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medical microbiology > Endocarditis > Flashcards

Endocarditis Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

What is Infective Endocarditis

A

A destructive process that affects mostly valves, leads to CHF, embolization and death if untreated

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2
Q

How to diagnose Endocarditis

A

Blood Tests 95% of cases

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3
Q

What are the causes of Endocarditis

A

Bacterial - Staphylococcus aureus and Streptococcus viridans cause > 80%, Yeast or Fungal infections

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4
Q

Where does Endocarditis occur?

A

Mostly valves, also paps or endocardial surface of ventricles, catheters, pacemaker wires, prosthetic materials

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5
Q

What is the classic presentation of Endocarditis?

A

Vegetations usually on the low pressure side of the valve(flow side) which is the atrial side for MV/TV and ventricle for PV/AOV

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6
Q

What does Endocarditis look like?

A

Shaggy smudgy, pedunculated, usually highly mobile and can seed other areas. Vegetations vary widely in appearance

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7
Q

what are the consequences of bacteria forming a plaque in heart valve?

A

Heart failure
Septicaemia with possible septic shock
Blood vessel blockage – tissue death

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8
Q

how does this happen?

A

Cant open properly
Can cause blockage
results in tissue death

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9
Q

what can predispose you to endocarditis?

A

Damaged heart valves
Replacement heart valves
Intravenous drug abuse
Long term venous access
Eg cancer patients, ICU patients

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10
Q

Subacute Endocarditis

A

Subtle presentation- Usually by streptococcus viridans carrying a low grade fever, fatigue, weight loss, cough, weakness, patient may not recognize seriousness of it

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11
Q

Acute Endocarditis

A

Usually staphylococcus aureus, carrying a high fever, rapid onset of symptoms like heart murmurs and can lead to CHF symptoms

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12
Q

Acute Endocarditis continued

A

Embolization signs with left heart involvement- petechiae and purpuric skin lesions and Janeway lesions, TIA, CVA

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13
Q

Purpuric skin lesions and petechiae

A

clumps on legs

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14
Q

Janeway lesions

A

on palms and soles of the feet

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15
Q

How to diagnose Endocarditis?

A

FUO, + new murmurs+ blood cultures

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16
Q

Blood cultures not always accurate for endocarditis

A

multiple samples needed, antibiotics for 2+ days affects results and fungal etiologies often have negative cultures

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17
Q

What size veg can echo detect?

A

> 3mm

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18
Q

What size veg can TEE detect?

A

> 1mm

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19
Q

If no veg does that mean no endocarditis?

A

No, must follow DUKE criteria

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20
Q

what are the major indicators of endocarditis

on criteria of DUKE?

A

Multiple positive blood cultures
- Typically 3 sets over 24 hours
Positive for typical endocarditis
- associated organism
Positive echocardiogram
- Visualisation of obstructing mass

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21
Q

what are the minor indicators of endocarditis?

A

Temperature above 38C
Predisposing heart condition
Immunologic phenomena
glomerulonephritis
Vascular phenomena
emboli
Positive blood culture – not fitting with major
Positive echo – not fitting with major

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22
Q

diagnosis based on DUKE criteria

A

2 major criteria
1 major and 3 minor criteria
5 minor criteria

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23
Q

Complications of endocarditis

A

Valvular regurgitation that worsens as lesion enlarges, valvular destruction, CHF from severe or acute regurg

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24
Q

Perivalvular abscesses (MV/AOV ring)

A

extensions of active infective disease, echolucent or echodense areas adjacent to valve apparatus, fistula formation, evaluate with color and doppler carefully, TEE

25
Q

Perivalvular abscesses - what can happen

A

Emobization -TIA, CVA, LV wma- pulmonary embolus, pericarditis and pericardial effusion can result, mycotic aneurysm can occur- echolucent but hard to tell from abscess

26
Q

Can Mechanical and tissue valves be affected by Infective endocarditis?

A

Yes - shadows and artifacts may impair visualization and perivalvular leaks or dehiscence may cause a rocking motion of the sewing ring

27
Q

which organism causes 40% of endocarditis?

A

Viridans streptococci

28
Q

where is it normally found?

A

a oral flora

29
Q

how can infection start?

A

from brushing teeth with cut up mouth

30
Q

which organism causes another 15% of infections?

A

Enterococci

31
Q

where is it normally found?

A

gut

32
Q

which organism causes 30% of infections?

A

Staphylococcus aureus

33
Q

which group of people if Staphylococcus aureus infections much higher?

A

iv drug users

34
Q

which group of organisms cause 10% of infections?

A

HACEK group -
Haemophilus aphrophilus
Actinobacillus actinomycetemcomitans
Cardiobacterium hominis
Eikenella corrodens
Kingella kingeae

35
Q

where are HACEK group found?

A

oral flora

36
Q

pathogenesis of endocarditis?

A

Damaged or inflammed valve
Organism binds to exposed antigens
Eg fibronectin
Immune response with fibrin deposition
Binding of organism to fibrin antigens

37
Q

how does the infection progress?

A

the cycle repeats
Formation of growth - “vegetation”
Disrupts valve function
May shed infective fragments

38
Q

in diagnosis, how is blood drawn for culture?

A

Clean skin site with alcohol - based wipe (make sure alcohol evaporates)
Draw 5 – 10mls venous blood

39
Q

how is the blood then processed?

A

Change needle on syringe
Inject blood into culture vial
Contains liquid culture media

40
Q

what does culture vial base include to aid diagnosis?

A

fluorescent dye

41
Q

how does the dye help?

A

Dye reacts with products of bacterial metabolism
Fluorescent spectrum of dye changes with such reactions

42
Q

how is this processed?

A

Automated system detects spectrum shift
Automated system sounds alarm to indicate possible positive culture

43
Q

what is done if a culture vial is flagged as positive?

A

~ 1ml removed
Gram stain

44
Q

what happens once Gram stain report completed?

A

Clinical team notified
- Presumptive diagnosis discussed
- presumptive antibiotics discussed

45
Q

what is done to confirm diagnosis more?

A

Subculture to solid media
- Purity plate for subsequent identification

46
Q

what is done to aid antibiotic prescribing?

A

Disc sensitivity testing

47
Q

what media is used for the subculture when gram negative bacillus suspected?

A

GNB’s
MacConkey and chocolate at 37C in 5% CO2
Blood agar at 37C anaerobic
Neomycin Blood agar 37C anarobic

48
Q

gram negative cocci?

A

GNC’s
chocolate at 37C in 5% CO2
Blood agar at 37C anaerobic

49
Q

clumped cells?

A

GPC’s
Chocolate at 37C in 5% CO2
Blood agar at 37C anaerobic
DNA’ase plate
Plasma solution

50
Q

chains?

A

GPC and GPB
Blood and MacConkey at 37C in 5% CO2
Blood agar at 37C anaerobic

51
Q

what must be passed onto clinical team?

A

With final identification
With actual sensitivity profile
Allows modification of initial therapy if needed

52
Q

how long is Normal blood culture incubation?

A

5 days

53
Q

why is it increased length of time in endocarditis?

A

increased to 10 days
Fastidious and slow growing HACEK organisms

54
Q

what is the standard therapy for Gram positive endocarditis?

A

a penicillin + gentamicin

55
Q

what are the roles of each antibiotic?

A

Penicillin – breaks cell wall
Gentamicin – attacks ribosome and prevent recovering from cell wall damage

56
Q

what special requirements do Streptococci need in sensitivity testing?

A

Use “High dose” gentamicin disc
Sensitive streptococci show synergy with penicillin and low dose gentamicin.
Resistant streptococci: no synergy so gentamicin not used

57
Q

why is Penicillin MIC testing a good idea?

A

Need an indication of degree of sensitivity
Influences treatment duration

58
Q

how long is treatment normally?

A

prolonged; months

59
Q

how do you check on progress?

A

But testing blood regularly to insure enough antibiotic are in the blood to kill the specific organism infecting

medical microbiology (29 decks)

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