Infective Endocarditis

Infective Endocarditis (IE) is a critical condition where microorganisms, predominantly bacteria, colonise heart valves or the endocardial lining. It's a high-stakes diagnosis in finals and OSCEs due to its severity and complex management. The incidence is rising, particularly in older patients with degenerative valve disease, those with prosthetic valves, and intravenous drug users (IVDU). Staphylococcus aureus is now the most common cause in the UK. Presentation can range from 'acute' (rapid onset, high fever, often S. aureus) to 'subacute' (insidious, low-grade fever, malaise, often viridans streptococci). Early diagnosis is crucial but challenging, relying on the Modified Duke Criteria. Complications are severe and include acute heart failure from valvular destruction, systemic emboli (e.g., stroke), and immunological phenomena (e.g., glomerulonephritis). Prevention through routine antibiotic prophylaxis for dental procedures is NOT recommended by NICE, but good oral hygiene is paramount.

IE begins with endothelial damage, often from turbulent blood flow (e.g., congenital heart disease, degenerative valve disease), leading to a sterile platelet-fibrin thrombus (Non-Bacterial Thrombotic Endocarditis, NBTE). During transient bacteraemia (e.g., dental procedures, skin infections, IV drug use), bacteria adhere to this NBTE. They proliferate and embed within a protective biofilm, forming a 'vegetation'. This biofilm shields bacteria from host immunity and antibiotics, necessitating prolonged, high-dose bactericidal therapy. Left-sided IE (mitral, aortic valves) is most common. Right-sided IE (tricuspid valve) is characteristic of IVDU or central line infections. Continuous bacteraemia is a hallmark, making timely blood cultures before antibiotics critical for diagnosis.

IE often presents with non-specific symptoms, making it a diagnostic challenge: fever (present in >90%), chills, night sweats, malaise, weight loss. A new or changing heart murmur is a crucial clinical sign. Peripheral stigmata, though rare, are high-yield for exams: 1. Splinter haemorrhages (nail bed). 2. Janeway lesions (painless erythematous macules on palms/soles). 3. Osler's nodes (painful, tender nodules on finger/toe pulps). 4. Roth spots (retinal haemorrhages with pale centres). 5. Splenomegaly. 6. Microscopic haematuria (due to immune complex glomerulonephritis).

**Red Flags & Complications:**
- **Cardiac:** Acute heart failure (due to severe valvular regurgitation), perivalvular abscess (suspect if new AV block/PR prolongation on ECG).
- **Embolic:** Ischaemic stroke (most common neurological complication), splenic/renal infarcts, septic pulmonary emboli (in right-sided IE).
- **Immunological:** Glomerulonephritis, vasculitis.

1. **Blood Cultures:** The most critical investigation. Obtain 3 sets (6 bottles total: aerobic + anaerobic for each set) from different venepuncture sites, ideally with at least 1 hour between the first and last, *PRIOR* to antibiotic administration. This is a Major Duke Criterion.
2. **Echocardiography:**
* **Transthoracic Echocardiogram (TTE):** Initial investigation. Good for detecting large vegetations, valvular dysfunction. Less sensitive for small vegetations or prosthetic valves.
* **Transoesophageal Echocardiogram (TOE):** More sensitive and specific. Indicated if TTE is negative but suspicion remains high, if prosthetic valve IE is suspected, or for assessing complications (e.g., abscesses, fistulae). This provides echocardiographic evidence (vegetation, abscess, new valvular regurgitation) – a Major Duke Criterion.
3. **Bloods:** FBC (normochromic normocytic anaemia, leucocytosis), ESR/CRP (usually significantly elevated), U&Es, LFTs, Urinalysis (microscopic haematuria suggests glomerulonephritis).
4. **12-lead ECG:** Monitor for new conduction abnormalities, especially PR interval prolongation, which can indicate an aortic root abscess extending into the conduction system.

Management is complex, requiring a multidisciplinary team (cardiology, microbiology, cardiac surgery).

1. **Medical (Antibiotics):** Prolonged (4-6 weeks) high-dose intravenous bactericidal antibiotics, tailored to blood culture sensitivities. Obtain ≥3 sets of blood cultures before starting empiric therapy.
* **Native Valve IE (empiric — ESC 2023):** Amoxicillin-Clavulanate 12g/day IV + Gentamicin 3mg/kg/day IV. If healthcare-associated or MRSA risk: Vancomycin + Gentamicin. Note: Gentamicin is reserved for short-term empiric use (≤2 weeks) and is no longer recommended for prolonged courses in streptococcal native valve IE due to nephrotoxicity risk. Once sensitivities confirmed, de-escalate per microbiology advice.
* **Prosthetic Valve IE (empiric — ESC 2023):** Vancomycin + Gentamicin + Rifampicin (Rifampicin added only after 3-5 days once bacteraemia is controlled).
* **Streptococcal native valve IE (targeted):** Benzylpenicillin 12-18 MU/day IV or Ceftriaxone 2g OD IV for 4 weeks (Gentamicin no longer routinely added for sensitive streptococcal IE per ESC 2023).
* **Staphylococcal native valve IE:** Flucloxacillin 12g/day IV (MSSA) or Vancomycin (MRSA).
2. **Surgical Intervention:** Indicated in approximately 50% of cases. Key indications include:
* Acute heart failure due to severe valvular regurgitation/destruction.
* Uncontrolled infection despite optimal antibiotics (e.g., persistent bacteraemia, perivalvular extension).
* Large vegetations (>10mm) with high ongoing embolic risk, especially after an embolic event.
* Fungal endocarditis (often requires surgery due to poor antibiotic penetration).
* Perivalvular abscess or fistula formation.