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: