John C. Nalagan
EPIDEMIOLOGY
In infective endocarditis (IE), the mitral valve is the most affected valve, followed by the aortic, tricuspid, and pulmonic valve.
Most cases occur in patients with an identifiable cardiac structural abnormality or a recognized risk factor for the disease.
In native valve endocarditis, rheumatic heart disease is the leading risk factor and mitral valve prolapse is a common predisposing cardiac lesion.
Endocarditis in injection drug users has a predilection for the tricuspid valve. It is also associated with a 40% recurrence rate and high mortality in patients with AIDS.
Early prosthetic valve endocarditis (cases within 60 days post-surgery) is usually acquired in the hospital, whereas late prosthetic valve endocarditis (>60 days) is community acquired.
PATHOPHYSIOLOGY
Normal endothelium is typically resistant to infection and thrombus unless injured by abnormal hemodynamic states such as valvular or congenital cardiac defects. The turbulent flow then leads to denuding of the endothelium.
In injection drug use, endothelial damage occurs from damage from particulate matter present in the injected substance, or from vasospasm from the drug itself.
Endothelial damage results in deposition of platelets and fibrin, resulting in the formation of sterile vegetations (nonbacterial thrombotic endocarditis).
Transient bacteremia may result in colonization of vegetations and conversion of nonbacterial thrombotic endocarditis to IE.
The infecting bacteria must be able to adhere to the thrombus to result in IE. Different organisms vary in this ability. Certain pathogens (eg, Staphylococcus aureus in injection drug users) are so invasive that nonbacterial thrombus on the endothelium does not need to be present to induce IE.
CLINICAL FEATURES
Fever is the most common manifestation (80%) followed by chills, weakness, and dyspnea (40% each).
Cardiac manifestations such as heart murmurs are present in up to 85% of cases.
Dyspnea is common and often due to acute or progressive CHF (70% of cases).
Embolic phenomenon occurs about 50% of the time and is due to the embolization of friable vegetation fragments. Findings include strokes (most common), chest and abdominal pain, flank pain with hematuria, and acute limb ischemia.
Cutaneous findings occur in 18% to 50% of patients and include petichiae, splinter/subungual hemorrhages, Osler nodes (tender subcutaneous nodules on finger/toe pads), and Janeway lesions (hemorrhagic plaques on the palms or soles).
DIAGNOSIS AND DIFFERENTIAL
Hospitalize all patients at risk for IE. This includes patients with unexplained fever and risk factors for the disease, patients with prosthetic valves, and those with new or changing murmurs and evidence of arterial emboli.
The necessary components for diagnosis are blood cultures, echocardiogram, and clinical observation. Blood cultures should be drawn prior to administration of antibiotics and from three separate sites, with an hour elapsing between the first and last set of cultures.
Echocardiography should be performed as soon as possible.
EMERGENCY DEPARTMENT CARE AND DISPOSITION
Patients may present with respiratory compromise and require emergent airway stabilization.
Intra-aortic balloon counterpulsion is indicated for mitral valve rupture but contraindicated for aortic valve rupture.
Patients with native valve endocarditis do not require anticoagulation. Patients with prosthetic valves already on anticoagulation should continue their current regimen unless requested otherwise by the consultant.
Antibiotics should be initiated in patients with suspected endocarditis after appropriate cultures are obtained. Table 95-1 lists empiric treatment regimens. Definitive therapy is based on culture and sensitivity results and typically requires 4 to 6 weeks of antibiotics.
Prophylactic antibiotics before procedures should be administered for patients only with the highest risk factors (eg, prior history of IE, patients with prosthetic heart valve, unrepaired congenital heart disease, or a cardiac transplant recipient with valve regurgitation).
The only ED procedures where prophylactic antibiotics should be considered are procedures on known infected skin, such as abscess drainage. Agents suggested are dicloxacillin 2 grams PO, cephalexin 2 grams PO, clindamycin 600 milligrams IM or IV, or vancomycin 1 gram IV, 30 to 60 minutes before procedure. Antibiotic prophylaxis is not indicated for common emergency department procedures.
TABLE 95-1 Empiric Therapy of Suspected Bacterial Endocarditis*
For further reading in Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 7th ed., see Chapter 150, “Infective Endocarditis,” by Richard E. Rothman, Samuel Yang, and Catherine A. Marco.