Right-Sided Infective Endocarditis: The Importance of Vegetation Size.

Background: Right-sided infective endocarditis (IE) carries favourable prognosis compared to left-sided IE. However, the prognostic significance of vegetation size in right-sided IE is less well defined. This study reports the clinical, microbiological, and echocardiographic findings associated with right-sided IE and examines the predictors of adverse outcomes.

Methods: Consecutive adults admitted with isolated right-sided IE at an Australian tertiary referral centre between June 1999 and May 2017 were retrospectively reviewed. Patients were stratified according to intravenous drug user (IVDU) status. Culprit organisms, sepsis severity, treatment regimens, inpatient complications, and vegetation size were recorded. Hospital survivors were followed mean 6.9±4.8 years for late mortality and IE recurrence.

Results: Of 318 consecutive cases of IE, 60 (19%) were isolated right-sided IE and included in this study. Forty-three (43) (72%) patients were current IVDUs, who were younger and more likely to have hepatitis. The majority (90%) of patients were medically managed with multi-agent antimicrobial regimens (median three agents) for a total duration of median 91 days. In-hospital mortality was 3% (2/60). Septic emboli were found in 82% (49/60) of patients, were significantly more common among IVDUs but were not related to vegetation size. Survival after hospital discharge was 100% at 1 year, 96% at 3 years, and 89% at 5 years. Vegetation size >2 cm, chronic kidney disease, and Pitt bacteraemia score were independent predictors of all-cause late mortality. Freedom from IE recurrence was 93% at 1 year, 87% at 3 years, and 84% at 5 years. Vegetation >2.5 cm, prisoner status, and multivalvular IE involvement conferred higher risks of recurrence.

Conclusions: Patients with right-sided IE and small vegetations do well with medical management and this should continue to be the preferred strategy. However, those with large vegetations have poorer late outcomes and may require more aggressive treatment and closer follow-up.