Infective Endocarditis
Infective endocarditis (IE) is a serious infection of the endocardial surface of the heart, most commonly affecting heart valves. It is typically caused by bacterial pathogens such as Staphylococcus aureus or Streptococcus species and can lead to significant morbidity and mortality if not recognised early.
This article provides a concise UKMLA-focused overview of infective endocarditis, including its causes, clinical features, diagnostic criteria (modified Duke criteria), investigations, and management, and is primarily based on NICE guidance [CG64]: Prophylaxis against infective endocarditis.
Background Information
Definition
IE is the infection of the endocardial surface of the heart, most commonly involving the heart valves.
Aetiology
Causative Agent
Bacterial causes are most common: [Ref1, Ref2]
| Organism | Description |
|---|---|
| Staphylococcus aureus | Leading cause overall
Esp. in
|
| Coagulase-negative staphylococci (e.g. Staphylococcus epidermidis) | 2nd most common cause of prosthetic valve and device-related (e.g. central catheter, implantable cardiac devices) endocarditis |
| Viridans group streptococci (e.g. Streptococcus mitis, Streptococcus sanguinis) | Common in poor dental hygiene, following dental procedures |
| Streptococcus gallolyticus (formerly known as Streptococcus bovis) | Notable association with colorectal cancer |
Other less common causes:
- Culture-negative endocarditis
Caused by organisms that do NOT typically grow on standard culture media.
Culture negative endocarditis can also be caused by typical pathogens implicated in endocarditis (inc. staphylococci, streptococci, enterococci) if cultures are taken after antibiotics.
- HACEKHaemophilus Aggregatibacter (formerly Actinobacillus actinomycetemcomitans), Cardiobacterium hominis, Eikenella corrodens, Kingella kingae organisms
- Coxiella burnetii (Q fever)
- Bartonella species
- Brucella species
- Chlamydia species
- Fungal (Candida, Aspergillus) (seen mostly in immunocompromised / critical care patients)
- Sterile (non-infective causes associated with medical conditions)
-
- Libman-Sacks endocarditis – associated with SLE and antiphospholipid syndrome
- Non-bacterial thrombotic endocarditis (NBTE) – associated with malignancies and hypercoagulable states
-
Risk Factors
Cardiac risk factors: [Ref]
- Previous IE
- Implanted prosthetic valves
- Acquired valve disease (mitral valve prolapse – most common)
- Hypertrophic cardiomyopathy
- Congenital structural heart disease
ESC define structural heart disease as an abnormality in the heart structure - valve / wall / chamber / great vessel. Note that coronary artery disease itself does not fall under the category of structural heart disease. Common congenital structural heart diseases:
- ASD
- VSD
- Tetralogy of Fallot
- Bicuspid aortic valve
Non-cardiac risk factors: [Ref]
- IVDUIntravenous drug use – one of the most important
- Indwelling devices (e.g. intravascular catheters, implantable cardiac devices)
- Poor oral hygiene
- Diabetes mellitus and other causes of immunosuppression (e.g. HIV, steroids)
- Long-term haemodialysis
- Chronic skin infection
Diagnosis
Clinical Features
Sudden-onset fever + new murmur (or worsening of existing murmur) should raise suspicion of IE.
Clinical features of IE can be grouped as following:
| Group | Features |
|---|---|
| Systemic symptoms |
|
| Cardiac manifestations |
|
| Vascular phenomena |
|
| Immunologic phenomena (immune-complex mediated) |
|
Note the classic IE features – Janeway lesions, splinter haemorrhages, Osler nodes and Roth spots are uncommon in practice. However, they are frequently featured in exams.
Investigation and Diagnosis
Perform both in suspected IE:
- Blood cultures (at least 3 sets from separate sites) – first priority
- TTETrans-thoracic echocardiography
- If TTE is -ve but clinical suspicion is strong → perform TOETrans-oesophageal echocardiography
Diagnostic Criteria – Modified Duke Criteria
It is very unlikely for exams to test one’s knowledge on the full Modified Duke Criteria. Learning the key clinical features of IE and investigations is generally sufficient.
See the clinical features section (above) for a student-friendly format of IE clinical features. Key initial investigations are:
- Blood cultures, and
- Echocardiogram (initial: trans-thoracic, if inconclusive: trans-oesophageal, which is more sensitive)
Interpretation:
- Definitive IE
- Pathological criteria
Microorganisms demonstrated by culture or histological examination of a vegetation, a vegetation that has embolized, or an intracardiac abscess specimen.
met, or - 2 major criteria, or
- 1 major criterion + 3 minor criteria, or
- 5 minor criteria
- Pathological criteria
- Possible IE
- 1 major criterion + 1 minor criterion, or
- 3 minor criteria, or
- 5 minor criteria
| Major Criteria | Blood culture +ve |
|
| Evidence of endocardial involvement | Echocardiogram positive for IE
|
|
| Minor Criteria | Presence of predisposition factor:
|
– |
| Fever (>38°C) | – | |
| Vascular phenomena |
|
|
| Immunological phenomena |
|
|
| Microbiological evidence |
|
Management
IE Prevention
General Advice to Prevent IE
- Maintain good oral hygiene
- Maintain strict skin hygiene (including optimised treatment of chronic skin conditions)
- Avoid non-essential invasive procedures (e.g. skin piercing, tattooing, infusion catheters)
- Avoid IVDUIntravenous drug use
- Patient education
Antibiotic Prophylaxis for IE
Antibiotic prophylaxis is NOT recommended routinely.
NICE specifically states that routine antibiotic prophylaxis against IE is not recommended in the following scenarios:
- Dental procedures
- This includes chlorhexidine mouthwash (not routinely offered for the purpose of IE prevention)
- Non-dental procedures at the following sites:
- Upper and lower GI tract
- Upper and lower respiratory tract (including ENT procedures and bronchoscopy)
- Genitourinary tract (including urological, O&G procedures, childbirth)
NICE recommends that if a person is at risk of IE and is receiving antimicrobial therapy due to a GIGastrointestinal / GUGenito-urinary procedure for suspected infection → give antibiotics that cover IE organisms.
Acute IE Management
Antibiotic Therapy
Initial Blind Antibiotic Therapy (culture and sensitivities NOT available)
BNF recommends antibiotic therapy depending on native or prosthetic valve IE:
- Native valve
- 1st line: amoxicillin / ampicillin ± gentamicin
- Penicillin allergic / MRSA suspected / severe sepsis: vancomycin + gentamicin
- Severe sepsis with RF for gram -ve infection: vancomycin + meropenem
- Prosthetic valve
- 1st line: vancomycin + rifampicin + gentamicin (low-dose)
Targeted Antibiotic Therapy
It is unlikely for exam questions to test one’s knowledge on the following specific antibiotics. If so, learning the bolded ones in the table is more than sufficient.
Duration of antibiotic therapy: generally 4-6 weeks
Recommended antibiotics by BNF:
| Organism | 1st line antibiotic | 2nd line (MRSA / penicillin allergic) |
|---|---|---|
| Staphylococci | Native valve → flucloxacillin | Native valve → vancomycin + rifampicin |
| Prosthetic valve → flucloxacillin + rifampicin + gentamicin | Prosthetic valve → vancomycin + rifampicin + gentamicin | |
| Streptococci | Benzylpenicillin | Vancomycin / teicoplanin + gentamicin |
| Enterococci | Amoxicillin / ampicillin + gentamicin / benzylpenicillin | Vancomycin / teicoplanin + gentamicin |
| HACEK microorganismsGram -ve organisms that are typically oropharyngeal commensals ⦁ Haemophilus species ⦁ Aggregatibacter actinomycetemcomitans ⦁ Cardiobacterium hominis ⦁ Eikenella corrodens ⦁ Kingella kingae | Amoxicillin / ampicillin + gentamicin | Ceftriaxone / cefotaxime + gentamicin |
Surgery
Indications
Main indications for surgery:
- Valve dysfunction (aortic / mitral insufficiency)
- Heart failure unresponsive to medical therapy
- New heart block (suggests perivalvular extension / abscess formation)
- Presence of annular / aortic abscess
- Features suggestive of non-resolving disease despite appropriate antimicrobial therapy
- Increase in vegetation size
- Persistent bacteremia
- Persistent fever
Choice of Surgical Intervention
Open heart surgery is the 1st line surgical approach (over trans-catheter approaches):
- Valve repair (preferred if possible), or
- Valve replacement
The decision regarding valve repair vs replacement is complex and decided intraoperatively.
Key influencing factors include:
- Valve type (repair is more feasible in a mitral valve, versus aortic valve)
- Valve integrity (replacement is preferred if there is extensive valve destruction or presence of an abscess)
References
NICE guideline Prophylaxis against infective endocarditis: antimicrobial prophylaxis against infective endocarditis in adults and children undergoing interventional procedures
BNF treatment summary: cardiovascular system infections, antibacterial therapy
AHA Infective Endocarditis in Adults: Diagnosis, Antimicrobial Therapy, and Management of Complications: A Scientific Statement for Healthcare Professionals From the American Heart Association