Complex mitral annular calcification: why surgical access still matters

Mitral annular calcification (MAC) represents a chronic degenerative alteration of the fibrous mitral ring characterized by calcium deposition that may be localized or circumferential (1). Although its exact pathophysiology remains incompletely clarified, MAC has been shown to be independently associated with a higher risk of stroke (2), myocardial infarction, and vascular death (3). MAC is also linked to a greater incidence of atrial fibrillation (4) and to conduction system abnormalities, including intraventricular conduction delay, bundle branch block, and atrioventricular block (5). Beyond these associations, MAC independently predicts all-cause mortality and is correlated with increased cardiovascular morbidity and mortality among patients with atrial fibrillation (6).

In the surgical setting, extensive annular calcification substantially complicates mitral valve repair or replacement (7). Dense calcification may prevent secure suture placement and prosthesis anchoring, predisposing to paravalvular leak (PVL), atrioventricular groove disruption, major hemorrhage, and circumflex coronary injury. Aggressive decalcification with annular reconstruction can enable valve implantation but at the cost of greater technical complexity and perioperative risk (8). Conversely, leaving calcium in place may compromise repair durability and increase recurrence of regurgitation. Therefore, surgical management of severe MAC falls into two broad categories: approaches that work around the calcified annulus without removing it, and those involving complete decalcification followed by annular reconstruction (7). The first category includes intra-atrial or intra-annular prosthesis placement, collar-reinforced implantation with or without partial debridement, and positioning the prosthesis at the leaflet level or around the calcium bar. Recently a new technique has been proposed by creating a neoannulus within the left atrium rather than confronting the calcification directly (9). A surrogate annular ring is fashioned in the atrial tissue proximal to the native, heavily calcified annulus, giving the surgeon a clean, pliable implantation surface for a conventional prosthesis, avoiding aggressive calcium removal or transcatheter alternatives. The edge-to-edge repair offers simplicity but carries a meaningful long-term failure risk when the annulus itself is left untreated (10,11). Finally, mitral leaflet augmentation using autologous pericardium addresses cases where MAC restricts posterior leaflet mobility, reduces coaptation area, and produces regurgitation, restoring adequate coaptation without requiring direct manipulation of the calcified annulus (12,13). On the other hand, complete decalcification with annular reconstruction consists of two stages: en-bloc calcium removal with annular rebuilding, followed by valve repair or replacement (14).

Despite surgery being the first choice for severe MAC, in the presence of circumferential MAC it carries substantial morbidity and mortality, and alternative approaches have thus emerged, which are however limited by the lack of long-term outcomes and by known complications like left ventricular outflow tract (LVOT) obstruction and PVL. Indeed, long-term durability data for transcatheter valves implanted in the mitral position remain scarce, with most published series limited to short- and mid-term follow-up insufficient to characterize structural valve deterioration or reintervention rates over time (15). Off-label implantation of transcatheter heart valves originally designed for the aortic position, followed by development of dedicated mitral devices, has enabled valve-in-MAC (ViMAC) procedures performed via transseptal, transapical, or open atrial access (16). Open surgical transatrial implantation of transcatheter valves has become an evolving strategy for patients with severe MAC, with ongoing evaluation of technique, outcomes, and long-term durability. Device selection is also unsettled, with off-label balloon-expandable aortic valves widely used but geometrically suboptimal for the mitral position, and dedicated systems emerging as tailored alternatives (17). The open transatrial approach is typically reserved for patients with extensive MAC, often circumferential (≥270° or “horseshoe” pattern), in whom conventional suture fixation is not feasible, as well as for those with a high predicted risk of LVOT obstruction, since this strategy permits direct resection of the anterior leaflet and performance of septal myectomy. Favorable anatomic features include a predicted skirt neo-LVOT area >175 mm², a mitral annular area >430 mm², and an intercommissural distance <35 mm in patients with acceptable operative risk (18-20).

Previous reports describing the deployment of the SAPIEN XT or SAPIEN 3 (Edwards Lifesciences, Irvine, CA, USA) in open transatrial surgery for MAC have been published (16). In a recent issue on Annals of Cardiothoracic Surgery focused on MAC, Kulshrestha and Kaneko described a case of transatrial mitral valve replacement with a SAPIEN 3 Ultra with a pericardial bovine skirt for severe mitral stenosis (21). This case underscores several key points that warrant discussion.

Beyond echocardiographic evaluation, computed tomography (CT) has proven its striking and essential utility in MAC patient evaluation. As currently recommended, CT should be systematically incorporated in patients with MAC to precisely define the severity, circumferential involvement, and anatomic distribution of calcium, thereby enabling accurate procedural planning and risk stratification (8). A cardiac CT-based MAC score has been developed to provide a systematic method to grade MAC severity which may assist in predicting valve embolization/migration during trans-septal or transapical ViMAC procedures (22). The final MAC severity staging incorporates this MAC score with other CT features, together with echocardiographic and clinical features, and categorizes patients into three MAC risk categories, with a possible algorithm of treatment options proposed (18). The case by Kulshrestha and Kaneko was a patient at high surgical risk (STS mortality predicted at 8%), with an MAC score of at least 7 (circumferential MAC) and high risk of LVOT obstruction, which is compatible with the algorithm-derived final proposal of transatrial approach.

The authors have elegantly constructed a pericardial skirt to enhance structural support of the mitral annulus and reduce PVL. Indeed, various techniques employing both synthetic and biologic materials have been described. Reported options include synthetic patches such as polytetrafluoroethylene and polyethylene terephthalate (23), as well as biologic substitutes including autologous pericardium (24), the patient’s own anterior mitral leaflet (25), and xenogeneic pericardial tissue derived from equine or bovine sources (26,27). Although echocardiography demonstrated a postoperative mild PVL, the addition of a pericardial skirt likely mitigated its severity. Accepting this limited residual leak represented a deliberate trade-off, allowing only minimal annular decalcification in order to lower the risks of embolic events and atrioventricular groove disruption. Given the geometric and structural mismatch of transcatheter aortic valves when deployed in the mitral position, adjunctive measures are often necessary to compensate for these inherent limitations. On this regard, surgical approaches that create a new suture plane might reduce the need for such compromises (9).

Regarding the open transatrial approach for mitral valve replacement, it provides direct exposure of the mitral apparatus, enabling precise balloon sizing, controlled deployment, anterior leaflet resection to reduce LVOT obstruction risk, secure anchoring to limit PVL or embolization, and the option for adjunctive procedures when needed, like myectomy (28). It also allows treatment of patients with large annuli or complex subvalvular calcification who are often excluded from transseptal or transapical strategies, particularly given the high predicted risk of LVOT obstruction in this population. However, these benefits come at the cost of increased procedural invasiveness, as the technique requires sternotomy, cardiopulmonary bypass, and cardiac arrest, potentially increasing perioperative risk.

Current outcomes in the transatrial approach are improving (29,30), but highlight how MAC remains a daunting surgical challenge. Currently, despite surgery being the primary strategy, no universally superior solution can be recommended, as conventional reconstruction, transcatheter, and hybrid strategies each carry distinct trade-offs. Therefore, managing patients with MAC requires coordinated effort from multiple specialties. The evaluation team should involve a cardiac surgeon with specific expertise in MAC procedures, an interventional cardiologist, and a specialist in advanced cardiac imaging. The choice between these strategies should evaluate three main factors: anatomy, operative risk, and institutional expertise. CT-defined calcification extent and LVOT geometry determine anatomical eligibility for each approach. Surgical risk profile then separates prohibitive-risk patients, best served by transseptal ViMAC or dedicated devices, from intermediate- and acceptable-risk candidates who may tolerate open hybrid or conventional reconstruction respectively. Underlying all of this is institutional experience, since outcomes across every technique in this space are strongly operator- and program-dependent.

Acknowledgments

None.

Footnote

Provenance and Peer Review: This article was commissioned by the editorial office, Journal of Visualized Surgery. The article has undergone external peer review.

Peer Review File: Available at https://jovs.amegroups.com/article/view/10.21037/jovs-2026-1-0006/prf

Funding: None.

Conflicts of Interest: The author has completed the ICMJE uniform disclosure form (available at https://jovs.amegroups.com/article/view/10.21037/jovs-2026-1-0006/coif). M.B. serves as an unpaid editorial board member of Journal of Visualized Surgery from September 2024 to August 2026. The author has no other conflicts of interest to declare.

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