The hemodynamic performance of different conduit sizes in the Fontan circulation

Abstract

The Fontan circulation is the final stage of surgical palliation for children born with congenital heart defect with a single ventricle. Currently, the most used procedure to complete the Fontan circulation is the Extracardiac Total Cavopulmonary connection and is performed when the patient is at an age of 3-5 years old. In this procedure, a prosthetic extracardiac conduit is implanted that connect the Inferior Vena Cava directly with the Pulmonary Arteries, bypassing the heart. This extracardiac conduit is available in several conventional sizes. However, little knowledge is available on the performance of these different conduit sizes, especially when patients grow older. Therefore, it is difficult to make a well-informed choice on the conduit size at the time of implantation.

This study aimed to obtain more insight into the performance of three conduit sizes (16, 18 and 20 mm), using computational fluid dynamic simulations conducted on anatomically three-dimensional models with accurate boundary conditions, both reconstructed from MRI (N = 19). In addition, it is proposed in the literature that body growth affects the conduit’s performance in the Fontan circulation. In order to include body growth in this study, the effect of an increasing body surface area is analysed for the patients with a 16 and 18 mm conduit implanted. Power loss, pressure drop, normalised resistance and the flow stagnation volume were used as parameters indicating the performance, i.e. efficiency of the Fontan circulation. Furthermore, to get a complete picture of the performance, two physical conditions (rest and exercise) are included and a distinction is made in respiratory phases (inspiration and expiration).

For all three conduit sizes, the power loss, pressure drop and normalised resistance increase with exercise. Also, the power loss and pressure drop increase with inspiration. An increase of these parameters indicate a decreased efficiency of the Fontan circulation. Furthermore, the results describe higher values for the 16 mm conduit than the 18 and 20 mm conduits according to the power loss, pressure drop and normalised resis- tance, with significant differences found during expiration in rest and exercise. In contrast, flow stagnation volume, decreases with exercise and inspiration, and no clear trend was seen for the flow stagnation volume between the conduit sizes. The flow stagnation levels were close to zero, indicating that the performance is not limited by oversized conduits in these patients.

According to the body growth, for the 16 mm conduit, significant correlations were found between the body surface area and power loss, pressure drop and normalised resistance. No trend was seen for the 18 mm conduit. From these findings it appears that probably a smaller conduit is disadvantageous considering the patient’s growth.

In conclusion, the results from this study indicate that the 16 mm conduit is the least beneficial compared to the 18 and 20 mm conduit. However, whether the 18 and 20 mm conduit perform sufficiently is question- able and should be investigated patient-specific by linking these results to clinical relevant parameters such as exercise tolerance. Furthermore, the main limitation of this study is the small patient population. Although already convincing trends have been found, the results should be confirmed by further research with a larger patient population.