Fontan risk profile in that group was no different to that of those who with fenestration closure These findings suggest that a strategy of selective closure can be used to identify a high-risk population, who despite their poorer outcome may well have a better outcome with a persistently patent fenestration than with their fenestration closed FIG 73.24 Freedom from death between open and closed fenestration (A) and stratified by mechanism of fenestration closure (B) The presence of an open fenestration was associated with the lowest survival (From Kotani Y., Chetan D, Saedi A, et al Persistent fenestration may be a marker for physiologic intolerance after Fontan completion J Thorac Cardiovasc Surg 2014;148:2532–2538, Fig 1.) Information comparing exercise performance before and after fenestration closure is sparse In one small study there was an improvement in ventilatory efficiency as measured by a decrease in VE and an increase in the VE/VCO2 slope, without a change in exercise capacity,351 whereas in another, exercise duration and maximal exercise capacity increased.352 Despite the theoretical risk of thromboembolism due to the obligatory right-to-left shunt and a propensity for venous thrombosis, a number of studies have been unable to demonstrate an association of this complication with a persistent fenestration.292 Given the aforementioned, there is considerable practice variability in relation to fenestration closure and its timing.249 Early in the course of practice, closure was undertaken shortly after recovery from the Fontan operation The realization that a significant minority of fenestrations close spontaneously after the Fontan operation led to a delay in closure.353 The time course of spontaneous closure is not well understood Some recommend closure 12 months after surgery and others up to 3 years later When closure is considered, test occlusion with a balloon catheter with side-holes proximal to the balloon (e.g., Berman angiographic) is recommended (Fig 73.25) (Videos 73.5 and 73.6) Oxygen saturation and pressure should be measured simultaneously in the Fontan pathway and the systemic arterial circulations Criteria to predict “failure” of test occlusion are poorly defined, but if test occlusion is associated with a Fontan pathway pressure greater than 18 mm Hg, a fall in the Fontan pathway oxygen saturation or a fall in the systemic blood pressure then closure is not advised.353 Likewise if the systemic oxygen saturation does not increase above 90%, fenestration closure may not improve systemic oxygen saturation and another source of right-to-left flow such as a systemic venous to atrial shunt or pulmonary arteriovenous malformations, or alternately lung disease, should be considered With these precautions, the risk of decompensation and Fontan failure related to fenestration closure is low.353 FIG 73.25 Angiograms in a patient with a fenestrated extracardiac Fontan demonstrating (A) patent fenestration (asterisk), (B) test occlusion of the fenestration (arrow marks occlusion balloon), and (C) device occlusion of the fenestration (arrow marks device) Venovenous Collaterals Venovenous collaterals are a common cause of progressive cyanosis after the Fontan procedure These vessels connect the systemic venous circulation (most often from the upper thorax) to the pulmonary veins or directly to the systemic venous atrium Many were originally small veins Dilatation occurs because of increased flow driven by the pressure gradient between the systemic and pulmonary veins This transpulmonary pressure gradient increases if there is pathway obstruction at any level, including stenosis within an extracardiac conduit, at the cavopulmonary anastomosis, within the pulmonary arteries, pulmonary vascular disease or other lung disease resulting in elevated pulmonary vascular resistance, or pulmonary vein stenosis Larger collaterals are associated with a longer time since the Fontan procedure and a higher pulmonary artery pressure (Fig 73.26).354 Transcatheter occlusion of venoveno collaterals will result in an increase in systemic arterial oxygen saturation However, venoveno collaterals are often a marker of problems within the Fontan circulation By allowing a portion of systemic venous return to bypass the pulmonary circulation, they fulfill the role of a fenestration, maintaining cardiac output and reducing CVP A recent report demonstrates an increased mortality risk in the years after venovenous collateral closure, with 50% of deaths occurring in patients with a pulmonary artery pressure greater than 18 mm Hg (Fig 73.27).355 These findings indicate that, in some patients, venovenous collaterals may be advantageous for long-term survival A search for potential risk factors and test occlusion in a similar way to that recommended prior to fenestration should be considered prior to occlusion FIG 73.26 (A) Venovenous collateral, originating from the brachiocephalic vein and draining to a left pulmonary vein (B) Following coil occlusion