9. Infective endocarditis

Question 1

Definition of infective endocarditis

Answer 1

A serious infection characterized by microbial colonization or invasion of the heart valves or the mural endocardium; traditionally classified as being acute (by highly virulent pathogens infecting normal valves) or subacute (by organisms of low virulence infecting abnormal valves)

Question 2

Causes of infective endocarditis

Answer 2

1. Subacute endocarditis
   - General medical patient: Streptococcus viridans (75%)
   - Geriatric patient: Streptococcus viridans (50%),
   Enterococcus faecalis & other gram negatives (50%)
2. Acute infective endocarditis
   - Staphylococcus aureus (especially in IV drug abusers)
3. Prosthetic Valve Endocarditis
   - Coagulase negative staphylococci (e.g. Staphylococcus epidermidis)

Question 3

Frequency of specific valve involvement

Answer 3

1. Mitral valve only (25-30%)
2. Aortic valve only (25-35%)
3. Mitral + aortic valve (10%)
4. Tricuspid valve (10%)
5. Prosthetic valve (10%)
6. Congenital heart disease (10%)

Question 4

Pathogenesis of subacute infective endocarditis

Answer 4

1. Source of low virulence pathogens: normal commensals of skin, mouth, gut, respiratory tract, genitourinary tract
2. Pre-existing abnormal heart valve causes derangement of blood flow, resulting in the formation of sterile platelet-fibrin deposits on endocardium & heart valves (vegetations)
3. Blood-borne pathogens can then get enmeshed in these vegetations
4. Causes insidious, less destructive infection

Question 5

Pathogenesis of acute infective endocarditis

Answer 5

1. Source of high virulence pathogens: intravenous drug abuse, open heart surgery, septicaemia
2. Highly virulent blood-borne pathogens can directly invade the endocardium and heart valves (even if they were previously normal)
3. Causes rapidly destructive lesions

Question 6

Morphology of infective endocarditis

Answer 6

1. [Gross] Hallmark is presence of vegetations (friable, bulky) on heart valves
2. [Histology] Vegetations comprises tangled mass of fibrin, organisms (visualized with Gram stain) & inflammatory cells

Question 7

Pathological effects & complications of infective endocarditis

Answer 7

1. Locally
   - Valve rupture & scarring
   - Myocardial ring abscess
   - Suppurative pericarditis
2. Distally
   - Embolization of vegetations (causing septic infarcts)
   - Immune complex mediated disorders (vasculitis,
   glomerulonephritis)
   - Anemia of chronic disease, splenomegaly

Question 8

Clinical features (of long-standing infective endocarditis)

Answer 8

1. Splinter hemorrhages in nails (manifestation of microthromboemboli)
2. Janeway lesions (erythematous or hemorrhagic non-tender lesions on the palms or soles)
3. Osler nodes (subcutaneous nodules in the pulp of digits)
4. Roth spots (retinal hemorrhages)

Question 9

Definition of non-infected vegetations

Answer 9

Vegetations (thrombi on heart valves) formed via non-infectious endocarditis; two such types of endocarditis are recognized

Question 10

Types of endocarditis from non-infected vegetations

Answer 10

1. Nonbacterial thrombotic (Marantic) endocarditis

2. Libmann-Sacks Disease

Question 11

Nonbacterial thrombotic endocarditis

Answer 11

1. Characterized by the deposition of small, sterile, platelet-rich thrombi on the leaflets of the cardiac valves which do not elicit local inflammatory reactions
2. Often encountered in:
   - Severely debilitated patients (e.g. cancer or sepsis) with an underlying systemic hypercoagulable state
   - Endocardial trauma (e.g. from indwelling catheter)

Question 12

Libman-Sacks Disease (Endocarditis of SLE)

Answer 12

Characterized by mitral & tricuspid valvulitis with small

sterile vegetations

Question 13

Complications of artificial heart valves

Answer 13

1. Thromboembolism
   - Necessitates long-term anti-coagulation therapy with its attendant risks of hemorrhagic complications
2. Infective endocarditis
3. Valve deterioration with valvular insufficiency
4. Mechanical hemolysis