The optimal timing of intervention for severe primary mitral regurgitation (MR) remains controversial when patients are asymptomatic and ventricular function is normal. Watchful waiting has long been standard practice in many cardiology centres. It allows intervention to be deferred but requires disease progression to be detected before its consequences compromise prognosis. In striking this balance, the absence of symptoms and an apparently normal ejection fraction have never guaranteed that waiting is the best strategy. By the next assessment, ventricular function may have deteriorated or the patient may have been admitted with decompensation, making a procedure that could have been performed earlier at lower risk less favourable.

Ahn et al. address this question using a registry from three tertiary hospitals in South Korea, including patients diagnosed between 2000 and 2022. The study enrolled 802 patients with asymptomatic severe primary MR. Mean age was 54.5 years and 59.4% were men. The aetiology was degenerative in 84.4% of cases. The authors compared surgery within six months of diagnosis in 344 patients with an initial watchful waiting strategy in 458 patients, in whom later intervention remained an option.

The main methodological feature was the emulation of a target trial using cloning, censoring and weighting. This approach seeks to compare the strategies from a common starting point and reduce immortal time bias, the artificial advantage that may be attributed to surgery when patients must survive until the operation to be classified in the surgical group.

Over a median observation period of 7.4 years, 27 patients died in the early surgery group and 103 in the watchful waiting group. After weighting, surgery was associated with lower mortality from any cause (HR 0.69, 95% CI 0.41 to 0.94, p = .02). The difference in restricted mean survival time (RMST) at five years was 66 days in favour of early surgery (95% CI 19 to 129 days). This is the average survival gain within the period analysed. It does not represent a fixed extension of life for each patient.

The finding most relevant to surgical timing comes from the 503 patients with a left ventricular ejection fraction (LVEF) above 60% and a left ventricular dimension at end systole (LVESD) below 40 mm. In this subgroup, early surgery remained associated with longer survival (HR 0.61, 95% CI 0.31 to 0.96, p = .04), with a gain of 79 days in RMST at five years. Analyses in patients with degenerative MR yielded consistent findings.

In this multicentre cohort study emulating a clinical trial, early surgery was associated with better survival over the long term in patients with asymptomatic severe primary mitral regurgitation. The authors consider these findings to support earlier consideration of surgery.

COMMENTARY:

The question raised by this study is familiar. If a severe valve lesion can be corrected at low risk, should we wait for symptoms or adverse effects on the ventricle before intervening? Early intervention has received particular attention in aortic stenosis. In MR, the debate has its own history, grounded in observational studies and the possibility of preserving the valve with a durable repair.

This study therefore builds on an established approach to surgery in asymptomatic MR. It strengthens the prognostic case for early intervention by tackling a central problem in the previous evidence, namely distinguishing the benefit of operating from the better baseline prognosis of patients selected for surgery.

Emulating a trial is a step forward, although treatment is still not randomly assigned. Treatment choice may depend on factors the registry does not fully capture, such as frailty, anatomical complexity, the feasibility of repair, clinical judgement and patient preferences. Adjustment improves comparability, but residual confounding remains possible. The study therefore shows an association consistent with benefit, while the question of causality remains open.

Even with this limitation, the finding in patients who did not meet conventional criteria for ventricular dysfunction deserves attention. In severe MR, a preserved LVEF does not rule out early myocardial dysfunction. Ejection into the left atrium, where pressure is lower, alters loading conditions and can keep the LVEF apparently reassuring as disease progresses. By the time conventional thresholds are reached, some patients may already have developed adverse changes, such as atrial remodelling that predisposes to atrial fibrillation (AF). Other changes may include remodelling of the pulmonary microcirculation, involvement of the right heart and further deterioration of the valve that makes repair more difficult or jeopardises its feasibility.

Preserved ventricular function does not rule out other indications for surgery. The subgroup was defined by LVEF and LVESD, so it could include patients with other factors that favour intervention, such as AF secondary to MR, pulmonary hypertension or significant left atrial dilatation.

Clinical practice guidelines already account for these situations. The 2020 ACC/AHA guidelines consider repair reasonable in asymptomatic patients with normal ventricular function when the likelihood of a successful and durable repair exceeds 95% and expected mortality is below 1% at a specialist centre. The 2025 ESC/EACTS guidelines also consider intervention before ventricular dysfunction and give greater weight to intervention in the presence of certain markers of cardiac involvement. This study could support a future expansion of these recommendations, particularly for patients who remain well short of conventional thresholds, as part of a shift already under way.

From a surgical perspective, earlier assessment offers an opportunity to plan treatment while patients retain good functional reserve and before the disease complicates their course. With favourable anatomy, this may facilitate a repair strategy and allow consideration of a minimally invasive approach. Early referral to an expert team is valuable even if the eventual decision is to continue watchful waiting.

However, the study does not establish that operating earlier increases repair rates or that a less invasive approach reduces morbidity. Only 66% of patients undergoing early surgery received a repair. The remainder underwent replacement. Postoperative complications were not recorded. These limitations matter when we propose treating people who feel well. For the 34% who underwent replacement, the operation marked the start of either the limited lifespan of a bioprosthesis or prolonged anticoagulation for a mechanical valve. Despite the potential consequences, early surgery remained associated with better survival than initial watchful waiting.

A first practical step would be to review how we refer and assess these patients. Confirming MR severity and the genuine absence of symptoms, following changes in cardiac chamber size, estimating the likelihood of repair and determining operative risk allow an individualised discussion of early surgery. In a patient at low operative risk with a long life expectancy and a valve highly amenable to repair, these data provide another reason to consider surgery before clinical deterioration.

Watchful waiting remains a valid option when appropriately indicated and carried out with a structured surveillance plan. It also has consequences that should be explained. In selected patients with severe primary MR, waiting may carry a prognostic cost even before symptoms appear. The opportunity to repair the valve and preserve cardiac function deserves discussion before progression makes intervention unavoidable.

REFERENCE:

Ahn J, Kwak S, Lim J, Kim K, Kim J, Sun BJ, et al. Early mitral valve surgery and survival in asymptomatic severe primary mitral regurgitation. JAMA Netw Open. 2026;9(10):e2637061. doi:10.1001/jamanetworkopen.2026.37061.