76 MITRAL REGURGITATION
David A. Fullerton M.D., Glenn J.R. Whitman M.D.

1. List the causes of mitral regurgitation.

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* Rheumatic fever
* Endocarditis
* Ruptured chordae tendineae
* Senile mitral annular calcification
* Papillary muscle dysfunction from ischemia
* Annular dilatation from left ventricular dilation

2. What is the pathophysiology of mitral regurgitation?

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The left ventricle ejects blood via two routes: (1) antegrade, through the aortic valve, or (2) retrograde, through the mitral valve. The amount of each stroke volume ejected retrograde into the left atrium is the regurgitant fraction. To compensate for the regurgitant fraction, the left ventricle must increase its total stroke volume. This ultimately produces volume overload of the left ventricle and leads to ventricular dysfunction.

3. What are the symptoms of mitral regurgitation?

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Dyspnea on exertion and loss of exercise tolerance are the symptoms of heart failure.

4. What determines left atrial pressure in mitral regurgitation?

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The compliance of the left atrium.

5. Why does acute mitral regurgitation cause severe symptoms?

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With acute mitral regurgitation, the normal left atrium is noncompliant. Hence, left atrial pressure increases rapidly, flooding the lungs (i.e., congestive heart failure) and causing severe symptoms. Conversely, chronic mitral regurgitation is associated with progressive dilatation of the left atrium. With increased left atrial compliance, the left atrial pressure may not increase.

6. What hemodynamic conditions exacerbate mitral regurgitation?

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Increased left ventricular afterload: Increased systemic arterial blood pressure increases the impedance against which the left ventricle must pump to eject blood antegrade. The regurgitant fraction is therefore increased (more blood goes backwards through the mitral valve).
Tachycardia: Because mitral regurgitation occurs during systole, tachycardia (i.e., more systoles per minute) increases the regurgitant fraction.
Volume overload: Left ventricular distension secondary to volume overload stretches the mitral anulus, impairs coaptation of the mitral valve leaflets, and increases mitral regurgitation.

7. What is the murmur of mitral regurgitation?

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A holosystolic murmur is best heard at the apex with radiation to the left axilla.

8. How is the diagnosis confirmed?

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By color Doppler echocardiography, especially transesophageal echocardiography (TEE; the left atrium lies right on the esophagus). The regurgitant jet may be accurately visualized and quantitated. Echocardiography also allows determination of the anatomic abnormality of the mitral valve apparatus that is responsible for the regurgitation.

9. What is the medical therapy for mitral regurgitation?

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* Afterload reduction with angiotensin-converting enzyme (ACE) inhibitors
* Diuretics (furosemide) for lower left ventricular preload
* Digoxin provides ventricular rate control for patients in atrial fibrillation
* Warfarin (Coumadin) is used for patients in atrial fibrillation

10. What are the indications for surgery in patients with mitral regurgitation?

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* Severe mitral regurgitation, especially with a ruptured chordae tendineae
* Symptoms despite medical therapy
* Progressive mitral regurgitation by echocardiography
* Deteriorating left ventricular systolic function. Because mitral regurgitation lowers the total impedance of left ventricular ejection (much of each stroke volume escapes via the low resistance mitral valvular “back door”), the left ventricular ejection fraction (LVEF) should be greater than normal in the presence of mitral regurgitation. An LVEF < 55% in the presence of mitral regurgitation suggests left ventricular dysfunction.
* Pulmonary artery pressure increases with exercise

KEY POINTS: MITRAL REGURGITATION

1. The symptoms are dyspnea on exertion and loss of exercise tolerance.
2. The murmur of mitral regurgitation is a holosystolic murmur heard best at the apex with radiation to the left axilla.
3. Mitral valve regurgitation is corrected with mitral valve repair or mitral valve replacement.
4. Mitral valve repair is preferable to replacement because of lower operative mortality rates, less risk of thromboembolism, less risk of endocarditis, better long-term left ventricular function, and less need (if any) for chronic anticoagulation.
5. Repair also avoids prosthetic valve-related complications.

11. How is mitral regurgitation corrected?

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Mitral valve repair. Mitral valve repair is the preferred surgical procedure. This preserves the mitral apparatus, maintaining the continuity between the left ventricular muscle and the mitral anulus via the chordae tendineae. Loss of this continuity by resection of the apparatus places the left ventricle at a mechanical disadvantage that over time leads to left ventricular dilatation and dysfunction.
Mitral valve replacement. An inability to repair the regurgitant valve mandates replacement. If replacement is necessary, efforts should be made to preserve the posterior leaflet of the mitral valve. In most series, mitral valve replacement is required in < 30% of cases.

12. Why is it preferable to repair rather than replace the mitral valve?

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* Lower operative mortality
* Less risk of thromboembolism
* Less risk of endocarditis
* Less need (if any) for chronic anticoagulation
* Better long-term left ventricular function
* Avoids valve-related complications

13. How is the mitral valve repaired?

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The redundant portion(s) of the valve leaflet(s) is resected, the leaflet is reapproximated, and the mitral anulus is plicated and reinforced with a prosthetic anuloplasty ring. The anuloplasty ring is sewn around the perimeter of the anulus on the left atrial side of the valve. In so doing, the mitral leaflets are supported by competent chordae tendineae, and the circumference of the mitral anulus is decreased. Competency of the repaired valve is assessed intraoperatively using TEE.

14. What is the operative mortality of mitral valve repair versus mitral valve replacement?

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Repair: 2%; replacement: 6%.

15. How durable are mitral valve repairs?

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The risk of requiring another mitral valve operation is approximately 2% per year.