Editorial Comment: Secondary mitral regurgitation in patients undergoing aortic valve replacement

Mitral regurgitation (MR) is frequently found in patients scheduled for aortic valve replacement (AVR). The aetiology of concomitant MR can be organic or functional. Organic MR is the result of rheumatic or myxomatous degeneration or, particularly in the elderly, calcification of the mitral apparatus. Functional MR, on the other hand, is secondary to increased left ventricular (LV) afterload and/or variable degree of LV remodelling and is the most common form of mitral insufficiency in patients requiring AVR. The evidence is clear to not surgically intervene if associate functional MR is only mild. Similarly, there is a general agreement that mitral valve (MV) surgery, possibly repair, should be performed when severe functional MR exists. On the other hand, the question is often raised of whether additional MV surgery is required in patients submitted to AVR who do have concomitant less than severe functional MR [1–3]. Indeed, no randomized trials have been conducted in this setting and the scattered information available is the result of observational studies with small sample sizes, retrospective analyses, heterogeneous populations and different aetiologies of MR. In addition, the presence of concomitant procedures like myocardial revascularization and the use of different echocardiographic parameters in grading preoperative MR further limits direct comparison between studies. In this scenario, not surprisingly, even the last 2012 European Guidelines on the management of Valvular Heart Disease [4] do not specifically address this issue and simply suggest that, as long as there are no significant organic abnormalities of the mitral apparatus, surgical intervention on the MV is generally not necessary at the time of AVR because non-severe secondary MR usually improves after the aortic valve is treated. The prognostic significance of ‘less than severe’ functional MR in patients undergoing isolated AVR is still debated. Some studies have shown no difference in survival in patients with moderate or moderate-to-severe functional MR vs no (or mild MR) after isolated AVR [2, 5]. Other reports, on the other hand, have demonstrated significantly poorer survival in patients with at least moderate MR submitted to isolated AVR. Organic MV disease and severe degree of MR, however, were usually included in this second group of studies [6, 7]. Those controversial findings explain why some authors have recommended an aggressive approach in operating on the MV [7, 8], whereas others continue to support a more conservative strategy, believing that functional non-severe MR is likely to decrease after the surgical correction of aortic valve disease [2]. Most of the data available demonstrate a general trend towards an improvement of the grade of less-than-severe functional MR after isolated AVR. This is usually due to the postoperative reduction in LV systolic pressure (aortic stenosis) or to the decrease in LV dimensions (aortic regurgitation). Only in about one-third of the patients, preoperative functional MR remains unchanged and in a minority of them it further deteriorates [7]. Whether persistence or worsening in MR severity following AVR directly correlates with mortality remains unclear. The study by Coutinho et al. [9] provides some more light in this controversial field showing that, in the great majority of patients, secondary MR decreases early after isolated AVR and, in ∼67% of them, this improvement persists in the medium to long term. This finding confirms a relatively benign evolution of secondary MR in patients submitted to isolated AVR. The second important message emerging from this series is that functional MR, in the context of AVR, can be treated with a high rate of repair and with low mortality and morbidity if simple procedures are used. In the study by Coutinho, MV surgery mainly consisted of suture or ring annuloplasty, which required an extra aortic cross-clamp time of <20 min and had no negative impact on the postoperative course of the patients. Those annuloplasty techniques provided satisfactory long-term results in this specific setting, although one might speculate on whether a larger adoption of ring prostheses would have further decreased the recurrence of late MR without significantly prolonging the duration of the cardioplegic arrest. Ten-year survival was not significantly different between patients with or without concomitant MV surgery, but those who had concomitant MR correction experienced less congestive heart failure symptoms at the follow-up, more pronounced reverse LV remodelling and a trend (although not statistically significant) towards improved late survival. If the option not to intervene on the MV did not influence overall and event-free survival, early persistence of MR greater than 2+ did. This means that patients who still had an important degree of MR by the first month after AVR, remained at risk of having persistent mitral insufficiency and compromised late survival. Persistence of MR at discharge emerged as the most powerful independent predictor for late mortality and mainly occurred in the absence of mitral surgery. Appropriate patient selection, therefore, remains crucial. Most of the patients will experience an important improvement of their preoperative functional MR even without concomitant mitral repair. Nevertheless, a small proportion of them will be left with their preoperative mitral insufficiency unchanged or worsened after isolated AVR, with deleterious prognostic implications. The efforts of the surgical community should be devoted to identify the patients with secondary MR who are unlikely to improve spontaneously after isolated AVR to specifically target on them the concomitant treatment of mitral insufficiency. Under those circumstances, the potentially increased surgical risk of a double-valve procedure would be completely justified by the prognostic benefit provided by the elimination of persistent/progressing MR. From this point of view, some predictors of MR progression following isolated AVR have already been identified including increased left atrial size (>5 cm), organic aetiology, poor LV ejection fraction and atrial fibrillation (AF) [1, 2, 6, 10]. The latter emerged as an important risk factor for decreased survival and persistent MR also in Coutinho's series, suggesting that AF and the other above-reported conditions should be carefully considered when deciding whether concomitant MV surgery would be appropriate in the individual patient. In conclusion, when less than severe secondary MR is present in candidates to AVR, the decision-making process regarding any intervention on the MV can be difficult and requires careful clinical and echocardiographic assessment. A tailored approach to the individual patient is required taking into consideration age, comorbidities, MR severity and aetiology, likelihood of spontaneous improvement, feasibility of mitral repair and the risk of future reoperation. In general, the data accumulated so far support a highly selective approach to intervention on the MV at the time of AVR when MR is less than severe and no structural abnormalities are detected. Conversely, concomitant mitral surgery should probably be more strongly considered in presence of organic MR, where an intrinsic mechanism of valve dysfunction is unlikely to be improved or corrected simply by a LV reverse remodelling process [1]. Certainly, this is one of the fields where randomized, controlled trials with appropriate power and follow-up are more urgently warranted and needed.