cardiovascular disorders
Infective Endocarditis
Etiology of Infective Endocarditis
The normal heart is relatively resistant to infection. Bacteria and fungi do not easily adhere to the endocardial surface, and constant blood flow helps prevent them from settling on endocardial structures. Thus, 2 factors are typically required for endocarditis: A predisposing abnormality of the endocardium Microorganisms in the bloodstream (bacteremia) Massive bacteremia or particularly virulent microorganisms (eg,Staphylococcus aureus) cause endocarditis on normal valves. Endocarditis usually involves the heart valves. Major predisposing factors are Overview of Congenital Cardiovascular Anomalies , Infective endocarditis occurs most often on the left side (eg, mitral or aortic valve). About 10 to 20% of cases are right-sided (tricuspid or pulmonic valve). Patients who use illicit intravenous drugs have a much higher incidence of right-sided endocarditis (about 30 to 70%). Microorganisms that infect the endocardium may originate from distant infected sites (eg, cutaneous abscess, inflamed or infected gums, urinary tract infection) or have obvious portals of entry such as a central venous catheter or a drug injection site. Almost any implanted foreign material (eg, ventricular or peritoneal shunt, prosthetic device) is at risk of bacterial colonization, thus becoming a source of bacteremia and hence endocarditis. Endocarditis also may result from asymptomatic bacteremia, such as typically occurs during invasive dental, medical, or surgical procedures. Even toothbrushing and chewing can cause bacteremia (usually due to viridans streptococci) in patients with gingivitis. cause 80 to 90% of cases. Enterococci, gram-negative bacilli, HACEK Infections ( The disease develops in 3 stages: Bacteremia: Microorganisms are present in the blood Adhesion: The microorganism adheres to abnormal or damaged endothelium via surface adhesions Colonization: Proliferation of the organism together with inflammation, leading to a mature vegetation Many of the causative microorganisms produce polysaccharide biofilms that shield them from host immune defences and impede antibiotic penetration. 