Infective Endocarditis (IE)

A 45-year-old man presents to the emergency department with a 1-week history of fever, chills, pleuritic chest pain, and shortness of breath. He reports fatigue and decreased appetite. His medical history is significant for intravenous drug use. On examination, his temperature is 39°C, pulse is 110/min, and blood pressure is 100/60 mm Hg. Cardiac auscultation reveals a holosystolic murmur best heard at the left lower sternal border that increases with inspiration. Multiple painless erythematous lesions on the palms and linear hemorrhages under the fingernails are noted. Laboratory studies show leukocytosis. Blood cultures grow Staphylococcus aureus. Chest imaging demonstrates multiple nodular infiltrates consistent with septic pulmonary emboli. Transesophageal echocardiography reveals a mobile vegetation on the tricuspid valve. Diagnosis?

Diagnosis is acute right-sided infective endocarditis, complicated by septic pulmonary emboli.

1. Definition

Infective endocarditis is a microbial infection of the endocardial surface, most commonly affecting the cardiac valves, characterized by vegetations composed of fibrin, platelets, and microorganisms, leading to valvular destruction and systemic embolization.

2. Epidemiology and Risk Factors

2.1 Epidemiology

1. Incidence increasing due to prosthetic valves, cardiac devices, and aging population
2. Mortality remains high (15–30%) despite treatment
3. Left-sided IE more common overall; right-sided IE common in IVDU

2.2 Risk Factors

Structural Cardiac Abnormalities

1. Prosthetic valves (highest risk)
2. Congenital heart disease (especially cyanotic)
3. Degenerative valvular disease
4. Prior infective endocarditis

Exposure-Related Risks

1. Intravenous drug use
2. Poor dentition / dental procedures
3. Indwelling vascular catheters
4. Cardiac implantable devices (pacemakers, ICDs)

Host Factors

1. Age >60 years
2. Diabetes mellitus
3. Immunosuppression
4. Chronic kidney disease / hemodialysis

Clinical heuristic: Endothelial injury + bacteremia + time → IE

3. Pathophysiology

3.1 Core Mechanism

1. Endothelial injury → turbulent flow or prosthetic surface
2. Formation of NBTE (platelet-fibrin nidus)
3. Transient bacteremia (oral, skin, GI/GU)
4. Microbial adhesion (adhesins, biofilm formation)
5. Formation of infected vegetations
6. Continuous bacteremia + immune activation

3.2 Key Pathological Features

1. Vegetations are avascular → poor antibiotic penetration
2. Biofilm formation (prosthetic valves) → antibiotic resistance
3. Valve destruction → regurgitation and heart failure

3.3 Systemic Effects

1. Septic emboli → infarcts (brain, spleen, kidney, lungs)
2. Immune complex deposition → glomerulonephritis, Osler nodes, Roth spots
3. Mycotic aneurysm formation

3.4 Special Forms

1. Marantic (NBTE) → malignancy, hypercoagulable states
2. Libman–Sacks endocarditis → SLE (sterile vegetations)

4. Microbiology

4.1 Common Organisms

1. Staphylococcus aureus → most common overall, acute IE
2. Viridans streptococci → subacute IE (oral source)
3. Enterococcus faecalis → GI/GU source
4. Coagulase-negative staphylococci → prosthetic valves

4.2 Special Situations

1. IVDU → S. aureus, ± Pseudomonas, Candida
2. Prosthetic valve IE → S. epidermidis, biofilm producers
3. Healthcare-associated IE → MRSA

4.3 Culture-Negative IE

1. Prior antibiotic exposure (most common)
2. Fastidious organisms:
• HACEK group
• Coxiella burnetii (Q fever)
• Bartonella spp.
3. Fungal IE

Important association: Streptococcus gallolyticus → colorectal cancer

4.4 Virulence Concept

1. High virulence (S. aureus) → infects normal valves, rapid destruction
2. Low virulence (Viridans) → requires pre-damaged valve

5. Clinical Features

5.1 Core Triad (often absent)

1. Fever
2. New valvular regurgitation murmur
3. Embolic or immunologic phenomena

5.2 Mechanism-Based Features

1. Infection

• Fever, malaise, weight loss

2. Cardiac Involvement

1. New regurgitant murmur (hallmark)
2. Heart failure (most serious complication)
3. Conduction abnormalities → periannular abscess

3. Embolic Phenomena

1. Left-sided IE → systemic emboli:
• Stroke
• Renal infarct
• Splenic infarct
2. Right-sided IE → septic pulmonary emboli:
• Dyspnea
• Pleuritic chest pain
• Hemoptysis

4. Immune-Mediated

1. Osler nodes (painful)
2. Roth spots
3. Glomerulonephritis

5. Vascular Phenomena

1. Janeway lesions (painless)
2. Splinter hemorrhages

Memory anchor: Janeway = painless (septic) | Osler = painful (immune)

5.3 Special Populations

1. Elderly → subtle, afebrile
2. IVDU → right-sided IE with pulmonary findings

6. Diagnostic Evaluation

6.1 Blood Cultures

1. Obtain 3 sets from separate sites
2. Draw before antibiotics
3. Do not delay antibiotics in unstable patients
4. Repeat until clearance of bacteremia

6.2 Echocardiography

1. TTE → initial
2. TEE (gold standard) → detects:
• Vegetations
• Abscess
• Prosthetic valve involvement

6.3 Diagnostic Criteria (Modified Duke Framework)

Major

1. Positive blood cultures
2. Echo evidence or new regurgitation

Minor

1. Fever
2. Predisposition
3. Vascular phenomena
4. Immunologic phenomena

6.4 Additional Imaging

1. CT/MRI → emboli, abscess
2. PET/CT → prosthetic/device infection

Diagnostic Pitfalls

1. Prior antibiotics → culture-negative IE
2. Negative TTE ≠ exclude IE → perform TEE

7. Key Clinical Insight

Persistent bacteremia + new valvular regurgitation + systemic manifestations = infective endocarditis

8. Management

8.1 Initial Stabilization

1. Assess hemodynamics
2. Provide oxygen
3. Establish IV access
4. Manage sepsis (fluids ± vasopressors)

8.2 Empiric Antibiotic Therapy

1. Start empiric IV bactericidal therapy after cultures
2. Choice depends on:
• Native vs prosthetic valve
• Community vs healthcare-associated
• Local resistance patterns

8.3 Targeted Therapy

1. Use culture-directed bactericidal antibiotics
2. Duration: 4–6 weeks IV

Key regimens:

• MSSA → nafcillin/oxacillin
• MRSA → vancomycin/daptomycin
• Viridans streptococci → penicillin/ceftriaxone
• Enterococcus → ampicillin + ceftriaxone

8.4 Monitoring

1. Repeat blood cultures
2. Persistent bacteremia → treatment failure
3. Monitor for:
• Heart failure
• Abscess
• Embolic events

8.5 Indications for Surgery

Absolute

1. Heart failure
2. Periannular abscess
3. Persistent bacteremia ≥5–7 days
4. Fungal/resistant organism

Relative

1. Vegetation >10 mm
2. Recurrent emboli

Right-Sided IE

1. Vegetation >20 mm + recurrent pulmonary emboli
2. Severe tricuspid regurgitation with heart failure

Clinical heuristic: HF + uncontrolled infection + embolic risk → surgery

8.6 Prevention

1. Remove source of bacteremia
2. Counsel for IVDU cessation
3. Maintain oral hygiene

9. Prophylaxis

Indications

1. Prosthetic valves
2. Prior IE
3. Cyanotic CHD (unrepaired or residual defect)
4. Cardiac transplant with valvular disease

Regimen

• Amoxicillin 2 g orally 30–60 min before dental procedure

Important: Routine prophylaxis NOT recommended

10. Complications

Cardiac

1. Heart failure
2. Valve destruction
3. Abscess → conduction block

Embolic

1. Stroke
2. Pulmonary emboli
3. Splenic infarction

Infectious

1. Persistent bacteremia
2. Mycotic aneurysm

11. Prognosis

Worse with:

1. Staphylococcus aureus
2. Prosthetic valves
3. Heart failure
4. Large vegetations
5. Delayed treatment

12. Exam-Level Pearls

1. Most common organism → Staphylococcus aureus
2. TEE > TTE
3. New regurgitation = key finding
4. Persistent bacteremia → surgery
5. Right-sided IE → pulmonary emboli
6. Osler (painful) vs Janeway (painless)
7. Strep gallolyticus → colon cancer