Infective Endocarditis - A Comprehensive Overview

Definition

• Robbins & Kumar Pathologic Basis of Disease
• Goldman-Cecil Medicine

Classification

Epidemiology

• Incidence: approximately 13.8 per 100,000 (range 5.7-35.8 per 100,000)
• In the United States: 10,000-20,000 new cases per year; approximately 1 case per 1,000 hospital admissions
• In-hospital mortality: up to 22%; 5-year mortality: up to 40%
• Deaths due to IE have increased 131% since 1990 (an estimated 66,322 deaths globally as of 2019)
• The opioid epidemic has dramatically increased IV drug-associated IE, particularly S. aureus right-sided disease
• Contemporary IE is most often an acute disease caused by S. aureus, involving the mitral valve (41.1%) and aortic valve (37.6%)
• Common complications: stroke (16.9%), embolization (22.6%), heart failure (32.3%), intracardiac abscess (14.4%); 48.2% require surgery
• Fuster and Hurst's The Heart, 15th Edition
• Braunwald's Heart Disease

Predisposing Conditions

• Mitral valve prolapse (especially with regurgitation)
• Degenerative valvular disease / myxomatous degeneration
• Injection drug use
• Congenital heart disease (e.g., VSD, bicuspid aortic valve)
• Previous IE
• Prosthetic heart valves
• Chronic hemodialysis / intravascular devices

• Rheumatic heart disease (historically the most common, now declining in developed countries)
• Idiopathic hypertrophic subaortic stenosis
• Coarctation of the aorta
• Goldman-Cecil Medicine

Microbiology

• Robbins & Kumar
• Washington Manual of Medical Therapeutics

Pathogenesis

1. Endothelial damage - turbulent blood flow (from valvular abnormalities, jets of regurgitation, congenital defects) disrupts the endothelium
2. Non-bacterial thrombotic endocarditis (NBTE) - sterile platelet-fibrin thrombus forms on damaged endothelium
3. Bacteremia - organisms enter the bloodstream (dental procedures, skin breaks, IV drug use, GI/GU procedures, gut/oral/skin epithelial barriers)
4. Colonization - organisms adhere to NBTE via surface adhesins (e.g., fibronectin-binding proteins in S. aureus)
5. Vegetation formation - organisms proliferate, recruit more fibrin and platelets, and embed deeply in a protected nidus inaccessible to host defenses and poorly penetrated by antibiotics
6. Local destruction and embolization - vegetations erode valve leaflets, chordae, annulus; fragments embolize systemically

• Robbins, Cotran & Kumar Pathologic Basis of Disease

Morphology / Pathology

• Most common sites: aortic and mitral valves (left-sided); right-sided (tricuspid, pulmonic) in IV drug users
• Vegetations can be single or multiple; may involve more than one valve
• Can erode into the myocardium causing ring abscess (perivalvular abscess)
• Embolization of infected fragments causes septic infarcts or mycotic aneurysms
• Subacute IE: less valvular destruction; granulation tissue may form
• Acute IE: neutrophilic infiltration, necrosis, greater destruction

Clinical Features

Symptoms

• Fever (most common, >90%) - may be absent in elderly, immunocompromised, or with prior antibiotics
• Constitutional: fatigue, malaise, night sweats, weight loss, arthralgias
• Symptoms of heart failure (dyspnea, orthopnea) if significant valve destruction
• Back/musculoskeletal pain
• Neurologic symptoms (stroke, confusion, seizures)

Signs

• New or changing heart murmur (new regurgitant murmur in most cases of left-sided IE)
• Signs of heart failure

• Fever, cough, pleuritic chest pain, hemoptysis
• Multiple pulmonary opacities (septic pulmonary emboli) on CXR/CT
• Right-sided murmur varying with respiration
• Pyuria (22%) and hematuria (35%) from immune complex glomerulonephritis
• Tintinalli's Emergency Medicine
• Fitzpatrick's Dermatology

Complications

Diagnosis

Modified Duke Criteria (Updated 2023 - Duke-ISCVID)

Major Criteria

• ≥2 separate blood culture sets positive for typical organisms: S. aureus, S. lugdunensis, E. faecalis, all streptococcal species (except S. pneumoniae and S. pyogenes), Granulicatella, Abiotrophia, Gemella, HACEK organisms
• ≥2 blood cultures drawn >12 hours apart, OR ≥3 of ≥4 separate cultures (first and last drawn ≥1 hour apart)
• Single positive blood culture for Coxiella burnetii (Q fever) OR anti-phase I IgG titer ≥1:800

• Echocardiographic: oscillating intracardiac mass on valve or supporting structure in path of regurgitant jet, OR abscess, OR new partial dehiscence of prosthetic valve
• New valvular regurgitation (change in pre-existing murmur is NOT sufficient)
• FDG-PET/CT or radiolabeled leukocyte SPECT/CT - equivalent to echo (new in 2023)

Minor Criteria

1. Predisposing heart condition or IV drug use
2. Fever ≥38°C
3. Vascular phenomena: arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial/conjunctival hemorrhage, Janeway lesions
4. Immunologic phenomena: glomerulonephritis, Osler nodes, Roth spots, rheumatoid factor
5. Microbiologic evidence: positive blood culture not meeting major criteria OR serologic evidence of active infection with organism consistent with IE

• Braunwald's Heart Disease
• Harrison's Principles of Internal Medicine, 22nd Ed. (2025)

Blood Cultures

• Collect 3 sets from separate venipuncture sites, ideally before antibiotics
• Each set: paired aerobic and anaerobic bottles (10 mL per bottle)
• At least 1 hour between first and last collection
• If negative at 48-72 hours, obtain 2-3 more sets and consult microbiology for special culture techniques (PCR, serology for Coxiella, Bartonella)
• Prior antibiotics are the #1 cause of culture-negative endocarditis

Echocardiography

• Braunwald's Heart Disease

Other Investigations

• CBC: leukocytosis (acute IE), normochromic normocytic anemia (subacute)
• Elevated ESR, CRP, rheumatoid factor, circulating immune complexes
• Urinalysis: hematuria, proteinuria, red cell casts (glomerulonephritis)
• Creatinine (renal involvement or antibiotic nephrotoxicity monitoring)
• ECG: new PR prolongation or heart block suggests perivalvular extension
• CXR / CT chest: septic emboli in right-sided IE
• Brain MRI: cerebral emboli, abscess, mycotic aneurysm
• CT angiography: mycotic aneurysm screening

Treatment

General Principles

• Bactericidal drugs are required (not bacteriostatic) - organisms are protected deep within vegetations with high bacterial burden (10⁸-10¹⁰ CFU/g)
• Prolonged parenteral courses needed (4-6 weeks for most; 2 weeks in selected uncomplicated cases)
• Multidisciplinary team: Infectious disease, cardiology, cardiac surgery (+ neurology if neurologic complications)
• All patients should be managed inpatient at a center with IE expertise

Antibiotic Regimens by Organism

Viridans Group Streptococci / S. gallolyticus (penicillin-susceptible, MIC ≤0.12 μg/mL)

• Penicillin G 12-18 million units/day IV × 4 weeks, OR
• Ceftriaxone 2g IV once daily × 4 weeks (equivalent; preferred for outpatient completion), OR
• Shortened 2-week regimen: Ceftriaxone + Gentamicin (for uncomplicated native valve IE in appropriate patients)
• Vancomycin × 4 weeks reserved for true penicillin allergy

Relatively resistant streptococci (MIC 0.12-0.5 μg/mL)

• Penicillin G 4 million units IV q4h × 4 weeks + Gentamicin × 2 weeks (synergy), OR
• Ceftriaxone + Gentamicin × 2 weeks
• Vancomycin for penicillin allergy

Staphylococcus aureus (native valve)

• MSSA: Nafcillin or oxacillin 2g IV q4h × 6 weeks (+ optional short-course gentamicin in first 3-5 days - no longer routinely recommended due to renal toxicity)
• MRSA or penicillin-allergic: Vancomycin 30-45 mg/kg/day IV in 2-3 divided doses × 6 weeks; OR Daptomycin 8-10 mg/kg/day IV (not for pulmonary involvement)
• TEE mandatory; early surgery evaluation

Staphylococcus aureus (prosthetic valve)

• MSSA: Nafcillin + Rifampin 300mg orally q8h × ≥6 weeks + Gentamicin × 2 weeks
• MRSA: Vancomycin + Rifampin × ≥6 weeks + Gentamicin × 2 weeks

Enterococci

• Ampicillin-sensitive: Ampicillin + Gentamicin × 4-6 weeks, OR Ampicillin + Ceftriaxone (double β-lactam synergy; preferred for aminoglycoside-resistant strains)
• Vancomycin-resistant enterococci (VRE): Linezolid or Daptomycin-based regimens
• Enterococci require synergistic combination therapy

HACEK organisms

• Ceftriaxone 2g IV once daily × 4 weeks (preferred)
• Ampicillin-sulbactam is an alternative

Culture-negative IE

• Broad-spectrum: Ampicillin-sulbactam + Gentamicin, with coverage tailored based on clinical context and serology
• Harrison's Principles of Internal Medicine 22e (2025)
• Washington Manual of Medical Therapeutics
• Jawetz, Melnick & Adelberg's Medical Microbiology

Prophylaxis (AHA 2021 Update)

• Prosthetic cardiac valve (including transcatheter-implanted)
• Previous IE
• Unrepaired cyanotic congenital heart disease
• Repaired congenital heart defect with prosthetic material (within 6 months)
• Repaired CHD with residual defect at or adjacent to prosthetic patch
• Cardiac transplant recipients with valvulopathy
• Ventricular assist devices and implantable hearts (NEW in 2021)

• Amoxicillin 2g orally 30-60 min before procedure (preferred)
• True penicillin allergy: Doxycycline 100mg orally (new 2021 addition; clindamycin REMOVED due to C. difficile risk)
• Cephalexin 2g, Azithromycin 500mg, or Clarithromycin 500mg are alternatives

• Braunwald's Heart Disease

Surgical Treatment

Indications (ACC/AHA 2021 Guidelines - Class I / Strong)

Class IIa / Reasonable

• Recurrent emboli + persistent vegetations despite antibiotics → Early surgery

Class IIb / May Consider

• Native left-sided IE with mobile vegetations >10 mm (with or without embolic phenomenon)
• IE with surgical indication + stroke (no intracranial hemorrhage, no severe neurological damage) → surgery without delay
• IE + major ischemic stroke + extensive damage or ICH + hemodynamically stable → delay surgery ≥4 weeks

Emergent surgery (same day)

• Valve dysfunction with pulmonary edema or cardiogenic shock
• Acute aortic regurgitation with pre-closure of mitral valve
• Sinus of Valsalva abscess ruptured into right heart
• Braunwald's Heart Disease
• Harrison's Principles of Internal Medicine 22e (2025)

Special Scenarios

Prosthetic Valve Endocarditis (PVE)

• Early PVE (within 1-2 months of surgery): usually S. aureus, S. epidermidis, gram-negatives, fungi - from perioperative contamination
• Late PVE (>12 months): similar to native valve IE - streptococci, S. aureus, enterococci
• TEE is mandatory (TTE has poor sensitivity with prostheses)
• Requires longer antibiotic courses (≥6 weeks); rifampin added for staphylococcal PVE
• Higher surgical rates than native valve IE

IV Drug Users (IVDU)

• Predominantly right-sided (tricuspid valve 55-94% of cases)
• Organism: S. aureus in >50%
• Chest X-ray shows multiple bilateral pulmonary opacities (septic emboli)
• Tricuspid valve IE: often curable with antibiotics alone (right-sided good prognosis without surgery)
• Recurrence is common with continued drug use; addiction medicine consultation is required before repeat surgical intervention

CIED-IE (Cardiac Implantable Electronic Device)

• Pacemakers, ICDs
• Complete system removal (generator + all leads) is Class I indication
• Medical therapy alone rarely curative

Culture-Negative IE

• ~10% of cases
• Causes: prior antibiotics (most common), fastidious organisms (Coxiella, Bartonella, Brucella, Tropheryma whipplei, HACEK)
• Workup: extended cultures, Coxiella serology, Bartonella serology/PCR, excised valve tissue 16S rRNA PCR, FDG-PET/CT

Prognosis and Outcome

• S. aureus infection
• Perivalvular abscess
• Prosthetic valve involvement
• Heart failure
• Neurologic complications
• Left-sided disease
• Fungal endocarditis

• Fuster and Hurst's The Heart, 15th Edition
• Harrison's Principles of Internal Medicine 22e (2025)

• Robbins, Cotran & Kumar - Pathologic Basis of Disease
• Braunwald's Heart Disease, 2-Vol Set (Baddour, Anavekar et al.)
• Harrison's Principles of Internal Medicine, 22nd Ed. (2025)
• Fuster and Hurst's The Heart, 15th Edition
• Goldman-Cecil Medicine
• Washington Manual of Medical Therapeutics
• AHA Scientific Statement 2021 (Prevention); AHA 2015 (Diagnosis and Management); ACC/AHA 2021 Valvular Heart Disease Guidelines