Infective Endocarditis

Introduction

Infective endocarditis is an infection of a heart valve, lining of a cardiac chamber or blood vessel. It is usually a bacterial infection and has a high rate of mortality.

Risk factors

• Congenital lesions e.g. Ventricular septal defects, bicuspid aortic valve, coarctation of aorta
• IV drug abuse
• Prosthetic valve replacement
• Cardiac/urinary catheterisation
• Invasive diagnostic or surgical procedures
• Colorectal cancer

Valves affected

Endocarditis usually produces valve regurgitation. Left-sided valves are most commonly affected, with the mitral valve being the commonest.

Right-sided lesions mostly occur following IV drug abuse. This is because blood from the peripheries, which can carry bacteria introduced by the needle, drains into the right side of the heart.

Causative organisms

Strep. viridians (50% of cases): dental procedures

Staph. aureus (20% of cases): IV drug abuse, prosthetic heart valves

Enterococcus faecalis (10% of cases): Urinary catheter, cystoscopy, colonoscopy

Staph. epidermidis: Prosthetic heart valves, dialysis

Strep. bovis: colorectal cancer

Fungi e.g. candida, aspergillus, histoplasma: Immunocompromised

HACEK organisms

Pathophysiology

Endocarditis usually arises as a consequence of 2 factors: abnormal cardiac endothelium (which facilitates organism adherence) and presence of pathogens in the bloodstream.

Circulating microorganisms can then adhere to cardiac tissues. Once adhered, they become encased in fibrin and platelets to grow rapidly into vegetations.

Clinical features

Presentation is variable and involves both structural and septic features. Common features include:

• Fever
• Malaise, anorexia and weight loss
• Embolic events
• New or changing murmurs
• Heart failure

Investigations

The most important investigations are blood cultures and echocardiograms.

• Blood cultures: take 3 samples of blood cultures. Must be taken before antibiotics are administered.
• Echocardiograms: definitive investigation for confirming vegetations.

Also consider:

• Urine dipstick – microscopic haematuria (glomerulonephritis due to circulating antigens)
• Fundoscopy – Roth’s spot
• ECG
• Routine blood tests – raised CRP/ESR, normocytic anaemia
• Chest x-ray

Diagnosing according to Duke’s criteria

A set of criteria for diagnosing infective endocarditis. Diagnose endocarditis if one of the following are met:

• 2 major criteria
• 1 major + 2 minor
• 5 minor

Management

Acutely, stabilise the patient and provide broad-spectrum antibiotics, such as IV gentamicin with benzylpenicillin; blood cultures should ideally be taken before starting antibiotics. Antibiotics should subsequently be tailored according to the sensitivity of organism and continued for 4-6 weeks.

Once the infection is eliminated, surgery should be offered to patients with large vegetations, new murmurs or abscesses.

Prognosis

20% fatality rate if treated. Mortality approaches 100% if untreated.