ventricular contraction, the leaflets are kept from opening in the wrong direction by the action of papillary muscles which attach to the leaflets via cord-like tendons called chordae tendineae, or tendinous chords.
The most common of all heart valve diseases is mitral valve prolapse, or MVP. In MVP, the mitral leaflets bulge into the left atrium every time the ventricles contract. In many people, the reason why this happens is unclear. In others, it is linked to connective tissue disorders such as Ehlers-Danlos or Marfan syndrome. Connective tissue problems are believed to weaken the leaflets, INcrease leaflet area and cause elongation of the chordae tendineae. In most people, MVP is Asymptomatic and does not require treatment. However, it does increase the risks of developing other heart diseases such as arrhythmias, endocarditis, and most frequently, mitral valve regurgitation. In fact, mitral valve prolapse is the most common cause of mitral regurgitation. The billowing leaflets may not fit together properly; elongated chords may also rupture, resulting in a LEAKY valve, which permits BACKflow of the blood to the left atrium when the ventricles contract. When the volume of regurgitated blood is significant, the left side of the heart experiences volume OVERLOAD and eventually fails; blood is backed up to the lungs, causing pulmonary congestion, a hallmark of left-sided heart failure.
Mitral valve prolapse and regurgitation produce characteristic ABNORMAL heart sounds, such as clicks and murmurs, which can be heard during auscultation. Diagnosis is usually confirmed by echocardiography, a procedure in which heart valves and blood flows can be visualized LIVE using ultrasound.
A leaky valve requires surgical repair or replacement. In a typical valve repair surgery, the floppy portion of the valve is removed and the remaining parts are REconnected. The procedure may also include tightening or replacing the mitral annulus, known as annuloplasty. Valve replacement is considered when repair is not possible. Artificial valves can be mechanical or bio-prosthetic. Mechanical valves last longer but usually require life-long administration of anticoagulant medications to prevent formation of blood clots.