DISCUSSION
Fontan circulation is inherently a non-physiological status where the pulmonary artery trust, i.e., the subpulmonic ventricle is lacking. There is a continous systemic venous congestion secondary to pulmonary vascular resistance and low cardiac output due to decreased filling pressures(11). In the biventricular physiology, the subpulmonic ventricle provides a forward flow to the lungs and the central venous pressure is kept around 2 to 6 mmHg. Under such circumstances, the negative intrathoracic pressure and peripheral muscular contractions are not mandatory for providing this pulmonary flow. However, since the forward flow augmentation to the lungs is lacking in Fontan circulation, the systemic venous pressure is increased approximately by three folds (11). In his extraordinary paper, Rychik defined this situation as the‘Fontan paradox’ where the high systemic venous pressure is indispensable for adequate cardiac output, and therefore an ideal Fontan may be defined as a failing Fontan as well: a good systemic cardiac output can only be achieved with high systemic venous pressures and congestion (12). The basic pathophysiology of the long-term untoward effects of Fontan circulation is based on these two factors; upstream congestion and downstream decreased flow (13).
Fenestration is one of the most important attempts in order to overcome this viscous cycle (13). In his original report, Dr. Bridges defined the three main advantages of a right to left shunt in Fontan patients; (i) the cardiac output is maintained in expense of systemic desaturation where the pulmonary blood flow is limited; (ii) the uncontrolled increases in systemic venous pressure is eliminated that leads to decreased duration of pleural effusions and (iii) ease of transcatheter closure when necessary (14). In a meta-analysis reported by Dongxu and colleagues, a total of 1929 Fontan patients derived from the data of 14 studies were evaluated (15). Although the postoperative systemic oxygen saturation levels were low in FP with fenestration, the late postoperative oxygen saturation levels did not show any difference statistically. In the same paper, incidence of arrhythmias was found to be lower in fenestrated cases, as well. We did not encounter any arrhythmia in our patient population with the mean follow-up period of 3.6 years. In patients with fenestration of the Fontan pathway, protein losing enteropathy is reported to be less and the thromboembolic complications are not statistically different when compared to non-fenestrated cases (16,17). We did not encounter such complications during the follow-up period.
At this point, the question of routine fenestration in FP is still debated in literature. Some centers advocate routine fenestration in order to decrease Fontan failure rates as well as the postoperative pleural effusion (18). However, some papers report worse or similar early outcomes in fenestrated patients (19,20). A recent meta-analysis in a total of 4806 patients sought for the statistical evidence for routine fenestration, however a general consensus was not agreed on (21). Probably the most important result of this analysis was the lack of any scientific evidence that fenestration is associated with lower incidence of Fontan failure. The duration of pleural effusion, MPAP and systemic oxygen saturation levels were lower in fenestrated patients, however the incidence of stroke, duration of hospital stay and early mortality were similar (21).
In our opinion, another advantage of the fenestration in IECF is its durability. All of the fenestrations in our IECF cases are functioning in the follow up period, except one case, which was closed via percutaneous route at another congenital heart disease center. In the era of LT and ECF, the spontaneous closure of surgically created fenestrations could be as high as 19% (14). Sinha et al. reported that only 66% of fenestrations were patent at the time of discharge in ECF patients, whereas this ratio was 95% in IECF patients (22). In a catheter-based analysis in 35 patients, Hirofumi and colleagues reported that persistent fenestration in Fontan circulation suppresses heart rate and CVP, which secures preload reserve without compromising systemic oxygen delivery (23). The high patency rate of IECF may be attributed to more deliberate use of anticoagulant or antiplatelet medications (21). Antiplatelet versus anticoagulation therapy after FP is another matter of debate and anticoagulation combined with antiplatelet drugs seem to be safe with similar incidence of thromboembolic events in Fontan patients (24). We prefer to use combined anticoagulation with antiplatelet treatment in our IECF patients. Recent papers report the promising efficacy and safety of non-vitamin K antagonist oral anticoagulants at least in adult patients with FP (25).
Another important feature of IECF is decreased incidence of arrhythmias in long-term follow-up (26). Rhythm disturbances in FP patients may lead to decreased cardiac output, AV valve regurgitation, thrombus formation in cardiac chambers and syncope (27). The lateral tunnel modification is traditionally known to cause atrial arrhythmias. However, the ECF technique, which was advocated in the early 1990’s as a solution for rhythm disturbances in patients with LT is not innocent as well (26). Transection of IVC and suturing the atrial cuff near terminal crest/Eustachian valve in ECF modification is speculated to damage the atrial conduction pathways and lead to arrhythmia in long term (26). Therefore, preservation of terminal crest and Eustachian valve and eliminating the sutures at the atrial cuff makes the IECF technique superior to LT and ECF with regard to incidence of arrhythmia (27,28). The suture lines in IECF are far from disturbing the conduction pathways and atrium-IVC continuity, as well. Moreover, high patency rates of the fenestration provide a percutaneous access route for intervening any rhythm disturbance if encountered. In our patient population, we did not have any patient with arrhythmia in the postoperative follow-up.
Since an important percentage of the systemic blood flow coming through IVC is directed to pulmonary vascular bed in conduit-based Fontan modifications, the improved hemodynamic performance and minimized energy losses are mandatory for satisfactory long-term results. The conduit in IECF directs the IVC blood in a straight path to the pulmonary arteries, minimizing the energy loss (29). The risk of compression of the pulmonary veins by the conduit, which may be an important problem in ECF is eliminated in IECF (30). The path of the conduit is far away from sinoatrial node and the right atriotomy is more limited, which may have additive effect on decreased incidence of arrhythmias in IECF, as well (26).
Patients undergoing FP with the diagnosis of heterotaxy syndromes is always a challenge and results of FP in these patients are variable in literature (31,32). The IECF modification is easy and reproducible in these patients no matter the anatomy is complex or not, since the cardiopulmonary bypass and aortic cross clamp times are not prolonged with IECF in these patients (27). Another advantage of IECF technique is its reproducibility in patients with separate hepatic venous drainage to the atrium. When ECF is preferred in such patients, the distance between the IVC and hepatic vein ostium as well as the position of the vertebrae should be considered (33). Moreover, it’s easy to incorporate the hepatic vein ostium into the IVC-conduit anastomosis within the atrium in IECF technique. We did not encounter any heterotaxy syndrome in our patient population, but we had two cases of separate hepatic vein drainage. In their recent series, Hirose K and colleagues recommend to perform IECF in cases with apicocaval juxtaposition (i.e., ipsilateral position of the cardiac apex and IVC) and separated hepatic venous drainage, since the ordinary ECF conduit may be long and too curved that could result in kinking and unbalanced pulmonary blood flow (34).
Two other important parameters when performing a FP are the mean pulmonary artery pressure and pulmonary artery size. Our group previously reported encouraging results of the patients undergoing FP with preoperative MPAP over 15 mmHg (35). This experience was important, since two parameters were still being strict in the traditional ‘ten commandments’: preoperatively impaired ventricular function and elevated pulmonary artery pressure (36,37). In our patient population, the mean pulmonary artery pressure value was 13.8 ± 3.3 mmHg which decreased to a mean of 10 ± 2.4 mmHg after IECF with routine fenestration. On the other hand, the mean pulmonary artery (Nakata) index was 209 ± 67 mm2/m2 in our cases, which was above the lower limit of 200 mm2/m2 stated by paper of Dr. Fontan himself (38). However, much lower limits of 110 mm2/m2 were emphasized by other authors in literature before a FP is planned (39).
Fontan procedure undoubtfully improved the life expectancy for infants born with complex heart diseases over the last 50 years, however, the morbidity is still high (40). The estimated number of alive Fontan patients only in Europe is over 25.000 (40). The IECF technique which originally combined the advantages of LT and ECF modifications has significant advantages in selected cases. The IECF procedure has the advantage of decreased energy loss through the conduit, since a straight and short pathway is provided with a better position of the graft. The expected incidence of postoperative arrhythmia is lower due to the preserved right atrium – IVC continuity and more limited right atriotomy when compared to ECF. Moreover, fenestration is easy, more durable and easier to be closed via percutaneous route if needed (34).
In our limited patient population, we think that fenestrated intra-extracardiac Fontan procedure may be performed with satisfactory mid-term results both in patients with anatomical complexity or selected patients where the lateral tunnel and extracardiac modifications are not preferred. We prefer IECF especially in patients with complex anatomy such as heterotaxy syndromes and apicocaval juxtaposition. Secondly, in cases where a fenestration is deemed mandatory at the preoperative planning, we prefer this technique, both with regard to technical ease of fenestration as well as its durability. On the other hand, long-term results of this modification are less frequently documented in literature, therefore more studies with larger patient series should be conducted.