Degenerative mitral regurgitation: improving clinical decision-making and risk stratification before valve surgery or trans-catheter repair

This commentary refers to ‘Factors influencing post-surgical survival in degenerative mitral regurgitation’, by S.C. Butcher et al., https://doi.org/10.1093/eurheartj/ehad004 and the discussion piece ‘Rescue surgery for degenerative mitral regurgitation should be recognized for what it is: indispensable but imperfect’, by S.C. Butcher et al., https://doi.org/10.1093/eurheartj/ehad242. Clinical decision-making and risk stratification for patients with degenerative mitral regurgitation (MR) are highly dependent on a reliable assessment of MR-related left ventricular (LV) dysfunction. Regarding this, the echocardiography has emerged as a major diagnostic tool, and in asymptomatic patients with advanced primary MR, the evidence of LV systolic dysfunction by an ejection fraction (EF) ≤ 60% and a LV end-systolic diameter (LVEDD) ≥ 40 mm is currently considered as a Class 1 recommendation for mitral valve (MV) surgery or transcatheter repair.1 As shown by Butcher et al.,2 despite their undisputed importance for the routine assessment of LV function, these echo-derived parameters have a lower ability for outcome discrimination in comparison with certain secondary outcome determinants (SODs) like left atrial volume, atrial fibrillation, tricuspid regurgitation, and pulmonary artery systolic pressure. Given, on one hand, the relatively high inter-operator, test–retest, and inter–cycle variability of LV ejection fraction (LVEF) measurements even for experienced operators (i.e. 9.1%, 6.8% and 7.4%, respectively),3 and on the other the small differences in the median LVEF values between patients without SODs and those with 3 or 4 SODs (66% and 64%, respectively) revealed by Butcher et al.2 in their study, the limited outcome discrimination demonstrated by the LVEF is not surprising. An even more important limitation of the LVEF for its use solely as a decisive parameter in the assessment of LV dysfunction in the presence of relevant MR is the fact that MR reduces the validity of LVEF as an index of contractile function.4,5 This is quite understandable because the difference between end-diastolic and end-systolic volume will not be anymore solely the forward stroke volume (SVf) but will become the sum of SVf and mitral regurgitant volume, and with aggravation of MR, the regurgitant fraction increases to the detriment of SVf.4,5 Thus, even patients with similar LV end-diastolic volume and LVEF can have different SVf measured at the LV outflow tract, and this suggests that patients with similar LVEF values, but different degrees of MR, can have significantly different degrees of LV dysfunction.5 Although MR-induced changes in LV preload and afterload allow, within certain limits, the maintenance of normal LVEF values even in patients with relevant LV dysfunction, it is quite remarkable that Butcher et al.2 have found even in the patient group with 3 or 4 SODs (75% of them being also symptomatic) misleadingly high LVEF values, ranging between 58% and 69%. This explains other observations which revealed that in patients with primary valve degeneration-induced MR, the preoperative existence of secondary impaired LV systolic function becomes often evident only after MV replacement or repair, despite a certain post-procedural increase in the SVf.5 Given the complexity of MR-related cardio-circulatory alterations, plus the particularly challenging evaluation of LV dysfunction in patients with relevant MR, nothing stands against the routine use also of other echo-derived LV functional parameters (particularly the SVf) in addition to LVEF and LVEDD and especially the combined use of the well-established Class 1 surgical indications with the prognostically highly relevant SODs validated by Butcher et al.2 The author confirms that the data supporting the comments and statements in the article are available within the cited references.