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.