What causes infective endocarditis?
Last reviewed: 23.04.2024
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Normally, the heart is relatively resistant to infections. Bacteria and fungi are difficult to attach to the surface of the endocardium, as this is prevented by a constant flow of blood. To develop infectious endocarditis, two factors are necessary: predisposing changes in the endocardium and the presence of microorganisms in the blood (bacteremia). Sometimes massive bacteremia and / or especially pathogenic microorganisms cause endocarditis of intact valves.
Endocardial causes of infective endocarditis
With endocarditis, heart valves are usually affected. The main predisposing factors are congenital heart defects, rheumatic valve disease, bicuspid or calcified aortic valves, mitral valve prolapse and hypertrophic cardiomyopathy. Prosthetic valves create a special risk. Sometimes there is an infection of intracavitary thrombi, defects of the interventricular septum and areas of the open arterial duct {ductus arteriosus). Usually, the place of primary infection is sterile vegetation from platelets and fibrin, formed with damage to the endothelium, when the cells of the latter synthesize the tissue factor.
Infective endocarditis most often occurs on the structures of the left heart (for example, on the mitral or aortic valve). Approximately 10-20% of cases are right-sided (tricuspid or pulmonary artery valve). Drug addicts injecting narcotics grandly have a much higher frequency of right-sided endocarditis (approximately 30-70%).
[1], [2], [3], [4], [5], [6], [7]
Bacterial causes of infective endocarditis
Microorganisms infecting the endocardium can migrate from distant infected areas (eg, cutaneous abscess, urinary system) or have a visible entrance gate (for example, a central venous catheter or injection site). Almost any implanted foreign material (for example, a ventricular or peritoneal shunt, valve prosthesis, etc.) is at risk of bacterial colonization, thus becoming a source of bacteremia and endocarditis. Also, endocarditis can be the result of asymptomatic bacteremia, which occurs, for example, during invasive dental, other medical manipulations or surgical operations. Even brushing and chewing can cause bacteremia (usually streptococcal) in patients with gingivitis.
The type of microorganisms varies depending on the location of the infection, the source of bacteremia and the risk factors of the host organism (eg, intravenous drug use), but in general, streptococci and Staphylococcus aureus cause 80% of all cases. Enterococci, gram-negative bacteria, anaerobic microorganisms and fungi cause most other cases. While it is not clear why streptococci and staphylococci often affect vegetation, and gram-negative aerobic bacteria are rare. However, the ability of Staphylococcus aureus to adhere to fibronectin may play a role, as does the synthesis of green streptococci - to dextran.
After colonization of vegetation, the microorganisms are covered with a layer of fibrin and platelets that block access to neutrophils, immunoglobulins, and the complement system, thus blocking immune defense.