Adult ASD: a mitral classification to better guide surgery

Impact of Atrial Septal Defect on Mitral Morphology: A Surgical Challenge

The closure of an atrial septal defect (ASD) in adults, although well-established, carries a major risk: the perioperative or late worsening of mitral regurgitation (MR). Data indicate that 10 to 20% of patients after percutaneous occlusion and 29 to 35% after surgical closure experience an increase in their MR, sometimes leading to complex reinterventions. This phenomenon highlights an incomplete understanding of the structural remodeling of the mitral apparatus induced by chronic left-to-right shunting.

This study, conducted on a cohort of 75 adults undergoing total thoracoscopic ASD repair compared to 63 control subjects, aims to precisely evaluate the structural characteristics of the mitral valve (annular diameters, leaflet length, coaptation depth) using 3D transesophageal echocardiography (TEE). The objective is twofold: to quantify the morphological differences between ASD patients and healthy adults, and then to establish a specific morphological classification (ASD-MV) to guide decisions for concomitant mitral repair. The authors test the hypothesis that early identification of coaptation anomalies and annular geometry allows for the prediction of post-closure MR risk and the optimization of the initial surgical strategy.

Methodology

The study adopts a comparative observational design to characterize mitral geometry in adults with an ostium secundum atrial septal defect (ASD). The analysis focuses on 138 subjects, divided between an observation group (75 patients scheduled for thoracoscopic repair) and a control group (63 individuals with a healthy heart).

The core of the protocol is based on high-resolution 3D transoesophageal echocardiography (TOE), using GE Vivid E9 or Philips EPIQ 7C systems. For patients in the observation group, data acquisition was performed under stable etomidate-based anaesthesia, ensuring high-quality imaging without major circulatory interference. The team captured 3D volumes at a frequency greater than or equal to 20 Vol/s, allowing for precise manual segmentation at the end of diastole and systole.

• Morphological parameters: Measurement of ring diameters (anteroposterior and commissural) and lengths of the anterior and posterior leaflets (segment 2).
• Coaptation analysis: Rigorous evaluation of the coaptation depth and length on the Y-plane, as well as the maximum trans-mitral flow velocity.

For the practitioner, this approach offers an exhaustive morphological mapping. It proves indispensable for planning the surgical approach and anticipating mitral valve modifications induced by the closure of the atrial septal defect.

Comparison of baseline and hemodynamic characteristics

The study focused on a sample of 75 adult patients with a secundum atrial septal defect (ASD) (observation group, OG) and 63 healthy controls (control group, CG). Baseline data analysis shows no statistically significant difference between the two groups regarding age, body mass index (BMI), or sex distribution.

Analysis of mitral geometry in adult ASD

The results of this study highlight the complexity of the structural interactions between the atrial septal defect (ASD) and the mitral valve apparatus. The finding is clear: a significant proportion of adult patients undergoing ASD closure experience worsening mitral regurgitation (MR) postoperatively. The challenge is therefore no longer just to close the shunt, but to anticipate an unfavorable hemodynamic response of the mitral valve.

The contribution of 3D transoesophageal echocardiography (3D-TOE) proves to be decisive here. By comparing patients with an ASD to a control group, the authors highlight significant morphological differences in the annulus and leaflets. This study suggests that the analysis of coaptation parameters and annular dimensions should guide the surgical decision. A concomitant intervention on the mitral valve, aimed at restoring optimal coaptation depth and length, allows for the stabilization of valvular function as soon as cardiopulmonary bypass is discontinued.

Although promising, this study has limitations, including its single-center nature and the need for longer-term follow-up data to confirm the durability of the repairs. However, the approach focused on preoperative morphological classification offers a concrete path to reduce the risk of reintervention, which is often more complex and costly for the patient.

Summary of results

This observational study of 75 adult patients with atrial septal defect (ASD) reveals that concomitant mitral repair is required in 44% of cases (n=33). Surgical interventions, using Gore-Tex sutures and prosthetic rings, allowed for the correction of morphological anomalies (types II and III) and increased the coaptation zone from 2 to 5 mm, thereby stabilizing valvular function.

In concrete terms, for the practitioner:

• Morphological targeting: Identify type II and III patients in preoperative TEE; these structural deformities require simultaneous mitral valve repair to prevent residual mitral regurgitation (MR), even if the initial leak is only moderate.
• Strict intraoperative monitoring: Systematically evaluate the MR grade immediately after weaning from cardiopulmonary bypass; a worsening of ≥ 2 grades from baseline requires immediate mitral intervention to avoid costly and risky reoperation.
• Coaptation optimization: Aim for a 2 to 5 mm gain in coaptation depth/length via annuloplasty and chordal reconstruction to secure the hemodynamic result after shunt closure.

Technical lexicon of the study

Surgical view (3D-Zoom): Three-dimensional echocardiographic imaging mode with high temporal resolution (≥ 20 Vol/s) allowing visualization of the mitral valve according to the surgeon's intraoperative axis of vision.

Commissural diameter: Measurement of the maximum left-right transverse axis of the mitral annulus, obtained in this study by manual segmentation on the Z reference plane.

X/Y/Z Plane: Three-dimensional segmentation coordinate system where the X plane defines the virtual mitral ring (A2-P2 attachment points), the Y plane the anteroposterior axis and the Z plane the commissural diameter.

Coaptation depth (Tent height): Perpendicular distance measured between the contact point of the mitral leaflets (coaptation) and the horizontal plane of the mitral annulus.

Qp/Qs ratio: Hemodynamic index calculated to quantify the magnitude of the left-to-right shunt by comparing pulmonary stroke volume to systemic stroke volume.

Coaptation length: Dimension of the zone of overlap and effective contact between the anterior and posterior leaflets of the mitral valve during the valve closure phase.

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