Cardiovascular Infections

Question 1

Describe the onset of acute and subacute/chronic endocarditis. Which areas of the heart are effected most?

Answer 1

• Acute - rapid onset, major pathogens
• Subacute/chronic - insidious onset, less virulent pathogens
• Mitral and aortic valves

Question 2

What is MSCRAMM?

Answer 2

Adhesive proteins that mediate binding to host ECM exposed on the lesion

Question 3

What is the general pathology of endocarditis?

Answer 3

Lesions form on valve leaflets, can progress to rupture chordae tendinae. Valve can’t close properly, blood regurgitation, heart murmur.

Question 4

Give examples of bacterial causes of endocarditis

Answer 4

• Streptococci and Staphyococci (Staph. aureus, Staph. pseudintermedius, Strep. canis/bovis)
• Mainly due to gram +ve bacteria

Question 5

Describe the pathogenesis of endocarditis

Answer 5

1. Damage to endocardium induces platelet and fibrin deposition - produces sterile thrombotic vegetation
2. Microbes bind to these vegetations
3. MOs become encased in further fibrin deposition. Multiply.
4. V. high conc. bacteria in vegetation (hinders antibiotic action)
5. Once bacteria stop replicating, resistant to beta lactams
6. Bacterial proteases break down valve tissue, rupture chordae tendinae and produce aortic root abscesses

Question 6

Once the vegetation is established, how is the subsequent clinical picture established?

Answer 6

• Bacteraemia
• Extent of local tissue destruction
• Embolisation
• Formation of circulating immune complexes

Question 7

What are the clinical signs of infectious endocarditis?

Answer 7

• Valvular insufficiency and congestive heart failure
• Bacteraemia
• Septic embolisation and organ infarction
• Metastatic infection and myocarditis
• Immunopathologic sequelae and immune complex deposition
• Glomerulonephritis
• Uveitis
• Polyarthritis
• Meningitis

Question 8

How is endocarditis diagnosed?

Answer 8

1. Without echocardiogram: recent onset/change in murmur, +ve blood culture
2. With echocardiogram: aortic valve pathognomic, mitral valve suggestive of endocarditis
3. Supportive clinical findings:

• Signalment, fever, limb oedema, lameness, limb ischaemia, inflammatory leukogram, +ve blood culture

Question 9

Describe the onset of infectious myocarditis

Answer 9

• Usually results from haematogenous spread of MOs to myocardium/extension of endocarditis lesions.
• Hard to diagnose in life

Question 10

Describe the onset of pericarditis

Answer 10

May result from direct inoculation of organisms into the pericardium e.g. penetrating wound, extension from adjacent organs, haematogenous dissemination of viral, bacterial and fungal pathogens to pericardium