The Fontan procedure was developed so that the heart could function and distribute oxygenated blood around the body without the need for two ventricles. As I have discussed previously (see here and here), today the Fontan procedure is done through a lateral tunnel/intra-cardiac route or an extra-cardiac route. Here is a nice image depicting what these two procedures look like.
- Extra-cardiac Fontan on the right and Fenestrated intra-cardiac/lateral tunnel Fontan on the left.
- In the lateral tunnel/intra-cardiac route for the Fontan procedure, a piece of plastic (‘baffle’) is built in the right atrium to direct the deoxygenated blood coming from the lower part of the body (via the inferior vena cava) to go directly to the lungs. One major development that was first described in 1990 to refine the lateral tunnel/intra-cardiac Fontan was the creation of a small hole called a ‘fenestration’ in the baffle during the Fontan procedure (Bridges et al., 1990, Circulation 82, 1681-1689). As the image below shows, a small hole/fenestration is created in the baffle in the right atrium (indicated by the arrow with #2)..
This image highlights the fenestration (small hole) created in the baffle in the right atrium (indicated by #2 with arrow).
This ‘fenestrated Fontan’ as it is commonly called today was described by Bridges et al. (1990). The goal of the fenestration was to try and lower the risk of mortality in the period of time soon after the Fontan surgery. At that time, high blood pressure in the right atrium (where the baffle was placed) and low cardiac output (basically the total amount of blood pumped by the heart) was a predictor of mortality in the post-operative period. That is, patients with high blood pressure in the right atrium or low cardiac output were more likely to die soon after surgery. Bridges et al. (1990) proposed that some of this pressure in the right atrium could be ‘relieved’ and cardiac output increased by creating a small hole in the baffle in the right atrium. They thought that this fenestration would relieve some of this pressure and increase cardiac output, which could potentially decrease mortality rates soon after the surgery. However, of course this fenestration would also cause right-to-left shunting where deoxygenated blood in the right atrium mixes with oxygenated blood in the single ventricle, which would of course lower blood oxygen concentrations leaving the heart. Bridges et al. (1990) proposed and treated patients with these fenestrated Fontan’s by closing the hole in the baffle during a heart catheterization 3-12 months after the Fontan surgery or letting the hole close spontaneously on its own.
How Common is the Fenestrated Fontan?
The creation of a fenestration in the baffle during both lateral tunnnel/intra-cardiac or extra-cardiac Fontan procedures is now extremely common. For example, from 1992-2002, of all the Fontan procedures (using both techniques) performed in 7 different hospitals where Fontan procedures are commonly performed (part of the Pediatric Heart Network), over 80% of them created a fenestration (Atz et al., 2011, J of American College of Cardiology 57, 2437-2443). This is not surprising given that the use of a fenestration in the baffle during a Fontan procedure has many positive short-term outcomes (see list below).
Short-term Costs and Benefits of a Fenestrated Fontan
1) Patients with a fenestrated Fontan have a shorter duration of chest-tube drainage. In a well-designed randomized study by Lemler et al. (2002, Circulation 105, 207-212), the authors show that patients at the Children’s Medical Center of Dallas that underwent a fenestrated Fontan (25 patients) had significant drainage from chest tubes (that is post-operative pleural effusions) for an average of 10 days (range was 5-62 days) whereas patients that underwent a non-fenestrated Fontan (24 patients) had significant drainage from chest tubes for an average of 16 days (range 3-45). Similarly, patients that had a fenestrated Fontan had significantly less total drainage from the chest tubes (measured in volume) than those that underwent the non-fenestrated Fontan. This study supports an earlier one by Bridges et al. (1992, Circulation 86, 1762-1769) that also shows that the duration of chest tube drainage is reduced by using a fenestrated Fontan procedure in high-risk patients.
2) Patients with a fenestrated Fontan have a shorter length of hospital stay after the surgery but no difference in time spent in the intensive care unit. Bridges et al. (1992) and Lemler et al. (2002) both show that patients that underwent a fenestrated Fontan procedure stayed in the hospital after the Fontan procedure for a shorter amount of time than those that underwent the non-fenestrated Fontan. For example, Lemler et al. (2002) showed that patients that underwent the fenestrated Fontan stayed in the hospital after the surgery for an average of 12 days (range was 6-26 days) whereas those that underwent the non-fenestrated Fontan stayed in the hospital after the surgery for an average of 23 days (range was 5-64 days). In contrast, the use of a fenestration didn’t affect how long patients spent in the intensive care unit after the Fontan.
3) Patients with a fenestrated Fontan have lower oxygen saturations after the surgery. As mentioned above, a major benefit of the fenestrated Fontan is that cardiac output (amount of blood pumped by the heart) is increased but this comes at a cost of the mixing of deoxygenated blood from the right atrium with oxygenated blood in the single ventricle. For example, Lemler et al. (2002) found that patients with a fenestrated Fontan had significantly lower oxygen saturations in the post-operative period (average of 90%) compared to those with a non-fenestrated Fontan (average of 93%). Though, it should be noted that the range of oxygen saturations in the non-fenestrated group was quite high (66-98%) compared to the fenestrated group (81-96%) suggesting that the difference when looking at averages was much higher if the patient with an oxygen saturation of 66% was dropped from the analysis.
5) Patients with a fenestrated Fontan were taking more medications at hospital discharge compared to those with a non-fenestrated Fontan. Atz et al. (2011) found that patients with a fenestrated Fontan (361 patients) were more likely to be taking an ACE inhibitor (e.g., captopril or enalapril) and anti-thrombotic drugs (e.g., asprin, warfarin) at hospital discharge after the Fontan than those that had a non-fenestrated Fontan (175 patients). However, this could be because of differences among the hospitals such as one hospital always performing fenestrated Fontan’s and always providing patients with an ACE inhibitor and asprin at discharge.
6) Do patients with a fenestrated Fontan have an increased risk of stroke? It has been suggested that patients with a fenestrated Fontan may have an increased risk of stroke, though this hasn’t been supported by previous studies. For example, one of the first studies (du Plessis et al. 1995 Pediatric Neurology 12, 230-236) documenting this potential increased risk of stroke from a fenestrated Fontan showed that of the total of 314 that underwent the Fontan procedure at the Boston Children’s Hospital from 1989-1993, a total of 209 patients had a fenestrated Fontan. Out of all of these patients, 10 of them had a stroke where 9 out of 209 patients with a fenestrated Fontan (4.3%) compared to only 1 patient with a non-fenestrated Fontan having a stroke (1/105 patients or 0.95%). This difference was not statistically significant and it also reflects that patients in the fenestrated Fontan group may have already been at a higher risk for stroke prior to the procedure. More recent studies, however, do not find that patients with a fenestrated Fontan have an increased risk of stroke compared to patients with a non-fenestrated Fontan (e.g., Coon et al., 2001, Annals Thorac Surg 71, 1990-1994; Atz et al., 2011).
Long-term Costs and Benefits of a Fenestrated Fontan?
Although the fenestrated Fontan is commonly used today, whether or not it is used seems to be highly dependent upon where the Fontan procedure is done. For example, the percentage of patients that had a fenestrated Fontan can vary from 13-91% at 7 major hospitals in North America (Atz et al., 2011). That is highly variable! Why might some surgeons always perform fenestrated Fontan’s while others choose not to create a fenestration during the Fontan procedure especially when there are such obvious short-term benefits during the post-operative period?
Well, what do we actually know about the long-term costs and benefits of a fenestrated Fontan? As mentioned above, the creation of the fenestration allows the deoxygenated blood from the right atrium to mix with the oxygenated blood in the single ventricle, which consequently can lower blood oxygen concentrations that leave the heart. Some researchers have suggested that the use of a fenestration is not a preferred option for some surgeons because there is little scientific evidence that it is beneficial in the long-term (Gersony (2008, Circulation 117, 13-15; de Laval and Deanfield 2010, Nature Reviews Cardiology 7, 520-527). This is primarily because the long-term impacts of a fenestrated Fontan are relatively unknown. Let’s look at what we do know about the long-term impacts of a fenestrated Fontan. In a recent study by Atz et al. (2011), they compared the medical status of patients that had underwent a fenestrated Fontan where the fenestration was either still open or had been closed (either spontaneously or during a heart catheterization).
1) Patients with a fenestrated Fontan may have an increased risk of death, stroke, heart transplant, etc. from 1-10 years after the Fontan procedure compared to those with a non-fenestrated Fontan. Tweddell et al. (2009, Ann Thorac Surg 88, 1291-1299) compared the fate of patients that underwent either a fenestrated Fontan (217 patients) or a non-fenestrated Fontan (38 patients) from 1994-2007 at the Children’s Hospital of Wisconsin. For these 38 patients, the fenestration that was originally present was closed in the operating room based upon the judgement of the surgeon. Interestingly, Tweddell et al. (2009) found that the patients with the fenestrated Fontan had a higher incidence of Fontan failure compared to those with a non-fenestrated Fontan. Here, Fontan failure was basically defined as the patient dying, needing a heart transplant or pacemaker, developing protein-losing enteropathy, or having a stroke. From 0-4 years of after the Fontan procedure, the incidence of Fontan failure was similar between patients with fenestrated and non-fenestrated Fontan’s. However, around 4 years after the Fontan procedure had been performed, patients with a fenestrated Fontan tended to have a higher incidence of Fontan failure. Although this study cannot confirm that fenestration resulted or caused this increase in Fontan failure, it is a highly interesting result given how often the fenestrated Fontan is performed.
2) Patients with a fenestrated Fontan have lower resting oxygen saturations than those in which the fenestration is closed. Atz et al. (2011) showed that of patients with a fenestrated Fontan (hole did not spontaneously close or wasn’t closed during a heart catheterization) had significantly lower oxygen saturations (average was 89%) compared to patients in which the fenestration was closed (average of 95%). This suggests that in terms of increasing blood oxygen saturations, closing the fenestration may be beneficial (see also Goff et al., 2000, Circulation 102, 2094-2099).
3) Few other long-term costs of a fenestrated Fontan have been documented. Atz et al. (2011) found that patients with a current fenestration compared to those with a closed fenestration did not differ in their overall health status, exercise performance, occurrence of stroke or protein-losing enteropathy, or body growth. Moreover, a previous study supports some of these results where patients with a fenestrated Fontan had a similar exercise capacity as did those with a non-fenestrated Fontan (Meadows et al., 2008, J Am Coll Cardiol 52, 108-113). This contrasts those results from Tweddell et al. (2009) at least in terms of documenting why patients with a fenestrated Fontan may have a higher incidence of Fontan failure. Essentially, there were few differences between patients with fenestrated and non-fenestrated Fontan’s.
Should the Fenestration be Closed?
Atz et al. (2011) found that around 40% of 361 patients that underwent a fenestrated Fontan had their fenestration close spontaneously. Many doctors recommend closing the fenestration at some time interval after the Fontan procedure. There may be specific benefits for closing the fenestration related to blood oxygen saturations. For example, Goff et al. (2000) found that 154 patients that underwent successful closure of the fenestration during a heart catherization had an increase (9.4% on average) in oxygen saturation when measured from 0.4-10.3 years after the fenestration closure. As indicated above, Atz et al. (2011) also found that patients in which the fenestration was closed also had higher blood oxygen saturations. These increases in blood oxygen saturations may be associated with favorable outcomes for body growth. For example, Goff et al. (2000) found that patients in which the fenestration was closed rose in their height and weight percentiles compared to what they were prior to closing the fenestration suggesting that closing the fenestration is associated with an increased rate of body growth. On the other hand, Atz et al. (2011) did not really find that there was many benefits associated with closing the fenestration other than increasing blood oxygen saturations. So is it worth it to have the fenestration closed? The current evidence suggests that there are some major benefits in terms of increasing blood oxygen saturations but few other benefits. Obviously this needs more study and we cannot make conclusions based upon one study.
Conclusion. It is somewhat surprising that most patients that undergo the Fontan procedure now have a fenestrated Fontan regardless of whether they have an intra-cardiac/lateral tunnel or extra-cardiac Fontan. This is surprising because although a fenestrated Fontan obviously has beneficial outcomes in the short-term (reducing duration and amount of chest tube drainage, reduced hospital stay), we still know very little about the long-term consequences of a fenestrated Fontan. In fact, some have now questioned whether fenestrations should always be performed and advocated the adoption of a patient-specific approach where only ‘high-risk’ patients undergo a fenestrated Fontan (Gersony, 2008). Second, the evidence is not clear regarding whether we should always be closing the fenestration later in life or even when the fenestration should be closed (i.e., how many years after the Fontan?). Some have even argued that closing the fenestration during a heart catheterization is not worth the risks even if they are low (discussed in Goff et al., 2000) and this is not surprising because the evidence at present doesn’t show that there are substantial benefits of closing the fenestration other than increases in blood oxygen saturations (Atz et al., 2011). Not discussed at length here is the fact that the presence of a fenestration can increase cardiac output (Bridges et al., 1990), which could decrease after the fenestration is closed. Given that the use of a fenestrated Fontan is highly variable among different hospitals (Atz et al., 2011), it seems wise to be informed about the potential short- and long-term costs and benefits of having a fenestrated vs. non-fenestrated Fontan. Clearly more work needs to be done here.