Second Stage of Univentricular Hearts
The goal of the second-stage procedure of UVH is to divert systemic
venous blood from the superior vena cava directly into the pulmonary
vascular bed (Figure 4) , allowing for effective pulmonary blood
flow while reducing volume load on the single ventricle to allow for
favourable ventricular remodelling, which improves the patients’
outcomes.10
The bidirectional cavopulmonary shunt (BPCS) or Hemi-Fontan procedure is
usually performed when the pulmonary arteries have grown adequately to
allow adequate pulmonary blood flow with low PVR, which is usually
between 2 to 6 months.11 In cases where the modified
BTTS or PAB is performed first, reassessment to measure pulmonary artery
size adequacy and pulmonary artery resistance index will be carried out
6 to 12 months later using cardiac catheterization or multi-slice
computed tomography (MSCT).
The selection of the second-stage shunting procedure determines the
technique utilized for the completion of the Fontan procedure. When a
BCPS is used, an extracardiac completion Fontan is performed, as there
is no point in reconnecting the superior vena cava to the right atrium
after a BCPS. Patients with Hemi-Fontan modifications have extremely
relevant anatomy for completion by the lateral tunnel Fontan operation,
thus preferably used in these patients.12 The criteria
for conducting BCPS or the Hemi-Fontan procedure at our centre include a
mean pulmonary artery pressure of less than 18 mmHg and a pulmonary
artery resistance index of less than Wood
units/m2, with confluent pulmonary arteries and
making sure the pulmonary artery size is according to the half size of
the patient, which depends on body weight. Usually, in cases of UVH in
BCPS, atrial septectomy will be performed if a restrictive atrial septal
defect is suspected.
Postoperative management include positioning of the patient, where we
usually position the patient in a semi-Fowler position to improve blood
flow from the upper body to the right atrium. Early extubation helps
improve pulmonary blood flow and systemic oxygen delivery as well as
avoid needless sedation to improve spontaneous breathing. Modest
hypercarbia of pCO2 ± 45 mmHg is acceptable as it enhances cerebral
vasodilation and reduces the superior vena cava pressure. The target of
saturation oxygen for BCPS/Hemi-Fontan patients is 85%. We typically
give inotropics such as dobutamine to improve stroke volume in patients
with poor contractility. Pulmonary vasodilators such as milrinone or
oral sildenafil (if the patient can tolerate oral feeding) may be given.
Patients with bilateral BCPS or concomitant reconstruction of pulmonary
artery branches are usually given 5 mg/kg of acetylsalicylic acid in our
centre.