Fontan pathway growth: a quantitative evaluation of lateral tunnel and extracardiac cavopulmonary connections using serial cardiac magnetic resonance

Abstract

Background: Typically, a Fontan connection is constructed as either a lateral tunnel (LT) pathway or an extracardiac (EC) conduit. The LT is formed partially by atrial wall and is assumed to have growth potential, but the extent and nature of LT pathway growth have not been well characterized. A quantitative analysis was performed to evaluate this issue.

Methods: Retrospective serial cardiac magnetic resonance data were obtained for 16 LT and 9 EC patients at 2 time points (mean time between studies, 4.2 ± 1.6 years). Patient-specific anatomies and flows were reconstructed. Geometric parameters of Fontan pathway vessels and the descending aorta were quantified, normalized to body surface area (BSA), and compared between time points and Fontan pathway types.

Results: Absolute LT pathway mean diameters increased over time for all but 2 patients; EC pathway size did not change (2.4 ± 2.2 mm vs 0.02 ± 2.1 mm, p < 0.05). Normalized LT and EC diameters decreased, while the size of the descending aorta increased proportionally to BSA. Growth of other cavopulmonary vessels varied. The patterns and extent of LT pathway growth were heterogeneous. Absolute flows for all vessels analyzed, except for the superior vena cava, proportionally to BSA.

Conclusions: Fontan pathway vessel diameter changes over time were not proportional to somatic growth but increases in pathway flows were; LT pathway diameter changes were highly variable. These factors may impact Fontan pathway resistance and hemodynamic efficiency. These findings provide further understanding of the different characteristics of LT and EC Fontan connections and set the stage for further investigation.

Figure 1

A: relationship between patient age (years) and the body surface area (BSA) (m²) for all the patients included in the study. B: relationship between the changes of age and BSA normalized to the variable value at the initial time point. Linear regression equations are indicated; p-values indicate the regression significance. T1: initial time point

Figure 2

Absolute (A) and Normalized (B) mean vessel diameters for the SVC, LPA and RPA in the cohort, LT and EC subgroups. T1 is shown in the open columns and T2 in the solid ones. (*): p-value<0.05

Figure 3

Absolute (A) and Normalized (B) minimum, mean and maximum Fontan Pathway diameters for LT and EC subgroups. T1 is shown in the open columns and T2 in the solid ones (*): p-value<0.05

Figure 4

Relationship between absolute mean FP diameters (mm) and body surface area (m2) in LT (A) and EC (B) patients. Dashed red line: decreasing absolute diameter; Solid black line: increasing absolute diameter.

Figure 5

Absolute (A) and Normalized (B) cross-sectional vessel Areas for the FP at the PA bifurcation and the descending Aorta. T1 is shown in the open columns and T2 in the solid ones. (*): p-value<0.05

Figure 6

Absolute and Normalized mean flows for the cohort (A), and the LT and EC groups (B). T1 is shown in the open columns and T2 in the solid ones. (*): p-value<0.05

Figure 7

Distance (in mm) between the geometry at the initial time point (color coded) and the latter time (translucent gray). Top row shows extra-cardiac patients (EC1 through EC4); bottom row shows Lateral Tunnel patients (LT1-LT4). Patient’s age and body surface area (BSA) for each time point of the study is indicated