When calcium refines morphology: toward quantitative imaging-guided selection for percutaneous commissurotomy

This editorial refers to ‘Cardiac CT-scan for mitral valve calcification assessment before percutaneous commissurotomy: the multicenter prospective CALCIMIT study’, by B. Alos et al., https://doi.org/10.1093/ehjci/jeag054. Percutaneous mitral commissurotomy (PMC) has long been the reference treatment for symptomatic rheumatic mitral stenosis with favourable anatomy. Since its introduction more than four decades ago, it has provided durable haemodynamic improvement and symptomatic relief in appropriately selected patients. However, the epidemiology and anatomical profile of rheumatic mitral stenosis have changed substantially in high-income countries.1,2 This shift has important implications for imaging and patient selection. The anatomical scoring systems that historically guided decision-making, particularly the Wilkins score, were developed in younger populations with predominantly fibrotic disease.3 In the current era, calcification has emerged as the dominant determinant of procedural success and long-term outcomes.4 Yet its assessment remains challenging with conventional echocardiography, which is operator-dependent and often limited by acoustic shadowing. As a result, a purely echocardiography-based anatomical approach may be insufficient to fully capture the risk profile of contemporary rheumatic mitral disease, particularly when calcification is underestimated. In this context, the prospective multicentre CALCIMIT study provides timely and important insights. In this issue, Alos et al.5 reported that computed tomography (CT)-derived mitral valve calcium scoring (MVCS) was independently associated with both immediate procedural success and long-term event-free survival after PMC.5 By demonstrating that CT-derived MVCS is independently associated with outcomes after accounting for conventional echocardiographic assessment, CALCIMIT supports the complementary role of objective, quantitative calcium quantification alongside semi-quantitative anatomical grading (Figure 1). Multimodality imaging of rheumatic mitral stenosis. 3D echocardiography shows restricted leaflet motion and commissural fusion, while cardiac CT demonstrates extensive mitral valve calcification (arrows), illustrating the additional value of CT for quantitative calcium assessment. For decades, echocardiographic scores have formed the cornerstone of patient selection for PMC. The Wilkins score, and its subsequent modifications, integrate leaflet mobility, thickening, subvalvular involvement, and calcification into a composite anatomical index.6 While these scores remain clinically useful, they have several inherent limitations. First, they rely on semi-quantitative and subjective grading. Interobserver variability is not negligible, particularly for the assessment of calcification. Second, echocardiography may underestimate the extent and distribution of calcium, especially when shadowing obscures deeper structures. In the CALCIMIT cohort, CT identified mitral calcification in approximately two-thirds of patients, significantly more than echocardiography or fluoroscopy.5 This observation underscores the limited sensitivity of conventional imaging modalities for calcium detection in contemporary rheumatic disease. More importantly, the study demonstrated that the amount of calcification, rather than its mere presence, had major clinical implications. A higher MVCS was independently associated with both poor immediate results and reduced long-term event-free survival. Patients with higher calcium scores had substantially lower procedural success, with only about one-third achieving a good immediate outcome when the score exceeded the predefined threshold. This quantitative approach parallels the evolution seen in aortic stenosis, where CT calcium scoring has become an essential diagnostic and prognostic tool, particularly in low-flow, low-gradient conditions.7 CALCIMIT suggests that a similar paradigm may now be emerging for rheumatic mitral stenosis, with MVCS playing a role analogous to aortic valve calcium scoring in tailoring intervention strategies. Another key strength of MVCS is its excellent reproducibility. In the CALCIMIT study, interobserver agreement for calcium quantification was nearly perfect, confirming its robustness as a quantitative imaging biomarker.5 This contrasts with traditional echocardiographic scores, which are inherently more subjective and operator-dependent. Taken together, these findings support CT-derived MVCS as an objective quantifier of calcific burden that may refine selection in contemporary rheumatic MS, particularly when echocardiographic assessment of calcification is limited. This evolution is consistent with the broader trend in valvular heart disease toward more quantitative and multimodality-based evaluation strategies, as emphasized in recent scientific documents.8,9 The high prevalence of calcification reported in the study, around two-thirds of patients, reflects the changing epidemiology of rheumatic mitral stenosis in Western populations.5 With aging cohorts and declining incidence of acute rheumatic fever, the disease is increasingly characterized by mixed fibrotic-calcific lesions rather than pure commissural fusion.2,3 This evolution challenges the traditional paradigm of PMC. Balloon commissurotomy was originally designed for valves with mobile leaflets and limited calcification. In heavily calcified valves, the mechanism of dilation becomes less predictable, increasing the risk of suboptimal valve opening or severe post-procedural regurgitation.4,10 In this setting, CT-derived calcium quantification may provide critical additional information. MVCS quantifies calcium burden (with density weighting), while CT can also define the anatomic distribution of calcium. The demonstration that MVCS predicts both immediate and long-term outcomes suggests that it captures a fundamental aspect of valve pathology that is not fully represented in conventional scores. The practical question, however, is how CT should be integrated into the routine evaluation of these patients. Echocardiography will undoubtedly remain the first-line modality, providing essential information on valve morphology, haemodynamics, and associated lesions. Recent EACVI recommendations highlight the central role of echocardiography as the primary imaging modality, while emphasizing the complementary value of CT and other techniques in selected cases.8 CT should therefore be viewed as a complementary tool rather than a replacement for echocardiography. A stepwise imaging strategy appears reasonable. Echocardiography would serve as the initial modality for diagnosis and anatomical assessment. In patients with intermediate or uncertain anatomical suitability, CT-based MVCS could be performed to refine risk stratification and guide decision-making. In patients with a high calcium burden, MVCS may also prompt closer surveillance or earlier consideration of surgery rather than a percutaneous approach. Such an approach is consistent with the broader evolution of structural heart interventions, where CT has become indispensable for procedural planning. It also aligns with current guidelines, which emphasize the role of multimodality imaging in the evaluation of valvular heart disease and in the decision-making process of the Heart Team.9 Beyond procedural success, the association between MVCS and long-term outcomes deserves particular attention. In the CALCIMIT study, higher calcium scores were independently linked to lower event-free survival over nearly 8 years of follow-up.5 This finding suggests that calcium burden is not merely a predictor of procedural mechanics but also a marker of global disease severity and structural degeneration. Patients with high calcium scores may therefore represent a distinct clinical phenotype, characterized by more advanced valvular degeneration and a higher likelihood of progressive dysfunction. In such cases, earlier surgical intervention or closer follow-up may be more appropriate than a purely percutaneous approach. Several challenges remain before CT-based MVCS can be fully integrated into routine practice. The optimal cutoff values identified in the study require validation in independent cohorts. Cost-effectiveness and accessibility issues must also be considered, particularly in regions where advanced imaging resources are limited. Future imaging strategies will likely combine CT-based calcium scoring with advanced echocardiographic techniques, including three-dimensional imaging and strain analysis, as well as potentially cardiac magnetic resonance. Such a multiparametric approach may provide a more comprehensive assessment of valve structure, mechanics, and myocardial adaptation. The CALCIMIT study represents an important step toward more objective and quantitative imaging-guided decision-making in rheumatic mitral stenosis. By demonstrating the independent prognostic value of CT-derived MVCS, it challenges the traditional reliance on semi-quantitative echocardiographic scores and supports the integration of CT into the pre-procedural assessment of selected patients. As the epidemiology of rheumatic mitral stenosis continues to evolve, imaging strategies must adapt accordingly. Quantitative calcium scoring may help bridge the gap between anatomical assessment and clinical outcomes, moving the field toward a more personalized and evidence-based selection of patients for percutaneous commissurotomy. Patrizio Lancellotti (Conceptualization [lead]; Supervision [lead]; Writing—original draft [lead]; Writing—review & editing [lead]), Augustin COISNE MD, PHD (Conceptualization [supporting]; Writing—review & editing [supporting]), and Yun Yun GO MD (Conceptualization [supporting]; Writing—review & editing [supporting]) None declared. This article is an editorial and does not contain original data. Data sharing is therefore not applicable.