Infective Endocarditis – Complete Clinical Reference

Definition

Infective endocarditis (IE) is a microbial infection of the endocardial surface of the heart, most commonly involving cardiac valves (native or prosthetic), but may also affect mural endocardium, chordae tendineae, or intracardiac devices.

Pathophysiology

1. Endothelial injury (turbulent flow, prosthetic material)
2. Platelet–fibrin deposition → non-bacterial thrombotic endocarditis
3. Transient bacteremia/fungemia
4. Microbial adherence to thrombus
5. Vegetation formation
6. Local destruction + systemic embolization + immune complex phenomena

Etiology and Causative Organisms

Common Organisms

| Setting | Organisms |

| ------------------------------ | ------------------------------------------------ |

| Native valve (community) | Viridans streptococci, Staphylococcus aureus |

| Healthcare-associated | S. aureus, Enterococci |

| Prosthetic valve (early <1 yr) | S. epidermidis, S. aureus, Gram-negatives |

| Prosthetic valve (late >1 yr) | Similar to native valve |

| IV drug users | S. aureus (often tricuspid) |

| Culture-negative | Coxiella burnetii, Bartonella, HACEK |

HACEK Group

• Haemophilus
• Aggregatibacter
• Cardiobacterium
• Eikenella
• Kingella

Risk Factors

• Rheumatic or degenerative valve disease
• Prosthetic valves
• Congenital heart disease
• Previous infective endocarditis
• IV drug use
• Indwelling catheters
• Immunosuppression

Classification

By Valve

• Native valve endocarditis (NVE)
• Prosthetic valve endocarditis (PVE)

By Course

• Acute (rapid, destructive – S. aureus)
• Subacute (indolent – viridans streptococci)

Clinical Features

Constitutional

• Fever (most common)
• Chills, malaise
• Weight loss, night sweats

Cardiac

• New or changing murmur
• Acute heart failure
• Conduction block (suggests abscess)

Vascular Phenomena

• Janeway lesions (painless palms/soles)
• Splinter hemorrhages
• Arterial emboli
• Pulmonary emboli (right-sided IE)

Immunologic Phenomena

• Osler nodes (painful fingers/toes)
• Roth spots
• Glomerulonephritis
• Positive rheumatoid factor

Other

• Stroke
• Hematuria
• Splenomegaly

Investigations

Blood Cultures (Cornerstone)

• 3 sets from different sites
• Before antibiotics
• Positive in >90%

Echocardiography

• TTE – initial
• TEE – gold standard

(prosthetic valves, abscess, poor TTE window)

Laboratory

• Normocytic normochromic anemia
• Raised ESR, CRP
• Microscopic hematuria
• Low complement levels

Imaging (Complications)

• CT/MRI brain – embolic stroke
• CT chest – septic emboli
• PET-CT – prosthetic valve infection

Diagnosis – Modified Duke Criteria

Major Criteria

1. Positive blood cultures with typical organism
2. Evidence of endocardial involvement (echo or new regurgitation)

Minor Criteria

• Predisposition
• Fever ≥38°C
• Vascular phenomena
• Immunologic phenomena
• Microbiological evidence not meeting major

Definite IE

• 2 major

OR

• 1 major + 3 minor

OR

• 5 minor

Differential Diagnosis

• Acute rheumatic fever
• Libman–Sacks endocarditis
• Marantic (non-bacterial) endocarditis
• Vasculitis
• Malignancy-associated fever
• Atrial myxoma

Management (Stepwise)

1. General Measures

• Hospital admission
• Strict bed rest (initial phase)
• Treat heart failure, arrhythmias
• Remove infected devices

2. Empiric Antibiotic Therapy

(Start after blood cultures)

Native Valve (Community-acquired)

• Ceftriaxone + Vancomycin

Prosthetic Valve / Healthcare-associated

• Vancomycin + Gentamicin + Rifampicin

Targeted Antimicrobial Therapy (Key Drugs)

Vancomycin

• Indication: MRSA, penicillin-allergic
• MOA: Inhibits cell wall synthesis
• Dose: 15–20 mg/kg IV every 8–12 h
• Adverse effects: Nephrotoxicity, red man syndrome
• Monitoring: Trough levels, renal function
• Contraindication: Severe hypersensitivity
• Counseling: Slow infusion, hydration

Ceftriaxone

• Indication: Streptococci, HACEK
• MOA: β-lactam cell wall inhibition
• Dose: 2 g IV once daily
• Adverse effects: Biliary sludge, allergy
• Contraindication: Severe cephalosporin allergy

Gentamicin

• Indication: Synergy (Enterococcus)
• MOA: 30S ribosomal inhibition
• Dose: 1 mg/kg IV every 8 h
• Adverse effects: Nephrotoxicity, ototoxicity
• Monitoring: Drug levels, renal function
• Contraindication: Renal failure (relative)

Rifampicin

• Indication: Prosthetic valve IE
• MOA: RNA polymerase inhibition
• Dose: 300–600 mg orally/IV every 12 h
• Adverse effects: Hepatotoxicity, orange discoloration
• Interactions: Induces CYP450 (↓ warfarin, OCPs)
• Monitoring: LFTs

Duration of Therapy

• Native valve: 4–6 weeks
• Prosthetic valve: ≥6 weeks

Indications for Surgery

Absolute

• Acute heart failure due to valve dysfunction
• Uncontrolled infection (abscess, persistent bacteremia)
• Large vegetations with recurrent emboli
• Prosthetic valve dehiscence

Relative

• Vegetation >10 mm
• Fungal endocarditis
• Resistant organisms

Complications

• Heart failure (most common cause of death)
• Stroke
• Septic emboli
• Mycotic aneurysm
• Valvular destruction
• Renal failure
• Conduction abnormalities

Prognosis

• Mortality: 15–30%
• Worse with:

S. aureus*

* Prosthetic valve

* Heart failure

* Delayed treatment

Prevention (Antibiotic Prophylaxis – High Risk Only)

High-Risk Patients

• Prosthetic valves
• Previous IE
• Certain congenital heart diseases

Dental Procedures

• Amoxicillin 2 g orally 30–60 min before
• Clindamycin 600 mg if penicillin-allergic

1. IV Drug User with Fever and Hemoptysis

Scenario: 28-year-old IV drug user, fever, pleuritic chest pain, hemoptysis. Echo: tricuspid vegetations.

Diagnosis: Right-sided IE (likely Staphylococcus aureus)

Management:

• IV vancomycin (or anti-staphylococcal beta-lactam if MSSA)
• Treat septic pulmonary emboli
• Surgery only if persistent bacteremia, large vegetations, or RV failure

2. Native Valve IE after Dental Extraction

Scenario: Fever 3 weeks after dental work, new murmur.

Organism: Viridans streptococci

Management:

• IV ceftriaxone or penicillin G for 4 weeks
• No surgery unless complications

3. Prosthetic Valve with Persistent Fever

Scenario: Mechanical valve, fever despite antibiotics, TEE shows abscess.

Diagnosis: Prosthetic valve endocarditis

Management:

• Vancomycin + gentamicin + rifampicin
• Urgent surgery (abscess = absolute indication)

4. Culture-Negative IE after Antibiotics

Scenario: Fever, negative cultures, prior antibiotic exposure.

Management:

• Stop antibiotics if safe → repeat cultures
• Empiric therapy covering fastidious organisms
• Serology for Coxiella, Bartonella

5. IE with Acute Heart Failure

Scenario: Acute pulmonary edema, severe MR on echo.

Cause: Valve destruction/chordal rupture

Management:

• Stabilize heart failure
• Emergency valve surgery

6. IE with Stroke

Scenario: IE patient develops sudden hemiparesis.

Management:

• CT brain (exclude hemorrhage)
• Continue antibiotics
• Surgery delayed 2–4 weeks unless heart failure or uncontrolled infection

7. Enterococcal Endocarditis

Scenario: Elderly patient, urinary source, positive Enterococcus cultures.

Management:

• Ampicillin + gentamicin OR ampicillin + ceftriaxone
• Duration: 6 weeks

8. Fungal Endocarditis

Scenario: Immunocompromised patient, large vegetations, Candida species.

Management:

• IV amphotericin B or echinocandin
• Early surgery mandatory

9. IE with New Conduction Block

Scenario: PR prolongation / heart block in IE.

Cause: Perivalvular abscess

Management:

• TEE urgently
• Early surgery

10. Recurrent Emboli despite Antibiotics

Scenario: Vegetation >10 mm, repeated emboli.

Management:

• Early surgical intervention

11. Right-Sided IE with Good Response

Scenario: Tricuspid IE, fever resolving.

Management:

• Continue IV antibiotics
• Surgery usually not required

12. IE with Renal Failure and Hematuria

Scenario: Hematuria, RBC casts.

Diagnosis: Immune complex GN

Management:

• Treat IE with antibiotics
• Avoid nephrotoxic drugs
• Dialysis if needed

13. Early Prosthetic Valve IE (<1 year)

Scenario: Fever 3 months post valve surgery.

Organism: Staphylococcus epidermidis

Management:

• Vancomycin + gentamicin + rifampicin
• Usually requires surgery

14. Late Prosthetic Valve IE (>1 year)

Scenario: Fever 2 years post surgery.

Management:

• Treat similar to native valve IE
• Surgery based on complications

15. HACEK Endocarditis

Scenario: Subacute IE, slow-growing Gram-negative bacilli.

Management:

• IV ceftriaxone for 4 weeks

16. IE in Congenital Heart Disease

Scenario: Unrepaired VSD, fever, murmur.

Management:

• Prolonged IV antibiotics
• Surgery if hemodynamic compromise

17. IE with Splenic Abscess

Scenario: Left upper quadrant pain, fever.

Management:

• IV antibiotics
• Percutaneous drainage or splenectomy if rupture risk

18. IE with Mycotic Aneurysm

Scenario: Severe headache, focal deficit.

Management:

• Neuroimaging
• Antibiotics
• Neurosurgical intervention if rupture risk

19. IE in Pregnancy

Scenario: Pregnant woman with IE.

Management:

• Safe IV antibiotics (avoid aminoglycosides if possible)
• Surgery only if life-threatening

20. IE with Persistent Bacteremia

Scenario: Positive cultures after 7 days therapy.

Management:

• Review antibiotic sensitivity
• Search for abscess
• Surgery often required

21. IE with Large Mobile Vegetation on Mitral Valve

Scenario: >15 mm vegetation.

Management:

• Early surgery even without emboli

22. IE in Hemodialysis Patient

Scenario: AV fistula, S. aureus bacteremia.

Management:

• IV vancomycin
• Remove infected access
• High threshold for surgery

23. Recurrent IE

Scenario: History of previous IE.

Management:

• Full IV antibiotics
• Strong consideration for valve replacement

24. IE with Severe Anemia and Splenomegaly

Scenario: Chronic IE.

Management:

• Treat infection
• Supportive care (transfusion if needed)

25. Suspected IE with Normal Initial Echo

Scenario: High clinical suspicion, negative TTE.

Management:

• Perform TEE
• Repeat echo if needed
• Continue diagnostic work-up