Impact of collateral vessels on Fontan circulation by using 0-1 dimensional Fontan circulation model considering concepts of oxygen supply and consumption
Authors: Sughimoto K , Miki T , Li R , Fujiwara T F , Liu H 
Published: November 2023

Abstract

Background/Purpose
In patients with univentricular heart disease, the Fontan operation has played a significant role in improving cyanosis and reducing the volume load on the systemic ventricle. However, Fontan patients may develop various complications, and their hemodynamics may deteriorate gradually, resulting in a poor long-term survival rate. Development of collateral vessels before and/or after the Fontan operation is one of the significant problems, and the patients may suffer from advanced cyanosis and heart failure. Although recent studies about the collateral vessels by MRI showed that a significant amount of blood is flown through the collateral vessels, little is known about its effect on the Fontan circulation. Therefore, understanding the mechanism and impact of collateral vessels on the Fontan circulation is important.

Methods
A 0-1-dimensional Fontan circulation hemodynamic model was developed to reproduce the hemodynamic changes of the blood flow in the entire body by introducing two types of collateral vessels (VVC: veno-venous collateral, APC: aorto-pulmonary collateral) into the model considering clinical status. Also, giving various conditions by ranging catecholamine dose and introducing the concept of oxygen delivery and consumption by changing workloads, arterial and central venous oxygen saturations (SaO2 and SvO2) are predicted in the Fontan circulation models. To evaluate the cardiac function, considering the impact of collateral vessels, four representative values were examined: (1) cardiac output (CO) per minute; (2) Ees relative to arterial elastance (Ees/Ea); (3) ejection fraction; and (4) the stroke work (SW) to pressure-volume area (PVA) ratio (SW/PVA).

Results
SaO2 and SvO2 were less in Fontan circulations with both VVC and APC present (92% and 54%) than those without collateral vessels (96% and 62%). Also, with collateral vessels, Ees/Ea was decreased while SW/PVA was increased, leading to poor perfusion to the tissue. Regardless of the presence or absence of collateral circulation, SaO2 and SvO2, and systemic blood flow rate decreased when pulmonary vascular resistance was high. By administering catecholamine at 10 microgram/kg/min, in the presence of both VVC and APC, SvO2 was increased from 53% to 58%, while SaO2 was decreased from 92% to 88%.

Conclusions
The simulated results of arterial and venous blood oxygen saturations and systemic blood flow rate were well-reproduced, matching the previously reported clinical results. It is suggested that pulmonary vasodilators may be beneficial in increasing blood oxygen saturation and improving tissue perfusion, even in Fontan patients with collateral vessels. However, the catecholamine's positive effect is limited. For reproducing various conditions of Fontan circulations, it is necessary to collect actual measurement data from a variety of patients and validate the predicted value to increase the credibility of the model.Arterial and venous oxygen saturationsPressure and volume curves