How to handle the ischemic mitral valve during CABG surgery

This post refers to two intriguing presentations of this year’s EACTS meeting, held in Vienna. Both presentations deal with the chronically ischemic mitral valve (graded at least moderate) as a concomitant finding in patients qualifying for coronary artery bypass grafting. The indication for revascularization is an important differentiator: chronic mitral regurgitation due to past myocardial infarction can also be an entity by itself (i.e. without the need for a revascularization procedure). This entity poses a delicate and difficult question on the best option of how to deal with it. Surgery does not always deliver the desired result, the newer interventional option of Mitraclip® is currently in evolving investigation. I will come back to this issue with a dedicated post. Stay tuned!

Our clinical situation:

  • Angiographically confirmed ischemic heart disease (IHD) needing surgical revascularization
  • Concomitant, at least moderate mitral valve regurgitation due to restricted leaflet motion (no prolapse – Carpentier class IIIB) and / or annular dilatation, called Ischemic Mitral Valve Regurgitation (IMVR)

The initial way to deal with this problem was towards a conservative approach (i.e. revascularization alone) hoping that the recovery of the revascularized myocardium would improve mitral geometry and function in the mid- / long term. Well designed and executed clinical studies generated significant evidence on this topic: one pivotal study from the Harvard University (full text here)  focused on the problem and confirmed that revascularization alone “would leave a significant number of patients with a residual moderate MR and may not be the optimal therapy for most patients. Intraoperative TEE may significantly underestimate the severity of ischemic MR. A preoperative diagnosis of moderate MR may warrant concomitant mitral annuloplasty.”

A prospective, randomised study (RIME trial, full text here ) from many well known centres in the UK and Monaco, compared revascularization alone to revascularization plus mitral annuloplasty and concluded that “adding mitral annuloplasty to CABG in patients with moderate ischemic MR may improve functional capacity, left ventricular reverse remodeling, MR severity, and B-type natriuretic peptide levels, compared with CABG alone. The impact of these benefits on longer term clinical outcomes remains to be defined”. This approach became in our days the standard of care.

Many cardiologists and cardiac surgeons dealing with these patients, however, developed the feeling that concomitant (restrictive) annuloplasty did not always yield a satisfactory clinical and functional results in the mid- or long term. This is mainly due to the need to restrict the annulus quite strongly to achieve a good leaflet coaptation and a competent mitral valve. Strong undersizing of the prosthetic ring can lead to a reduced effective orifice area and significant gradients over the valve.

During this year’s annual meeting of the EACTS two presentations confirmed this feeling and challenged the mitral procedure to chose when performing coronary surgery in these patients. Here they are:

Presentation #011 (Papworth Hospital, UK) – Abstract #011

Mitral valve replacement (MVR) as valuable option in ischemic mitral valve regurgitation (IMVR)

732 patients undergoing CABG + MV surgery for IMVR. Analysed retrospectively with propensity score matching to adjust for confounding factors. Impact of MVR versus reductive MV annuloplasty (MVA) on early & late mortality, as well as for repeat MV surgery.

  • 2 matched groups of each 248 patients
  • MVR did not increase early / late mortality  & had an inferior need for repeat MV surgery.
  • No difference between mechanical or biological prosthesis

Conclusion: MVR is a valid option in IMVR.

Critical remarks: conclusion is based only on early & late mortality. No functional data (LV function postop, functional class postop, exercise tolerance). This lack of information was covered by the next presentation.

Presentation # 012 (Bergamo, Bristol, Liège) – Abstract #012

Mitral valve annuloplasty (MVA) versus mitral valve replacement (MVR) for ischemic mitral valve regurgitation (IMVR).

74 consecutive patients with Carpentier IIIB type IMVR (37 vs 37 matched for age, gender, Body Surface Area (BSA) and indexed Effective Orifice Area (EOA)).

  • Exercise-induced  improvement in EOA and IEOA better for mitral valve replacement (MVR)
  • 6-minute-walking-distance (6-MWD) improved significantly in both groups, but significantly more in MVR
  • on multivariate analysis “mitral valve replacement” and “postoperative IEOA” were independent determinants of 6-MWD postop.

Conclusion: MVA may cause functional mitral stenosis especially during exercise.

Critical remarks: the MVA procedure was strongly restrictive (mean ring size 26mm)

Take home message

A moderate MR of chronic ischemic origin (i.e. due to a tethered posterior leaflet and / or annular dilatation) should be approached during coronary bypass surgery. (Important: the echocardiographic diagnosis must be established prior to surgery on an awake patient!). Should a slightly undersized annuloplasty (using specifically developed prosthetic rings, such as the ETlogix® ring, if indicated) not yield a good result, the surgeon should directly replace the valve without a bad conscience.