CVS: Infective Endocarditis

Question 1

Describe the pathophysiology of IE

Answer 1

i) Transient bacteraemia (dental procedures, surgery, distant primary infections, non-sterile injections)
ii) adhesion and invasion of a non-bacterial thrombotic endocarditis (sterile fibrin-platelet vegetation)
iii) infection of endocardial surface of heart, which may involve 1 or more heart valves, mural endocardium or a septal defect

Question 2

Which valves are most most commonly affected by IE?

Answer 2

aortic valve > mitral valve > combined aortic and mitral valves > tricuspid valve > pulmonary valve (rare)

Question 3

Name possible causative organisms for IE

Answer 3

1. Staph. aureus - most common, esp. with prosthetic valves, acute IE and IV drug-abuse related IE (high mortality)
2. Streptococci:
   - S. viridans - 50-60% of subacute IE cases
   - Group D streptococci - usually subacute
3. Pseudomonas aeruginosa - usually acute IE, requires surgery for cure

Question 4

Describe the 2 types of IE. Which organisms are usually responsible?

Answer 4

1. Acute IE: days-weeks (<2wks), commonly S. aureus (greater virulence)
2. Subacute IE: mild to moderate disease, weeks-months (>2wks), often S. viridans

Question 5

Suggest risk factors for devel of IE

Answer 5

60% have a predisposing heart condition

• valvular heart disease with stenosis or regurgitation (e.g. bicuspid aortic valve)
• valve replacement
• structural congenital heart disease
• prev. IE
• hypertrophic cardiomyopathy
• IV drug use (non-sterile)
• invasive vascular procedures

Question 6

Which symptoms would a pt with IE present with?

Answer 6

Emboli to brain, lung or spleen is presenting complaint in 30%.

Symptoms:

• fever (90%)
• systemic symptoms: chills, poor appetite, weight loss (esp. in subacute)
• loin pain and haematuria - due to renal infarction

Question 7

Describe what signs you might find in a pt with IE

Answer 7

1. heart murmurs (85%)
2. peripheral stigmata:
   - splinter haemorrhages
   - Janeway’s lesions
   - Osler’s nodes
   - petechiae (conjunctiva, dorsum hands and feet, chest and abdo wall, oral mucosae and soft palate)
   - clubbing (in chronic disease)
3. fundoscopy: Roth spots
4. splenomegaly - if splenic infarction

Question 8

Which investigations would you request for a pt with suspected IE?

Answer 8

1. Blood
   - FBC = increased WCC, anaemia
   - CRP and ESR = increased
   - lactate = increased in severe sepsis
   - bilirubin = increased in severe sepsis
   - blood cultures (+/- blood PCR) = cornerstone of Dx, 3 sets taken at 30min intervals at diff sites
2. Bedside tests:
   - urine dipstick = microscopic haematuria
   - ECG = detect 20% who develop conduction defects
3. Imaging:
   - CXR
   - OPG: dental hygiene
   - ECHO = vegetation, abscess or pseudoaneurysm and new dehiscence of prosthetic valve are diagnostic for IE
   - CT = alternative for Dx in some pts (e.g. risk of vegetation embolisation)
   - cerebral MRI: for detection of cerebral consequences of IE in pts with neurological Sx
4. Histology
   - pathological examination of resected valvular tissue or embolic fragments = gold standard for IE Dx

Question 9

Describe the modified Duke criteria for diagnosis of IE

Answer 9

Dx requires 2 major criteria, 1 major + 3 minor criteria or 5 minor criteria.

MAJOR CRITERIA

• +ve blood culture for IE
• +ve echo for IE

MINOR CRITERIA

• predisposing heart condition or IV drug use
• fever >38 degrees
• vascular phenomena = major arterial thrombi, septic pulmonary infarcts, mycoctic aneurysms, intracranial or conjunctival haemorrhage, Janeway’s lesions
• immunological phenomena = glomerulonephritis, Osler’s nodes, Roth’s spots and rheumatoid factor
• microbiological phenomena = +ve blood cultures but does not meet a major criterion, or serological evidence of active infection with organism consistent with IE
• PCR = broad-range PCR of 16S
• ECHO findings consistent with IE but does not meet major criterion

Question 10

How would you treat a pt with IE?

Answer 10

ANTIMICROBIAL THERAPY

1. initial empirical therapy whilst awaiting culture results
   - native valve endocarditis (NVE) = amoxicillin +/- gentamicin
   - prosthetic valve endocarditis = vancomycin + gentamicin + rifampicin
2. when culture results available, start targeted antimicrobial therapy according to sensitivities and local guidelines

Question 11

In which cases of IE is surgical Tx required?

Answer 11

Required in about 50% due to severe complications. 3 main indications for early surgery in IE are:

1. HF
2. uncontrolled infection
3. prevention of embolic events

Question 12

Suggest possible complications of IE

Answer 12

1. congestive HF (most frequent complication, 42-60% NVE cases) - mainly caused by new or worsening aortic/mitral regurgitation
2. uncontrolled infection - perivalvular extension of IE is most frequent cause, e.g. abscess formation, pseudoaneurysms and fistulae.
3. embolic events (20-50%) - brain and spleen emboli most frequent in L-sided IE whilst PE most frequent in R-sided IE
4. AKI (6-30%) - causes often multi-factorial: i. immune complex and vasculitic glomerulonephritis, ii. renal infarction due to septic emboli, iii. antibiotic toxicity. etc.
5. Arrhythmias - due to spread of infection beyond endocardium to conduction pathways. mainly 1st, 2nd and 3rd degree atrio-ventricular blocks.
6. Septic shock

Question 13

What is the overall 1yr mortality rate

Answer 13

30%