William W.J. Glenn wrote the world’s first report of a right heart bypass circulation in 1958 [1]. This original procedure is an end-to-side anastomosis of the transected right pulmonary artery to the lateral aspect of the SVC aiming to increase the effective pulmonary blood flow for the relief of cyanosis in patients with right to left shunt (Fig. 12.1). This concept was inherited by the procedure called “bidirectional Glenn procedure” or BCPS (Fig. 12.2), in which the transected SVC was anastomosed to the superior aspect of the right pulmonary artery [2, 3]. Since late 1980s, this procedure is considered to be a part of staged Fontan strategy to disperse the adverse event related to Fontan operation [4–6]. Nowadays, the word “Glenn procedure” exclusively means “bidirectional Glenn procedure” as the second stage to proceed to complete Fontan circulation. In this chapter, the explanation is solely dedicated to describe the bidirectional Glenn procedure in single ventricular physiology patients.

The amount of pulmonary flow in single ventricular patients before the Glenn operation is determined by the parallel circulation from the ventricle either through BT shunt, stenotic pulmonary trunk, or banded pulmonary artery(ies)* (trunk or bilateral banding). The pulmonary to systemic blood flow ratio (Qp/Qs) is usually more than 1.5; otherwise, it is difficult to maintain arterial blood oxygen saturation more than 70%. However, after the bidirectional Glenn procedure, Qp/Qs usually becomes anywhere between 0.5 and 0.8, if there is no additional pulmonary blood flow (i.e., some surgeon prefer to leave BT shunt or tightly banded pulmonary trunk even after BDG). The sudden reduction in the preload to the single ventricle leads to a reduction in the end-diastolic ventricular volume, which usually causes a diastolic dysfunction. The patients usually tolerate this situation because the cardiac output is maintained by the stable blood supply from IVC to systemic single ventricle, whereas severe low cardiac output occurs if this is a Fontan circulation. This is the main reason why the staged strategy to Fontan circulation is preferred by most of the surgeons.

In case the patient could not undergo the completion of Fontan circulation and remains with Glenn circulation, there will be serious complications in the long-term follow-up period. Cyanosis, polycythemia, high SVC pressure, systemic ventricular failure, AV valve dysfunction, development of pulmonary AV fistula, and development of AP collaterals which leads to fatal hemoptysis are the possible complications [7, 8]. Palliative treatments for these circumstances include home oxygen therapy, pulmonary vasodilator (sildenafil, tadalafil, bosentan, ambrisentan, macitentan, beraprost), beta blocker therapy, ACE inhibitor, ARBs, systemic atrioventricular valve repair/replacement, medication/catheter ablation for atrial arrhythmia, and coil embolization of unfavorable collaterals (Table 12.2). There is a certain kind of patient group whose pulmonary blood flow is coincidentally optimal by a native pulmonary stenosis or pulmonary arterial banding who survives with acceptable quality of life [9]. However, most patients who could not reach Fontan completion, the possible solution for this situation is to have a new heart transplanted.

To understand the problems of adults with Fontan circulation, it is necessary to know how the modification of this procedure was developed to improve the outcome. The original Fontan operation [10] was a combination of SVC to right PA anastomosis, creation of right atrial appendage to left PA connection with pulmonary valve homograft, and ASD closure. Shortly, the procedure was simplified as to anastomose the right atrial appendage to the pulmonary trunk and close the ASD. This type of operation is called APC (atrio-pulmonary connection) and became the standard procedure in 1970s–1980s. As the outcome being stable in patients with tricuspid atresia in which the systemic ventricle is almost normal left ventricle, the indication was extended to other single ventricular physiology patients including heterotaxia and hypoplastic left heart syndrome [11]. The classic ten commandments for Fontan procedure [12] no more exist. Fontan procedure is performed at younger age of life such as between 1 and 2 years old. In the late 1980s, de Leval et al. [13] reported the better hemodynamics with total cavo-pulmonary connection (TCPC). The main concept of this theory is that the atrial contraction between the cavae and pulmonary arteries is not necessary but is even worse. This theory was proved using flow dynamic technology and also proved recently using computer fluid dynamics (CFD) [14] method. TCPC became a standard method as a goal of the treatment of single ventricle. Aortic cross clamping was necessary to place an intra-atrial baffle with this procedure. However, after Marcelletti et al. [15] reported the less invasive method by connecting the IVC to pulmonary artery with extra-cardiac conduit, this type of procedure is the most employed in the world. As the outcome is improved, the indication for TCPC was extended to more marginal cases such as patients with poor ventricular function and high pulmonary vascular resistance, so that the incidence of late complication tends to increase. In the 1990s, the classic Fontan patients (with APC or similar procedures) were recommended to undergo “TCPC conversion” [16] because of their deteriorating hemodynamics with a dilated atrio-pulmonary connection. The dilated right atrium causes a turbulent flow in the atrium, and energy loss is prominent with the dilated Fontan pathway (Fig. 12.3a, b).

Arrhythmia is the most frequent adverse event both early and late after Fontan procedure. The incidence is less in patients with TCPC and extra-cardiac TCPC than in conventional Fontan with atrio-pulmonary connection, because the origin of the arrhythmia is mostly the damaged atrial wall, which is chronically dilated by the high central venous pressure of circulation.

Patients after Fontan operation often have indefinite complains possibly due to autonomic functional disorder. Symptoms include migraine, muscle tension headache, anxiety with palpitation even with normal sinus rhythm, orthostatic hypotension, and more. Although these problems are not fatal, they could definitely decline the patient’s quality of life. There is only few evidence relating to this problem [47]. Further investigation in this field is demanding.

Angioplasty is recommended in any circumstance where there is an obstructive lesion along the Fontan circuit. Even a single-digit pressure gradient in the venous systems can cause severe energy loss in the Fontan circuit. Once liver dysfunction or PLE occurs because of the obstructive Fontan circuit, these problems often persist even after a successful angioplasty. Therefore, the catheter or surgical angioplasty should be considered in the early stage of the problems.