Residency · Residency · Cardiothoracic Surgery

Mitral Regurgitation: Functional and Secondary Disease

Overview

Functional (secondary) mitral regurgitation arises not from intrinsic valve pathology but from left ventricular remodeling that distorts the mitral apparatus geometry. Unlike degenerative MR, where repair is highly durable, the management of functional MR remains one of the most debated topics in cardiac surgery. This chapter covers the pathophysiology, surgical options, and the landmark CTSN trial data that inform current practice.

Pathophysiology

Mechanism of Secondary MR

In functional MR, the mitral leaflets and chordae are structurally normal. The problem lies in the ventricle: LV dilatation and spherical remodeling displace the papillary muscles laterally and apically, which tethers the leaflets and restricts their systolic motion (Carpentier Type IIIb). Annular dilatation — primarily of the posterior annulus — contributes further to malcoaptation. The result is incomplete leaflet coaptation with a central regurgitant jet.

Ischemic vs. Non-Ischemic Functional MR

Ischemic MR results from coronary artery disease with regional wall motion abnormalities and LV remodeling, often producing asymmetric tethering (particularly when the posteromedial papillary muscle is dysfunctional or infarcted). The jet may be eccentric and posteriorly directed if the posterior papillary muscle is predominantly affected. Non-ischemic functional MR, from dilated cardiomyopathy, involves global LV dilatation with symmetric leaflet tethering, producing a central jet, with annular dilatation more prominent.

Ischemic vs. Non-Ischemic Functional MR Comparison

The Vicious Cycle

Functional MR creates a self-perpetuating spiral: MR increases LV volume overload, worsening dilatation, which further displaces the papillary muscles and increases tethering, producing more MR. This cycle drives progressive heart failure.

Echocardiographic Assessment

Severity Grading — Important Differences from Primary MR

The thresholds for defining severe secondary MR are lower than for primary MR. An EROA of 0.2 cm2 or greater defines severe secondary MR (compared to 0.4 cm2 for primary MR), and a regurgitant volume of 30 mL or greater defines severe secondary MR (compared to 60 mL for primary). The rationale is that even smaller regurgitant volumes have prognostic significance in the setting of LV dysfunction. Tenting height and tenting area quantify leaflet tethering severity, and a coaptation depth greater than 10 mm predicts higher recurrence after repair.

Dynamic Nature

Functional MR severity varies with loading conditions, heart rate, and LV function. Exercise echocardiography may unmask significant MR not evident at rest, and severity may improve with guideline-directed medical therapy (GDMT) and cardiac resynchronization therapy (CRT).

Medical Therapy

Guideline-Directed Medical Therapy (GDMT)

GDMT for heart failure — ACE inhibitors/ARBs/ARNI, beta-blockers, mineralocorticoid receptor antagonists, and SGLT2 inhibitors — should be optimized before considering surgical intervention. Volume status is optimized with diuretics. CRT can reduce functional MR by 1 to 2 grades in responders through improved LV synchrony and reverse remodeling. Medical therapy should be maximized before committing to surgery.

Surgical Options

Restrictive Mitral Annuloplasty

The standard surgical approach uses an undersized complete rigid ring (typically 2 sizes smaller than the measured annulus) that pushes the posterior annulus anteriorly, improving leaflet coaptation. However, this does not address the ventricular pathology — tethering forces remain. The fundamental problem is recurrence: MR returns in 30-60% of patients at 2 years in many series.

Repair Adjuncts

Several adjunctive techniques attempt to address the subvalvular pathology. Papillary muscle approximation brings the two papillary muscles closer together to reduce tethering. Selective cutting of secondary (strut) chordae can relieve leaflet tethering. Papillary muscle relocation or sling repositions the displaced papillary muscles toward the annulus. These adjuncts add complexity, however, and lack strong supporting evidence.

Mitral Valve Replacement

Chordal-sparing MVR preserves the subvalvular apparatus and LV geometry while eliminating MR completely and durably (no recurrence). Mortality may be slightly higher than repair in some series, and the trade-off includes anticoagulation for mechanical valves or acceptance of structural valve deterioration risk for bioprosthetics.

Concomitant CABG

In ischemic MR, revascularization alone may improve MR by restoring wall motion. CABG plus mitral intervention (repair or replacement) is the standard for significant ischemic MR. Whether to intervene on moderate ischemic MR at the time of CABG remains debated.

Landmark CTSN Trials

CTSN Severe Ischemic MR Trial (Acker et al., 2014)

This multicenter RCT randomized 251 patients with severe ischemic MR to mitral valve repair (restrictive annuloplasty) versus replacement (chordal-sparing). The primary endpoint was LV end-systolic volume index (LVESVI) at 12 months. At 2 years, there was no difference in LVESVI, mortality, or LV reverse remodeling. However, MR recurrence was dramatically higher after repair (58.8% with moderate or greater MR) compared to replacement (3.8%). The repair group also had higher rates of heart failure events and cardiovascular admissions. This trial challenged the assumption that repair is always preferable to replacement for severe ischemic MR.

CTSN Trials Summary

CTSN Moderate Ischemic MR Trial (Michler et al., 2016)

This RCT randomized 301 patients with moderate ischemic MR undergoing CABG to CABG alone versus CABG plus mitral repair (restrictive annuloplasty). At 2 years, there was no difference in LVESVI or degree of LV reverse remodeling. Adding repair did reduce MR (11.2% with moderate or greater MR versus 31.6% in the CABG-alone group), but there was no improvement in functional capacity, quality of life, or survival. The CABG-plus-repair group had higher rates of neurological events and supraventricular arrhythmias. The conclusion: routine addition of mitral annuloplasty to CABG for moderate ischemic MR is not supported.

<image>Pathophysiology diagram of functional (secondary) mitral regurgitation. The illustration shows a four-chamber heart view comparing a normal heart (left panel) with symmetric papillary muscles and proper leaflet coaptation versus a dilated cardiomyopathy heart (right panel) with LV spherical remodeling, laterally displaced papillary muscles, increased tethering distance, annular dilatation, and incomplete leaflet coaptation resulting in a central regurgitant jet. Key measurements are labeled: tenting height, tenting area, coaptation depth, and annular diameter. Arrows indicate the direction of tethering forces on the leaflets.</image>

Current Controversies and Decision-Making

Repair vs. Replacement for Severe Ischemic MR

The CTSN trial suggests replacement may be more durable than repair. However, repair preserves the option for future TAVR or transcatheter edge-to-edge repair (TEER) if needed. Many surgeons still favor repair in patients with minimal tethering (coaptation depth below 10 mm). Replacement is increasingly preferred for severe tethering (coaptation depth above 10 mm), posterior leaflet tethering angle above 45 degrees, and LV end-diastolic diameter above 65 mm (unlikely to reverse remodel).

Role of Transcatheter Edge-to-Edge Repair (TEER/MitraClip)

The COAPT trial demonstrated a mortality benefit for TEER in functional MR with specific criteria. Whether to refer for surgery versus TEER depends on overall operative risk, anatomy, and ventricular function.

When NOT to Operate

Severe LV dysfunction (EF below 20%) with extensive fibrosis and no viability may be better served by transplant or LVAD. Functional MR may improve dramatically with optimal GDMT and CRT — reassessment after 3 to 6 months of optimized therapy is appropriate before committing to surgery.

<image>Decision algorithm for management of ischemic mitral regurgitation. The flowchart begins with severity assessment (moderate vs. severe), then branches based on whether the patient needs CABG. For moderate MR + CABG: CABG alone is recommended (CTSN moderate MR trial). For severe MR: branches to repair vs. replacement based on tethering severity (coaptation depth and leaflet angles). Patients with minimal tethering may be candidates for repair with restrictive annuloplasty, while those with severe tethering are directed toward chordal-sparing replacement. A parallel pathway shows TEER (COAPT criteria) for patients who are high surgical risk. Each decision node cites the supporting trial evidence.</image>

Clinical Pearls

Functional MR is a ventricular disease, not a valve disease — treating only the valve without addressing the ventricle leads to recurrence. The CTSN severe ischemic MR trial is practice-changing: restrictive annuloplasty alone has a 58% rate of MR recurrence at 2 years, questioning the dogma that repair is always superior to replacement. For moderate ischemic MR at the time of CABG, adding mitral annuloplasty does not improve outcomes (CTSN moderate MR trial) — CABG alone is sufficient in most cases. The severity thresholds for defining severe secondary MR are lower than for primary MR (EROA of 0.2 cm2 versus 0.4 cm2) — apply the correct criteria. Coaptation depth above 10 mm and posterior leaflet tethering angle above 45 degrees predict high recurrence after repair, and these patients may be better served by replacement. Maximize GDMT and consider CRT before committing to surgery — functional MR is dynamic and may improve significantly with medical optimization. Chordal-sparing MVR preserves LV geometry and is critical — never cut the subvalvular apparatus during replacement for functional MR.

References

• Acker MA, Parides MK, Perrault LP, et al. CTSN Severe Ischemic MR Trial: Mitral-valve repair versus replacement for severe ischemic mitral regurgitation. N Engl J Med. 2014;370(1):23-32.
• Goldstein D, Moskowitz AJ, Gelijns AC, et al. CTSN 2-year outcomes of repair vs. replacement for severe ischemic MR. N Engl J Med. 2016;374(4):344-353.
• Michler RE, Smith PK, Parides MK, et al. CTSN Moderate MR Trial: Two-year outcomes of surgical treatment of moderate ischemic mitral regurgitation. N Engl J Med. 2016;374(20):1932-1941.
• Otto CM, Nishimura RA, Bonow RO, et al. 2020 ACC/AHA Guideline for Valvular Heart Disease. Circulation. 2021;143(5):e72-e227.
• Kron IL, Hung J, Overbey JR, et al. Predicting recurrent mitral regurgitation after mitral valve repair for severe ischemic mitral regurgitation. J Thorac Cardiovasc Surg. 2015;149(3):752-761.

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