Staphylococcus aureus endocarditis: should mitral replacement be preferred?

Repair or replace? The dilemma facing Staphylococcus aureus

In cardiac surgery, the current dogma for native mitral valve infective endocarditis (IE) systematically favours repair over replacement. However, this recommendation faces the clinical reality of Staphylococcus aureus, a pathogen formidable for its virulence and high risk of recurrence. In the presence of an active MSSA (methicillin-susceptible Staphylococcus aureus) infection, the durability of valvular reconstruction is questioned: does the classic benefit of repair survive bacterial aggressiveness?

This study analyzed a cohort of 44 patients operated on between 2012 and 2022 for native mitral IE exclusively caused by MSSA. The objective was to compare the results of 23 mitral repairs against 21 prosthetic replacements. By examining data over a two-year follow-up, the study evaluates whether the choice of technique truly influences overall survival and the reinfection rate, thus testing the hypothesis of a superiority — or a vulnerability — of repair against this specific microorganism.

Study design and population

This retrospective study analyzed data from consecutive patients surgically treated for active native mitral valve infective endocarditis between 2012 and 2022. From an initial pool of 170 operated patients, the authors isolated a specific cohort of 44 patients with confirmed Staphylococcus aureus infection. The diagnosis was rigorously established according to the modified Duke criteria and validated by systematic blood cultures. Notably, the study deliberately excluded cases involving methicillin-resistant strains (MRSA) to focus exclusively on sensitive strains (MSSA).

Experimental groups and surgical protocol

Patients were divided into two arms according to the surgical strategy decided by the operator:

• Repair Group (n=23): Direct closure of defects or patch plasty, completed by chordal transfer or replacement and annuloplasty.
• Replacement Group (n=21): Complete valve replacement after radical resection of infected tissue.

The standard protocol included a median sternotomy, cardiopulmonary bypass with cold crystalloid cardioplegia (Custodiol) and local disinfection of the remaining tissues with povidone and vancomycin. Postoperatively, intravenous antibiotic therapy was maintained for up to 6 weeks in accordance with current recommendations.

Statistical analysis and objectives

To compensate for the confounding biases inherent in the choice of technique, the authors used inverse probability of treatment weighting (IPTW). The analysis was performed using SPSS software version 30. The primary endpoints were all-cause mortality, the incidence of endocarditis recurrence, and the rate of reintervention over a two-year follow-up.

Study results: Valve Repair vs Replacement

Of the 170 patients who underwent surgery for native mitral valve infective endocarditis between 2012 and 2022, 44 cases (26%) were attributable to Staphylococcus aureus (methicillin-susceptible strains, MSSA). The cohort was divided into two groups: mitral repair (n=23) and valve replacement (n=21).

Medium-Term Mortality and Survival

The inverse probability of treatment weighting (IPTW) analysis reveals a significant divergence in outcomes at two years, in contrast to the initial raw data. While 30-day mortality shows no statistically significant difference between the two approaches, the trend clearly reverses during the follow-up period.

Recurrences and Reoperations

Valve-related morbidity was more pronounced in the repair group:

• Endocarditis recurrence: 3 cases recorded in the repair group, compared to none (0) in the replacement group.
• Reoperation rate: 3 patients in the repair group required a new intervention due to infectious recurrence. In the replacement group, only one reoperation was performed for a paravalvular leak.

Operative and Echocardiographic Data

The primary surgical indication, particularly in the repair group, was the presence of large or embolic vegetations. Technically, the replacement group initially showed significantly longer cardiopulmonary bypass and aortic clamping times (unweighted data), often reflecting more complex concomitant procedures, notably on the tricuspid valve. However, after propensity score adjustment, these variables were balanced to allow for the comparison of clinical outcomes.

In summary, for S. aureus infections, valve replacement appears to offer superior protection against recurrence and better two-year survival compared to repair, despite general recommendations usually favoring the latter.

Clinical analysis: The Staphylococcus aureus challenge

The results of this study mark a departure from conventional recommendations. While guidelines systematically favour mitral valve repair to limit the risk of infection, the data reported here suggest a different reality for S. aureus endocarditis. With a two-year mortality rate of 57% for the repair group versus 32% for the replacement group (p = 0.02), the virulence of this pathogen appears to neutralise the usual benefits of valve preservation.

The findings are particularly striking regarding event-free survival: only 29% in the repair group compared to 59% in the replacement group at two years (p < 0.01). The persistence or recurrence of infection in three patients in the repair group (compared to zero in the replacement group) suggests that radical excision enabled by valve replacement may be more decisive than the preservation of the subvalvular apparatus when facing such an invasive bacterium.

Limits and perspective

This study, although rigorous in its statistical analysis (Inverse Probability of Treatment Weighting - IPTW), is based on a modest sample of 44 patients operated over a 10-year period. The choice of surgical strategy remained at the surgeon's discretion, which may induce selection bias despite the adjustment. Furthermore, the study was limited to methicillin-susceptible Staphylococcus aureus (MSSA), excluding resistant strains (MRSA), which limits generalisability to all cases of staphylococcal infections.

Summary of results

This study, conducted on 44 patients (23 repairs vs 21 replacements), reveals that in subjects with S. aureus (MSSA) endocarditis, valve replacement outperforms repair. Weighted data show significantly higher two-year mortality for repair (57% vs 32%, p = 0.02) and markedly lower event-free survival (29% vs 59%, p < 0.01), primarily due to a more pronounced recurrence rate.

In concrete terms, for the practitioner:

• Re-evaluate the dogma of systematic repair: while general recommendations favor repair in mitral endocarditis, the virulence of S. aureus seems to be an exception; replacement offers better medium-term safety here.
• Priority to radical debridement: as repair failure is linked to recurrence, prioritize replacement if complete excision of infected tissues compromises the stability of a complex plasty.
• Increased post-operative surveillance: for any patient who has undergone repair under MSSA, strengthen echocardiographic and clinical follow-up during the first two years to detect early infectious relapse.

Technical lexicon of the study

Modified Duke Criteria: Standardised clinical, microbiological, and echocardiographic classification system used to establish the definitive diagnosis of infectious endocarditis.

Inverse Propensity Treatment Weighting (IPTW): Statistical method of weighting by the inverse of the propensity score used here to adjust for confounding factors and balance baseline characteristics between the repair and replacement groups.

MSSA (Methicillin-sensitive Staphylococcus aureus): Specific bacterial strain identified in the 44 patients of the cohort, characterized by high virulence and a high risk of intraoperative complications.

Patch plastie: Valve reconstruction technique used in the repair group to close perforations or tissue loss after complete resection of infected tissues.

Polyvidone and Vancomycin: Topical disinfection agents systematically applied to the residual valvular tissue after debridement of vegetations to minimize the risk of local bacterial persistence.

Event-free survival: Composite endpoint evaluating the absence of death, recurrence of endocarditis, or mitral valve reoperation during the two-year follow-up period.

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