Mitral repair: secondary chordal cutting reduces coaptation

The dilemma of secondary chordae in mitral surgery

During mitral valve repair, the fate of secondary chordae tendineae (CT) often divides practitioners. While their sectioning is sometimes performed to improve anterior leaflet mobility or correct left ventricular outflow tract obstruction, their actual contribution to valvular biomechanics remains underestimated. This experimental study addresses this clinical ambiguity by evaluating how the loss of these structures influences the geometric stability of the valve in systolic configuration.

The objective of this work was to precisely quantify the impact of secondary chordae resection on coaptation parameters and valvular billowing. Using a model of 11 explanted porcine mitral valves analysed by micro-CT scan, the authors sought to verify whether these chordae are essential for maintaining functional geometry.

The central hypothesis is based on the critical stabilizing role of secondary chordae, particularly the A2 strut chordae. Researchers postulate that their transection leads to pathological leaflet deformation and a reduction in coaptation surfaces, potentially compromising the durability of the surgical repair. Three states were compared: a physiological baseline, the isolated section of the A2 chordae, and finally the resection of all secondary chordae.

Design and experimental protocol

This ex vivo experimental study (benchtop) used 11 explanted porcine mitral valves to analyze the biomechanical impact of secondary chordae. The valvular architecture was captured by micro-computed tomography (micro-CT) in a systolic configuration. The protocol sequentially evaluated three experimental conditions on each sample:

• Physiological baseline: all secondary chordae are kept intact.
• Selective transection: specific sectioning of the strut chordae in the A2 zone.
• Total transection: sectioning of all secondary chordae tendineae of the valve.

Analysis and statistics settings

For each condition, researchers quantified leaflet geometry using three key indicators: billowing height (Billowing Height, BH), coaptation height (Coaptation Height, CH) according to a parasternal long-axis view, and coaptation area (Coaptation Area, CA). Billowing was defined as pathological whenever the increase in BH was ≥ 2 mm compared to the baseline. Data were statistically processed by comparing medians with adjusted p-values (padj), allowing the correlation of chordal support loss to valvular morphological changes.

Impact of secondary chordae sectioning on valvular geometry

Micro-CT analysis of the 11 porcine valves reveals a progressive and significant degradation of the geometric stability of the leaflets as the secondary chordae are severed. The results highlight an immediate loss of structural support as soon as the A2 strut chordae is sectioned.

Alteration of bulging and coaptation

• Sectioning of the A2 support chordae: This isolated procedure leads to an exceeding of the pathological bulging threshold (defined as ≥ 2 mm) by 1.1 mm. The 0.6 mm reduction in coaptation height indicates a potential loss of sealing at this stage.
• Total sectioning of secondary chordae: Instability increases with a bulging height reaching 2.8 mm above the pathological threshold. The coaptation surface collapses significantly (-0.35 cm²), compromising the functional integrity of the valve in systolic configuration.

Qualitative observations from micro-CT imaging confirm that secondary chordae, often considered accessory, are in fact essential biomechanical pillars. Their absence induces excessive leaflet billowing and a reduction in coaptation metrics, two predictive factors for failure or sub-optimal results during mitral repair procedures.

Analysis of the biomechanical role of secondary chordae

This ex vivo study on 11 porcine valves demonstrates that secondary chordae, often neglected during mitral valve repairs, are the guarantors of the geometric stability of the leaflets. The isolated section of the A2 "strut" chord causes immediate pathological billowing, with a median increase of 3.1 mm, significantly crossing the critical threshold of 2 mm. This phenomenon is accompanied by a significant reduction in coaptation height (-0.6 mm), which weakens the valvular sealing zone.

Complete removal of secondary chordae further worsens this picture, with billowing reaching 4.8 mm and a reduction in the coaptation surface area of 0.35 cm². These results suggest that the integrity of these structures is essential to prevent excessive leaflet deformation under systolic pressure. Regarding limitations, although the porcine model and the static nature of the micro-CT measurements do not perfectly replicate the dynamic complexity of a pathological human heart, the observed physical constraints remain highly relevant for reconstructive surgery.

Summary of results

This ex vivo study demonstrates that the sectioning of A2 secondary chordae increases valvular prolapse by 3.1 mm (p=0.003), exceeding the pathological threshold of 2 mm. Total resection of these chordae significantly reduces the coaptation area by 0.35 cm² (p=0.029), directly altering the geometric stability of the leaflets during the systolic phase.

In concrete terms, for the practitioner:

• Preserve secondary chordae: Their systematic sacrifice during mitral repairs compromises valvular mechanics by promoting excessive and pathological bulging.
• Prioritize the A2 strut: Its preservation or reconstruction is essential to maintain a physiological coaptation height and prevent deleterious mechanical stresses.
• Anticipate the risks of failure: A reduction in the coaptation area following the resection of secondary chordae constitutes a major risk factor for the long-term durability of the repair.

Technical lexicon of the study

Secondary chordae tendineae (CT): Second-order mitral chordae inserting onto the ventricular surface of the leaflets (between the free edge and the annulus), whose role is the geometric stabilization of the valve during the systolic phase.

A2 strut CT: Specific structural secondary chordae, often called "strut" chordae, attaching to the central part of the anterior leaflet (A2 segment).

Billowing height (BH): Height of the leaflet billowing towards the left atrium relative to the mitral annulus plane; an increase ≥ 2 mm is defined as pathological in this study.

Coaptation height (CH): Vertical contact height between the anterior and posterior leaflets, measured here in a parasternal long-axis view.

Coaptation area (CA): Total surface area of contact and overlap between the mitral valve leaflets, determining the seal during valve closure.

Micro-CT scan: High-resolution tomographic imaging technique used to accurately quantify the three-dimensional geometry of valvular components in systolic stress configuration.

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