Mitral Annuloplasty #3: Full Ring vs Partial Ring

Mitral annuloplasty is performed to restore and stabilize annular geometry when annular dilatation or distortion contributes to mitral regurgitation. A fundamental technical decision is whether annular remodeling should involve the entire circumference with a full ring or primarily the posterior annulus with a partial ring or band.

This distinction is particularly important in pediatric and congenital mitral valve surgery. In adults, annular dimensions are relatively fixed and durable stabilization can often be prioritized. In children, the surgeon must additionally consider somatic growth, future annular enlargement, leaflet development, and the risk of creating functional mitral stenosis. Thus, the choice between a full and partial prosthesis is not simply a choice of device; it represents a decision regarding how much of the annulus should be constrained and how permanent that constraint should be.

Current pediatric evidence suggests an important trade-off: larger full rings may provide durable stabilization, whereas small full rings can become restrictive and predispose to mitral stenosis. Partial bands may be more suitable for small annuli but can permit recurrent regurgitation. Biodegradable annuloplasty represents another strategy intended to combine early stabilization with subsequent annular growth [1,2].

1. The Mitral Annulus as a Dynamic Structure

The mitral annulus is not a rigid circular structure. It is a three-dimensional, dynamically deforming junction between the left atrium, left ventricle, and mitral leaflets. During the cardiac cycle, the annulus changes in:

• area,
• circumference,
• anterior–posterior diameter,
• commissural dimension,
• and three-dimensional saddle configuration.

These dynamic changes contribute to leaflet coaptation and influence leaflet and chordal stress.

Posterior annulus

The posterior annulus is relatively muscular and geometrically variable. It is particularly susceptible to dilatation associated with atrial or ventricular enlargement. Posterior annular enlargement increases overall annular circumference and may increase the anterior–posterior dimension, thereby reducing leaflet overlap.

For this reason, many reconstructive strategies concentrate annuloplasty on the posterior annulus.

Anterior annulus

The anterior annulus is closely related to the aortic root through the aortomitral continuity. It is generally less distensible than the posterior annulus and contributes to the structural relationship between left ventricular inflow and outflow.

Circumferential fixation therefore has different implications from isolated posterior remodeling. Incorporating the anterior annulus into a full ring provides stronger geometric control, whereas leaving it unrestricted with a partial ring preserves more native annular motion.

Experimental three-dimensional analysis supports this concept. In a sheep model, both complete and partial flexible rings stabilized annular dimensions, but the partial ring preserved more physiologic annular folding, whereas the complete ring dampened this motion [5]. These data provide mechanistic insight but should not be interpreted as direct evidence of superior pediatric clinical outcomes.

2. Why Annuloplasty Improves Mitral Competence

Congenital mitral regurgitation usually reflects abnormalities involving multiple components of the mitral apparatus:

1. leaflet tissue,
2. chordae,
3. papillary muscles,
4. ventricular geometry,
5. commissures,
6. and the annulus.

Annuloplasty principally addresses the annular component.

When the annulus becomes disproportionately enlarged, available leaflet tissue may no longer provide sufficient coaptation. Reducing and reshaping the annulus can restore an appropriate leaflet-to-annulus relationship and increase the zone of leaflet overlap.

The objectives of annuloplasty are therefore to:

• restore an appropriate annular dimension,
• improve leaflet coaptation,
• stabilize other components of the repair,
• reduce the likelihood of progressive annular dilatation,
• and improve long-term durability.

However, annular reduction has an important limit. Excessive reduction may create a valve that is competent but functionally stenotic. This concern becomes especially important in infants and small children, in whom the annulus must accommodate substantial future somatic growth.

The surgical objective is therefore not maximal annular reduction, but rather the minimum effective remodeling required to obtain a stable and competent valve with an adequate effective orifice.

3. Full-Ring Annuloplasty

A full ring surrounds essentially the entire mitral annulus. Annular sutures are placed circumferentially through both posterior and anterior portions of the annulus and secured to a predetermined prosthetic geometry.

Mechanism

A full ring can control:

• total annular circumference,
• anterior–posterior diameter,
• commissural width,
• overall annular shape,
• and, depending on ring design, three-dimensional annular configuration.

Because the entire annulus is incorporated, subsequent annular enlargement is more strongly constrained.

Advantages

The principal advantage is complete and reproducible annular stabilization.

A full ring may be particularly useful when:

• annular dilatation is severe or global,
• the annular geometry is substantially distorted,
• significant downsizing is necessary,
• recurrent annular enlargement is a major concern,
• or complex leaflet reconstruction requires a stable geometric framework.

The potential advantage of complete stabilization is supported indirectly by adult experience. In functional mitral regurgitation, complete rings were associated with less recurrent regurgitation than partial rings in one retrospective series [7]. This observation should not be directly extrapolated to congenital mitral disease, but it illustrates the fundamental mechanical advantage of circumferential stabilization.

Limitations

The same circumferential constraint that improves stability can become disadvantageous in a growing child.

A permanently implanted ring establishes a fixed maximum annular dimension. If the ring is small, somatic growth may eventually produce a mismatch between required cardiac output and the available mitral valve orifice.

The principal concerns are therefore:

• functional mitral stenosis,
• increasing transmitral gradient,
• inadequate accommodation of growth,
• and eventual reoperation.

This risk is strongly suggested by pediatric long-term data. In a retrospective cohort of 112 children undergoing repair of isolated congenital mitral regurgitation, patients with rings ≥26 mm had the lowest reoperation risk. In contrast, 13 of 14 reoperations in children with rings <26 mm were performed for mitral stenosis [3]. Importantly, the groups differed substantially in age and annular size, so these findings do not establish that a specific ring diameter itself causes stenosis [4]. Nevertheless, they demonstrate the practical problem associated with placing a small permanent ring in a growing child.

4. Partial-Ring or Band Annuloplasty

A partial ring or annuloplasty band supports predominantly the posterior annulus while leaving the anterior annulus free of circumferential prosthetic fixation.

The surgical rationale is straightforward: because annular dilatation commonly involves the posterior annulus, targeted posterior remodeling may restore leaflet coaptation without imposing a fixed circumference around the entire valve.

Mechanism

Posterior annular reduction can:

• reduce annular circumference,
• decrease excessive anterior–posterior enlargement,
• move the posterior leaflet toward the anterior leaflet,
• improve leaflet overlap,
• and stabilize the region most susceptible to dilatation.

Because the anterior annulus remains unrestricted, partial annuloplasty preserves more native annular deformation.

Potential Advantages

Preservation of annular dynamics

Experimental data indicate that partial flexible annuloplasty can preserve physiologic annular folding better than complete ring annuloplasty [5].

Reduced circumferential constraint

A partial band does not define a fixed circumference around the entire mitral valve. This characteristic is particularly attractive in younger children with small annuli.

Potential accommodation of growth

Avoiding a small complete ring may reduce the risk that the prosthesis itself becomes the limiting orifice as the child grows.

This does not mean that a conventional partial band guarantees normal annular growth. Pediatric data directly quantifying growth after partial versus full annuloplasty remain limited. Rather, the conceptual advantage is that the entire native annulus is not incorporated into a fixed circumferential prosthesis.

Potential Disadvantages

The principal disadvantage is less complete annular stabilization.

The pediatric long-term series described above illustrates this trade-off. Among children treated with a band, 6 of 7 reoperations were performed for recurrent regurgitation rather than stenosis [3]. Thus, avoiding a small ring may reduce one mode of failure while increasing another.

This distinction is clinically important:

Small full ring → greater concern for stenosis

Partial band → greater concern for recurrent regurgitation

These outcomes should not be interpreted as proof that one strategy is universally preferable, because patient age, annular size, and underlying valve pathology differed between treatment groups [3,4].

5. Full Ring Versus Partial Ring: The Central Trade-Off

The decision can therefore be conceptualized as a balance between two competing objectives:

Full ring

Maximum annular stabilization and geometric control

versus

Partial ring or band

Less circumferential restriction and greater preservation of native annular behavior

Neither strategy is universally superior.

A larger child with an adequately sized annulus and severe annular dilatation may tolerate and benefit from a complete ring. Conversely, a small child with a small annulus may face an unacceptable long-term risk if a fixed, undersized prosthetic ring is implanted.

The available pediatric evidence supports individualized rather than formulaic decision-making.

6. Biodegradable Annuloplasty: A Pediatric-Specific Strategy

Biodegradable annuloplasty was developed specifically to address the tension between early stabilization and future growth.

The biodegradable ring is implanted within the annulus and provides temporary structural remodeling. Experimental studies show degradation within approximately 12 months, with replacement by fibrous tissue. The concept is that the fibrous remodeling maintains annular support while avoiding a permanent rigid limitation on annular enlargement [1].

Reported experience suggests preservation of three-dimensional annular motion and growth potential in children [1].

Clinical data are also encouraging. In a series of 68 children with congenital mitral valve disease, 39 underwent repair using a biodegradable ring and 29 underwent non-ring annuloplasty. Freedom from valve failure was approximately 90% versus 74%, and freedom from reoperation was 100% versus 84%, respectively. Importantly, transmitral gradients were similar between groups, approximately 4.3 versus 4.2 mmHg [2].

These findings suggest that biodegradable annuloplasty may provide a useful intermediate strategy: stronger remodeling than a purely non-ring technique without the permanent fixed circumference of a conventional prosthetic ring.

However, this study did not directly compare biodegradable rings with conventional full and partial rings, and it does not eliminate the need for long-term surveillance of annular growth, recurrent regurgitation, and valve gradients.

7. Functional Mitral Stenosis and Annuloplasty Geometry

Annuloplasty must be evaluated not only by residual regurgitation but also by the resulting valve orifice.

Adult data provide indirect physiologic support for this principle. In patients undergoing degenerative mitral repair, complete rings were associated with higher resting and exercise transmitral gradients and smaller valve areas than partial bands [6]. These findings cannot be quantitatively extrapolated to children, but they reinforce an important surgical concept: greater annular stabilization can carry a hemodynamic cost if the resulting orifice becomes restrictive.

This issue is magnified in children because:

• baseline annular dimensions may already be small,
• heart rates are higher,
• cardiac output requirements increase with growth,
• and the prosthetic ring does not enlarge proportionally with the patient.

Therefore, an annuloplasty that appears satisfactory immediately after repair may become functionally restrictive later.

8. Annuloplasty in a Growing Child

Growth is one of the major factors distinguishing pediatric from adult mitral repair.

An infant may undergo several-fold increases in body size before adulthood. Accordingly, the surgeon must consider not only the immediate reconstructed valve but also its anticipated relationship to future cardiac output.

Strategies intended to reduce fixed restriction include:

• partial posterior bands,
• selective posterior annuloplasty,
• commissural plication,
• suture annuloplasty,
• and biodegradable annuloplasty.

Posterior suture annuloplasty can preserve annular dynamics without a permanent prosthetic circumference. Long-term adult experience suggests that selected suture techniques can provide durable results comparable with posterior bands [8]. However, comparable long-term pediatric evidence is insufficient, and adult degenerative-valve results should not be assumed to predict congenital outcomes.

The fundamental pediatric decision remains a balance between two risks:

future stenosis from excessive permanent restriction

and

future regurgitation from inadequate stabilization.

9. How Valve Pathology Should Influence the Choice

Annuloplasty should not be selected independently of the underlying congenital morphology.

Predominantly posterior annular dilatation

When dilatation is predominantly posterior and anterior annular geometry remains appropriate, a partial ring or band may provide sufficient remodeling while avoiding unnecessary circumferential fixation.

Global annular dilatation

When the annulus is globally enlarged or extensively distorted, a full ring provides more comprehensive geometric stabilization.

Small annulus in a young child

In this setting, implantation of a small permanent complete ring deserves particular caution because of the observed association between small rings and subsequent mitral stenosis [3].

A band or growth-accommodating strategy may be preferable when adequate competence can still be achieved.

Complex leaflet reconstruction

Following cleft closure, leaflet augmentation, chordal reconstruction, commissural repair, or combined procedures, the durability of the reconstructed leaflet geometry may depend on adequate annular stabilization.

Thus, preserving theoretical growth is not beneficial if insufficient annular support allows early recurrent regurgitation.

10. Intraoperative Assessment After Annuloplasty

Regardless of the technique selected, the reconstructed valve should be evaluated systematically.

The surgeon should assess:

1. leaflet mobility,
2. coaptation depth and length,
3. symmetry of the coaptation line,
4. residual prolapse or restriction,
5. commissural opening,
6. and the effective valve orifice.

The saline test is useful for defining residual regurgitation and coaptation but cannot reproduce physiologic loading.

After separation from cardiopulmonary bypass, echocardiography should evaluate:

• residual mitral regurgitation,
• location and mechanism of residual jets,
• leaflet opening,
• transmitral inflow,
• mean diastolic gradient,
• ventricular function,
• and overall hemodynamic significance.

In small children, transmitral gradient must be interpreted in relation to heart rate, cardiac output, loading conditions, and body size. Competence alone should never be considered sufficient evidence of a successful repair if leaflet opening is restricted.

11. Practical Surgical Principle

The choice between a full ring and partial ring should be based on the minimum annular constraint required to obtain a stable, competent, and adequately sized valve.

A full ring offers stronger circumferential remodeling and potentially greater protection against recurrent annular dilatation.

A partial ring or band preserves more native annular behavior and avoids complete circumferential fixation, but may provide less protection against recurrent regurgitation.

For pediatric congenital mitral repair, four questions are particularly useful:

1. How much of the annulus is actually abnormal?
2. How much stabilization is required to maintain leaflet coaptation?
3. How much effective valve area can safely be reduced?
4. How will the reconstruction accommodate future growth?

The optimal solution may be a conventional full ring, partial band, biodegradable ring, or non-ring annuloplasty depending on patient size, annular morphology, and the remainder of the mitral reconstruction.

Key Takeaways

• A full ring provides circumferential remodeling and strong stabilization of both the anterior and posterior annulus.
• A partial ring or band predominantly stabilizes the posterior annulus while preserving greater anterior annular freedom.
• Pediatric long-term data suggest that rings ≥26 mm can provide durable repair, whereas reoperation after smaller rings is frequently related to mitral stenosis [3].
• Bands may be preferable in younger children with small annuli, but recurrent regurgitation remains an important failure mode [3,4].
• Biodegradable annuloplasty offers a strategy for temporary stabilization while preserving annular growth potential and has shown favorable midterm pediatric results [1,2].
• Experimental and adult studies support the mechanical distinction between complete and partial annuloplasty, but these data are indirect and should not be used as quantitative evidence for pediatric outcomes [5-7].
• Direct pediatric comparisons of full versus partial annuloplasty remain limited.
• The objective is not maximal annular reduction, but a competent valve with adequate leaflet mobility, sufficient effective orifice area, durable geometry, and the greatest reasonable capacity to accommodate future growth.

References

[1] Myers PO, Kalangos A. Valve repair using biodegradable ring annuloplasty: from bench to long-term clinical results. Heart Lung Vessel. 2013;5(4):213-218.

[2] Yakub MA, Sivalingam S, Dillon J, Matsuhama M, Latiff HA, Ramli MF. Mitral valve repair for congenital mitral valve disease: impact of the use of a biodegradable annuloplasty ring. Ann Thorac Surg. 2015;99(3):884-890.

[3] Van DN, Pham NHM, Nguyen VMT, Nguyen PV, Phan P, Van CNM, Vuong NL. Isolated congenital mitral regurgitation repair in children: long-term outcomes of artificial rings. Ann Thorac Surg. 2022;113(2):638-645.

[4] Wells DA, Morales DLS. “Band-Aids” for small annuli. Ann Thorac Surg. 2022;113(2):645-646.

[5] Dagum P, Timek T, Green GR, Daughters GT, Liang D, Ingels NB Jr, Miller DC. Three-dimensional geometric comparison of partial and complete flexible mitral annuloplasty rings. J Thorac Cardiovasc Surg. 2001;122(4):665-673.

[6] Mesana TG, Lam BK, Chan V, Chen K, Ruel M, Chan K. Clinical evaluation of functional mitral stenosis after mitral valve repair for degenerative disease: potential affect on surgical strategy. J Thorac Cardiovasc Surg. 2013;146(6):1418-1425.

[7] Kwon MH, Lee LS, Cevasco M, Couper GS, Shekar PS, Cohn LH, Chen FY. Recurrence of mitral regurgitation after partial versus complete mitral valve ring annuloplasty for functional mitral regurgitation. J Thorac Cardiovasc Surg. 2013;146(3):616-622.

[8] Garatti A, Canziani A, Parolari A, Castelvecchio S, Guazzi M, Daprati A, Abu Farah A, Grimaldi F, Tripepi S, Menicanti L. Long-term results of suture annuloplasty for degenerative mitral valve disease: a propensity-matched analysis. J Cardiovasc Med. 2018;19(1):22-28.