Introduction
Infective endocarditis (IE) is a potentially life-threatening condition characterized by infection of the endocardial surface of the heart, typically involving heart valves. It is a complex disease with a wide range of clinical presentations, making early diagnosis and effective management crucial for reducing morbidity and mortality. This article will provide an in-depth discussion of IE, focusing on diagnosis using the Duke Criteria, microbiological evaluation, management protocols, and key considerations for Clinicians.
I. Overview of Infective Endocarditis (IE)
Infective endocarditis occurs when bacteria or fungi adhere to the heart's inner lining or valves, leading to inflammation and vegetation formation. The condition is categorized into acute and subacute/chronic types:
Acute IE typically progresses rapidly, often caused by aggressive organisms like Staphylococcus aureus, leading to valve destruction and heart failure.
Subacute/chronic IE is a slower process, often due to less virulent organisms such as Streptococcus viridans.
II. Pathogenesis of IE
IE usually occurs in individuals with predisposing heart conditions, including:
Congenital heart disease
Rheumatic heart disease
Prosthetic heart valves
IV drug use (a significant risk factor for right-sided IE)
Degenerative valve disease in elderly populations
The key pathophysiological feature of IE is the formation of vegetations—clusters of microorganisms, immune cells, and fibrin—which can lead to complications such as:
Embolization to distant organs (causing stroke, pulmonary embolism, or organ infarction)
Valvular destruction and heart failure
Immune complex deposition, leading to glomerulonephritis and vasculitis
III. Clinical Presentation
The clinical presentation of IE can be highly variable. Common symptoms include:
Fever (present in over 90% of cases)
Malaise and fatigue
New or changing heart murmur
Chills, night sweats
Embolic phenomena (stroke, splinter hemorrhages, petechiae, Osler’s nodes, Janeway lesions)
Signs of heart failure (dyspnea, edema)
Given the diverse presentation, Clinicians must maintain a high index of suspicion, especially in at-risk populations such as IV drug users or patients with prosthetic valves.
IV. Duke Criteria for Diagnosis
The Duke Criteria is the standard diagnostic tool for infective endocarditis. It includes both major and minor criteria:
A. Major Criteria
Positive Blood Cultures:
Two separate positive blood cultures for typical IE-causing organisms:
Streptococcus viridans
Streptococcus gallolyticus (formerly S. bovis)
HACEK organisms (Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella)
Staphylococcus aureus
Enterococcus (without a primary source of infection)
Persistently positive blood cultures: ≥ 2 positive cultures drawn ≥12 hours apart, or all of 3 or a majority of 4 separate blood cultures, with the first and last drawn at least 1 hour apart.
"Persistently positive blood cultures" หมายถึงการตรวจพบเชื้อในเลือดที่เป็นบวกอย่างต่อเนื่อง ซึ่งสามารถวินิจฉัยได้ดังนี้:
พบว่าผลเลือดเป็นบวก อย่างน้อย 2 ครั้ง โดยเก็บตัวอย่างเลือดที่มีผลบวกห่างกัน ≥ 12 ชั่วโมง
หรือพบว่าเป็นบวกใน 3 ตัวอย่างจากทั้งหมด 3 ครั้ง หรือ มากกว่า 3 ครั้งจากทั้งหมด 4 ครั้ง ที่เก็บตัวอย่างเลือด โดยให้ตัวอย่างเลือดครั้งแรกและครั้งสุดท้ายห่างกันอย่างน้อย 1 ชั่วโมง
การตรวจพบเชื้อแบบต่อเนื่องนี้ช่วยยืนยันการติดเชื้อในหลอดเลือดที่สัมพันธ์กับการเกิด Infective Endocarditis (IE)
Echocardiographic Evidence:
Vegetation (the hallmark finding in IE)
Abscess formation
New partial dehiscence of a prosthetic valve
New valvular regurgitation
B. Minor Criteria
Predisposing cardiac condition or IV drug use.
Fever ≥ 38°C (100.4°F).
Vascular phenomena:
Arterial emboli
Septic pulmonary infarcts
Intracranial hemorrhage
Janeway lesions
Immunologic phenomena:
Glomerulonephritis
Osler's nodes
Roth spots
Microbiological evidence:
Positive blood cultures that do not meet major criteria, or serologic evidence of infection.
C. Diagnostic Interpretation
Definitive IE:
2 major criteria, or
1 major and 3 minor criteria, or
5 minor criteria.
Possible IE:
1 major and 1 minor criterion, or
3 minor criteria.
V. Microbiological Evaluation: Hemoculture Protocol
A. Timing of Blood Cultures
Blood cultures are essential for diagnosing IE. Here's the recommended protocol:
Draw 3 sets of blood cultures from different venipuncture sites, spaced over a period of 30 minutes to 1 hour. For patients with hemodynamic stability, it’s advisable to wait for culture results before initiating antibiotic therapy.
In critically ill patients or those with strong suspicion of IE, obtain all 3 sets of cultures within 60 minutes, and then start empiric antibiotics.
Volume of blood: Each set should include 10 mL of blood for both aerobic and anaerobic bottles to maximize pathogen recovery.
B. Repeat Cultures
If cultures are negative after 48-72 hours, repeat the blood cultures, especially if clinical suspicion remains high.
C. Organisms Commonly Associated with IE
Staphylococcus aureus (most common in IV drug users)
Streptococcus viridans (associated with dental procedures)
Enterococcus (linked with genitourinary or gastrointestinal manipulations)
HACEK organisms (slow-growing gram-negative bacteria)
VI. Management of Infective Endocarditis
A. Empiric Antibiotic Therapy
Empiric therapy should be guided by patient-specific factors (e.g., IV drug use, prosthetic valves):
Native valve endocarditis (empiric therapy): Combination of vancomycin (to cover MRSA) and ceftriaxone (to cover Streptococcus and Enterococcus species).
Prosthetic valve endocarditis: Consider adding rifampin for biofilm-active coverage in the case of Staphylococcus aureus or coagulase-negative Staphylococci.
B. Definitive Therapy
Once the causative organism is identified, tailor antibiotic therapy accordingly:
Streptococcus viridans: Penicillin G or ceftriaxone for 4-6 weeks.
Staphylococcus aureus: For MSSA, use nafcillin or oxacillin; for MRSA, use vancomycin or daptomycin.
Enterococcus: Combination of ampicillin or vancomycin with gentamicin.
VII. Indications for Surgery
Surgical intervention is required in certain cases of IE, particularly when:
Heart failure is present due to valvular dysfunction.
Abscesses or other complications (e.g., fistulas) are detected.
Prosthetic valve involvement is causing uncontrolled infection.
Recurrent embolic events occur despite appropriate antibiotic therapy.
VIII. Prevention and Prophylaxis
Prophylaxis is indicated in high-risk individuals undergoing dental or other procedures that involve mucosal surfaces. These individuals include:
Patients with prosthetic heart valves.
Those with a history of previous IE.
Patients with congenital heart disease.
Prophylaxis typically involves amoxicillin (2g orally) or clindamycin (600mg orally) for patients allergic to penicillin.
IX. Conclusion
Infective endocarditis is a complex and serious condition requiring prompt diagnosis, microbiological evaluation, and tailored management. Clinicians must be adept at recognizing the clinical features, employing the Duke Criteria for diagnosis, and initiating appropriate antimicrobial therapy. For those cases requiring surgical intervention, timely collaboration with cardiothoracic surgery teams is critical. Mastering these principles is essential for improving outcomes and reducing complications in patients with IE.
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