Prevalence, Clinical Characteristics, and Hemodynamic Impact of Coronary Artery–Ventricular Microfistulas in Patients with Fontan Circulation

Abstract Background: Coronary artery–ventricular microfistulas (CAMFs), which are defined as diffuse communications between dilated coronary arteries and the main ventricle, are poorly understood in Fontan circulation. We evaluated their prevalence, clinical features, and longitudinal hemodynamics. Methods: We retrospectively reviewed 167 Fontan patients undergoing cardiac catheterization between 2005 and 2025. Excluded were sinusoidal communications in PA/IVS, LV fistulas in HLHS, or solitary focal fistulas. Clinical, surgical, and serial hemodynamic parameters, such as the subendocardial viability ratio (SEVR) and aortic regurgitation (AR) index, were assessed. Results: CAMFs were identified in 6 of the 153 eligible Fontan patients (prevalence: 3.9%). Polysplenia was more frequent in the CAMFs group (33% vs. 5%, p = 0.03). At initial diagnosis, systemic cardiac index (median 3.3 L/min/m² [range, 2.2–3.9 L/min/m²]) and ejection fraction (median 52% [range, 44%–65%]) were preserved. Notably, resting SEVR (median 91% [range, 85%–156%]) and AR index (median 54% [range, 44%–59%]) remained stable and well-compensated over a decade of follow-up. Late morbidities included protein-losing enteropathy (17%), pulmonary arteriovenous fistulas (17%), esophageal varices (17%), and death (17%). Conclusions: CAMFs occur in 3.9% of Fontan patients and correlate with polysplenia. Although resting SEVR and AR index remain well-compensated over mid-term follow-up, their impact on long-term outcomes beyond two decades post-Fontan remains uncertain. Careful long-term monitoring is necessary for late extra-cardiac complications and hemodynamic changes.