infective%20endocarditis
INFECTIVE ENDOCARDITIS
Infective endocarditis is microbial infection of the endovascular structures of the heart.
It often presents in an occult fashion and early diagnosis depends on a high index of clinical suspicion especially in patients with congenital heart disease, prosthetic valves or previous infective endocarditis.
The established diagnosis of infective endocarditis is demonstrated by a positive blood culture and involvement of the endocardium detected during sepsis or systemic infection. It may also be established if there is involvement of the endocardium detected during sepsis or systemic infection but blood culture is negative.

Introduction

Infective Endocarditis (IE): An infection of the endocardial surface of the heart including infections of the large thoracic vessels and intracardiac foreign bodies characterized by the presence of vegetation which is a nidus for microorganism invasion

Native Valve Endocarditis (NVE): An endovascular microbial infection of native heart valves that may be local (cardiac) including valvular and perivalvular destruction or distal (non cardiac) due to detachment of septic vegetation with embolism, metastic infection and septicemia

  • May also be broken down as acute and subacute; the only difference is that subacute endocarditis has a more indolent course than the acute form
Prosthetic Valve Endocardits (PVE): An endovascular microbial infection of prosthetic heart valves (intracardiac foreign body) and may be classified as an infection likely to have been acquired perioperatively and thus being nosocomial (early PVE) or likely to have been community-acquired (late PVE)
  • Early PVE occurs within <12 months of valve implantation and late PVE occurs ≥12 months after valve implantation

Etiology

Bacterial

  • Staphylococcus sp: Causes approximately 25% of NVE
    • S aureus (coagulase-positive staphylococci): Commonly cause PVE, IE in intravenous drug abusers (IVDA) and in patients with previously normal cardiac valves
      • Main causative organism in healthcare-associated IE and in IVDA
    • IVDA often present with right-sided cardiac involvement
    • Non-IVDA usually present with left-sided cardiac involvement and have skin and soft tissue infections with underlying congenital abnormalities
    • S epidermidis, S lugdunensis (coagulase-negative staphylococci): Most common causes of PVE and have been known to cause NVE
      • Mostly Methicillin-resistant and S lugdunensis is associated with very destructive valvular and perivalvular lesions
    • Methicillin-susceptible S aureus (MSSA): May cause right-sided endocarditis in intravenous (IV) drug users
    • Methicillin-resistant S aureus (MRSA): Occurs particularly in PVE, right-sided endocarditis in IV drug users and nosocomial endocarditis
    • Causes aggressive endocarditis with increased risk of embolism, persistent bacteremia, stroke and death
  • Streptococcus sp (viridans group of streptococci; S pneumoniae; S pyogenes; Lancefield group B, C, G streptococci; S gallolyticus (previously known as S bovis), S mitis, S mutans, S sanguis and Abiotrophia sp): Most common causes of NVE
    • Group B streptococci: Most common beta-hemolytic streptococci and cause the most virulent IE among streptococci which is characterized by a fulminant disease with large crumbling vegetations with the frequency of embolization related to size
    • Group G streptococci: Both native and prosthetic valves can be affected with left-sided involvement being more common
    • Viridans streptococci: Most common cause of NVE in patients with congenital heart disease or defects and in patients who are not IV drug users
    • S gallolyticus: Also causes bacterial endocarditis
  • Enterococci: Third leading cause of IE
  • Culture-negative organisms: Common causative organisms of endocarditis producing culture-negative blood cultures
    • HACEK (Haemophilus parainfluenzae, aphrophilus, and paraphrophilus; Aggregatibacter (formerly Actinobacillus) actinomycetemcomitans; Cardiobacterium hominis, Eikenella corrodens; and Kingella): Can cause NVE and PVE
    • Bartonella henselae: Exposure to infected cats may predispose patient to IE
    • Brucella
    • Chlamydia psittaci: Exposure to infected birds may predispose patient to IE
    • Coxiella burnetii: Exposure to infected sheep, cattle and wild rabbits may predispose patient to IE
    • Legionella: Characterized by a febrile course that extends up to months with cardiac signs of newly developed murmurs and extremely high anti-Legionella titers
    • Mycobacterium
    • Pseudomonas aeruginosa: Most commonly occurs in IVDAs and is an important pathogen in early PVE
      • Commonly involves the tricuspid valve and may present as subacute infection with septic pulmonary emboli and right-sided heart failure

Fungal

An increasing cause of PVE in IVDAs and immunocompromised patients

  • Candida: Most common cause of fungal endocarditis
  • Aspergillus
  • Nocardia

Signs and Symptoms

  • Embolic event(s) of unknown origin
  • Fever, plus:
    • Positive blood culture (organism identified is typical for NVE/PVE)
    • Previous history of IE, valvular or congenital heart disease
    • Evidence of congestive heart failure (CHF) or pulmonary embolism
    • Focal or nonspecific neurological signs and symptoms
    • Cutaneous (Osler, Janeway) or ophthalmic (Roth) manifestations
    • Newly developed ventricular arrhythmias or conduction disturbances
    • Peripheral abscesses (renal, splenic, spine) of unknown origin
    • Predisposition and recent diagnostic/therapeutic interventions known to result in significant bacteremia
    • Prosthetic material inside the heart
    • Pulmonic infiltrations that are multifocal/rapid changing (right IE)
  • Hematuria, glomerulonephritis and suspected renal infarction
  • New valve lesion/regurgitant murmur
  • Sepsis of unknown origin

Risk Factors

Cardiac Risk Factors for IE

High Risk Factors

  • Aortic regurgitation
  • Aortic stenosis
  • Coarctation of aorta
  • Cyanotic congenital heart disease
  • Mitral regurgitation
  • Mitral stenosis with regurgitation
  • Patent ductus arteriosus
  • Previous IE
  • Prosthetic heart valves
  • Surgically repaired intracardiac lesion with residual hemodynamic abnormality
  • Ventricular septal defect

Intermediate Risk Factors

  • Asymmetrical septal hypertrophy
  • Bicuspid aortic valve disease
  • Calcific aortic sclerosis with minimal hemodynamic abnormality
  • Degenerative valve diseases in elderly patients
  • Mitral valve prolapse
  • Pulmonary stenosis
  • Pure mitral stenosis
  • Surgically repaired intracardiac lesion with minimal hemodynamic abnormality <6 months after surgery
  • Tricuspid valve disease

Non-Cardiac Risk Factors Predisposing Patient to IE

  • Older age
  • Nonbacterial thrombotic vegetation (NBTV): Microorganisms may adhere more easily in the presence of fresh, platelet thrombi associated with leukemia, cirrhosis of the liver, carcinomas which may cause hypercoagulability (marantic endocarditis), inflammatory bowel disease, systemic lupus erythematosus (SLE) and  steroid medication
  • Compromised host defense typical in steroid medication and possibly in chronic alcoholism
  • IVDA risk of IE is 12-fold higher than non-IVDAs
  • Compromised local non-immune defense mechanism
    • Found in increased transmucosal permeability in mucous membrane lesions eg chronic inflammatory bowel disease
    • Reduced capillary clearance in arteriovenous fistulas of patients on chronic hemodialysis
  • Increased risk or an increased frequency for bacteremia
    • Patients with broken skin (eg DM, burns), on intensive care (eg lines, respirators), with polytrauma, with poor dental status or on hemodialysis
    • Previous exposure to endocarditis-causing microorganisms

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