Secondary Staphylococcus capitis Infection of a Long-Standing Non-Coronary Sinus of Valsalva-to-Right Atrial Fistula Initially Misdiagnosed as a Gerbode Defect: A Case Report.

Background: Aorto-atrial fistula is a rare pathological communication associated with diagnostic difficulties, progressive hemodynamic consequences, and potential infective complications. Methods and Results: We present a 53-year-old woman with a long-standing congenital non-coronary sinus of Valsalva-to-right atrial fistula that had been followed for nine years under the working diagnosis of a Gerbode defect. The communication was first detected at the age of 44 years during pregnancy and was managed conservatively while the patient remained largely asymptomatic. At the age of 53 years, recurrent exertional dyspnea prompted definitive reassessment. Right heart catheterization demonstrated a hemodynamically significant left-to-right shunt at the right atrial level, with a pulmonary-to-systemic blood flow (Qp/Qs) ratio of 2.1. Intraoperatively, the communication was shown to originate immediately above the non-coronary cusp and drain into the right atrium, establishing the diagnosis of a congenital aorto-right atrial fistula. A granulomatous, windsock-like endocardial lesion was identified at its right atrial opening, and Staphylococcus capitis was isolated from surgically obtained tissue. Histopathology showed nonspecific regressive changes without specific features of active infective endocarditis. The fistula was closed with an autologous pericardial patch, and intravenous flucloxacillin was administered because of probable localized infective involvement. Conclusions: This case illustrates the diagnostic difficulty of distinguishing an aorto-atrial fistula from a Gerbode defect and supports careful multimodality evaluation of the anatomical origin and flow characteristics of intracardiac shunts. Persistent high-velocity flow may contribute to endocardial injury and create a substrate for subsequent bacterial colonization, although causality cannot be established from a single case. Isolation of a low-virulence skin commensal from pathological cardiac tissue should be interpreted in the complete clinical, operative, microbiological, and histopathological context rather than automatically classified as contamination.