Mitral Valve Replacement #2: Anatomy and Surgical Techniques

1. Introduction

Mitral valve replacement (MVR) requires more than inserting a correctly sized prosthesis. Safe implantation depends on understanding the relationship between the mitral annulus, ventricular inflow, subvalvular apparatus, aortomitral continuity, coronary arteries, and cardiac conduction tissues. The principal technical decisions are how much native valve to remove, which chordal attachments to preserve, where to place annular sutures, how to size and seat the prosthesis, and how to orient its moving components.

The accompanying illustration contrasts complete leaflet resection with preservation of native leaflet–chordal attachments and depicts an intra-annular mechanical prosthesis. These drawings emphasize annular–papillary continuity, periannular structures at risk, and unrestricted mechanical leaflet motion. They represent operative options rather than a single universal technique.

2. Surgical Anatomy of the Mitral Annulus

2.1. Aortomitral continuity and fibrous trigones

The anterior mitral leaflet attaches to the aortomitral curtain, a fibrous region continuous with the aortic root between the left and noncoronary aortic cusps. The right and left fibrous trigones mark important anchoring regions at either end of this continuity. Unlike the predominantly muscular posterior annulus, this anterior segment has relatively firm fibrous support.

This relationship matters during anterior leaflet excision and suture placement. Sutures that penetrate too deeply or extend into the aortic root may compromise the aortic valve or adjoining fibrous structures. Excessive traction can distort the aortomitral junction. In patients with prior aortic surgery, endocarditis, or extensive calcium, the anatomy may be substantially altered and require reconstructive rather than routine annular suturing.

2.2. Posterior annulus and atrioventricular groove

The posterior mitral annulus is adjacent to the left atrioventricular groove, where the circumflex coronary artery, coronary sinus, and coronary venous branches course. Their distance from the annulus varies, and the circumflex artery may lie particularly close in left-dominant coronary anatomy. An anatomical study of 15 hearts identified separations as small as approximately 1 mm in some specimens [1].

Deep posterior annular bites can injure or compress the circumflex artery. Circumflex compromise may result from a suture, tissue distortion, external compression by the sewing ring, or injury during aggressive annular debridement. Sudden inferolateral ischemia or new regional wall-motion abnormalities after MVR should prompt urgent consideration of this complication [2].

The posterior atrioventricular groove is also vulnerable to disruption when annular tissue is friable or densely calcified. Excessive decalcification, oversized prostheses, and forceful traction may precipitate atrioventricular groove injury or ventricular rupture. This danger is particularly relevant in older patients with severe mitral annular calcification [3].

2.3. Conduction tissues

The atrioventricular node is situated in the triangle of Koch on the right atrial side of the central fibrous body, and the penetrating His bundle passes through the fibrous skeleton. These structures are not uniformly adjacent to the entire posterior mitral annulus. Rather, conduction risk becomes more important around the medial fibrous region, associated septal operations, extensive annular reconstruction, and congenital abnormalities such as atrioventricular septal defects. The relevant landmarks must be interpreted according to the individual heart.

3. Leaflet Resection and Subvalvular Preservation

3.1. Functional importance of annular–papillary continuity

The native mitral valve forms a mechanical connection between the annulus and the ventricular wall through the leaflets, chordae tendineae, and papillary muscles. During systole, this apparatus contributes to ventricular shape, regional wall mechanics, and coordinated contraction. Complete excision eliminates this continuity and may impair postoperative left ventricular (LV) performance.

Comparative clinical studies and randomized evidence support preserving appropriate chordal attachments during MVR when technically feasible. In a randomized comparison of partial and complete chordal-sparing replacement, the effect of preservation strategy on LV geometry and performance was directly investigated [4]. Longer-term clinical observations likewise associate chordal preservation with better ventricular performance, although populations and techniques are heterogeneous [5]. These findings are especially relevant in chronic mitral regurgitation, in which postoperative removal of the low-impedance regurgitant pathway changes LV loading.

Chordal preservation is a functional objective, not an absolute requirement. Retention is inappropriate when infected, heavily calcified, fused, or redundant tissue prevents safe implantation or interferes with prosthetic motion.

3.2. Complete leaflet and chordal resection

Conventional MVR can involve excision of both leaflets and their chordal attachments. This provides a relatively unobstructed orifice and may be necessary with destructive endocarditis, severe rheumatic fusion, bulky calcification, or anatomy in which retained tissue would obstruct the prosthesis.

The disadvantage is loss of annular–papillary continuity. Complete excision should therefore be considered selectively rather than routinely, particularly when useful chordae can be retained without compromising prosthetic function. The surgeon should avoid unnecessary traction on papillary muscles and LV endocardium during leaflet removal.

3.3. Posterior leaflet preservation

Posterior leaflet preservation is widely used because it often retains a substantial portion of the chordal apparatus while leaving the principal prosthetic inflow relatively unobstructed. The posterior leaflet can be left intact, partially resected, or divided and incorporated into the annular suture line, depending on tissue bulk and the intended prosthesis.

A commonly used approach excises diseased anterior leaflet tissue while retaining the posterior leaflet with attached chordae. The retained leaflet may be folded toward the posterior annulus to avoid protrusion into the prosthetic orifice. The resulting annular bites must capture secure tissue without allowing mobile leaflet remnants to interfere with an occluder.

3.4. Anterior leaflet and bilateral chordal preservation

Preservation of anterior chordae can maintain additional LV connections, but the retained leaflet or chordal bundles may project toward the left ventricular outflow tract (LVOT) or enter the path of mechanical leaflets. Techniques include selective anterior leaflet resection with retention of chordal-bearing strips, division and reattachment of leaflet segments near the annulus, or other chordal-sparing reconstructions.

The selected technique must balance ventricular continuity against prosthetic clearance. Anterior tissue cannot be preserved merely because preservation is theoretically advantageous. Before final seating, the surgeon must judge the space available for the valve housing and confirm that retained tissues will neither obstruct LV inflow nor narrow the LVOT.

4. Exposure and Operative Sequence

4.1. Access and systematic inspection

MVR is generally performed with cardiopulmonary bypass and cardioplegic arrest through a left atriotomy, transseptal approach, or other exposure selected according to atrial size, prior surgery, and associated procedures. Exposure should permit visualization of both trigones, commissures, the complete annular circumference, chordae, and papillary muscles.

After opening the atrium, the surgeon reconfirms the valve pathology and repairability. Leaflet mobility, commissural fusion, chordal length and fusion, papillary muscle abnormalities, calcification, and infected tissue are assessed. These observations determine the extent of resection and preservation.

4.2. Excision and annular preparation

Leaflet resection begins with protection of normal annular support and nearby structures. In a chordal-sparing operation, only tissue that is diseased, obstructive, or incompatible with the prosthesis is excised. Papillary muscles should not be avulsed or excessively mobilized.

The annulus is then inspected circumferentially for adequate suture-bearing tissue. Localized calcium may be managed selectively, whereas extensive calcification requires an individualized reconstruction or calcium-preserving strategy. Aggressive removal of calcium embedded in the atrioventricular groove can be more dangerous than leaving well-anchored calcium in place. The surgeon must also avoid leaving irregular surfaces that prevent complete prosthetic seating or create paravalvular leakage.

4.3. Prosthesis sizing

The annulus should be sized with the dedicated manufacturer-specific sizers after resection and preparation. The objective is a prosthesis that fits the available annular and ventricular geometry without distortion. Forcing a larger valve into a smaller annulus risks suture-line tension, annular injury, prosthetic tilt, and LVOT encroachment. Conversely, an unnecessarily small effective orifice can produce elevated transmitral gradients and prosthesis–patient mismatch.

Sizing must account for the external sewing-ring diameter and the position of the valve housing, not simply the labeled prosthesis size. The prosthesis selected should leave sufficient clearance for its moving components and any retained subvalvular tissue.

4.4. Annular suture placement

Interrupted pledgeted mattress sutures are commonly used, although other secure techniques are established. Each suture should incorporate adequate healthy annular or periannular tissue without deep penetration into vulnerable adjacent structures. Care is particularly important in the posterior annulus near the circumflex artery and coronary venous system, and anteriorly around the fibrous trigones and aortomitral curtain.

Uniform spacing and controlled suture tension help achieve circumferential apposition. Excessively deep or widely displaced bites can distort the annulus, compromise coronary flow, or create a nonplanar seating surface. Pledget position and mattress orientation are chosen according to tissue quality, prosthesis geometry, and surgeon preference rather than a universal rule.

4.5. Seating, tying, and inspection

The prosthesis is lowered under direct visualization while retaining control of each suture to avoid crossing or entrapment. Tissue folds, residual chordae, and pledgets should be kept clear of the sewing ring and occluder hinges. The valve must seat evenly without rocking.

After sutures are tied, mechanical leaflets are checked directly with an appropriate instrument for unrestricted opening and closure. This assessment should be repeated after all knots are secured, since a valve that moves freely before final tying can subsequently develop interference.

5. Intra-annular, Supra-annular, and Mechanical Valve Orientation

Intra-annular implantation places the prosthetic sewing ring at the native annular level, preserving an anatomically appropriate relation between atrial inflow and ventricular entry when dimensions permit.

Supra-annular implantation places the prosthesis on the atrial side of the native annulus. In small children, it may permit implantation of a larger valve when standard annular seating is not possible, but it alters inflow geometry and may introduce risks of pulmonary venous obstruction, atrial inflow impairment, conduction disturbance, or subsequent reintervention. Pediatric series show feasibility in selected small-annulus patients; they do not establish supra-annular implantation as universally superior [6,7].

Mechanical bileaflet valve orientation is dictated by prosthesis design and surrounding anatomy. The drawing illustrates an anti-anatomical orientation of the bileaflet occluders, a convention used for certain prostheses and surgical approaches. Importantly, the term does not prescribe a universal orientation for every device. Rotation should prioritize unobstructed leaflet excursion, clearance from retained tissue and ventricular structures, and the manufacturer's recommendations. The prosthesis should not be left in a nominally preferred orientation if mechanical interference is present.

6. Special Considerations in Congenital and Pediatric Surgery

Pediatric MVR adds the constraints of small annular diameter, altered papillary muscle positions, congenital leaflet dysplasia, short or fused chordae, and future somatic growth. A parachute or hammock mitral valve may have an abnormal subvalvular apparatus that cannot be preserved in the same fashion as an adult degenerative valve.

When the native annulus cannot accommodate an adequately functioning prosthesis, options may include supra-annular seating, selected annular enlargement, or staged reintervention. Repeated replacement as a child grows is a major lifetime consideration. In retrospective cohorts of children aged five years or younger, outcomes and risks differ with anatomy and implant position; interpretation is limited by small groups and evolving surgical practice [8].

The adjacent LVOT deserves particular attention in patients with atrioventricular septal defects, Shone complex, or prior outflow reconstruction. An oversized or maloriented prosthesis may worsen a pre-existing narrow outflow tract. For these patients, anticipated LVOT clearance may be as important as the nominal mitral valve diameter.

7. Completion Assessment and Early Complications

Following atrial closure, de-airing, and separation from cardiopulmonary bypass, transesophageal echocardiography should confirm prosthetic leaflet or disc mobility, normal flow direction, acceptable transmitral gradients at the prevailing heart rate and flow, and no clinically important paravalvular regurgitation. LV and right ventricular systolic function, regional wall motion, and LVOT flow should also be reassessed.

Important findings requiring immediate investigation include:

• Restricted mechanical leaflet excursion, potentially caused by retained chordae, leaflet tissue, or suture material.
• Significant paravalvular regurgitation from incomplete seating, annular defects, or disrupted sutures.
• Unexpectedly high transmitral gradients after accounting for flow, heart rate, and prosthesis size.
• New LVOT obstruction caused by prosthetic encroachment or retained anterior leaflet tissue.
• New inferolateral wall-motion abnormalities or ischemic electrocardiographic changes suggesting circumflex compromise.
• Unexplained hemorrhage or hematoma concerning for atrioventricular groove injury.

Delayed circumflex injury can also present with ventricular dysfunction or acute ischemia. Published case reports emphasize the importance of prompt angiographic evaluation and appropriate revascularization when clinically suspected [2,9].

After mechanical MVR, anticoagulation planning is essential because the prosthesis remains thrombogenic. Early management must balance thromboembolic risk, postoperative bleeding, and individual valve characteristics. Pediatric anticoagulation requires particularly close coordination among the surgical, cardiology, and hematology teams.

8. Key Surgical Principles

• Map the annulus before placing sutures: protect the circumflex artery, coronary sinus, aortomitral curtain, fibrous trigones, and relevant conduction anatomy.
• Preserve useful chordal continuity when feasible: ventricular geometry matters, but retained tissue must never compromise prosthetic function.
• Avoid forceful annular enlargement by oversizing: prosthesis fit must respect annular integrity and LVOT clearance.
• Maintain complete sewing-ring apposition: secure anchoring and evenly distributed tension reduce paravalvular leakage and distortion.
• Treat mechanical orientation as an anatomical decision: direct proof of unrestricted occluder movement is more important than a fixed orientation convention.
• Use imaging to verify the completed operation: evaluate gradient, paravalvular flow, leaflet mobility, LVOT, and new regional ventricular dysfunction.

References

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8. Tierney ESS, Pigula FA, Berul CI, Lock JE, del Nido PJ, McElhinney DB. Mitral valve replacement in infants and children 5 years of age or younger: evolution in practice and outcome over three decades with a focus on supra-annular prosthesis implantation. J Thorac Cardiovasc Surg. 2008. DOI: 10.1016/j.jtcvs.2007.12.076. PMID: 18954636.
9. Gaba P, Kaneko T, Kochar A, Sung J, O'Gara PT, Bhatt DL. Left circumflex artery injury following surgical mitral valve replacement: a case report. Eur Heart J Case Rep. 2021. DOI: 10.1093/ehjcr/ytab464. PMID: 34993405.