Anatomical and functional assessment of the intra-atrial lateral tunnel in the Fontan circulation.

Objectives: In patients after completion of the total cavopulmonary connection (TCPC) with an intra-atrial lateral tunnel, deviations of the tunnel from an ideal straight tubular shape were observed. However, little is known about frequency and adverse effects of such shape deviations. We sought to analyse tunnel anatomy, dimensions and blood flow using cardiac magnetic resonance imaging (CMR).

Methods: Fifty-four patients with hypoplastic left heart syndrome (HLHS; mean age 6.0 ± 2.4 years) underwent CMR with gradient-echo cine sequences, 2D- and 3D-phase-contrast imaging. We analysed anatomy, diameters, cross-sectional areas, volumes and blood flow of the tunnel.

Results: Twenty-five patients had a tubular tunnel. In 29 patients, bulging and/or narrowing of the tunnel were present. Cross-sectional areas and volumes of the tunnel were not significantly different between the two groups. There were also no differences for the mean blood flow and the mean and maximal flow velocity (P = 0.05-0.6). In all the patients, the normalized tunnel volume was related to age (r = 0.44; P = 0.002) and body surface area (BSA; r = 0.42; P = 0.005). The mean tunnel blood flow correlated with age (r = 0.73; P = 0.001) and BSA (r = 0.83; P < 0.0001).

Conclusions: A considerable percentage of patients with an intra-atrial lateral tunnel develop mild deviations of the tunnel from ideal tubular shape. The correlation between tunnel volume and mean blood flow with age and BSA suggests that the capacity of the tunnel adjusts to body growth, independent of tunnel shapes that deviate from a fluid-dynamically favourable shape. Follow-up CMRs are needed to detect long-term effects of irregular tunnel shapes on flow dynamics.