Electrode Usage Trends in Children

Pacemaker electrode usage issues can be catagorized as to:

Epicardial versus endocardial implantation

Epicardial versus Endocardial Implantation

The use of epicardial versus endocardial electrodes has always been debatable. While certain conditions require epicardial implantation, many children could have electrodes placed by either route.

In 1985-1986 endocardial electrode placement was employed in only 22% of all pediatric implants. This percentage has increased to approximately 45% by 93-94. This has in part been due to smaller electrode and generator size and to a greater familarity with endocardial implantation by those caring for children. While this percentage may continue to increase there will always be children in whom endocardial electrode placement will not be possible. Situations currently felt to preclude endocardial electrode placement are:

Lack of venous access to the ventricle (i.e. following the Fontan procedure)
Superior vena caval obstruction
The presence of right to left intracardiac shunting
Hypercoagulable states
Pulmonary vascular obstructive disease
The presence of a mechanical tricuspid valve

The size and/or age of the child below which endocardial placement should be performed is debateable. Children as small as 3 kg in weight have undergone endocardial electerode placement. Yet the longterm consequences in such small children is unknown.

Epicardial Electrode Types Employed

Epicardial electrodes type can be grouped into those that sit on the epicardial surface without penetrating it and those that enter the myocardium and more properly should be called intramyocardial. The former are represented currently only by the investigational steroid eluting electrode while the latter are comprised of three major varieties. These are the barbed "fish-hook" electrode (Medtronic 4951(M)), the coil or "cork-screw" electrode (Medtronic 6917 and 5069, Intermedics 471, and CPI 4312) and the intramyocardial wire or "suture-type" (Telectronics 030-170).

The most frequently employed epicardial electrode is the "fish-hook" electrode accounting for 52% of all epicardial electrodes implanted. The coil electode accounts for 44%. The "suture-type" has not found wide acceptance in pediatic patients.

Endocardial Electrode Types Employed

Pacemakers can be configured such that both the positive and negative electrodes are in the heart (Bipolar) or the negative electrode is in the heart with the pacemaker body serving as the positive electrode (Unipolar). There is much debate as to the preferred method to employ. Registry data show that 68% of endocardial implants utilized the bipolar approach appearing to be the preferred approach in children. This may well be due to the high incidence of skeletal muscle pacing in the unipolar approach due to the long current path passing through the chest wall muscles. Initially bipolar electrodes were larger making them less appropriate for children. This is no longer a major factor as the electrodes have become smaller.

Endocardial electrodes can be grouped into three groups. The largest group accounting for 38% of electrodes implanted use a metal coil that enters the endocardium to anchor the electrode to the heart (Active fixation). This is similar to the epicardial coil or "cork-screw" electrode. As it does penetrate the endocardium the potential for scar formation exists. Yet it does not rely on the presence of trabecular recesses for fixation as does the next group.

The second group is anchored to the heart with tines or a flange around the electrode body that lodge among the trabeculations of the right ventricle (Passive fixation). This avoids acute injury but still may result in local fibrosis. A passive fixation electrode cannot be implanted in a morphologic smooth walled left ventricle. This group accounts for 38% of all endocardial electrodes implanted.

The final group is similar to the passive fixation electrodes in its method of fixation but incorporates a slowly eluting steroid source in the electrode tip (Steroid). Theoretically this should reduce initial inflamation and subsequent fibrosis around the electrode tip. This group accounts for 20% of electrodes implanted.

Passive fixation electrodes appear to be preferred (55% of the total). Yet there are situations where active fixation electrodes are required such as implantation in a morphologic left ventricle or when the right ventricular apex is unsuitable and another right ventricular site is used. In addition active fixation electrodes may be easier to extract although this is debatable.

Return to the Main Page

Revised February 1, 1995