11.6.5 Indications and surgical results

 Mitral valve plasty (MVP)

If anatomical conditions allow (single leaflet prolapse, flexible, long and slightly deformed leaflets, competent subvalvular apparatus, absence of calcification), valvuloplasty with annuloplasty is performed instead of immediate prosthetic valve replacement; this is possible in 50% to 90% of cases, all pathologies combined (see Mitral plasty) [3]. Although technically more demanding, plasty is preferable for several reasons [18,19].

• Preservation of the subvalvular apparatus preserves LV geometry and ensures better postoperative left ventricular function;
• Mortality is lower (<1% compared to 2-4%);
• Thromboembolic and infectious risks are minimal;
• The risk of structural deterioration is virtually non-existent;
• Anticoagulation is not required in the long term, but only for the first 3 months (the time needed for the prosthetic ring to endothelialise); only aspirin (75-250 mg/d) is prescribed for life;
• In children and adolescents, the valve may grow with the patient.

Prolapse and chordal tears in fibroelastic lesions are generally easy to repair, especially in the posterior leaflet, but the redundancy of tissue in Barlow's disease makes repair more delicate. Rheumatic lesions and calcifications reduce the chances of successful repair, even in experienced hands [32]. Repairs to the posterior leaflet generally give better results than those to the anterior leaflet. If the LA is normal, LV function is good and the patient has never had AF, aspirin (loading dose 250 mg/d, maintenance 75-250 mg/d) may be sufficient [32]. In other cases, anticoagulation is prescribed for 3 months to achieve an INR of 2.0-2.5, followed by lifelong aspirin intake.

The re-operation rate after structural replacement is the same as after mechanical prosthesis replacement; it is 7-10% at 10 years, one third due to progression of the underlying disease and two thirds due to technical problems [11,23]. This incidence is lower than the attrition rate of a bioprosthesis. In contrast, secondary ischaemic MI has a recurrence rate of around 30% at 2 years [12]. Mortality is <1% if surgery is performed before LV dilatation and 3-6% in cases of advanced ventricular dysfunction [10,32].

Percutaneous mitral valvuloplasty is a new non-invasive transcatheter technique in which the central part of the two leaflets is clipped to form a double orifice and reduce the regurgitant surface (Alfieri procedure) [5]. This technique is primarily reserved for patients in poor general condition for whom operative mortality would be prohibitive. Long-term results are not yet available to assess the value of these techniques, which have a low mortality rate but a high recurrence rate. The results are described in the valve endoprostheses section.

 Mitral valve replacement (MVR)

If valvuloplasty is not possible, a prosthetic valve is inserted. As far as possible, a large proportion of the leaflets should be preserved and the subvalvular apparatus should not be resected (see Figure 11.41), as preservation of the 3rd  chords alone is not sufficient to prevent some spherification of the LV and deterioration of its systolic function in the long term [26]. In rheumatic disease, the subvalvular apparatus is connected and restrictive and cannot be preserved; in this case, despite the competence of the prosthesis, ventricular function progressively deteriorates due to the loss of the dynamic internal skeleton represented by the pillars and chords . Sparing mitral tissue and chords can sometimes lead to dynamic obstruction of the LVOT by remnants of the anterior leaflet. Bioprostheses may partially obstruct the LVOT via the anteriormost strut.

MVRs require anticoagulation, which lasts for only 3 months with a bioprosthesis but is permanent if a mechanical prosthesis is implanted (see Endoprosthetic heart valves). Because the risk of thromboembolism is greater in the mitral position than in the aortic position, an INR of 3.0-3.5 is aimed for indefinitely [2,24]. With bioprostheses, the risk of structural deterioration is greater in the mitral position than in the aortic position, with a 15-year reoperation rate of 50% and 29%, respectively [14].

The results of mitral valve replacement surgery are still relatively poor: the operative mortality rate is 2-6%, depending on the patient's condition [7]. The 10-year survival rate for symptomatic patients is 61% (>85% after surgery) [8]. It is 76% for patients who underwent surgery when they were asymptomatic [30]. For post-ARF lesions, the 5-year survival rate is 70% [27]. In comparison, 5-year survival without surgery varies between 20% and 30% [15]. Patients implanted with a prosthesis for a purely symptomatic MI have a worse outcome than those with pure stenosis or mixed mitral disease, probably because their ventricular function is already more severely impaired when they become symptomatic [20].

 Operative indications for primary MI

It is important to operate on patients with severe MI before functional deterioration occurs, which prevents satisfactory recovery after surgery and triples mortality. With a mortality rate of 90% at 10 years without intervention [21], surgery is virtually inevitable, but the problem is choosing the right time to intervene. This is difficult for several reasons.

• The patient remains asymptomatic for a long time;
• Ventricular function deteriorates silently;
• The usual indices of contractile function are not relevant;
• Function may deteriorate postoperatively;
• It is difficult to predict whether valvuloplasty will be successful;
• Operative mortality is significant; it is 1-2% for repair and 2-6% for prosthetic replacement [29]; to justify early intervention, mortality must be in the lower range of these figures.

Current recommendations (class I and IIa) consider the following elements as indications for surgery in severe MI of organic origin (primary structural MI) [2,9,24, 25,31].

• Severe clinically symptomatic MI (stage D).
• Severe MI with the development or presence of ventricular dysfunction (LV telesystolic diameter > 4.5 cm or > 2.5 cm/m², EF < 0.6, PAPsyst > 60 mmHg on exertion), atrial fibrillation or pulmonary hypertension, even if asymptomatic (stage C2).
• Severe MI with worsening remodelling on echocardiographic follow-up (LA diameter > 5 cm, LV telesystolic diameter > 4.5 cm or 2.5 cm/m² ), even if the patient remains asymptomatic (stage C2).
• Severe asymptomatic MI with preserved ventricular function (stage C1), if the regurgitant orifice is > 0.4 cm² , if repeated examinations show a decrease in LV function or progressive dilatation, if the probability of success of the procedure is > 90% and the probable operative mortality is < 1%; this is justified by the high risk of complications within 5 years [9,28]. At 7 years, the survival rate is 98% for plasty surgery and 85% for medical treatment [16].
• Moderate or moderate-to-severe MI (stage B) as a concomitant procedure if the patient is undergoing other cardiac surgery, if the likelihood of successful plasty is high, and if the operative risk is not excessive.

In acute or subacute heart failure, surgery is indicated as soon as possible if pulmonary venous hypertension cannot be controlled by medical treatment: persistent APO, paroxysmal nocturnal dyspnoea, low systemic flow, elevated creatinine, systolic PAP > 50 mmHg at rest.

Elderly patients (> 65 years) recover much less well from mitral valve surgery than from surgery for aortic stenosis, because in the latter the LV is immediately relieved of excessive afterload, whereas in the former it exchanges a well-tolerated volume overload for a poorly tolerated pressure overload. As operative mortality in these patients exceeds 14%, only severe MI with symptoms of decompensation warrants surgical intervention [2,24].

 Correction of secondary MI

• Moderate or moderate to severe secondary MI: uncertain benefit, generally no indication for surgery.
• Severe symptomatic secondary MI (stage D): indication depends on the situation.
  • Class IIa Indication when repair is straightforward, EF > 30%, operative risk is low and long-term survival is highly likely;
  • Class IIa indication if MI worsens on stress testing; conversely, a reduction in MI on dobutamine indicates LV contractile reserve that favours revascularisation alone without concomitant mitral intervention;
  • Class IIa indication if the patient is undergoing another cardiac surgical procedure with ECC (CABG, AVR, etc.).