Infective Endocarditis
Infective endocarditis (IE) is an inflammation of the endothelial lining of the heart muscle, valves and great vessels. The valves have a particularly high propensity for infection due to the lack of blood supply and limited access to immune cells. IE is relatively rare in children. It has an estimated annual incidence of 3 to 9 cases per 100,000 persons in industrialized countries. The highest rates are observed among patients with prosthetic valves, intracardiac devices, unrepaired cyanotic congenital heart diseases, or a history of infective endocarditis. About 50% of cases of infective endocarditis develop in patients with no known history of valve disease. Other risk factors include chronic rheumatic heart disease (which now accounts for <10% of cases in industrialized countries), age-related degenerative valvular lesions, hemodialysis, and coexisting conditions such as diabetes, human immunodeficiency viral infection, and intravenous drug use.
Pathogenesis
Bacteremia and the presence of endothelial damage are important factors in the pathogenesis of IE. Cyanosis and polycythemia, if present, increase the viscosity of the blood and further enhance the likelihood of developing IE. Foreign materials such as prosthetic valves or shunts also significantly increase the risk for developing IE. It is not surprising that cyanotic CHD with an artificial shunt or prosthetic valves constitutes the highest risk for IE.
Neonatal endocarditis frequently occurs on the right side of the heart and is associated with disruption of endocardium or valvular endothelial tissue by catheter-induced trauma in hospitalized infants. Premature neonates often experience transient episodes of bacteremia from trauma to the skin and mucous membranes, vigorous endotracheal suctioning, parenteral hyperalimentation, or placement of umbilical or peripheral venous catheters. The combination of endothelial damage and bacteremia is critical for the induction of IE.
Pathology
Vegetations develop at the site of endothelial damage, which is usually located at the lower pressure side of the lesion i.e. in the right ventricle in patients with VSD and on the atrial surface of the mitral valve with mitral insufficiency.
After bacteria adhere to the damaged endothelium, platelets and fibrin are deposited over the organisms, leading to the formation of a vegetation. The organisms trapped within the vegetation are protected from phagocytic cells and other host defense mechanisms.
Microbiology
Viridans group streptococcus, enterococci and S. aureus are responsible for most cases of IE. Streptococcus pneumoniae, coagulase negative staphylococcus, gram negative bacilli and fungi may also cause IE. The type of pathogens depends on the following factors: i) whether the valve is a native or a prosthetic valve, ii) patient age and iii) source of infection.
The blood cultures may be negative in patients who have already received antibiotics or in patients who have IE caused by fastidious microorganisms such as petronella species, brucella species, Coxiella burnetii, bacteria in the HACEK group (haemophilus species, actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens and Kingella kingae), and Tropheryma whipplei. In these cases, serologic testing, blood polymerase chain reaction (PCR) assay and highly specialized microbiologic techniques may lead to the identification of the pathogen in up to 60% of cases.
Clinical presentation
Persistent or recurrent low grade fever is the most common symptom of IE. Other symptoms are nonspecific and include malaise, myalgia, arthralgia, anorexia, night sweats and headaches. Splenomegaly can be found in 15-50% of patients with IE. A new or changing murmur indicates valvular involvement.
The classic peripheral manifestations of IE are rarely seen nowadays. These include petechiae, splinter hemorrhages (hemorrhages in the nail beds), Osler nodules (small, tender nodules on the pads of fingers and toes), Janeway lesions (painless hemorrhages on palms and soles), and Roth spots (hemorrhages in the retina with a white center).
Making the diagnosis
- The above signs and symptoms in a patient with underlying CHD following transient bacteremia should raise the suspicion of IE.
- In the absence of prior antimicrobial therapy, positive blood cultures are found in >90% of patients.
- Other supporting laboratory evidence includes anemia, leukocytosis with a left shift, positive rheumatoid factor, hematuria and elevated ESR/CRP.
- The finding of vegetations on echocardiography is confirmatory. However, since IE is a clinical diagnosis, a negative echocardiogram does not rule out IE and treatment should not be delayed if there is strong clinical suspicion of IE. The Duke Criteria helps in making the diagnosis of IE.
The Duke Criteria for diagnosis of infective endocarditis: Requires 2 major + 1 minor OR 1 major + 3 minor OR 5 minor criteria for diagnosis
| Major criteria |
Minor criteria |
|---|---|
|
Positive blood Cx for IE |
Predisposing heart condition or IV drug use |
|
Typical micro-organism for IE from 2 separate blood Cx 1 |
Fever > 38° C |
|
Evidence of endocardial involvement2 |
Vascular phenomena (arterial emboli, septic pulmonary infarcts, conjunctival hemorrhage, intracranial hemorrhage and Janeway lesions) |
|
|
Immunologic phenomena (glomerulonephritis, Osler nodes, Roth spots, rheumatoid factor) |
|
|
Positive blood Cx but not meeting major criteria |
|
|
Echocardiographic findings consistent with IE but not meeting major criteria |
* : Viridans streptococci, Streptococcus bovis and HACEK group OR Staph aureus/enterococci in the absence of a primary focus and persistently positive blood Cx defined as 2 blood Cx drawn 12 hours apart
# : Positive echocardiogram for vegetations OR new valvular regurgitation
Management
The management of IE includes 4-6 weeks of high dose IV antibiotics. The choice of antibiotics depends on the organism isolated and the results of antibiotic sensitivity testing. Initial empiric therapy may be based on the table below. Surgical intervention may be necessary if vegetations are causing obstruction, or if there is significant malfunction of a prosthetic valve.
|
Antibiotic |
Dosage |
|---|---|
|
Native valves or prosthetic valves 1 year after surgery |
|
|
Ampicillin + Oxacillin + Gentamicin |
12 g/day IV in 4-6 doses
12 g/day IV in 4-6 doses
3 mg/kg/day IV in 1 dose |
|
Prosthetic valves within 1 year of surgery |
|
|
Vancomycin + Gentamicin + Rifampin |
30 mg/kg/day IV in 2 doses
3 mg/kg/day IV in 1 dose
900-1200 mg IV/PO in 2 or 3 divided doses |
Antimicrobial prophylaxis: (2007 AHA guidelines)
Antimicrobial prophylaxis is indicated in patients undergoing dental procedures who have:
- A prosthetic heart valve
- A history of IE
- A heart transplant with abnormal heart valve function
- CHD only under the following conditions:
a) Unrepaired cyanotic CHD including those with palliative shunts and conduits,
b) Completely repaired CHD with a prosthetic material or device during the first 6 months after the procedure
c) Repaired CHD with a residual defect
Antibiotics are NOT recommended for patients who have procedures involving the reproductive, urinary or gastrointestinal tract.
References
Prevention of Infective Endocarditis. 2007 Guidelines From the American Heart Association. Circulation. 116:1736-1754.
Ferrieri, P, et al. Unique Features of Infective Endocarditis in Childhood. Circulation. 2002;105:2115. Scientific statement from American Heart Association
Hoen B , Duval X . Clinical practice. Infective endocarditis. N Engl J Med . 2013 Apr 11;368(15):1425-33
