Impact of Aortopulmonary Collateral Flow on Single Ventricle Function and Blood Flow Hemodynamics in Patients after the Fontan Procedure: A Longitudinal CMR Study

Objectives: Single ventricle (SV) patients are affected by various extent of aortopulmonary collateral (APC) flow. Although frequently closed by transcatheter procedures, the long-term clinical significance of APC remains unknown. The aim of our study was to assess the impact of APC flow on SV properties and blood flow hemodynamics in Fontan patients by using serial cardiac magnetic resonance (CMR) data.

Methods: Fontan patients who had two CMR examinations with a time interval of at least 4 years as part of their routine clinical assessment were included. The protocol consisted of standard short-axis cine volumetry and 2-dimensional blood flow measurements in the inferior vena cava (IVC), the superior vena cava (SVC) and the ascending aorta (Ao). Aortopulmonary collateral flow was calculated as Ao − (SVC + IVC).

Results: Forty-five Fontan patients (age at first CMR 12.5 ± 6.4 years, mean follow-up 5.2 ± 0.9 years) without APC closure between the two CMR studies and without patent tunnel fenestration were included. Functional class and transcutaneous oxygen saturations (94 ± 4 to 94 ± 5%, p = 0.32) remained stable. Heart rate decreased significantly from 80 ± 16 to 73 ± 19 bpm (p = 0.01) while SV end diastolic volume (80 ± 25 to 88 ± 40 mL/m², p = 0.14) and ejection fraction remained constant (EDVi 80 ± 25 to 88 ± 40 mL/m², p = 0.14; EF 56 ± 12 to 55 ± 8%, p = 0.70). Aortic flow decreased significantly (3.3 ± 1.0 to 2.9 ± 0.8 L/min/m², p = 0.01), IVC flow remained equal (1.6 ± 0.5 to 1.6 ± 0.4 L/min/m²), while SVC flow (1.0 ± 0.3 to 0.8 ± 0.3 L/min/m², p = 0.003) and APC flow (0.8 ± 0.7 to 0.5 ± 0.7 L/min/m², p = 0.005) decreased significantly. Qp/Qs ratio showed significant decrement from 1.3 ± 0.3 to 1.2 ± 0.3 (p = 0.02). Higher APC flow during first CMR exam was not associated with impairment of clinical status, changes in oxygen saturation nor SV dilatation or dysfunction.

Conclusion: APC flow gradually decreases over time in Fontan patients. Baseline APC flow at first CMR was not associated with clinical deterioration or adverse ventricular remodelling at follow-up. These findings might suggest a conservative strategy regarding APC embolization.