Infective endocarditis - Stages, Etiological Agents, Classification, Risk Factors
Introduction to Infective endocarditis
It is infective inflammation of the endocardium (inner lining of the heart) where especially heart valves are involved. The infection is caused by cardiac abnormalities such as congenital valvular disease, direct trauma from IV catheters, etc.
Stages/Process
The congenital valvular disease leads to turbulence in blood flow because of the above-mentioned causes, and the cardiac endothelium is damaged.
Deposition of platelets and fibrin on the damaged capillary endothelial surface occurs.
If bacteremia (even transient) occurs, they stick and colonize the damaged cardiac endothelial cell surface (also attach to prosthetic heart valves resulting in the seeding of microorganisms).
The colony is rapidly covered with a protective layer of fibrin and platelets and the protective layer provides a favorable environment for further bacterial multiplication.
The web of platelets, fibrin, inflammatory cells and entrapped organisms is called vegetation.
These vegetations seed bacteria into the blood at a slow but constant rate.
The etiological agent of infective endocarditis
The etiological agent of infective endocarditis includes:
Viridians streptococci *
S. aureus *
CoNs (Coagulase Negative Staphylococci)
Streptococcus pyogenes
Streptococcus bovis
Haemophilus spp.
Enterococci *
Enterobacteriaceae (E. coli)
Pseudomonas spp.
Staphylococcus epidermidis
HACEK / AACEK group (fastidious gram-negative bacilli)
Aggregatibacter aphrophilus
Actinobacillus actinomycelemcomitans
Cardiobacterium hominis
Eikenella corrodens
Kingella kingae
* most common microorganisms with native valve endocarditis in non-drug-using adult
* Streptococcus sanguis and Streptococcus mutans are frequently isolated in Streptococcal endocarditis
These microorganisms are normal inhabitants of the oral cavity, often gaining entrance to the bloodstream as a result of gingivitis, periodontitis, dental manipulation, etc. Heart valves (especially previously damaged) provide a convenient surface for attachment.
Risk factors of infective endocarditis
The risk factors of infective endocarditis are as follows:
1. Prosthetic heart valves, arterial lines
2. Congenital heart disease
3. Invasive surgery
4. IV drug abuse
5. Rheumatic heart disease
Classification of infective endocarditis
The classification of of infective endocarditis are as follows:
On the basis of duration
Acute endocarditis
sudden onset
develops over a period of days to weeks
characterized by spiking fever, tachycardia, fatigue, progressive damage to cardiac structures
S. aureus is commonly associated with pathogen
infection is metastatic (spreading type) in nature
Sub-acute endocarditis
This develops over the course of weeks to months. Often the patients will complain of constitutional symptoms (fatigue, weight loss, fever, etc).
On the basis of the location of infection
Native valve infection
mainly seen in IV drug users
right-sided valve is often involved
commonly associated pathogens are Staphylococcus, Streptococcus, and gram-negative bacilli (AACEK)
Prosthetic valve endocarditis
This accounts for 10-30% of all cases of infection endocarditis
Defined as early or late depending upon whether the infection has occurred before or after 1 year of replacement of heart valves
CoNs and S. aureus are mainly responsible for early prosthetic valve endocarditis
* Staphylococcus aureus, Streptococcus spp., and gram-negative bacilli are responsible for late prosthetic valve endocarditis.
Right-sided endocarditis
This accounts for 5-10% of all cases of infective endocarditis
It is commonly seen in IV drug users
Tricuspid value is mainly involved
Device-related endocarditis
This occurs in patients with intracardiac devices (eg. pacemakers) or devices in the circulatory system
The mortality rate is high due to difficulty in diagnosis