Chapter 431 Infective Endocarditis
Infective endocarditis includes acute and subacute bacterial endocarditis, as well as nonbacterial endocarditis caused by viruses, fungi, and other microbiologic agents. It is a significant cause of morbidity and mortality in children and adolescents despite advances in the management and prophylaxis of the disease with antimicrobial agents. The inability to eradicate infective endocarditis by prevention or early treatment stems from several factors. The disease represents a complex interplay between a pathogen and host factors such as endothelial disruption and immune function that is still not completely understood; the nature of the infecting organism has changed over time; diagnosis may be difficult during early stages and is thus often delayed until a more serious infection has set in; and special risk groups have emerged, including intravenous drug users; survivors of cardiac surgery, especially those with mechanical prosthesis; patients taking immunosuppressant medications; and patients who require chronic intravascular catheters. Some patients get endocarditis on what was thought to be a previously healthy native valve, although on surgical inspection is found to have mild structural abnormalities.
Etiology
Viridans-type streptococci (α-hemolytic streptococci) and Staphylococcus aureus remain the leading causative agents for endocarditis in pediatric patients. Other organisms cause endocarditis less frequently and, in ≈6% of cases, blood cultures are negative for any organisms (Table 431-1). No relationship exists between the infecting organism and the type of congenital defect, the duration of illness, or the age of the child. Staphylococcal endocarditis is more common in patients with no underlying heart disease; viridans group streptococcal infection is more common after dental procedures; group D enterococci are seen more often after lower bowel or genitourinary manipulation; Pseudomonas aeruginosa or Serratia marcescens is seen more frequently in intravenous drug users; and fungal organisms are encountered after open heart surgery. Coagulase-negative staphylococci are common in the presence of an indwelling central venous catheter.
Table 431-1 BACTERIAL AGENTS IN PEDIATRIC INFECTIVE ENDOCARDITIS
COMMON: NATIVE VALVE OR OTHER CARDIAC LESIONS
UNCOMMON: NATIVE VALVE OR OTHER CARDIAC LESIONS
HACEK group†
PROSTHETIC VALVE
* These fastidious bacteria plus some fungi may produce culture-negative endocarditis. Detection may require special media, incubation for more than 7 days, or serologic tests.
† The HACEK group includes Haemophilus species (H. paraphrophilus, H. parainfluenzae, H. aphrophilus), Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, and Kingella species.
‡ Candida species, Aspergillus species, Pseudallescheria boydii, Histoplasma capsulatum.
Epidemiology
Infective endocarditis is often a complication of congenital or rheumatic heart disease but can also occur in children without any abnormal valves or cardiac malformations. In developed countries, congenital heart disease is the overwhelming predisposing factor. Endocarditis is rare in infancy; in this age group, it usually follows open heart surgery or is associated with a central venous line.
Patients with congenital heart lesions where there is turbulent blood flow due to a hole or stenotic orifice, especially if there is a high pressure gradient across the defect, are most susceptible to endocarditis. This turbulent flow traumatizes the vascular endothelium, creating a substrate for deposition of fibrin and platelets, leading to the formation of a nonbacterial thrombotic embolus (NBTE) that is thought to be the initiating lesion for infective endocarditis. Biofilms form on the surface of implanted mechanical devices such as valves, catheters, or pacemaker wires that also serve as the adhesive substrate for infection. The development of transient bacteremia then colonizes this NBTE or biofilm, leading to proliferation of bacteria within the lesion. Bacterial surface proteins, such as the FimA antigen in viridans streptococci, act as adhesion factors to the NBTE or biofilm, after which bacteria can rapidly proliferate within the vegetation. Given the heavy colonization of mucosal surfaces (the oropharynx, or gastrointestinal, vaginal, or urinary tracts) by potentially pathogenic bacteria, these surfaces are thought to be the origin of this transient bacteremia. There is controversy over the extent to which daily activities (such as brushing or flossing the teeth) vs invasive procedures (such as dental cleanings or surgery) contribute to this bacteremia. Transient bacteremia has been reported to occur in 20-68% of patients after tooth brushing and flossing, and even in 7-51% of patients after chewing food. The magnitude of this bacteremia is also similar to that resulting from dental procedures. Maintenance of good oral hygiene may be a more important factor in decreasing the frequency and magnitude of bacteremia.
Children at highest risk of adverse outcome after infective endocarditis include those with: prosthetic cardiac valves or other prosthetic material used for cardiac valve repair, unrepaired cyanotic congenital heart disease (including those palliated with shunts and conduits), completely repaired defects with prosthetic material or device during the 1st 6 mo after repair, repaired congenital heart disease with residual defects at or adjacent to the site of a prosthetic patch or device, valve stenosis or insufficiency occurring after heart transplantation, and previous infective endocarditis. Patients with high velocity blood flow lesions such as ventricular septal defects and aortic stenosis are also at high risk. In older patients, congenital bicuspid aortic valves and mitral valve prolapse with regurgitation pose additional risks for endocarditis. Surgical correction of congenital heart disease may reduce but does not eliminate the risk of endocarditis, with the exception of repair of a simple atrial septal defect or patent ductus arteriosus without prosthetic material.
In ≈30% of patients with infective endocarditis, a predisposing factor is presumably recognized. Although a preceding dental procedure may be identified in 10-20% of patients, the time of the procedure may range from 1 to 6 mo prior to the onset of symptoms, hence the continued controversy over the absolute risk of infective endocarditis after dental procedures. Primary bacteremia with Staphylococcus aureus is thought to be another risk for endocarditis. The occurrence of endocarditis directly after most routine heart surgery is relatively low, but it can be an antecedent event, especially if prosthetic material is utilized.
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