Why Does Prosthetic Replacement Seemingly Have Higher Perioperative Mortality Than Valve Repair in Ischemic Mitral Regurgitation?

Reply by the Authors of the Original Article

We read the meta-analysis by Yun-Dan et al with great interest.[1] The ideal treatment for chronic ischemic regurgitation is subject to ongoing research. Although mitral valve replacement offers a definite solution to the recurrence problem and requires no outstanding skills and experience, until recently, the established practice was to refrain from it wherever possible. Many previous reports supported the idea that repairs are always better than replacement, justified mostly by the higher mortality perception in the replacement series, despite the fact that the supporting literature was in many ways biased. Now that the second postoperative year's results of an important randomized trial have been published,[2] the presumed survival advantages of repair techniques over those of prosthetic replacement are becoming questionable. The relatively higher operative mortality in the replacement groups may or may not be of statistical significance, but since the survival curves include the operative mortality, it may still affect the long-term survival comparison in favor of the repair by blunting any possible advantage of the replacement.

This seemingly higher operative mortality in the replacement groups may be attributed to patient selection bias in nonrandomized studies, but still exists in the recent randomized trials[2]; therefore, possible reasons should be contemplated.

Among the advantages of the mitral valve replacement is absolute elimination of the regurgitation. This effectively stops the vicious cycle of ongoing volume overload. Contrarily, there is often some residual regurgitation even with best repairs, and even mild regurgitations may reinstitute the vicious cycle causing more dilatation, more regurgitation, more volume overload, and consequently more heart failure episodes and worse prognosis.[3] Accordingly, reverse remodeling seems better with mitral valve replacement, as reflected by the catch-up with the survival curve of the mitral valve repair during follow-up.

However, this advantage in the long term becomes the prosthetic replacement's Achilles' heel during the perioperative period. Relatively higher operative mortalities in this group may be attributed to the abrupt elimination of the regurgitation to the atrium, causing a sudden increase in the afterload of the compromised ventricle, with no escape to a low-resistance chamber. This occurs at the most vulnerable moment, during weaning-off cardiopulmonary bypass. These infarct-burden ventricles can poorly tolerate sudden increases in loading conditions. In contrast, immediately after mitral valve repair, there is almost always some potential for residual regurgitation, serving as an escape route. Even a subtle regurgitation may help decompress the ventricle, smoothing the perioperative course, no matter how it may adversely affect reverse remodeling later in the follow-up.

This may be considered somewhat similar to that a liberal right ventricular outflow tract resection better relieves pressure gradients and facilitates the weaning off cardiopulmonary bypass during total correction of a Fallot's tetralogy case, while a limited resection may provide better-preserved right ventricular functions in the long term.

Even with this perspective, the survival curves become similar shortly after the operation. Is this signaling an even better survival for mitral valve replacement in the longer follow-up, especially now that total subvalvular preservation being the standard policy? We should see when survival comparisons extend beyond 5 to 10 years.

• References

• 1 Yun-Dan D, Wen-Jing D, Xi-Jun X. Comparison of outcomes following mitral valve repair versus replacement for chronic ischemic mitral regurgitation: a meta-analysis. Thorac Cardiovasc Surg 2016; (e-pub ahead of print) DOI: 10.1055/s-0036-1580603.
• 2 Goldstein D, Moskowitz AJ, Gelijns AC. , et al; CTSN. Two-year outcomes of surgical treatment of severe ischemic mitral regurgitation. N Engl J Med 2016; 374 (04) 344-353
• 3 Agricola E, D'Amato R, Stella S. , et al. Effects of mild ischemic mitral regurgitation on ventricular remodeling and its contribution to congestive heart failure. J Am Soc Echocardiogr 2011; 24 (12) 1376-1382