Infective Endocarditis: Causes and Risk Factors

• Infective endocarditis is an infection of the endothelium, which is the inner surface of the heart.
• Infective endocarditis most commonly affects the heart valves.
• Infective endocarditis classified as acute, subacute, or chronic, based on the rapidity and acuteness of symptom presentation, in addition to the causative organism.

Risk Factors

• Risk factors include intravenous drug use and structural heart pathology.
• Other risk factors include chronic kidney disease (particularly on dialysis), immunocompromised state (e.g., cancer, HIV or immunosuppressive medications), and a history of infective endocarditis.
• Structural pathologies that increase infective endocarditis risk are valvular heart disease and congenital heart disease.
• Further structural pathologies that increase risk include hypertrophic cardiomyopathy, prosthetic heart valves, and implantable cardiac devices (e.g., pacemakers).

Causes

• The most common cause is Staphylococcus aureus.
• Other causes include Streptococcus and Enterococcus (e.g., Enterococcus faecalis).
• Rarer causes include Pseudomonas, HACEK organisms, as well as fungi

Presentation

• Presenting symptoms are typically non-specific for an infection.
• Symptoms include fever, fatigue, night sweats, muscle aches, and anorexia (loss of appetite).
• Key examination findings include a new or changing heart murmur.
• Other key examination findings include splinter hemorrhages, which are thin red-brown lines along the fingernails.
• Petechiae (small non-blanching red/brown spots) on the trunk, limbs, oral mucosa, or conjunctiva may also present
• Janeway lesions (painless red flat macules on the palms of the hands and soles of the feet) may be observed.
• Osler's nodes (tender red/purple nodules on the pads of the fingers and toes) may also present
• Additional signs include Roth spots (haemorrhages on the retina seen during fundoscopy), splenomegaly (in longstanding disease), and finger clubbing (in longstanding disease).

Investigations

• Blood cultures are essential before starting antibiotics; get three samples, separated by at least 6 hours sampled from different sites.
• The gap between repeated blood culture sets may be shorter if antibiotics are required more urgently, such as in sepsis
• Echocardiography is the typical imaging investigation.
• Transoesophageal echocardiography (TOE) is more sensitive and specific than transthoracic echocardiography in identifying vegetations (an abnormal mass or collection) on the valves.
• Special imaging investigations may be used in patients with prosthetic heart valves to determine the presence of infection.
• 18F-FDG PET/CT and SPECT-CT modalities can be utilized

Modified Duke Criteria

• The Modified Duke criteria is used to diagnose infective endocarditis.
• Diagnosis requires one major plus three minor criteria, or five minor criteria.
• Major criteria include persistently positive blood cultures (typical bacteria on multiple cultures) and specific imaging findings (e.g., a vegetation seen on the echocardiogram).
• Minor criteria include predisposition (e.g., IV drug use or heart valve pathology).
• Other minor criteria include fever above 38°C, and vascular phenomena (e.g., splenic infarction, intracranial haemorrhage, and Janeway lesions).
• Immunological phenomena (e.g., Osler's nodes, Roth spots, and glomerulonephritis), and microbiological phenomena (e.g., positive cultures not qualifying as a major criterion) are also considered minor criteria.

Management

• Patients require admission as well as management by a specialist team.
• IV broad-spectrum antibiotics (e.g., amoxicillin and optional gentamicin) are the mainstay of treatment.
• Antibiotic choice may be more specific once the causative organism is identified on cultures.
• Antibiotics are typically continued for at least 4 weeks for native heart valves and 6 weeks for patients with prosthetic heart valves.
• Surgery may be required for heart failure relating to valve pathology, large vegetations or abscesses, or infections not responding to antibiotics.
• Infective endocarditis has a high mortality rate, key complications include heart valve damage (causing regurgitation) plus heart failure.
• Other key complications include infective and non-infective emboli (causing abscesses, strokes, and splenic infarction) and glomerulonephritis (causing renal impairment).

Prophylaxis

• NICE guidelines state antibiotics are not routinely recommended for dental and non-dental procedures as prophylaxis of infective endocarditis.
• Prophylaxis is still considered on a case-by-case basis in those at particularly high risk.
• Patients at higher risk should take good care of their oral health to reduce the risk of infective endocarditis.