**2. Evolution of the Fontan operation**

A number of modifications of the aforementioned surgery were made by these [1, 2] and other groups of investigators [9, 10] in the field. In this section, these concepts/procedures will be reviewed.

### **2.1 Initial surgical modifications**

During the first 20 years after Fontan's [1] and Kruetzer's [2] description of the procedure, a number of modifications of the surgery were undertaken by several surgeons, as extensively reviewed and referenced elsewhere [9, 10]. In general, there was a consensus that there is no need for a classic Glenn anastomosis and that a prosthetic valve is not necessary in the IVC. Detailed review of these papers revealed that four major types of Fontan operations were being performed for physiologic correction of tricuspid atresia. These include (1) RA-PA anastomosis, direct or through a non-valved conduit; (2) RA-PA anastomosis through a valved conduit; (3) RA-RV anastomosis, direct or non-valved anastomosis; and (4) RA-RV anastomosis through a valved conduit.

In order to understand the advantages of one operation over the other, 17 papers published as of December 1990 that have documented adequate information to evaluate mortality and reoperation rates for each of the four types of Fontan surgery were reviewed. Pooled data from these 17 articles and statistical comparisons were presented in Tables I–IV for the interested reader [9]. This analysis revealed that atriopulmonary (RA-PA) connection appears to be better than atrioventricular (RA-RV) anastomosis and direct connection is better than valved or non-valved conduit anastomosis. Nevertheless, atrioventricular valved (homograft) conduit anastomosis appears to have advantages of (1) restoring a four-valved, four-chambered, biventricular heart and (2) lower right atrial pressure than with atriopulmonary connection. Based on these data [9, 10], the following conclusions were drawn: (1) direct atriopulmonary connection for children with tricuspid atresia with normally related great arteries and a small (<30% of normal) right ventricle without trabecular right ventricular component and for patients who had tricuspid atresia with transposition of the great arteries and (2) atrioventricular valved (homograft) conduit anastomosis for patients with tricuspid atresia and normally related great arteries but with a right ventricular size greater than 30% of normal and a trabecular right ventricular component [9, 10].

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*Fontan Operation: A Comprehensive Review DOI: http://dx.doi.org/10.5772/intechopen.92591*

*2.2.1 Bidirectional Glenn procedure (cavopulmonary anastomosis)*

Bidirectional cavopulmonary anastomosis is a modified version of classic Glenn procedure in which the upper end of the divided SVC is anastomosed end to side to the right PA without disconnecting the latter from the main PA. Thus, the SVC blood is diverted into both the right and left PAs, justifying the term, "bidirectional." Experimental bidirectional cavopulmonary anastomosis was first studied by Haller et al. [11] in animal models, and its first clinical use was described by Azzolina et al. [12] in 1972. Other investigators [13–17] later applied this technique to palliate complex heart defects with decreased pulmonary blood flow. Hemodynamic advantages of the bidirectional Glenn procedure are improvement of effective pulmonary blood flow, decrease in total pulmonary blood flow, and reduction of left ventricular volume overloading. In addition, preservation of continuity of the pulmonary artery is an added advantage and may help facilitate a low-risk Fontan procedure. When both right and left SVCs are present, bilateral bidirectional Glenn shunts should be performed, especially if the bridging innominate vein is absent or small. Based on our own experience and that

published in the literature [13–17], the author recommended serious consideration in employing bidirectional cavopulmonary anastomosis as an interim palliative procedure for patients who are at an increased risk for the Fontan procedure [9, 10].

Puga et al. [18] positioned a patch inside the right atrium to divert the IVC blood into the PAs; they had good results in the 12 patients that they used this technique. This was later called lateral tunnel and was widely used until extra-cardiac conduits

To better understand the valve-less atriopulmonary anastomosis type of Fontan, de Leval et al. [19] performed hydrodynamic studies and found that (1) the right atrium is not an efficient pump in non-valved atriopulmonary connections, (2) pulsations in a non-valved circulation truly generate turbulence with consequent decrease in net flow, and (3) energy losses occur in the non-pulsatile chambers, corners, and obstructions. In an attempt to address these deficiencies, they developed a procedure which they named "total cavopulmonary connection." In this procedure, they connected the divided SVC, end to side, to the undivided right pulmonary artery (bidirectional Glenn), and the IVC blood is diverted through a composite intra-atrial tunnel (with the use of posterior wall of the right atrium as posterior wall of the tunnel) into the cardiac end of the divided superior vena cava, which in turn was connected to the PA. They felt that technical simplicity, maintenance of low right atrial and coronary sinus pressure, and reduction of risk of atrial thrombus formation are advantages of this type of operation. They performed this procedure on 20 patients and observed two early deaths and one late death. Postoperative hemodynamic studies were performed in 10 of the survivors which indicated good results. They recommended this type of operation for patients with a non-hypertrophied right atrium. While the total cavopulmonary connection was initially devised for patients with complex atrial anatomy and/or systemic venous anomalies, it has since been used extensively for all types of cardiac anatomy

with one functioning ventricle and irrespective of venous anomalies.

**2.2 Other developments**

*2.2.2 Lateral tunnel*

came into vogue.

*2.2.3 Total cavopulmonary connection*
