Lateral tunnel versus extracardiac conduit Fontan procedure: a concurrent comparison

In this paper by Kumar et al. (2003, Ann Thorac Surg 76, 1389-1397), the authors compare the outcomes of patients that underwent the Fontan procedure either using the intra-cardiac (lateral tunnel) or extra-cardiac conduit method. I have previously discussed the differences of these two types of the Fontan procedure here. and how the use of each type has changed over time here. In brief, the intra-cardiac or lateral tunnel method is the ‘older’ method (introduced in 1987) and the extra-cardiac method was more recently developed (1990). The lateral tunnel/intra-cardiac method involves sewing a piece of plastic inside the right atrium to route all blood from the lower part of the body (via the inferior vena cava) to the lungs whereas the extra-cardiac method involves placing a tube (either a tissue graft or plastic) outside the heart so that all blood from the lower part of the body (again via inferior vena cava) goes to the lungs. Regardless, some hospitals still perform the intra-cardiac method is the preferred option (see here).

The first thing to point out that this study was published over 10 years ago and uses data from patients that underwent the Fontan procedure from 1995-2002. As I have discussed elsewhere, there have been significant improvements in patient care and outcomes from the Fontan procedure. The other issue that these authors indicate is that most institutions only use one of the types of Fontan or they have suddenly changed over time. As such, it is hard to compare the outcomes of a lateral tunnel vs. extra-cardiac Fontan at a single hospital over the same time period. This study presents data where they performed both lateral tunnel (37 patients) and extra-cardiac (33 patients)  Fontan procedures at the same institution (Medical University of South Carolina) at the same time period.

Summary of Major Points of this Paper:

1) Theoretical advantages of extra-cardiac method. The lateral tunnel or intra-cardiac method requires placing a piece of plastic (“baffle”) inside of the atrium. The lateral tunnel/intra-cardiac method has had good early, medium, and long-term outcomes as well in previous follow-up studies. However, this requires sewing the piece of plastic (Gore Tex) inside the heart, which may increase the risk of atrial arrhythmias. The extra-cardiac method avoids having to sew this piece of plastic inside of the heart and so a theoretical advantage is that this method may decrease risk of future heart rhythm issues. However, note that this generally requires that the surgery be performed later in life because you are placing a piece of plastic in the heart that will not grow with the patient. Another possible advantage of the extra-cardiac method is that it can allow surgeons to perform the procedure without aortic cross-clamping (where they prevent the blood from leaving the heart) and even without cardiopulmonary bypass, which may have some advantages for short- and long-term outcomes (discussed here). For example, in this study, aortic cross clamping was always used for the lateral tunnel/intra-cardiac method but used in ~51% of patients for the extra-cardiac method.

2) No difference in time on cardiopulmonary bypass between intra-cardiac and extra-cardiac method but patients undergoing intra-cardiac method were on aortic cross clamping longer than those using extra-cardiac method. Patients undergoing the lateral tunnel/intra-cardiac method were on bypass (mean = 134 min) nearly the same amount of time as those undergoing the extra-cardiac method (mean = 145 min). However, 100% of patients undergoing the lateral tunnel/intra-cardiac method had aortic cross-clamping and for a longer period of time (mean = 55 min) than those that had the extra-cardiac method (52% of patients, mean = 26 min).

3) No difference in time on ventilator, time in intensive care unit, duration of chest tube drainage, and hospital stay between those having the lateral tunnel/intra-cardiac method vs. those undergoing the extra-cardiac method. This is an interesting result given that the lateral tunnel/intra-cardiac method is theoretically supposed to improve short-term outcome (that soon after the surgery) because of decreased chest tube drainage, etc. However, here they didn’t find any differences between the two methods.

4) No difference in type or frequency of medications given to patients that underwent intra-cardiac vs. extra-cardiac Fontan ~3 years previous. Though this probably attributable to the hospital itself and how they treat their patients, most of the patients were on asprin (94%) and there were no other differences between the type of frequency of medications taken between patients that underwent intra-cardiac or extra-cardiac method ~3 years previous.

5) No difference in heart rhythm problems between patients that had underwent intra-cardiac vs. extra-cardiac Fontan at ~3 years after the surgery. This is somewhat surprising that 15% of patients that had underwent the intra-cardiac Fontan ~3 years previous had heart rhythm issues (sinus node dysfunction) whereas MORE (28%) of patients that had underwent the extra-cardiac Fontan had heart rhythm issues ~3 years previous. Although this is not statistically different, this is opposite than what would be expected. Two patients underwent permanent pacemaker implantation (1 lateral tunnel and 1 extra-cardiac method) and in one case for slow junctional rhythm.

6) No difference in the post-operative blood pressure in various parts of the atrium and in the Fontan pathway (“Fontan pressure” and transpulmonary gradient) between patients that underwent the intra-cardiac vs. extra-cardiac Fontan. The authors provide brief discussion how these pressures can be predictive of early Fontan failure but they found no difference between these two methods in the first 24 hours after the Fontan.

Summary: This study highlights the lack of any real differences between the intra-cardiac/lateral tunnel vs. extra-cardiac Fontan in both the short- and long-term. This study also highlights the low rates of mortality or Fontan takedown (4.3%) around and soon after the actual surgery and high rates of survival 3-5 years after the Fontan for both the intra-cardiac (97%) and extra-cardiac (91%) methods.

The authors discuss their results in light of other studies that were contemporary at the time of this publication (2003). There results are similar to those of Gaynor et al. (2001, J Thorac Cardiovasc Surg 121, 28-41) who reported results from patients undergoing either intra- or extra-cardiac Fontan at Children’s Hospital of Philadelphia (1992-1999) and who again found no real differences between the methods. However, in another previous study that did a similar comparison between patients that underwent the intra-cardiac or extra-cardiac method at the Hospital for Sick Children in Toronto (data from 1994-1998), there was a significantly higher incidence of heart rhythm problems for patients undergoing the lateral tunnel/intra-cardiac method (45%) than those that underwent the extra-cardiac method (15%) at the post-operative period. Why the differences? The authors indicate that it may come from how the Fontan procedure was staged. The second surgery prior to the Fontan is either the hemi-Fontan procedure or the bidirectional Glenn shunt. The authors indicate that they selectively perform the hemi-Fontan for patients that were to undergo the lateral tunnel/intra-cardiac Fontan and perform the bidirectional Glenn shunt for patients that are due to undergo the extra-cardiac Fontan. In contrast, the patients at the hospital in Toronto were all staged with the bidirectional Glenn shunt regardless of whether they were to undergo the intra-cardiac or extra-cardiac Fontan (well, all patients except 1). The authors discuss how the hemi-Fontan (2nd surgery) prior to the lateral tunnel Fontan is a preferred option than doing the bidirectional Glenn shunt prior to the lateral tunnel Fontan (as the surgeons in Toronto did) because the latter involves making incisions in the same area where the previous incisions for the bidirectional Glenn shunt were made. Cutting into the same places where previous incisions were made in the sinus node region is probably not a preferable option. Interesting result. These findings confirm other studies that the risk of heart rhythm issues is higher for patients that underwent the bidirectional Glenn shunt prior to the lateral tunnel/intra-cardiac Fontan than if they had underwent the hemi-Fontan prior to the lateral tunnel/intra-cardiac Fontan. I wonder if all hospitals now always do the hemi-Fontan before the lateral tunnel/intra-cardiac method now?

Finally, the authors discuss how sometimes one method has to be done over another because of other issues with the heart anatomy. In other words, the choice of an intra-cardiac vs. extra-cardiac Fontan is not randomized among patients. For example, the lateral tunnel Fontan is often done for patients with hypoplastic left-heart syndrome but the extra-cardiac method is preferred for patients with heterotaxy syndrome. This makes it difficult to assess whether the short-, medium, or long-term outcomes are a result of the surgical procedure itself (i.e., which Fontan method) or the actual underlying condition.

Link to this paper:

https://www.sciencedirect.com/science/article/pii/S0003497503010105

Cardiac pacing in paediatric patients with congenital heart defects: transvenous or epicardial?

In this article by Silvetti et al. (Europace, in press), the authors report on the results from one hospital in which pacemakers were implanted in 287 patients (1-11 years of age). All of these patients had a congenital heart defect and nearly all of them had underwent at least one heart surgery.

As I will examine in future posts, open heart surgeries (particularly the Fontan using the lateral tunnel approach) may increase the risk of heart rhythm problems such as sinus node dysfunction or atrioventricular block (though the empirical data do not always support these predictions). All of the patients in this study had a pacemaker implanted because of sinus node dysfunction or atrioventricular block. Sinus node dysfunction is a broad term for a variety of abnormal heart rhythm conditions (arrhythmias such as bradycardia or tachycardia where the heart beats too slow or too fast, respectively) associated with a general abnormal functioning of the hearts main internal pacemaker (the sinus node or sinoatrial node located in the right atrium of the heart). The sinus node generates the electrical pulses required for proper heart function. Unfortunately, during many heart surgeries, the sinus node can be scarred and function abnormally after surgery. For example, during the Fontan surgery using the lateral tunnel technique, the sinus node may be damaged because of sewing a baffle within the right atrium. In an older retrospective study, Manning et al. (1996, Journal of Thoracic and Cardiovascular Surgery 111, 833-840) found that patients undergoing the multistaged Fontan (i.e., what is done in practice today for most children) have a higher probability of having some sinus node dysfunction following the Fontan.

Patients in this study also had atrioventricular block, which occurs when the electrical signals generated in the right atrium (again in the sinus node) do not travel to the ventricles. The ventricles can still beat on their own using their own intrinsic pacing capacity, though at a lower rate.

To treat the sinus node dysfunction or atrioventricular block, a pacemaker was implanted in these patients. Pacemakers can either be implanted through an endocardial (or transvenous) system (117/287 patients, or 40.1% of patients), where the leads for the pacemaker are inserted into a vein and guided to the heart (like a heart catheter procedure). The lead(s) are inserted into the heart (leads on the inside of the heart) and the other end of the wire is placed into a pacemaker, which is placed in a ‘pocket’ of skin that is created in the chest. The endocardial system is common in adults but less so in children. Its advantages are that it can be performed under local anaesthetic. However, the endocardial method may be more risky with children because they have smaller veins (again, this method threads the leads up the veins).

The second way to implant a pacemaker is the epicardial method, which is more common in children (in this study 170/287 patients, or 59%). The epicardial method involves placing the leads into the heart on the outside of the heart (hence ‘epi’) and putting the pacemaker in a ‘pocket’ of skin created in the abdomen. The epicardial method was initially chosen because the lead implantation procedure could compensate for growth in the child without the leads becoming dislodged. The endocardial system is generally chosen for children that have undergone the Fontan procedure because the actual Fontan procedure can make the area requiring pacing inaccessible through the endocardial (transvenous method). The epicardial method requires general anaesthesia and is generally a more complicated procedure (e.g., requiring partial or full sternotomy or thoracotomy) or more unpleasant experiences…

The main results from this study are below. Though remember that this is the experience of one hospital and we need to compare the epicardial vs. endocardial pacemaker techniques among all hospitals performing these approaches to really compare if one approach is ‘better’ than another.

1) Pacemakers fail about 1/3 of the time! They followed these patients 2-10 years after pacemaker implantation. In that time, the pacing system failed 29% of the time. That means 1/3 of all pacemakers implanted failed at some point!

2) The rate of failure for the two different methods over this 2-10 period differed. Pacemakers implanted using the endocardial technique (i.e,. the transvenous technique) failed 13% of the time whereas those using the epicardial technique failed 40% of the time. That is interesting because the epicardial technique is supposedly preferred for implanting pacemakers in infants and children.  The mechanism by which these pacemakers implanted using the epicardial technique is not clear but appears to be because of lead malfunction.

3) Pacemakers implanted at an earlier age tended to fail more often.

Link to this article:

doi: 10.1093/europace/eut029