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Severe mitral valve regurgitation in the setting of degenerative mitral valve disease is a mechanical problem with an only definitive mechanical solution; at this time, the only definitive treatment is mitral valve repair.119 As mentioned before, all prolapsing valves are repairable and mitral valve replacement should not be an option if appropriate referral patterns are followed.120 Degenerative mitral valve disease along with annular dilatation is the most repairable form of surgical mitral valve disease, and repair should be recommended. Mitral valve repair is favored over replacement for several reasons, including a lower perioperative risk, improved preservation of left ventricular function, improved event-free survival in the majority of operated patients, and greater freedoms from prosthetic valve-related complications such as thromboembolism, anticoagulant-related hemorrhage, and endocarditis (Fig. 48–15).121,122,123 Although no randomized trials comparing outcomes of mitral valve repair versus replacement exist (and it seems very unlikely that such trials would be conducted, particularly in the setting of degenerative mitral valve disease), the vast majority of available retrospective data strongly support the long-term advantage of mitral valve repair.
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Mitral Valve Repair in the Elderly
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The risk-adjusted advantage of mitral valve repair versus mitral valve replacement is also patent in the elderly (Fig. 48–16).124,125 The prevalence of mitral valve disease increases with age, and around 10% of patients aged above 75 years who require hospitalization have significant mitral regurgitation, predominantly caused by fibroelastic deficiency.16 However, surgery is often contraindicated in elderly patients with multiple comorbidities such as coronary artery disease, renal failure,126 or neurological impairments.124 In a recent series, Chikwe and associates analyzed a consecutive series of 322 octogenarian patients with degenerative mitral valve disease (most of them with fibroelastic deficiency) and showed that 30-day mortality was 2.5-fold higher in those patients who underwent mitral valve replacement. Later on, Badhwar and associates conducted a retrospective study that involved over 14,000 patients over 65 years of age from the STS National Cardiac Registry and US Medicaid. The authors reported an overall 2.6% mortality with a 68% 5-year survival.127 Finally, Dodson and coworkers interrogated the National Medicare database to elucidate outcomes of isolated mitral valve surgery among patients aged above 65 years. This study, the largest to date, demonstrated that the proportion of patients undergoing mitral valve repair significantly increased from 24.7% to 46.9% (versus bioprosthetic valve replacement 23.8% to 33.0%). Although the latest data clearly suggest that elderly patients with degenerative mitral valve disease benefit from the better success rates and numerous advantages of mitral valve repair, the reality is that surgeons, especially those at low-volume centers, are often reluctant to attempt repair because of the potential need for longer bypass times or a more likely conversion to standard sternotomy.128 In addition, the integration of quality of life and functional scoring systems seems to be important in order to assess surgical benefit versus futility.129 In this context, novel transapical techniques may become an alternative therapeutic option only for patients who are not eligible for any surgical approach until transcatheter techniques130 show proof of better efficacy.131,132 This is an important point in patients with degenerative mitral valve disease, because residual moderate mitral regurgitation has been demonstrated to be associated with poorer outcomes in survival and symptom relief, and with greater recurrence.129
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Hospital and Surgeon Procedural Volume as a Quality Metric
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Surgical management of degenerative mitral valve disease has evolved considerably and so have the quality metrics to assess outcomes. Now that there is quorum among surgical leaders about the superiority of mitral valve repair over replacement and the need for repair in every single patient with mitral prolapse, attention has been shifted to nonpatient factors that influence feasibility of repair and operative mortality, such as hospital teaching status, surgeon procedural volume, and hospital procedural volume.133
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Although mitral valve repair rates have risen throughout the past decade, and currently approach 70% in the Society of Thoracic Surgery Database,134 its application remains quite variable with some surgeons performing five or fewer mitral operations per year, with repair rates of less than 30%, particularly for more complex scenarios such as anterior or bileaflet prolapse (Fig. 48–17).135 In Europe, an analysis of over 5000 mitral valve operations from the United Kingdom mandatory adult cardiac surgical database suggests a significant impact of surgeon volume on mitral valve repair rates.136 Even in high-volume centers, the repair rates can be low; in patients with degenerative mitral regurgitation, repair rates at high-volume centers were as low as 36%, and only three high-volume centers had repair rates above 85%.136 One of the first institutional reports to demonstrate the implications of surgeon volume in mitral valve repair rates was published in 2008.137 Gillinov and coworkers observed that some surgeons were independent predictors of mitral valve replacement in patients with degenerative mitral valve disease. Since then, several authors have emphasized the exponential correlation between surgeon volume and mitral valve repair rates, repair quality, and shortened cross-clamp times (Fig. 48–18).138,139,140 The most recent analysis of the Nationwide Inpatient Sample (NIS) including over 50,000 patients showed that although hospital volume accounted for 11% of the surgeon volume effect on increased mortality for low-volume surgeons, surgeon volume accounted for 74% of the hospital volume effect on increased mortality in low-volume hospitals.141 Furthermore, significant trends were observed in repair rates, with increasing surgeon volume demonstrating stronger correlation with the odds of repair than hospital volume, thus highlighting the importance of learning curves in mitral valve repair.142
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Feasibility and Durability of Mitral Valve Repair
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Carpentier’s repair philosophy and techniques are the foundation of contemporary mitral valve repair strategies.7 A “lesion-specific approach” addresses leaflet, chordal, and annular pathology according to the wide spectrum of lesions encountered in patients with degenerative mitral valve disease. After systematic analysis, mitral valve repair should be performed following a sequential approach such as (1) annuloplasty sutures, (2) repair of the posterior leaflet, (3) annuloplasty, (4) leaflet resuspension when required, and (5) repair of any prolapse of the anterior leaflet or commissures after inspection of the line of closure during a saline test (Fig. 48–19). An optimal mitral valve repair should meet the following criteria: (1) the valve is competent on saline testing, (2) there is good surface of coaptation, (3) the closure line is symmetric and located where the anterior leaflet occupies at least 80% of the valve area, (4) there is no residual leaflet billowing, and (5) there is no tendency to systolic anterior motion.143,144
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The most frequent lesion encountered in degenerative mitral valve disease is posterior leaflet prolapse, which accounts for about 70% of patients. In this scenario, triangular resection and leaflet resuspension (if the adjacent native chords do not look totally healthy or in light of further disease progression) remain the most popular techniques.145 Most centers would report repair rates above 90% in patients with isolated posterior leaflet prolapse. However, repair rates fall drastically in the presence of more complex lesions such as severe annular dilatation, involvement of three or more segments, anterior leaflet prolapse, various degrees of calcification, scarcity of leaflet tissue, and opposite dysfunction. Regardless of the leaflet and chordal approach, essentially all mitral valve repairs should include an annuloplasty,146 which reshapes the annulus and addresses posterior annular dilatation that is always present in long-standing severe mitral valve regurgitation (Fig. 48–20).147,148,149
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As a fast-growing number of asymptomatic patients with degenerative mitral valve disease are expected to be referred for surgery, it seems mandatory to ensure mitral valve repair rates above 95% with minimal perioperative risk and optimal long-term outcomes. This goal has been proved to be feasible at reference centers with specialized valve teams that include cardiologists, anesthesiologists, intensivists, and surgeons. From a surgical point of view, the use of a systematic surgical strategy that embraces a broad armamentarium of techniques (as opposed to subscribing to a single technique or philosophy) should lead to achieving very high repair rates in experienced hands. On the other hand, the role of a multidisciplinary heart team approach is crucial to achieve contemporary benchmarks. In this context, the presence of advanced myxomatous degeneration, long-standing regurgitation with ventricular dysfunction, calcification, or previous failed repairs might require longer cross-clamp times to perfect the repair, which in turn might make postoperative management and recovery more difficult.
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Mortality after mitral valve repair in patients with degenerative disease correlates with age, with an average risk of 1% for patients aged below 65 years (estimated risk for all comers in high-reference centers regardless of age), 2% for those aged 65 to 80 years, and 4% for octogenarians.150 Some of the identified independent predictors of postoperative survival include severe symptoms (NYHA class III or IV), left ventricular dysfunction (ejection fraction < 60% or LVESD > 40 mm), a regurgitant orifice area ≥ 40 mm2, left atrial dimensions (left atrial index ≥ 60mL/m2 or left atrium > 55 mm), or the presence of pulmonary hypertension or long-standing atrial fibrillation. It is important to highlight that those patients referred to surgery with severe symptoms will have greater postoperative risk despite symptom relief as a result of the absence of ventricular remodeling, particularly if the ejection fraction is < 50%. Repair durability, strictly defined as echocardiographic freedom from moderate or greater mitral regurgitation (as opposed to freedom from symptoms or reoperation), has been reported to be around 90% at 10 years in reference centers such as the Mayo Clinic, the Cleveland Clinic, Toronto General Hospital, and Mount Sinai Hospital, with a recurrent rate of 1% per year up to 20 years after the procedure (Fig. 48–21).151,152,153,154 When durability rates are stratified according to leaflet involvement,155 patients with bileaflet or isolated anterior leaflet prolapse have slightly lower repair durability, ranging from 75% to 85% at 5 years.120,156 Additional factors that impact durability of repair include failure to use an annuloplasty device or the use of chordal shortening techniques (which are now abandoned).157 Although technical failures account for residual and some early repair failures,158 progression of disease with new pathology is the most common cause of long-term failure.159
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Mitral valve surgery has progressively evolved over the past decade, particularly in patients with degenerative mitral valve disease. Without doubt, surgical indications, repair techniques. and approaches represent the most important160 aspects of an already established best practice revolution in mitral valve repair. Regarding the latter aspect, the current gold standard and still most popular approach is median sternotomy, which allows central cannulation and assures good myocardial protection (direct cardioplegia), and most importantly, permits direct access if a complication occurs. The trend towards more cosmetic incisions has triggered the adoption of very limited median incisions as small as 7 to 9 cm in selected patients.161 However, the term “minimally invasive” in today’s cardiac surgery is understood as a video-assisted approach including right thoracotomy and robotic surgery.162 In this context, cardiopulmonary bypass is accomplished through peripheral cannulation (most commonly via femoral artery and vein-retrograde arterial perfusion). Although traditionalists have claimed that minimally invasive mitral valve surgery is technically more complex (thus potentially affecting mitral valve repair rates) and implies a learning curve that not every surgeon overcomes,142 even in high-volume centers, the reality is that extraordinary outcomes from a few experienced high-volume centers have challenged their opinions.156,163,164 This is also true165 even in complex scenarios such as Barlow disease or anterior leaflet prolapse.166,167
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The most important goal for patients with degenerative mitral valve disease and the physicians involved in their care (referring cardiologist and surgeons) is to achieve not only a competent repair of the mitral valve, but a durable one, as emphasized by the new guidelines. In ideal conditions, these axioms should be met in all prolapsing valves regardless of the surgical approach and the final cosmetic outcome. We are convinced that as technology advances, minimally invasive techniques will expand. However, at this time, the average repair rates dictate that the use of these techniques should be restricted to selected, high-volume, specialized centers.
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Concomitant Tricuspid Valve Repair in Patients With Degenerative Mitral Valve Disease
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Tricuspid valve disease affects around 1% of the general population, and most patients remain asymptomatic despite having moderate-to-severe degrees of tricuspid regurgitation. However, increasing attention has been given to the tricuspid valve in parallel to a better understanding of the negative impact of right-sided heart failure on the clinical outcome of patients regardless of the presence or severity of left-sided valve disease.168 Although primary tricuspid regurgitation is rare (often seen in patients with pacemakers, chest trauma, or endocarditis), secondary (functional) tricuspid regurgitation as a result of pulmonary hypertension and right ventricular dilation as a result of left-sided valve disease is common. However, although the number of tricuspid procedures has double over the last decade,169 the management of secondary tricuspid regurgitation remains as one of the most heated debates, particularly in regard to the best surgical option in patients with severe tricuspid regurgitation and whether concomitant “prophylactic” tricuspid procedures are necessary in patients with mild-to-moderate tricuspid regurgitation.170,171
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At the present time, there are two opposing schools of thoughts regarding the need for concomitant tricuspid valve repair at the time of mitral repair in patients with degenerative valve disease, both of them supported by leading experts in mitral valve repair. The main explanation for these contrary opinions is the difficulty in accurately assessing the degree of tricuspid regurgitation as a result of the significant dependence of the right ventricle on preload conditions. In order to avoid this bias, many authors have suggested an annular dilatation of 40 mm or 21 mm/m2 as an independent criterion for tricuspid intervention. Recently, our group demonstrated that this strategy, applied in two-thirds of patients undergoing mitral valve repair, does not lead to a difference in mortality, morbidity, or requirement of a permanent pacemaker.172 An even more recent paper from De Bonis and colleagues confirmed these findings and also noted that half of the untreated patients presented with either severe tricuspid regurgitation or a progression of at least two grades of tricuspid regurgitation 7 years after the procedure.173 On the other hand, only around 10% of patients receive concomitant tricuspid annuloplasty at Toronto General Hospital or the Mayo Clinic. Objectively, we can assert that preoperative functional class (as a surrogate of ventricular dysfunction) should play a major role in decision making. Those patients in NYHA class III or IV, who have not developed at least moderate tricuspid regurgitation at the time of surgical intervention, will most likely not develop tricuspid regurgitation after mitral valve repair. Likewise, patients with preserved left ventricles and none or mild degrees of tricuspid regurgitation are also unlikely to develop tricuspid regurgitation. It may be that earlier mitral valve repair will lead to fewer patients requiring tricuspid intervention.
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Overall, secondary or functional tricuspid regurgitation is the most common etiology of tricuspid valve disease, and thorough interrogation is mandatory in patients undergoing mitral valve repair. Concomitant tricuspid valve repair does not carry a significant additional surgical burden and might lead to improved perioperative outcomes, functional class, and survival. Tricuspid regurgitation does not always regress after correction of left-sided valve disease174 and reoperations for residual or recurrent tricuspid regurgitation are associated with a higher mortality in experienced centers (up to 15%).175 The final decision should be guided not only by the degree of regurgitation (≥ moderate) but also by annular dimensions (diameter ≥ 7 cm from anteroseptal to anteroposterior commissures, or 40 mm when measured by echocardiography); leaflet coaptation or mismatch between leaflet and annulus on direct inspection; and presence of atrial fibrillation, pulmonary hypertension, right ventricular dysfunction, and/or left ventricular dysfunction. As for the type of repair, the authors favor the use of a disease-specific open ring with a rigid component located in the region corresponding to the right ventricular free wall aspect of the annulus (remodeling) with flexible open ends for wider accommodation of the conduction system to reduce iatrogenic injury.176
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Percutaneous Approaches to Mitral Valve Repair and Replacement
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At present there are over 20 investigational devices for repair or replacement of the mitral valve. Some make use of the proximity of the coronary sinus to the mitral annulus, wherein devices cinch the coronary sinus, thereby reducing annular dimension and reducing mitral regurgitation. Percutaneous valve replacement is in its infancy with a large number of valve designs being tested.130,177
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Currently the MitraClip is the only device approved in the United States and is employed for treatment of inoperable patients with primary mitral regurgitation. The device is inserted transeptally and clips the two mitral leaflets together in their mid-portions, substantially reducing mitral regurgitation, usually from severe to moderate degrees of regurgitation. Five-year follow-up is now available and demonstrates both persistent reductions in mitral regurgitation as well as persistent symptomatic improvement.178