Final Diagnosis -- Infectious Endocarditis Secondary to Bioprosthetic Aortic Valve


DIAGNOSIS

Infectious Endocarditis Secondary to Bioprosthetic Aortic Valve

DISCUSSION

Endocarditis is generally classified by whether it involves a native or prosthetic valve, and, for prosthetic valves, the timeframe relative to surgery. Infective endocarditis that occurs less than one year after prosthetic valve replacement is considered "early-onset" and after one year is "late onset" (Korfer et al 2001). The case presented here is an example of late-onset prosthetic valve endocarditis caused by a viridans streptococcus. The endocarditis progressed and formed an aortic root abscess, which disrupted the heart conduction system. The atrial-ventricular node lies in the wall between the aortic root and right side of the heart. With erosion of this conduction system, the patient experienced complete heart block and subsequent cardiac arrest.

A study from 1972 of 142 cases of bacterial endocarditis found that complete heart block was a complication in 6 (4%) of the cases, all of which showed aortic valve involvement by the infectious endocarditis. Five of these patients suffered sudden death in the hospital setting. Autopsy findings of four of them showed that in addition to aortic valve involvement, there was an extension of the infection into adjacent structures, including a cardio-aortic fistula. The authors postulate that complete heart block was due to disruption of the major conductive tissues. (Wang et al 1972). A subsequent case report with review of the literature reiterated that complete heart block is an infrequent complication of endocarditis, but that its development implies significant extension of the infection. In their literature review they found that cardiac abscesses are found in 30% of cases of native valve endocarditis whereas they are seen in over 60% of prosthetic valve endocarditis (Brown et al 2015).

A study specifically comparing native and prosthetic valve endocarditis found worse early and late outcomes in the prosthetic valve group (Romano et al 2004). A large study of prosthetic valve endocarditis found that the organisms responsible for infection (in decreasing order) were Staphylococcus aureus, coagulase-negative staphylococcus, viridans streptococci, enterococci, other streptococci, and other organisms. S. aureus was the most frequent cause of both early and late-onset prosthetic valve endocarditis. Cases of viridans streptococci were usually late-onset (Lee et al 2011).

REFERENCES

  1. Brown et al, J Clin Med Res. 2015;7(11):890-895.
  2. Korfer et al, Heart 2001;85:590-593.
  3. Lee et al. Cardiovascular Pathology 20 (2011) 26-35.
  4. Romano et al. .J Heart Valve Dis. 2004 Mar;13(2):200-8; discussion 208-9.
  5. Wang et al, Circulation, Volume XLVI, November 1972.

Contributed by Megan Zilla, MD and Jeffrey Nine, MD




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