ABSTRACT: For carefully selected patients with mitral regurgitation, mitral valve repair is superior to mitral valve replacement.
CME OBJECTIVE: The reader will better understand the pathophysiology of mitral valve regurgitation and the criteria for and benefits of mitral valve repair.
David C. McGiffin, MD, no conflicts of interest
Mitral valve repair is the procedure of choice for patients with mitral regurgitation, since it eliminates the long-term risk of anticoagulation associated with mitral mechanical protheses and results in improved left ventricular function and long-term survival, compared with results associated with synthetic mitral valves, according to UAB cardiothoracic surgeon David C. McGiffin, MD.
Myxomatous degeneration of the valve and ischemic heart disease are among the most prevalent causes of mitral regurgitation; less frequent causes include degenerative disease (often associated with older age), endocarditis, rheumatic disease (usually associated with mitral stenosis), and congenital abnormalities.
"Mitral regurgitation secondary to coronary artery disease can occur acutely on rare occasion, due to papillary muscle rupture as a consequence of acute myocardial infarction, or chronically due to a spectrum of mechanisms, including papillary muscle dysfunction, abnormal left ventricular wall geometry, and annular dilation," he says.
The pathophysiology of myxomatous mitral valves includes leaflet redundancy, chordal elongation or rupture (or both), and annular dilation. Mitral regurgitation may be asymptomatic for many years, during which time left ventricular structure and function becomes progressively disordered. The symptomatic patient will experience fatigue and symptoms of pulmonary venous hypertension, and atrial fibrillation invariably develops.
Mitral Regurgitation
The mitral valve is a complex structure, both anatomically and physiologically, with five components — the mitral annulus, leaflets, chordae tendineae, papillary muscles, and left ventricular wall — that must perform in concert to function normally.
"Mitral regurgitation begets mitral regurgitation," McGiffin says. "The more the mitral valve leaks, the more the annulus dilates. Mitral regurgitation results in left atrial dilation, and eventually left ventricular dilation, and in the final stages of the process, left ventricular systolic dysfunction."
The pathophysiology of chronic mitral regurgitation is heterogenous and prognosis can vary dramatically. "In coronary heart disease, for example, the condition can be due to a localized infarction resulting in papillary muscle dysfunction, while the overall left ventricular structure remains sound," McGiffin says. "On the opposite end of the spectrum is a patient with a dilated and poorly functioning left ventricle. The patient with better left ventricular function has a much different outlook than the second patient, who may require cardiac transplantation."
Individuals with rheumatic disease account for about 15% of all patients with mitral regurgitation — a figure that has declined since the 1970s (Franco KL, Verrier ED. Advanced Therapy Cardiac Surgery. London: BC Decker Inc; 2003:210).
Compared with individuals in Asia, patients in the West with rheumatic disease often have more involvement of the subvalvular apparatus, chordae, and papillary muscles than those with ischemic disease, making valves much less amenable to repair, McGiffin says.
"In general, mitral valve repair is indicated when symptoms such as dyspnea with exertion, orthopnea, and fatigue are present. Mitral valve surgery in asymptomatic patients is advisable when there is evidence of left ventricular enlargement or left ventricular systolic dysfunction," he says.
Mitral Valve Repair
Preoperative transesophageal echocardiography (TEE) and transthoracic echocardiography help determine patient suitability for repair and aid in surgical planning by revealing leaflet anatomy and mobility, annulus size, mechanism of mitral regurgitation, and an assessment of the function of other cardiac valves.
"A number of repair techniques may be used for incompetent mitral valves, particularly those with myxomatous degeneration," McGiffin says. "Some examples of repair techniques are: Leaflet resection with reconstruction of the leaflet and annulus, chordal transfer from one leaflet to the other to replace ruptured chordae, and insertion of Gore-Tex sutures from the free edge of a leaflet to the papillary muscle as substitutes for ruptured chordae."
Long-standing mitral regurgitation is associated with some degree of annular dilation, and in most cases, an annuloplasty is indicated. During a ring annuloplasty, which can be accomplished with a flexible or semirigid ring, sutures are placed around the ring to decrease the size of the valve orifice, thereby increasing leaflet coaption area.
Postrepair Assessment of Competency
Postrepair valve competency can be assessed by filling the left ventricle with saline and observing the valve. Following discontinuation of cardiopulmonary bypass, both valve competency and left ventricular function can be assessed with TEE.
Most patients undergoing mitral valve repair are hospitalized for 5 days, and full recovery takes 8 weeks. Anticoagulation is required for 6 weeks until the annuloplasty ring is endothelialized.
An analysis of contemporary mitral valve repair (Ann Thor Surg. 2003; 75:820-825) in the US shows at 15 years:
- 93.9% of patients were free from thromboembolism
- 96.6% free from endocarditis
- 95.6% free from anticoagulant hemorrhage
- 87.3% free from reoperation (degenerative disease [92.7%], rheumatic disease, [76.1%])
- 91% of survivors had little or no mitral regurgitation
Twenty years after mitral valve repair, only about 15% of appropriately selected individuals need a second procedure, McGiffin says. "Most regurgitant mitral valves are repairable, and mitral reconstruction should be the procedure of choice."
For more information
Dr. David McGiffin
1-800-UAB-MIST
mist@uabmc.edu
Published in UAB Insight, Winter 2005