What are the diagnostic criteria and treatment guidelines for endocarditis?

Diagnostic Criteria for Infective Endocarditis

The diagnosis of infective endocarditis (IE) is based on the modified Duke criteria with additional 2015 ESC updates that incorporate advanced imaging techniques, which significantly improve diagnostic accuracy especially in difficult cases like prosthetic valve endocarditis. 1

Modified Duke Criteria for IE Diagnosis

Definite IE (meets any of the following):

• 2 major criteria, or
• 1 major criterion and 3 minor criteria, or
• 5 minor criteria

Possible IE:

• 1 major criterion and 1 minor criterion, or
• 3 minor criteria

Rejected IE:

• Firm alternate diagnosis, or
• Resolution of symptoms with ≤4 days of antibiotics, or
• No pathological evidence of IE at surgery/autopsy with ≤4 days of antibiotics, or
• Does not meet criteria for possible IE

Major Criteria

1. Blood Cultures Positive for IE

• Typical microorganisms from 2 separate blood cultures:
  • Viridans streptococci, Streptococcus gallolyticus (S. bovis), HACEK group, Staphylococcus aureus
  • Community-acquired enterococci without primary focus
• Persistently positive blood cultures:
  • ≥2 positive cultures drawn >12 hours apart, or
  • All of 3 or majority of ≥4 separate blood cultures (first and last drawn ≥1 hour apart)
• Single positive blood culture for Coxiella burnetii or phase I IgG antibody titer >1:800

2. Imaging Evidence of Endocardial Involvement

• Echocardiogram positive for IE:
  • Vegetation
  • Abscess, pseudoaneurysm, intracardiac valvular perforation/aneurysm
  • New partial dehiscence of prosthetic valve
  • New valvular regurgitation
• Advanced imaging (2015 ESC update):
  • Paravalvular lesions on cardiac CT
  • Abnormal activity around prosthetic valve on 18F-FDG PET/CT (if prosthesis >3 months old) or radiolabeled leukocyte SPECT/CT

Minor Criteria

1. Predisposition: Predisposing heart condition or injection drug use
2. Fever: Temperature ≥38°C
3. Vascular phenomena: Major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhage, conjunctival hemorrhages, Janeway lesions
4. Immunological phenomena: Glomerulonephritis, Osler's nodes, Roth's spots, rheumatoid factor
5. Microbiological evidence: Positive blood culture not meeting major criteria or serological evidence of active infection with organism consistent with IE
6. Silent embolic events or infectious aneurysms detected by imaging only (2015 ESC update)

Diagnostic Algorithm

1. Clinical suspicion of IE based on fever, new murmur, embolic phenomena, predisposing conditions
2. Blood cultures: Obtain at least 3 sets before starting antibiotics
3. Echocardiography:
   • Start with transthoracic echocardiography (TTE)
   • Proceed to transesophageal echocardiography (TOE) if TTE negative but high suspicion, or for better assessment of complications
4. Apply modified Duke criteria with 2015 ESC updates
5. Consider advanced imaging in difficult cases:
   • Cardiac CT for paravalvular lesions
   • 18F-FDG PET/CT or radiolabeled leukocyte SPECT/CT for prosthetic valve endocarditis
   • MRI for embolic events

Special Considerations

Blood Culture-Negative IE (BCNIE)

• Common cause: prior antibiotic administration (withdraw antibiotics and repeat cultures)
• Consider serological testing for:
  • Coxiella burnetii (Q fever)
  • Bartonella species
  • Brucella
  • Mycoplasma
  • Legionella
  • Tropheryma whipplei

Prosthetic Valve Endocarditis (PVE)

• Lower sensitivity of standard Duke criteria (echocardiography normal/inconclusive in up to 30% of cases)
• Advanced imaging crucial:
  • 18F-FDG PET/CT (if prosthesis >3 months old)
  • Radiolabeled leukocyte SPECT/CT

Cardiac Device-Related IE

• Consider extraction of device and lead cultures
• Similar diagnostic approach with emphasis on echocardiography and advanced imaging

Common Pitfalls to Avoid

1. Premature antibiotic administration before adequate blood cultures (at least 3 sets)
2. Relying solely on TTE when suspicion is high (TOE has higher sensitivity)
3. Failure to consider BCNIE in patients with prior antibiotic use
4. Not utilizing advanced imaging in difficult cases, especially PVE
5. Missing the diagnosis due to absence of classical Osler manifestations (bacteremia, fever, peripheral stigmata)

The diagnostic accuracy of the modified Duke criteria with the 2015 ESC updates significantly improves the detection of IE, especially in challenging cases. Early and accurate diagnosis is crucial for appropriate management and improved outcomes in this life-threatening condition.