What is the next course of action for a patient with a history of aortic valve replacement, presenting with infective endocarditis, a 2.5cm vegetation on the aortic valve, and persistent Methicillin-Sensitive Staphylococcus Aureus (MSSA) bacteremia despite 14 days of antibiotic therapy with Gentamicin and two other antibiotics?

Urgent Cardiac Surgery Referral

This patient requires immediate referral to the cardiac surgery team for surgical intervention. 1, 2

Rationale for Surgical Intervention

This case presents multiple Class I and Class IIa indications for surgery in prosthetic valve endocarditis:

Absolute Indications Present

• Persistent bacteremia despite appropriate antibiotic therapy is a Class IIa indication for surgery in prosthetic valve endocarditis, defined as reasonable surgical intervention 1, 2

• Large vegetation (2.5 cm) on a prosthetic valve with persistent infection represents high-risk anatomy that portends poor outcomes with medical management alone 1

• Prosthetic valve endocarditis itself mandates consultation with cardiac surgery as a Class I recommendation, regardless of other factors 1, 2

Why Medical Management Has Failed

The persistence of MSSA bacteremia after 14 days of appropriate antibiotics (including gentamicin, which is guideline-concordant for staphylococcal prosthetic valve endocarditis) indicates:

• Treatment failure requiring source control through surgical debridement 3

• High likelihood of perivalvular extension (abscess, dehiscence, or fistula formation) that cannot be adequately treated with antibiotics alone 1

• The ACC/AHA guidelines explicitly state that prosthetic valve endocarditis caused by S. aureus is "almost always a surgical disease" 2

Why Other Options Are Inappropriate

Adding Vancomycin (Option A)

• Vancomycin is explicitly inferior to beta-lactams for MSSA and should only be used when beta-lactams cannot be administered 4
• The patient is already on appropriate antibiotics including gentamicin; adding vancomycin would not address the fundamental problem of inadequate source control 4

Adding Daptomycin (Option B)

• While daptomycin can be used for persistent MSSA bacteremia, the FDA label specifically warns about "persisting or relapsing S. aureus bacteremia/endocarditis" and states that "appropriate surgical intervention and/or consideration of a change in antibacterial regimen may be required" 3
• Changing antibiotics without addressing the infected prosthetic valve will not cure this infection 3
• Daptomycin may have a role post-operatively, but surgery is the definitive treatment needed 5

Switching to Oral Linezolid (Option D)

• Oral therapy is completely inappropriate for active prosthetic valve endocarditis with persistent bacteremia 1, 4
• This represents de-escalation when escalation to surgery is required 2

Critical Clinical Pearls

• Persistent bacteremia beyond 48-72 hours in prosthetic valve endocarditis indicates either inadequate source control or development of complications (abscess, dehiscence) 4, 3

• The 2.5 cm vegetation size alone approaches the threshold where surgery may be considered even without persistent bacteremia (>10mm vegetations are Class IIb indication for native valve, and prosthetic valves have lower thresholds) 1, 2

• TEE should be repeated urgently if not recently performed, as perivalvular abscess may have developed and would be an additional Class I indication for surgery 1

• The combination of prosthetic valve + S. aureus + persistent bacteremia + large vegetation creates a scenario where mortality with medical management alone approaches 50-80% 6

Timing of Surgery

This patient requires urgent surgery within days, not emergency surgery within 24 hours, unless hemodynamic instability or heart failure develops 2

The answer is c. Refer cardiac surgery team.