From the Guidelines
Staphylococcus aureus endocarditis in intravenous drug users (IVDU) most commonly affects the tricuspid valve due to the direct path of venous blood flow from injection sites. When drugs are injected intravenously, bacteria (particularly S. aureus, which often colonizes the skin) can enter the bloodstream and travel through the venous system. This contaminated blood returns to the right side of the heart first, specifically through the tricuspid valve, before reaching the lungs. The mechanical stress on the tricuspid valve as it manages this infected blood flow creates an ideal environment for bacterial attachment and colonization. Additionally, injected particulate matter can cause minor damage to the valve surface, creating attachment sites for bacteria. This contrasts with non-IVDU endocarditis, which typically affects left-sided heart valves (mitral and aortic) due to different pathophysiological mechanisms, as noted in a study published in Circulation in 2015 1.
The pathophysiology of right-sided endocarditis in IVDU patients is supported by the fact that cure rates for right-sided S aureus IE in IDUs are high (>85%) and may be achieved with relatively short courses of either parenteral or oral treatment (2–4 weeks) 1. In contrast, left-sided endocarditis is associated with higher mortality rates, ranging from 25% to 40% 1. The predominance of right-sided endocarditis in IVDU patients is so characteristic that finding tricuspid valve involvement should raise suspicion of intravenous drug use as a risk factor.
Key points to consider in the management of S aureus endocarditis in IVDU patients include:
- The use of combined short-course (2 weeks) β-lactam plus aminoglycoside therapy, which has been shown to be highly effective in several studies 1
- The potential for glycopeptides (teicoplanin or vancomycin) plus gentamicin to be less effective due to limited bactericidal activity, poor penetration into vegetations, or increased drug clearance among IDUs 1
- The importance of considering the patient's overall clinical presentation, including the presence of complications such as renal failure, extrapulmonary metastatic infections, aortic or mitral valve involvement, meningitis, or infection by MRSA, when selecting an treatment regimen 1.
From the Research
Etiology of Endocarditis from Staphylococcus aureus
- The most common etiology of endocarditis from Staphylococcus aureus is intravenous drug use (IVDU) 2, 3, 4.
- Staphylococcus aureus is the most common etiologic agent of infective endocarditis in IVDU 2, 3, 4.
Tricuspid Valve Involvement
- In IVDU, Staphylococcus aureus endocarditis usually involves the tricuspid valve 2, 3, 4.
- The tricuspid valve is the most commonly affected valve in right-sided endocarditis 2, 4.
- Right-sided endocarditis, particularly tricuspid valve endocarditis, is often associated with IVDU 2, 4.
Clinical Features and Prognosis
- Patients with right-sided endocarditis, including those with tricuspid valve involvement, tend to have a better prognosis than those with left-sided endocarditis 4.
- The mortality rate for right-sided endocarditis is generally lower than for left-sided endocarditis 4.
- However, the prognosis can vary depending on factors such as the presence of complications, HIV status, and the need for surgical intervention 4.
Treatment and Management
- Treatment of Staphylococcus aureus endocarditis typically involves antibiotic therapy, with options including vancomycin, nafcillin, and daptomycin 2, 5, 6.
- Surgical intervention, such as valve replacement or repair, may be necessary in some cases, particularly for patients with complicated endocarditis or those who do not respond to antibiotic therapy 2, 4.