3. Infective Endocarditis

Quick Recap

Infectious Diseases System, Protocol 3/6.

1. Definition & Diagnostic Framework (Modified Duke Criteria)

Infective endocarditis (IE) = infection of the endocardial surface of the heart, typically valvular, causing vegetation formation with risk of local destruction, embolization, and systemic sepsis.

Definite IE: 2 major criteria, OR 1 major + 3 minor, OR 5 minor criteria.

Possible IE: 1 major + 1 minor, OR 3 minor criteria.

Major criteria:

• Positive blood cultures: typical IE organisms (viridans streptococci, Streptococcus gallolyticus/bovis, HACEK group, S. aureus, or community-acquired enterococci without a primary focus) from 2 separate cultures; OR persistently positive cultures from samples drawn >12h apart; OR 3/3 or majority of >=4 separate cultures with first/last drawn >=1h apart; OR a single positive culture for Coxiella burnetii or phase I IgG titer >1:800
• Evidence of endocardial involvement: echocardiogram showing vegetation, abscess, new partial dehiscence of a prosthetic valve, or new valvular regurgitation (worsening/changing murmur alone is insufficient)

Minor criteria: predisposing condition (heart lesion or IV drug use); fever >=38C; vascular phenomena (major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhage, conjunctival hemorrhages, Janeway lesions); immunologic phenomena (glomerulonephritis, Osler nodes, Roth spots, rheumatoid factor); microbiologic evidence not meeting major criteria; echocardiographic findings not meeting major criteria.

Key pearl: classic peripheral stigmata (Janeway lesions, Osler nodes, Roth spots, splinter hemorrhages) are INSENSITIVE and often ABSENT in acute, fulminant S. aureus IE — do not require these findings to raise suspicion in a rapidly deteriorating bacteremic patient.

2. When to Actively Suspect IE and Pursue Echocardiography

High-risk bacteremia scenarios warranting endocarditis workup:

• S. aureus bacteremia of ANY source (including catheter-associated) — high rates of endocarditis reported even with an apparent alternative source (e.g., catheter)
• Persistently positive blood cultures despite appropriate antibiotic therapy
• New murmur, unexplained embolic phenomena (stroke, splenic/renal infarct), or unexplained heart failure in a bacteremic patient
• Injection drug use with fever/bacteremia
• Prosthetic valve or other high-risk cardiac lesion with bacteremia

Imaging approach:

• Transthoracic echocardiogram (TTE) has only MODERATE sensitivity — a negative TTE does NOT exclude IE
• Transesophageal echocardiogram (TEE) should be pursued if TTE is negative/inconclusive but clinical suspicion remains high, as long as no contraindications exist — TEE has substantially higher sensitivity, particularly for prosthetic valves, small vegetations, and posterior/aortic valve pathology poorly visualized on TTE
• Candida endocarditis (the most common cause of fungal endocarditis) frequently shows LARGER vegetations than bacterial IE on echo and is MORE LIKELY TO EMBOLIZE — suspect with persistently positive Candida blood cultures and confirm echocardiographically

3. Immediate Stabilization (ABCDE)

Circulation: treat as evolving septic shock if hemodynamically unstable (apply Septic Shock protocol principles); acute severe valvular regurgitation from IE (particularly acute aortic or mitral regurgitation from leaflet destruction) can cause acute decompensated heart failure/cardiogenic shock — apply Acute Heart Failure/Cardiogenic Shock protocol principles if this develops, and recognize it as a surgical EMERGENCY indication (Section 6), not a medical-management-alone scenario.

Neurologic: any new focal neurologic deficit in a bacteremic/IE patient should prompt urgent neuroimaging — embolic stroke and mycotic aneurysm (with hemorrhage risk) are both feared IE complications requiring specific management pathways (Section 7).

Checklist:

4. Empiric and Definitive Antibiotic Therapy

Empiric therapy (before organism identification) should cover the most likely organisms based on valve type and epidemiologic context:

• Native valve, community-acquired, non-IVDU: vancomycin (covers MRSA and most streptococci/enterococci) +/- an agent with gram-negative/HACEK coverage (e.g., ceftriaxone) pending cultures
• Prosthetic valve, or healthcare-associated: broader coverage including vancomycin plus an antipseudomonal agent and consideration of rifampin (for prosthetic material biofilm penetration) and gentamicin (synergy), pending culture-directed narrowing
• IV drug use: high suspicion for S. aureus (including MRSA) — vancomycin-based empiric coverage

Definitive, organism-directed therapy (once cultures/susceptibilities available) follows established regimens (AHA/IDSA guidance):

• Viridans streptococci (penicillin-susceptible): penicillin G or ceftriaxone, 4 weeks (native valve) or 6 weeks (prosthetic)
• S. aureus, methicillin-susceptible (native valve): nafcillin/oxacillin or cefazolin, 4-6 weeks
• S. aureus, methicillin-resistant: vancomycin or daptomycin, 4-6 weeks
• Enterococcus: ampicillin + ceftriaxone (synergistic, reduced nephrotoxicity vs gentamicin-based regimens) OR ampicillin/vancomycin + gentamicin (synergy dosing) depending on resistance pattern, typically 4-6 weeks
• HACEK organisms: ceftriaxone, 4 weeks
• Culture-negative IE: empiric broad coverage guided by epidemiologic risk (consider Coxiella, Bartonella, fungal causes) with ID consultation

Prosthetic valve IE generally requires LONGER duration (6 weeks vs 4 for native valve) and often combination therapy given biofilm-related treatment resistance.

Treat complicated bacteremia (confirmed IE, septic thrombophlebitis, prolonged bacteremia) for 4-6 weeks minimum — substantially longer than uncomplicated bacteremia (which may be treated for as little as 14 days if endocarditis is excluded, cultures clear within 72h, and no prosthetic material is present).

5. Source Control — Catheter and Device Management

For catheter-associated bacteremia with S. aureus or Candida specifically: remove the catheter given these organisms' propensity to establish metastatic foci of infection (including endocarditis) — do not attempt catheter salvage/antibiotic lock therapy for these two organisms the way might be reasonable for coagulase-negative staphylococci. Any infected prosthetic cardiac material (valve, device lead) generally requires removal for source control in confirmed device-associated IE — antibiotics alone rarely clear infection from prosthetic material given biofilm formation.

6. Surgical Indications — The Central Decision Point

Surgery (valve repair or replacement) should be considered EARLY and in parallel with medical therapy, not reserved as a last resort, for:

• Heart failure due to valve dysfunction (acute severe regurgitation, as noted in Section 3) — the single most common indication for surgery in IE and a true emergency if causing cardiogenic shock
• Uncontrolled infection: persistent bacteremia/fever despite appropriate antibiotics beyond 5-7 days, perivalvular abscess, fistula formation, new heart block (suggesting perivalvular extension into the conduction system), fungal IE (rarely cured with antibiotics alone), or infection with highly resistant/difficult-to-treat organisms
• Prevention of embolism: large vegetations (generally >10mm, especially on the mitral valve) with a prior embolic event, or large vegetations with other risk factors, particularly if antibiotic therapy has been running for less than 2 weeks (highest embolic risk window)
• Prosthetic valve IE with early dysfunction or dehiscence

Early surgical consultation (cardiothoracic surgery involvement from the time IE is suspected/confirmed, not deferred until a complication develops) is recommended given how time-sensitive these indications can become.

7. Neurologic Complications

Embolic stroke: occurs in a meaningful proportion of IE cases, particularly early in the course before antibiotics have had time to sterilize/stabilize vegetations.

Mycotic (infectious) aneurysm: a feared complication from septic embolization to the vasa vasorum or direct arterial wall infection — any IE patient (particularly with a mycotic-aneurysm-associated organism, or with unexplained headache/neurologic symptoms) should be considered for cerebral vascular imaging (CTA/MRA) to screen for this complication, since rupture causes intracranial hemorrhage.

Timing of cardiac surgery after a neurologic embolic event is a genuine clinical tension: early surgery may be needed for hemodynamic indications, but recent hemorrhagic stroke or large ischemic stroke raises perioperative bleeding/hemorrhagic transformation risk with cardiopulmonary bypass anticoagulation — requires multidisciplinary (cardiology, cardiac surgery, neurology/neurosurgery) discussion rather than a fixed rule, individualized to stroke type/size and the urgency of the cardiac surgical indication.

8. Investigations

Blood cultures x3 from separate venipuncture sites before antibiotics (per Duke criteria); TTE then TEE per Section 2; inflammatory markers; renal function (embolic renal infarct, immune complex glomerulonephritis); urinalysis (hematuria from renal involvement); ECG (screen for new conduction abnormality suggesting perivalvular abscess extension); cerebral vascular imaging if neurologic symptoms or mycotic aneurysm risk; dental evaluation (potential source, relevant for pre-surgical planning); consider HIV testing and thorough IVDU-related infectious workup where relevant.

9. Organ Support

Fluid/vasopressor support per Septic Shock or Cardiogenic Shock protocols depending on the physiology (either can occur); mechanical circulatory support (IABP, Impella) as a bridge to surgery in select cases of IE-associated cardiogenic shock; standard ICU supportive care.

10. Consultation Matrix

11. Monitoring Framework

Serial blood cultures until clearance, serial echo to monitor vegetation size/valvular function trend (especially if surgery being deferred), ECG monitoring for new conduction abnormality, renal function trend, neurologic status surveillance.

12. Complications

Acute heart failure/cardiogenic shock (valve destruction), embolic stroke, mycotic aneurysm/intracranial hemorrhage, perivalvular abscess/fistula/heart block, splenic/renal infarction, immune complex glomerulonephritis, persistent/relapsing bacteremia. Prevention: early surgical consultation for at-risk vegetations, prompt source control (catheter/device removal), appropriate duration antibiotic therapy. Rescue: emergent valve surgery for hemodynamic decompensation, standard stroke/hemorrhage management for neurologic complications.

13. Escalation & De-escalation

Escalate: heart failure from valve dysfunction, uncontrolled infection, or high embolic-risk vegetation -> urgent/emergent surgery.

De-escalate: cultures clearing, hemodynamically stable, no surgical indication -> continue full-duration organism-directed antibiotic therapy, transition to outpatient IV antibiotic therapy (OPAT) once clinically stable per infectious disease guidance.

14. ICU Discharge Criteria

Hemodynamically stable, blood cultures cleared, surgical indication addressed or excluded, antibiotic regimen finalized with a defined duration and outpatient administration plan, neurologic complications stabilized/addressed, cardiology/ID follow-up arranged.

15. Documentation & Medicolegal Checklist

16. Key Guidelines

Baddour LM, Wilson WR, Bayer AS, et al. Infective endocarditis in adults: diagnosis, antimicrobial therapy, and management of complications: AHA scientific statement. Circulation. 2015;132(15):1435-1486. Li JS, Sexton DJ, Mick N, et al. Proposed modifications to the Duke criteria for the diagnosis of infective endocarditis. Clin Infect Dis. 2000;30(4):633-638.

17. Controversies

Optimal timing of cardiac surgery after embolic stroke remains genuinely unresolved and requires individualized, multidisciplinary decision-making rather than a fixed interval, balancing the urgency of the cardiac indication against perioperative hemorrhagic risk. The vegetation-size threshold for prophylactic surgery to prevent embolism (commonly cited >10mm) is guideline-consensus-based rather than derived from a single definitive RCT, and practice varies with additional risk-factor weighting. Duration and setting (inpatient vs outpatient parenteral antibiotic therapy, OPAT) for the extended antibiotic courses required in IE involves practice variation based on organism, social factors, and institutional OPAT infrastructure.

18. References

1. Bacteremia and Catheter-Related Bloodstream Infections (S. aureus/endocarditis workup sections). Washington Manual of Critical Care, 4th ed, 2025 (Ch. 41).
2. Invasive Fungal Infection (Candida endocarditis section). Washington Manual of Critical Care, 4th ed, 2025 (Ch. 42).
3. Baddour LM, Wilson WR, Bayer AS, et al. Infective endocarditis in adults: diagnosis, antimicrobial therapy, and management of complications: AHA scientific statement. Circulation. 2015;132(15):1435-1486.
4. Li JS, Sexton DJ, Mick N, et al. Proposed modifications to the Duke criteria for the diagnosis of infective endocarditis. Clin Infect Dis. 2000;30(4):633-638.
5. Habib G, Lancellotti P, Antunes MJ, et al. 2015 ESC Guidelines for the management of infective endocarditis. Eur Heart J. 2015;36(44):3075-3128.

See also: Sepsis/Septic Shock (Infectious Diseases System) and Cardiogenic Shock, Acute Heart Failure (Cardiovascular System) for the shared hemodynamic management frameworks; Stroke, Subarachnoid Hemorrhage (Neurology System) for embolic/mycotic aneurysm complication management.