Historically, mitral regurgitation (MR) has been categorized into two main groups based on its etiology: degenerative MR, arising from primary valvular pathology, and functional MR (FMR), secondary to other cardiac conditions that lead to mitral valve dysfunction. For degenerative MR, surgical correction has generally yielded a favorable prognosis, with mitral valve repair being superior to replacement. However, the high recurrence rate of MR following repair in FMR patients—particularly among poorly selected cases—has led to considering mitral valve replacement as a more durable surgical option. Nonetheless, the optimal management strategy for FMR patients remains uncertain, with this patient population often experiencing less favorable outcomes.
Notably, FMR patients with reduced ejection fraction (EF) exhibit poorer outcomes and prognoses compared to those with preserved EF. FMR with reduced ventricular function is often associated with ventricular pathology (ventricular FMR, VFMR), wherein ventricular dilation leads to annular dilation and/or posterior leaflet tethering. In contrast, FMR with preserved EF may be linked to atrial pathology, designated as atrial FMR (AFMR), which typically involves left atrial (LA) remodeling and enlargement, resulting in isolated mitral annular dilation and subsequent MR. Emerging research supports that these FMR types should be regarded as distinct conditions, with differing surgical approaches and outcomes. In terms of the preferred surgical intervention for AFMR, debate persists, and the prognosis remains incompletely understood.
Accordingly, data from all patients undergoing mitral valve repair due to MR at Michigan Hospital between 2000 and 2020 were reviewed. Patients with degenerative/myxomatous disease, EF < 50% (VFMR), and diverse etiologies such as endocarditis and rheumatic disease were excluded to isolate a “pure” AFMR patient population. Out of 2,697 patients undergoing mitral repair, 123 were identified as AFMR cases. Among these, the mean preoperative LA diameter was elevated to 4.9 cm (95% CI, 4.7-5.0 cm), while the mean preoperative left ventricular diastolic diameter remained near normal at 5.0 cm (95% CI, 4.9-5.2 cm). Preoperative atrial fibrillation (AF) was observed in 61% (74/123). Echocardiograms were performed in 58% (71/123) of patients after a median of 569 days (interquartile range, 75-1782 days) post-surgery. Of these, 72% (51/71) exhibited trivial or no MR, 22% (16/71) had mild MR, and only 6% (4/71) had moderate or greater MR. Only 1.6% (2/123) required mitral valve reoperation. The estimated 5-year survival was 74%.
The authors conclude that AFMR shows favorable outcomes following mitral valve repair with ring annuloplasty, marked by low rates of reoperation, mortality, and MR recurrence. Mitral annuloplasty should be considered the surgical treatment of choice for AFMR.
COMMENTARY:
The study presented today sheds light on an aspect many surgeons may not have previously regarded with sufficient seriousness when addressing FMR. This study underscores that not all FMR cases are equivalent; in some cases, the mechanism of mitral regurgitation results from atrial dilation rather than ventricular dilation or leaflet tethering due to prior infarctions. Thus, if we were to summarize the two most practical and significant findings from this study, they would be:
- It is crucial to consider the possibility of AFMR in any FMR patient with preserved ventricular function, especially in the absence of underlying coronary disease.
- Although current guidelines do not yet reflect this, restrictive annuloplasty appears to emerge as the preferred and reference technique for treating AFMR, given its favorable clinical and echocardiographic outcomes.
AFMR is a FMR subtype characterized by left atrial and mitral annular dilation and is frequently associated with AF and heart failure (HF) with preserved ventricular function. Given the rising incidence of AF and HF with preserved ventricular function—largely due to population aging—this FMR subtype has begun gaining recognition among HF specialists. However, current clinical guidelines, often lagging behind recent evidence, do not yet clearly differentiate AFMR from FMR caused by ventricular dysfunction, typically associated with ischemic cardiomyopathy and reduced EF.
In this article, Wagner et al. have significantly expanded our understanding of AFMR, thanks to the high patient volume at Michigan Hospital. They present outcomes of ring annuloplasty in this patient cohort. After excluding 2,574 patients undergoing mitral repair over two decades—of whom 75% underwent repairs for degenerative MR or concomitant coronary surgery—123 patients were identified with a clear “pure” AFMR diagnosis. This leads to the primary deduction that AFMR is an uncommon entity, accounting for only 4.5% of all mitral repairs.
From a surgical standpoint, it is noteworthy that most cases involved restrictive annuloplasty with a complete, rigid ring, though no further information is provided. Additionally, a tricuspid annuloplasty was performed in cases of moderate or severe tricuspid insufficiency and/or annular dilation exceeding 4.0 cm (50%). Furthermore, an ablation procedure was performed in all preoperative AF cases (61%), despite preoperative AF not always warranting this procedure. This lack of selection may have increased surgical time and intervention risk without evident clinical benefit.
Interestingly, approximately 40% of AFMR patients did not present with preoperative AF. This suggests that AF may have gone undiagnosed (paroxysmal AF) or that another cause, such as hypertension, contributed to LA dilation in these patients. Hence, AFMR should not always be linked with AF, marking a shift from previous understanding. Moreover, the potential presence of undiagnosed underlying AF raises new questions about systematically closing the left atrial appendage in these patients with atrial dilation, even without documented arrhythmia.
Regarding follow-up and results, it is important to highlight that only slightly more than half of the cohort (58%) had subsequent echocardiographic follow-up, with a mean duration of 569 days. Of this group, only 6% had MR equal to or greater than moderate, and only 1.6% required reintervention, which demonstrates exceptional results. On the other hand, it is relevant to highlight that, although the incidence of AF after surgery was 34%, in the long-term follow-up, 72% of patients maintained sinus rhythm, including 61% of those who underwent the ablation procedure. This indirectly reflects the effectiveness of mitral repair. The perioperative mortality rate was 1.6%, and 5-year survival reached 74%, which are data consistently higher than any series of VFMR and which determine the different prognosis that both forms of FMR have, so they can no longer be considered as the same disease.
It should not be overlooked that this study has some obvious limitations. It is a retrospective case series, with no comparison groups and with 42% of patients missing follow-up, which could, in principle, undermine any meaningful conclusions. Despite these limitations, the cases that did have follow-up show outstanding results. It should be emphasized that this study is based on interventions performed over a 20-year period, which partly explains the high rate of loss to follow-up of patients, especially those operated on during the first decade. Furthermore, since this hospital is a referral center for mitral surgery and serves patients from remote areas, follow-up is naturally difficult. Although this may detract from the conclusions, it should be emphasized that the competence of mitral repair was confirmed in virtually 100% of cases by postoperative echocardiography. Furthermore, among the patients with follow-up (60%), almost unbeatable results were obtained. Therefore, with a high degree of confidence, it can be stated that restrictive annuloplasty in the treatment of MIFA proves to be durable and effective.
Regarding the methodology used for patient exclusion, 2,027 patients with both degenerative/myxomatous MR and those who underwent concomitant coronary surgery were excluded in the same exclusion category, without making a distinction between them. This means that we do not have the capacity to determine the real percentage of cases of VFMR vs. degenerative MR in this population. It should be noted that AFMR is more frequent in older patients than in younger patients, therefore, with a greater possibility of presenting concomitant coronary disease. The fact of having excluded all mitral repairs with coronary surgery may have left out of the analysis many patients with AFMR with coronary surgery, only as a consequence of the finding of coronary disease, but without repercussion on ventricular dimensions or function. In contrast, some patients with coronary artery disease and normal EF, who did not undergo CABG for various reasons, could have been included in the “pure” AFMR group. In summary, for a more complete understanding of MI-related outcomes and more accurate patient selection, additional information such as history of myocardial infarction and preoperative catheterization findings are lacking in the study.
It is obvious that the approach to any secondary MR begins with appropriate medical management following established guidelines. Furthermore, according to the results of this study, rhythm control together with restrictive mitral annuloplasty in AFMR appears to offer a long-lasting benefit in these patients. This opens the door for future research that can further explore the impact of this approach on disease progression.
All in all, the findings of this study have significant clinical implications and motivate us to consider FMR from a broader perspective. When a possible diagnosis of AFMR is presented, we now know that restrictive annuloplasty is not only feasible, but has a high potential for success backed by some additional evidence that encourages us to consider it as a treatment option.
REFERENCE:
Wagner CM, Brescia AA, Watt TMF, Bergquist C, Rosenbloom LM, Ceniza NN, et al.; Michigan Mitral Research Group. Surgical strategy and outcomes for atrial functional mitral regurgitation: All functional mitral regurgitation is not the same! J Thorac Cardiovasc Surg. 2024 Feb;167(2):647-655. doi: 10.1016/j.jtcvs.2022.02.056.
