Mitral Annuloplasty #1: Mitral Regurgitation and Annuloplasty

The mitral valve is a dynamic three-dimensional apparatus composed of the annulus, anterior and posterior leaflets, chordae tendineae, papillary muscles, left ventricular myocardium, and the surrounding atrial and ventricular structures. Valve competence therefore depends not only on leaflet morphology but also on the geometric relationship among these components throughout the cardiac cycle. In congenital mitral regurgitation (MR), abnormalities may involve any combination of leaflet tissue, commissures, chordae, papillary muscles, and the annulus.

Annular dilatation is particularly important because it can amplify regurgitation even when leaflet tissue is potentially adequate for repair. As the annulus enlarges—particularly in the septolateral or anteroposterior dimension—the distance that the leaflets must bridge during systole increases. Coaptation becomes shallower, the effective coaptation surface decreases, and a regurgitant orifice may develop or enlarge.

1. Annular Dilatation as a Mechanism of Mitral Regurgitation

The normal mitral annulus is neither circular nor static. It has a nonplanar, saddle-shaped configuration and changes its dimensions throughout the cardiac cycle. This geometry contributes to efficient leaflet coaptation while limiting excessive leaflet stress.

With annular dilatation, the relationship between annular size and available leaflet tissue becomes unfavorable. Even structurally preserved leaflets may no longer meet adequately during systole. In congenital disease, this mechanism frequently coexists with intrinsic abnormalities such as leaflet dysplasia, deficient zones of apposition, chordal shortening or elongation, abnormal chordal insertion, and papillary muscle malposition.

For this reason, annuloplasty should rarely be conceptualized as an isolated treatment for congenital MR. It is usually one component of a broader repair that addresses the dominant mechanism of regurgitation while restoring a more favorable relationship between leaflet tissue and annular dimensions.

Pediatric series support the general durability of reconstructive approaches but also demonstrate that recurrent MR and reoperation remain clinically important. In a standardized repair-oriented series of 106 infants and children, native-valve preservation was feasible, although recurrent MR and reoperation remained substantial during follow-up [1]. Another cohort of 107 children showed satisfactory early and mid-term results after various mitral repair techniques, with freedom from moderate or severe recurrent MR of approximately 92% at intermediate follow-up [2].

2. Physiologic Goals of Annuloplasty

The principal objectives of annuloplasty are to:

1. Restore annular geometry.

Annular reduction decreases the excessive distance between opposing leaflet insertion points and restores a more favorable leaflet-to-annulus relationship.

2. Increase effective leaflet coaptation.

Reduction of the septolateral dimension can increase coaptation length and surface area. Experimental work using saddle-shaped annuloplasty demonstrated greater leaflet coaptation than flatter configurations, supporting the concept that annuloplasty geometry—not simply annular circumference—affects valve competence [3].

3. Stabilize the reconstructed valve.

Annular support may limit progressive redilatation after leaflet, commissural, or subvalvar reconstruction and thereby contribute to long-term durability.

The objective, however, is not maximal annular reduction. An annuloplasty that eliminates MR at the cost of excessive inflow resistance is not a successful pediatric repair. The surgeon must preserve an adequate effective mitral orifice and avoid creating iatrogenic mitral stenosis.

3. The Pediatric Balance: Competence, Inflow, and Growth

This balance is particularly important in infants and young children because the annulus must accommodate future somatic growth. Long-term pediatric data illustrate the consequences of excessive or insufficient annular restriction.

In a retrospective study of 112 children with isolated congenital MR followed for a median of approximately 11 years, patients receiving complete rings measuring at least 26 mm had the lowest observed reoperation risk. In contrast, 13 of 14 reoperations after smaller complete rings were related primarily to mitral stenosis, whereas 6 of 7 reoperations after band annuloplasty were associated with recurrent MR [4]. An accompanying editorial emphasized the same trade-off: a small complete ring may provide strong annular control but risk later obstruction, while a band may preserve greater annular capacity but provide less durable control of recurrent dilatation [5].

These observations should not be interpreted as evidence that a 26-mm threshold is universally applicable. The groups differed substantially in age, body size, and annular dimensions, and the study was retrospective. Ring size is therefore partly a surrogate for patient size and anatomy rather than an independent treatment variable.

The practical pediatric objective is to achieve durable competence without compromising current or future ventricular inflow. Final assessment should therefore consider residual MR, leaflet mobility, coaptation, transmitral gradient, annular size relative to body size, and anticipated growth.

Mitral Annuloplasty #2: Mitral Annulus and Suture Placement

Successful annuloplasty requires a precise understanding of the mitral annulus as a three-dimensional surgical structure and of its relationship to the aortic root, aorto-mitral curtain, coronary sinus, and circumflex coronary artery. The visible leaflet hinge is only the internal landmark of a more complex atrioventricular junction. Safe suture placement therefore requires the surgeon to understand what lies outside and beneath each portion of the annulus.

1. Three-Dimensional Annular Anatomy

The anterior annulus is closely related to the fibrous continuity between the mitral and aortic valves. The central anterior leaflet insertion forms part of the aorto-mitral curtain between the fibrous trigones. Consequently, excessively deep anterior sutures may involve structures associated with the aortic root or interfere with normal leaflet hinge motion.

The posterior annulus is anatomically different. It is less uniformly fibrous and lies adjacent to the atrioventricular groove. The coronary sinus courses near the posterior annulus, while the left circumflex coronary artery may lie particularly close to the posterolateral region. The precise relationship varies between individuals.

The three-dimensional configuration is also mechanically important. Intraoperative three-dimensional echocardiography has demonstrated that implantation of a complete annuloplasty ring can make the annulus more planar, whereas partial bands may preserve more of the native nonplanar configuration [6]. Experimental comparison of complete and partial flexible devices similarly demonstrated that partial annuloplasty better preserved physiologic annular folding, whereas complete rings reduced this dynamic motion [7].

These studies are predominantly adult or experimental and should not be directly extrapolated to congenital pediatric outcomes. Nevertheless, they reinforce a fundamental surgical principle: annuloplasty modifies not only annular diameter but also annular motion and three-dimensional geometry.

2. Principles of Annular Suture Placement

Annuloplasty sutures should capture sufficient annular tissue to provide secure fixation without extending unnecessarily deep into adjacent structures. The bite is placed immediately outside the leaflet hinge rather than through the leaflet tissue itself.

Important structures at risk include:

• the leaflet hinge, where an excessively internal bite may restrict leaflet excursion;
• the aortic root and aorto-mitral continuity along the anterior annulus;
• the coronary sinus along the posterior annulus; and
• the left circumflex coronary artery, particularly along the posterolateral annulus.

The supplied clinical literature does not provide comparative data defining an optimal suture depth or quantifying these specific suture-related complications in children. These precautions are therefore primarily anatomy-driven surgical principles.

3. Practical Sequence of Annular Suturing

One practical method begins with the first annular stitch at approximately the 6-o’clock position. This stitch can be placed with a forehand or backhand needle movement and then gently retracted toward the surgeon. Retraction improves visualization of the adjacent annular tissue and facilitates controlled placement of subsequent stitches.

From this reference point, suturing may proceed toward approximately 4–5 o’clock and then counterclockwise toward 12 o’clock, using backhand movements where they provide the most natural needle trajectory. The surgeon then returns to the 6-o’clock position and progresses clockwise toward 8–9 o’clock with forehand movements before completing the remaining anterior portion.

The precise sequence is less important than the principles behind it:

• maintain direct visualization of the tissue being incorporated;
• use a needle trajectory appropriate for local annular anatomy;
• maintain consistent bite depth and spacing;
• avoid excessive traction that distorts the annulus;
• repeatedly reassess the relationship between the annulus and leaflet hinge.

4. Geometry Matters Beyond Ring Size

Annuloplasty should not be considered simply a circumferential downsizing procedure. Three-dimensional geometry influences leaflet coaptation. In patients with functional MR, semirigid band annuloplasty substantially increased regional leaflet coaptation, particularly in the central portion of the valve [8]. Experimental data similarly suggest that a saddle-shaped configuration may provide superior leaflet coaptation compared with a flattened annulus [3].

The final repair should therefore be evaluated in functional terms. Saline testing before atrial closure provides an initial assessment, followed by transesophageal or epicardial echocardiography after separation from cardiopulmonary bypass. Important endpoints include residual MR, leaflet mobility, coaptation depth and distribution, transmitral gradient, ventricular function, and any new regional wall-motion abnormality that might raise concern for circumflex coronary compromise.

Mitral Annuloplasty #3: Full Ring vs Partial Ring

Annuloplasty can be performed with a complete circumferential ring or with a partial ring or band. The distinction is not simply the amount of prosthetic material implanted. Each strategy alters annular stabilization, three-dimensional motion, and the balance between repair durability and preservation of inflow capacity.

1. Full-Ring Annuloplasty

A complete ring provides circumferential remodeling of both the anterior and posterior annulus. Its principal advantage is strong stabilization against recurrent annular dilatation.

This may be desirable when annular enlargement is global, when the repair depends on maintaining a defined geometry, or when adequate annular size permits implantation without meaningful risk of obstruction.

However, complete rings also modify native annular mechanics. Three-dimensional echocardiographic studies have demonstrated greater flattening of the saddle-shaped annulus after full-ring implantation than after partial annuloplasty [6]. Experimental work similarly suggests that complete rings dampen physiologic annular folding more than partial rings [7].

In adults with fibroelastic deficiency, full rings were also associated with a more favorable postoperative aorto-mitral angle than C-shaped bands, suggesting that ring configuration can influence the spatial relationship between the mitral and aortic valves [9]. This finding is anatomically interesting but should not be considered direct evidence for pediatric device selection.

2. Partial-Ring or Band Annuloplasty

A partial ring or band predominantly supports the posterior annulus while leaving the central anterior annulus free from circumferential prosthetic fixation. This may preserve greater annular flexibility and more physiologic folding [7].

In small children, these characteristics are potentially attractive because complete fixation of a small annulus raises concern for future restriction. However, leaving part of the annulus unsupported may permit progressive dilatation and recurrent MR.

The pediatric long-term series demonstrates this trade-off particularly clearly: reoperations after bands were predominantly performed for recurrent regurgitation, whereas reoperations after small complete rings were predominantly performed for stenosis [4].

Thus, neither strategy is inherently superior. A partial device may sacrifice some annular stability to preserve flexibility and potential capacity, whereas a complete ring may provide greater stability at the cost of more complete geometric constraint.

3. Biodegradable Annuloplasty

Biodegradable rings have been developed as an alternative strategy for growing patients. The conceptual objective is temporary annular stabilization during healing and remodeling, followed by degradation of the implanted material and replacement by fibrous tissue, potentially allowing continued annular growth.

Developmental and observational experience suggests that biodegradable annuloplasty can reinforce the repair while preserving dynamic annular behavior and subsequent growth [10]. However, the available evidence does not establish superiority over conventional rings, bands, or suture-only annuloplasty through robust direct pediatric comparisons. Long-term comparative data regarding recurrent MR, stenosis, reintervention, and annular growth remain limited.

4. Choosing the Annuloplasty Strategy

The choice should integrate:

• patient age and body size;
• absolute annular size and annular z-score;
• distribution of annular dilatation;
• anterior and posterior leaflet dimensions;
• underlying congenital valve morphology;
• associated leaflet and subvalvar reconstruction;
• predicted risk of recurrent MR;
• predicted risk of mitral stenosis; and
• expected somatic growth.

A full ring may be favored when circumferential stabilization is essential and the annulus can accommodate an appropriately sized device. A partial ring or band may be attractive when preservation of annular flexibility and future capacity is a major concern. Biodegradable or other growth-conscious strategies may be considered in selected young patients, although the supporting comparative evidence remains less mature.

The most important principle is that annuloplasty is geometric reconstruction rather than simple annular reduction. An effective pediatric repair must establish a broad and stable coaptation zone while maintaining unobstructed left ventricular inflow. Durability cannot be judged solely by the absence of MR immediately after cardiopulmonary bypass; the reconstructed valve must also remain functional as the child grows.

The long-term objective is therefore a valve that is simultaneously competent, nonobstructive, anatomically balanced, and durable. The optimal annuloplasty strategy is the one that best achieves those competing goals for the individual child.

References

[1] Kalfa D, Vergnat M, Ly M, Stos B, Lambert V, Baruteau A, Belli E. A standardized repair-oriented strategy for mitral insufficiency in infants and children: midterm functional outcomes and predictors of adverse events. Journal of Thoracic and Cardiovascular Surgery. 2014. doi:10.1016/j.jtcvs.2014.02.057.

[2] Jiang Z, Mei J, Ding F, Bao C, Zhu J, Tang M, Ma N, Huang J, Shen S. The early and mid-term results of mitral valve repair for mitral regurgitation in children. Surgery Today. 2014. doi:10.1007/s00595-013-0816-x.

[3] Bouma W, Aoki C, Vergnat M, Pouch A, Sprinkle SR, Gillespie MJ, Mariani M, Jackson B, Gorman RC, Gorman JH. Saddle-Shaped Annuloplasty Improves Leaflet Coaptation in Repair for Ischemic Mitral Regurgitation. Annals of Thoracic Surgery. 2015. doi:10.1016/j.athoracsur.2015.03.096.

[4] Van D, Pham NHM, Nguyen VMT, Nguyen PV, Phan P, Nguyen Minh Van C, Vu NL. Isolated Congenital Mitral Regurgitation Repair in Children: Long-term Outcomes of Artificial Ring. Annals of Thoracic Surgery. 2021. doi:10.1016/j.athoracsur.2021.01.024.

[5] Wells D, Morales D. “Band-aids” for Small Annuli. Annals of Thoracic Surgery. 2021. doi:10.1016/j.athoracsur.2021.01.070.

[6] Mahmood F, Subramaniam B, Gorman JH, Levine RA, Gorman RC, Maslow A, Panzica PJ, Hagberg R, Karthik S, Khabbaz K. Three-Dimensional Echocardiographic Assessment of Changes in Mitral Valve Geometry After Valve Repair. Annals of Thoracic Surgery. 2009. doi:10.1016/j.athoracsur.2009.07.007.

[7] Dagum P, Timek T, Green G, Daughters G, Liang D, Ingels N, Miller DC. Three-dimensional geometric comparison of partial and complete flexible mitral annuloplasty rings. Journal of Thoracic and Cardiovascular Surgery. 2001. doi:10.1067/MTC.2001.116313.

[8] Greenhouse D, Dellis SL, Schwartz C, Loulmet D, Yaffee DW, Galloway A, Grossi E. Regional changes in coaptation geometry after reduction annuloplasty for functional mitral regurgitation. Annals of Thoracic Surgery. 2012. doi:10.1016/j.athoracsur.2012.02.066.

[9] Ma W, Ye W, Zhang J, Zhang W, Wu W, Kong Y. Impact of different annuloplasty rings on geometry of the mitral annulus with fibroelastic deficiency: the significance of aorto-mitral angle. International Journal of Cardiovascular Imaging. 2018. doi:10.1007/s10554-018-1383-4.

[10] Myers P, Kalangos A. Valve repair using biodegradable ring annuloplasty: from bench to long-term clinical results. Heart, Lung and Vessels. 2013.