Residency · Residency · Cardiology

Infective Endocarditis

Epidemiology and Risk Factors

Predisposing Conditions

Prosthetic valves carry the highest risk for infective endocarditis, with an annual incidence of 0.3 to 1.2%, and the distinction between early prosthetic valve endocarditis occurring within 60 days and late disease beyond 60 days has important microbiologic and prognostic implications. Prior endocarditis confers a 5 to 10% recurrence risk. Structural heart disease including bicuspid aortic valve, mitral valve prolapse with regurgitation, rheumatic heart disease, and congenital heart disease, particularly unrepaired cyanotic lesions, repaired defects with prosthetic material within six months, and residual defects adjacent to prosthetic patches, all predispose to infection. Injection drug use predominantly causes right-sided endocarditis, with the tricuspid valve affected more commonly than the pulmonic valve, and Staphylococcus aureus as the predominant pathogen. The incidence of injection drug use-related endocarditis continues to increase in parallel with the opioid epidemic. Healthcare-associated endocarditis from intravascular catheters, hemodialysis, and pacemaker or ICD leads now accounts for 25 to 30% of all IE cases. Cardiac implantable electronic device-related endocarditis involves lead vegetations with staphylococcal species predominating.

Microbiology

Staphylococcus aureus is the most common overall organism, accounting for 30 to 40% of cases, with an acute and virulent presentation affecting both native and prosthetic valves, including both methicillin-sensitive and methicillin-resistant strains. Viridans group streptococci, including S. mitis, S. sanguinis, and S. mutans, cause 20 to 25% of cases and typically present with a subacute course originating from dental sources, with high penicillin sensitivity. Enterococcus, with E. faecalis more common than E. faecium, accounts for 10 to 15% and originates from gastrointestinal or genitourinary sources, presenting treatment challenges due to intrinsic resistance patterns and affecting predominantly older patients. Coagulase-negative staphylococci, particularly S. epidermidis, are the leading cause of early prosthetic valve endocarditis. HACEK organisms, encompassing Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, and Kingella, account for 3 to 5% and are slow-growing, potentially causing initially culture-negative results but generally responding to ceftriaxone. Streptococcus gallolyticus, formerly S. bovis, carries a well-established association with colorectal malignancy, mandating colonoscopy in every case. Fungal endocarditis from Candida or Aspergillus occurs in prosthetic valves, injection drug users, and immunocompromised patients, producing large vegetations with poor prognosis and typically requiring surgical intervention. Culture-negative endocarditis accounts for 5 to 15% of cases, most commonly resulting from prior antibiotic use, with fastidious organisms including Coxiella burnetii causing Q fever, Bartonella, Tropheryma whipplei, and Brucella requiring serologies and PCR of valve tissue for identification.

Diagnosis

Modified Duke Criteria (2023 Update)

The 2023 update to the Duke criteria defines definite infective endocarditis as the presence of two major criteria, or one major plus three minor criteria, or five minor criteria. Possible infective endocarditis requires one major plus one minor criterion, or three minor criteria.

Major Criteria

Blood culture criteria require typical organisms in two or more separate cultures, including S. aureus, viridans streptococci, S. gallolyticus, HACEK organisms, or Enterococcus without a primary focus. Alternatively, persistently positive cultures are defined as two or more cultures drawn more than 12 hours apart, or three of three or a majority of four or more separate cultures with the first and last drawn more than one hour apart, or a single positive Coxiella burnetii culture or phase I IgG exceeding 1:800. The imaging criterion in the 2023 update has been broadened beyond echocardiography to include FDG-PET/CT showing abnormal metabolic activity at a valve, prosthesis, or lead, cardiac CT demonstrating abscess, pseudoaneurysm, or vegetation, and new paravalvular leak identified on CT for prosthetic valves.

Minor Criteria

Minor criteria encompass a predisposing condition or injection drug use, fever of 38.0 degrees Celsius or greater, vascular phenomena including arterial emboli, septic pulmonary infarcts, mycotic aneurysm, Janeway lesions, and conjunctival hemorrhage, immunologic phenomena including Osler nodes, Roth spots, glomerulonephritis, and positive rheumatoid factor, and microbiologic evidence not meeting major criteria.

Echocardiography

Transthoracic echocardiography is the initial study, with sensitivity of 50 to 60% for native valve vegetations and lower sensitivity for prosthetic valves. Transesophageal echocardiography offers substantially improved sensitivity of 85 to 95% for native valve and 85 to 90% for prosthetic valve vegetations and is required when TTE is negative or non-diagnostic with persisting clinical suspicion, with prosthetic valves, with cardiac implantable electronic devices, or when perivalvular complications are suspected. Repeat TEE should be performed in 5 to 7 days if initially negative when clinical suspicion remains high. Echocardiographic findings include vegetations appearing as oscillating masses on valve leaflets or supporting structures, abscesses presenting as thickened heterogeneous perivalvular regions, pseudoaneurysms as pulsatile perivalvular spaces, fistulae, and prosthetic dehiscence with paravalvular regurgitation. Vegetation size is clinically important, with lesions of 10 mm or greater associated with higher embolic risk and those of 15 mm or greater, especially on the anterior mitral leaflet, carrying the highest risk.

Advanced Imaging

Cardiac CT complements TEE for evaluating perivalvular abscess, pseudoaneurysm, and fistula, offering better spatial resolution for prosthetic valve complications. FDG-PET/CT, now incorporated as a major Duke criterion in the 2023 update, detects elevated metabolic activity around prosthetic valves or leads and is most useful for prosthetic valve and CIED endocarditis, requiring a myocardial suppression protocol with a high-fat, low-carbohydrate diet, and achieving sensitivity of approximately 73% and specificity of approximately 80% for PVE. Cerebral MRI identifies subclinical embolic events in up to 80% of left-sided IE cases and can change management by prompting delay of surgery if a large hemorrhagic stroke is discovered. Whole-body CT or PET/CT identifies metastatic infections including splenic abscess, vertebral osteomyelitis, renal infarcts, and mycotic aneurysms.

<image> A detailed diagnostic flowchart for suspected infective endocarditis. Start with "Clinical Suspicion of IE: new murmur, fever, bacteremia, embolic events, IDU." Step 1: "Obtain >= 3 sets of blood cultures from separate venipuncture sites before antibiotics; CBC, CRP/ESR, BMP, UA." Step 2: "Transthoracic Echocardiography." Two branches: "TTE positive (vegetation, abscess, new regurgitation)" → "Apply Modified Duke Criteria; TEE for better characterization and surgical planning." "TTE negative or non-diagnostic" → "TEE (mandatory if: prosthetic valve, CIED, high clinical suspicion, prior positive TTE with possible complications)." If TEE negative: "Repeat TEE in 5-7 days if suspicion persists; consider PET/CT (especially for prosthetic valve/CIED), cardiac CT." If Duke criteria met: "Definite IE → initiate targeted antibiotic therapy, surgical consultation, embolism screening (brain MRI, abdominal CT)." Sidebar: "Culture-negative workup: Coxiella serology, Bartonella serology, fungal cultures, Brucella serology, T. whipplei PCR." Use red for urgent pathways, blue for diagnostic steps, green for treatment. </image>

Antibiotic Therapy

Native Valve Endocarditis (NVE)

Staphylococcus aureus

For methicillin-sensitive S. aureus, treatment consists of nafcillin or oxacillin 2 grams IV every 4 hours for 6 weeks, or cefazolin 2 grams IV every 8 hours, which is better tolerated with similar efficacy per POET trial subgroup data. For methicillin-resistant S. aureus, vancomycin at 15 to 20 mg/kg IV every 8 to 12 hours, targeting a trough of 15 to 20 or AUC/MIC of 400 to 600, is administered for 6 weeks. Daptomycin at 8 to 10 mg/kg IV daily serves as an alternative, provided there is no concurrent pneumonia since daptomycin is inactivated by surfactant. For right-sided uncomplicated MSSA NVE in injection drug users, a shortened course of nafcillin plus gentamicin for 2 weeks may be sufficient, and oral switch is possible per the POET trial.

Viridans Group Streptococci

For penicillin-susceptible strains with MIC of 0.12 or below, penicillin G at 12 to 18 million units IV continuously or every 4 hours for 4 weeks, or ceftriaxone 2 grams IV daily for 4 weeks, is standard. A short-course option of ceftriaxone plus gentamicin for 2 weeks is available. For relatively resistant strains with MIC between 0.12 and 0.5, penicillin plus gentamicin for 4 weeks or ceftriaxone for 4 weeks is appropriate. Vancomycin for 4 weeks is the alternative for penicillin-allergic patients.

Enterococcus

For ampicillin-susceptible enterococcal endocarditis, ampicillin 2 grams IV every 4 hours combined with ceftriaxone 2 grams IV every 12 hours provides synergistic therapy while avoiding aminoglycoside nephrotoxicity, administered for 6 weeks. Alternatively, ampicillin with gentamicin for 4 to 6 weeks may be used with renal function and drug level monitoring. For ampicillin-resistant or VRE strains, daptomycin at 8 to 10 mg/kg IV with or without ampicillin for 6 weeks is appropriate, with linezolid 600 mg IV or PO every 12 hours as an alternative requiring monitoring for myelosuppression.

Prosthetic Valve Endocarditis (PVE)

Prosthetic valve endocarditis from MSSA is treated with nafcillin or oxacillin combined with rifampin 300 mg PO every 8 hours for a minimum of 6 weeks, with gentamicin added for the first 2 weeks. MRSA PVE substitutes vancomycin for the antistaphylococcal penicillin. Rifampin is specifically added for prosthetic valve infections because of its anti-biofilm activity, and it should be started after 3 to 5 days of effective bactericidal therapy to reduce the risk of resistance development. Rifampin must never be used as monotherapy. Streptococcal and S. gallolyticus PVE are treated with the same agents as NVE but with courses extended to a minimum of 6 weeks.

OPAT and Oral Step-Down

The POET trial established that after a minimum of 10 days of IV therapy with demonstrated clinical stability, oral switch to a combination regimen is non-inferior to continued IV therapy for left-sided NVE caused by S. aureus, streptococci, E. faecalis, or coagulase-negative staphylococci. The trial excluded prosthetic valve endocarditis. Oral regimens are tailored to the organism and susceptibilities, with examples including high-dose amoxicillin plus rifampin, dicloxacillin plus rifampin, linezolid plus rifampin, and moxifloxacin plus rifampin. Requirements for oral switch include being afebrile for at least 48 hours, declining inflammatory markers, negative repeat blood cultures, absence of abscess or other surgical indication, adequate gastrointestinal absorption, and a reliable patient.

Surgical Indications

Class I (Strong) Indications for Early Surgery

Early surgery is strongly indicated for heart failure from severe valvular dysfunction causing pulmonary edema or cardiogenic shock from aortic or mitral regurgitation, perivalvular abscess, fistula, or pseudoaneurysm, persistent bacteremia beyond 5 to 7 days despite appropriate antibiotics and source control, fungal or highly resistant organisms that typically require surgical debridement, and prosthetic valve endocarditis with dehiscence, obstruction, or heart failure.

Class IIa (Reasonable) Indications

Reasonable indications for surgery include recurrent emboli despite appropriate antibiotics, large vegetations exceeding 10 mm with embolic events, large vegetations exceeding 10 mm on the anterior mitral leaflet even without prior events due to the highest embolic risk profile, mobile vegetations exceeding 15 mm, and early prosthetic valve endocarditis within 60 days, which is often staphylococcal with high mortality on medical therapy alone.

Timing of Surgery

Emergent surgery within 24 hours is indicated for refractory pulmonary edema or cardiogenic shock from acute severe aortic or mitral regurgitation. Urgent surgery within days addresses uncontrolled infection, abscess, and high embolic risk. Elective surgery during hospitalization after 1 to 2 weeks of antibiotics applies when large vegetations are the sole surgical indication. Regarding cerebrovascular events and surgical timing, ischemic stroke without hemorrhage permits surgery to proceed after 2 to 4 days, while hemorrhagic stroke or large ischemic stroke ideally requires a delay of 4 weeks. Cerebral MRI guides this decision, and neurosurgical consultation is essential.

Specific Surgical Considerations

Valve repair is preferred over replacement when feasible, especially for the mitral valve, offering a lower reinfection rate and avoidance of anticoagulation. Aortic root abscess requires aortic root replacement with homograft or bioprosthetic conduit and radical debridement of infected tissue. For tricuspid valve endocarditis, vegetation debridement or valvectomy without replacement may serve as a bridge in injection drug users with concern for reinfection, with bioprosthetic tricuspid valve replacement performed if insufficient tissue remains for repair.

CIED-Related Endocarditis

Diagnosis

Blood cultures and TTE/TEE evaluate for lead vegetations and valve involvement. FDG-PET/CT is particularly useful for generator pocket infection and occult lead infection. Lead tip cultures obtained after extraction guide the duration of antibiotic therapy.

Management

Complete device and lead extraction is mandatory for definite CIED endocarditis. Percutaneous extraction using laser or mechanical rotating dilator sheaths is performed at experienced centers, with surgical extraction reserved for large vegetations exceeding 2 cm or failed percutaneous attempts. Antibiotic therapy extends 4 to 6 weeks for lead endocarditis with valve involvement and 2 weeks for isolated bacteremia with pocket infection. Reimplantation on the contralateral side is performed after a minimum of 72 hours of negative blood cultures, with temporary pacing as a bridge if the patient is pacemaker-dependent.

<image> An anatomical illustration showing common complications of infective endocarditis. Central image: a heart with aortic valve vegetation (irregular, lobulated mass on the ventricular side of the aortic cusp) and a perivalvular abscess (dark cavity in the aortic root near the intervalvular fibrosa, with label showing proximity to the His bundle/conduction system explaining new heart block). Radiating outward from the heart, show embolic complications in four panels: (1) Brain: ischemic stroke from septic embolus with hemorrhagic conversion shown in cross-section, mycotic aneurysm of MCA with label. (2) Spleen: splenic infarct (wedge-shaped hypoattenuated region) and abscess. (3) Kidney: multiple renal infarcts and immune complex glomerulonephritis (enlarged kidney with granular surface). (4) Skin: Janeway lesions on palm (painless erythematous macules) and Osler nodes on fingertips (painful, raised). All panels connected to central heart by dotted arrows showing embolic pathways. Label vegetation size as 15mm for reference. </image>

Prophylaxis

Indications (2021 AHA/ACC Update)

Endocarditis prophylaxis is recommended for patients with prosthetic cardiac valves including mechanical, bioprosthetic, or transcatheter valves or prosthetic material used for valve repair, prior endocarditis, unrepaired cyanotic congenital heart disease, repaired congenital heart disease with prosthetic material within the first 6 months, and cardiac transplant recipients with valve regurgitation due to structural abnormality. Notably, mitral valve prolapse, bicuspid aortic valve, and rheumatic heart disease are not indications for prophylaxis under current guidelines.

Regimen

For dental procedures involving gingival manipulation or the periapical region, amoxicillin 2 grams orally as a single dose 30 to 60 minutes before the procedure is standard. Penicillin-allergic alternatives include azithromycin 500 mg, clindamycin 600 mg, or cephalexin 2 grams, with cephalosporins avoided if there is a history of penicillin anaphylaxis. For patients unable to take oral medications, ampicillin 2 grams IV/IM or cefazolin 1 gram IV/IM is appropriate. Prophylaxis is also recommended for high-risk patients undergoing respiratory tract procedures through infected tissue and gastrointestinal or genitourinary procedures through infected tissue.

Key Clinical Pearls

• Obtain >= 3 sets of blood cultures from SEPARATE venipuncture sites before starting antibiotics -- this is the single most important diagnostic step; never draw cultures from lines
• S. aureus bacteremia is NEVER a contaminant -- always investigate with echocardiography (TEE preferred) and complete a minimum 2-week course from first negative culture even without endocarditis
• S. gallolyticus (bovis) endocarditis mandates colonoscopy to screen for colorectal malignancy -- this association is so strong that it should never be omitted
• New conduction disease (PR prolongation, new BBB) during aortic valve endocarditis strongly suggests perivalvular abscess extending toward the conduction system -- urgent surgical consultation
• The threshold for surgical referral in IE should be low -- mortality of medically treated complicated IE exceeds 40%; early surgery (within 48 hours) for appropriate indications improves survival
• Daptomycin must NOT be used for pneumonia (inactivated by surfactant) but is an excellent alternative for left-sided S. aureus endocarditis when vancomycin is not tolerated or MRSA has MIC >= 2

References

• Fowler VG, et al. The 2023 Duke-ISCVID Criteria for Infective Endocarditis: Updating the Modified Duke Criteria. Clin Infect Dis. 2023;77:518-526.
• Otto CM, et al. 2020 ACC/AHA Guideline for the Management of Patients with Valvular Heart Disease. Circulation. 2021;143:e72-e227.
• Baddour LM, et al. Infective Endocarditis in Adults: Diagnosis, Antimicrobial Therapy, and Management of Complications: AHA Scientific Statement. Circulation. 2015;132:1435-1486.
• Iversen K, et al. Partial Oral versus Intravenous Antibiotic Treatment of Endocarditis (POET). NEJM. 2019;380:415-424.
• Habib G, et al. 2015 ESC Guidelines for the Management of Infective Endocarditis. Eur Heart J. 2015;36:3075-3128.

Read this lecture as Markdown