Page 289 - Concise Pathology for Exam Preparation ( PDFDrive )

274 SECTION II Diseases of Organ Systems

(b) Subacute bacterial endocarditis
(i) Caused by less destructive and less virulent microorganisms
(ii) Usually affects previously diseased heart

Predisposing Factors
• Conditions which initiate transient bacteraemia and septicaemia
• Periodontal infections
• Genitourinary tract infections
• Infections of gastrointestinal and urinary tract
• Tonsillectomy, adenoidectomy, bronchoscopy and surgery on respiratory mucosa
• Underlying heart disease
• RHD
• Congenital heart disease (VSD, subaortic stenosis, myxomatous mitral value and
artificial valves)
• Impaired host defences
• Immunodeficiency
• Diabetes mellitus
• Neutropenia or deficient function of neutrophils
Causative Agents
• Staphylococcus aureus (in 10–20% cases); affects healthy or diseased heart and is the
major offender in intravenous drug users
• Streptococcus viridians (in 50–60% cases); causes endocarditis in previously damaged/
abnormal valves
• Staphylococcus epidermidis (in 10% cases) is the most common cause of prosthetic valve
endocarditis
• Other organisms implicated are the HACEK group (Hemophilus, Actinobacillus, Cardio-
bacterium, Eikenella and Kingellakingae)

Gross Pathology
• Valves of left heart, ie, mitral and aortic are most frequently affected
• Vegetations involve atrial surface of AV valves and ventricular surface of semilunar
valves
• Size varies between a few mm to cm; the vegetations are grey, single or multiple and
friable
• Acute bacterial endocarditis vegetations are bulkier than subacute endocarditis

Microscopy
The vegetations have three recognizable zones:
• Outer layer or cap composed of eosinophilic material (fibrin and platelets)
• Basophilic zone composed of bacterial colonies
• Deeper zone composed of nonspecific inflammatory cells
Clinical Features
Fever with chills, weakness, malaise and weight loss

Complications and Sequelae
• Cardiac complications:
• Valvular stenosis or insufficiency
• Perforation, rupture, aneurysm formation
• Abscess in valve ring extending to myocardium
• Suppurative pericarditis
• Cardiac failure
• Extracardiac complications:
• Emboli can arise from the left or right side of the heart

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