In this chapter, the design and development of a computational model of the cardiovascular system is presented for patients who have undergone the Fontan operation. The model has been built from a physiological basis, considering some of the mechanisms associated to the cardiovascular system of patients with univentricular heart disease. Thus, the model allows the prediction of some hemodynamic variables considering different physiopathological conditions. The original conditions of the model are changed in the Fontan procedure and these new dynamics force the hemodynamic behaviours of the different considered variables. The model has been proved considering the classic Fontan procedure and the techniques from the lateral tunnel and the extracardiac conduit. The results compiled knowledge of several cardiovascular surgeons with many years of experience in such interventions, and have been validated by using other authors' data. In this sense, the participation of a multidisciplinary team has been considered as a key factor for the development of this work.
TopIntroduction
The incidence of Congenital Heart Diseases (CHD) is approximately 1% of total births (Masoller et al., 2016), assuming that the main cause of death in children is due to congenital defects (Parnell et al., 2017) and resulting in a high cost in hospitalization due to the necessary surgical interventions. The significant progress in the diagnosis, prevention and treatment of CHD has made possible that the vast majority of patients who suffer this type of disease reach the adult stage (Biglino et al., 2017). However, in most cases, CHD cannot be cured and treatments are more palliative than corrective (Ferguson et al., 2016).
Within the wide variety of CHD illnesses, tricuspid atresia is considered one of the most complex and critical types. It is estimated that the emergence of this malformation of the heart occurs on approximately 1 out of every 10000 births (Bangash et al., 2016), although the true prevalence is not known (Rao et al., 2012). Tricuspid atresia is determined by the absence of the tricuspid valve and the small size of the right ventricle. This physical defect does not allow blood to be pushed to the lungs in a normal way, thus leading to a poorly oxygenated blood and the apparition of cyanosis.
In 1971, Francis M. Fontan presented a surgical correction for the tricuspid atresia (Fontan et al., 1971). This intervention became the most common treatment over time used for congenital malformations that are characterized for the presence of a single ventricle. It is usually based on the realization of three interventions during the first years of the patient, with the objective of providing an appropriate delivery of oxygen to the peripheral system without overloading the ventricle (Corsini et al., 2014). The classic Fontan procedure or atriopulmonary anastomosis (APC) is currently obsolete (Hazinski, 2013). The most current techniques are based on intracardiac total cavopulmonary connection or lateral tunnel (ELT), or the extracardiac conduit (ECC) (Bartelse et al., 2016). Health institutions carrying out this kind of interventions are usually specialized on these last two techniques. As a consequence, several works have been proposed (Clifford et al., 2015; Ravishankar et al., 2016; Trusty et al., 2016) with the objective of comparing both techniques from a postoperative hemodynamics perspective, and to assess the prevalence of arrhythmias and functional status for patients.
Despite the improvements accomplished in the last decades with the Fontan procedure, the postoperative consequences remain a long-term concern (Sakamoto et al., 2016). First, a progressive circulatory failure is caused in some patients, resulting in a pathophysiological status that is not currently sufficiently understood (Cheng et al., 2016). Furthermore, other problems can arise, such as the cognitive impairment (Tyagi et al., 2016), the chronic venous congestion (Opotowsky et al., 2017) or the appearance of kidney diseases such as cirrhosis or hepatic dysfunction (Opotowsky et al., 2016).