11.7.5 Indications and surgical results

 There are three possible techniques for relieving stenosis: percutaneous valvuloplasty, surgical commissurotomy or prosthetic valve replacement. The classic surgical indications are mainly for ARF. In degenerative mitral stenosis associated with calcification of the mitral annulus, the interventional options are more limited because percutaneous balloon commissurotomy cannot dilate the calcified block and prosthesis implantation requires surgical decalcification of the annulus, which is dangerous because of the risk of ventricular rupture and damage to the circumflex artery [14]. Whatever the procedure, it is only indicated for severe and/or symptomatic stenosis; moderate asymptomatic stenosis is not an indication.

 Commissurotomy

When anatomy permits, percutaneous commissurotomy is the first choice. The accepted indications are the following situations [2,10,17]

  • Symptomatic patients (NYHA class II, III and IV) with moderate (1.0-1.5 cm2) or severe (< 1 cm2) stenosis.
  • Asymptomatic patients with moderate or severe stenosis and pulmonary hypertension (PAPsyst > 50 mmHg at rest or > 60 mmHg on exercise).
  • Favourable morphology: flexible leaflets, no calcifications at the commissures or on the leaflet body, no fusion of the chords, minimally restrictive subvalvular apparatus.
  • No MI or mild MI (moderate to severe MI: contraindication).
  • No atrial thrombus.

Indication is based on a score (Wilkins or Cormier scores) based on the thickness of the leaflets, their mobility, the degree of calcification, the state of the subvalvular apparatus and the presence of MI [16]. The Anwar score is based on 3D imaging [17]. The procedure is performed by catheterisation with radiological and transesophageal echocardiographic monitoring. A balloon-tipped catheter is introduced via the transseptal route into the left atrium; an hourglass-shaped balloon or, more recently, a watch-glass-shaped balloon (Inoue balloon) is placed astride the mitral valve and tears it as it inflates. For the short time it is inflated, the balloon interrupts the output of the left heart. With a mortality rate of 0.5-2%, the gradient is reduced by an average of 10-12 mmHg and the effective surface area is doubled from 1 to 2 cm2 [12]. The immediate success rate is 85-98% (S > 1.5 cm2, PLA < 18 mmHg) [5]. The rate of residual mitral regurgitation is 2-10%. The restenosis rate is 15% at 5 years and 25% at 10 years [5,11]. Complications (3%) include arterial embolism, residual ASD, cardiac perforation and acute insufficiency [4]. On the other hand, the failure rate is prohibitive when the valve is severely calcified, the subvalvular apparatus is very restrictive or there is significant insufficiency (> minor MI).

In centres with little experience of percutaneous commissurotomy, surgical commissurotomy through a left thoracotomy is preferred in ECC. The mitral valve is decalcified under visual control, the commissures are incised, and the fused chords are separated; additional plasty is possible in the event of insufficiency. The left atrial appendage is resected or ligated and any atrial thrombi are removed. The operative mortality rate is 1-3% [6] and the 15-year complication-free survival rate is 90% [1].

These procedures delay prosthetic valve implantation in young adults by several years and avoid the need for anticoagulation, but they remain strictly palliative, as the pathology remains and flow is not normalised. They are reserved for valves with a low degree of atherosclerosis and no insufficiency.

 Mitral valve replacement ( MVR )

If the valve and subvalvular apparatus are calcified or deformed, if there is an atrial thrombus, or if the patient has a significant regurgitant component, a prosthesis should be implanted in ARF or rare aetiologies [10]. Surgical MVR is also indicated in patients requiring coronary artery bypass grafting or replacement of another valve. In the case of calcific degeneration, the procedure is more difficult and dangerous: the fixity of the annulus means that a relatively small prosthesis has to be placed, decalcification of the annulus means that there is a risk of ventricular rupture or damage to the circumflex artery, congruence of the valve with the annulus is imperfect and the incidence of significant paravalvular leakage exceeds 10% [14]. As patients with degenerative mitral stenosis tend to be elderly and polymorbid, there is an emerging trend towards percutaneous implantation of an aortic valve bioprosthesis (TAVI). This technique is still in its infancy, but it is less invasive and less risky, with an immediate success rate of over 90% and a 1-year mortality of 14% [7].

Surgical valve replacement also allows the volume of the LA to be reduced, the atrial appendage to be resected or ligated, and possibly a maze operation to reduce atrial fibrillation. In MVR for stenosis, it is more difficult, if not impossible, to preserve the subvalvular apparatus to ensure the internal skeleton of the LV and limit dysfunction in the long term, as is done in MVR for insufficiency. In the mitral position, mechanical prostheses are preferred because they have a lower gradient than bioprostheses of the same diameter and they clear theoutflow tract better. On the other hand, the attrition rate of bioprostheses is higher in the mitral position than in the aortic position.  
 
Operative mortality is 3-5% in adults without pulmonary hypertension, but rises to 10-20% in the elderly or in patients with PHT [3]. Survival is 80% at 5 years [9]. After MVR, anticoagulation is required for life with mechanical valves (INR 3.0-3.5), but for 3 months with biological valves.
 
 Indications for surgery
 
Without intervention, the 5-year and 10-year survival rates for symptomatic mitral stenosis are 40% and 10%, respectively [8,13]. The indication should be given before symptoms become severe or when the area is equal to or less than 1 cm2 /m2 and, if possible, while the patient is still in sinus rhythm. Indications for mitral valve repair are as follows [2,10,15].
 
  • Symptomatic patient with severe stenosis (S < 1.0 cm2).
  • Symptomatic patient with moderate-to-severe or severe stenosis who develops pulmonary hypertension on exercise testing (PAPsyst > 60 mmHg, PAPmean > 35 mmHg) or a transmitral gradient > 15 mmHg.
  • Asymptomatic patients with severe stenosis who are at high risk of thromboembolism: history of stroke, left atrial dilatation (diameter > 5.0 cm) with strong spontaneous contrast, recent paroxysmal atrial fibrillation.
  • Asymptomatic patients with severe stenosis who wish to become pregnant or are due to undergo major elective surgery.
 
In patients with favourable status, percutaneous commissurotomy is suggested as the first choice. There is no evidence that commissurotomy or MVR is beneficial in asymptomatic patients with moderate stenosis and no risk factors [2].
 
 
 
Surgical indications for mitral stenosis 
Indications for surgery in severe stenosis (S < 1.0 cm2 /m2 ):
- Symptomatic patients
- Exercise-induced pulmonary hypertension (PAPsyst > 60 mmHg)
- Asymptomatic patients at high risk of thromboembolism
- Asymptomatic patients if pregnancy or elective major surgery is desired
 
Conditions for percutaneous commissurotomy (mortality 0.5 - 2%):
- Flexible leaflets, no calcification, no fusion or constriction of cords
- No MI (or minor MI)
- Absence of atrial thrombus
 
Indications for MVR (mortality 3-5%, up to 10-20% for high risk):
- Commissurotomy not possible
- Simultaneous Maze operation (reduction of AF)
- CABG or other concomitant valve surgery
 
 
 
 
© CHASSOT PG, BETTEX D, August 2011, last update November 2019

 

References

 

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