Constructing Semi Permanent ECG Pads

Content on this page has been provided by Robert Malkin, Professor of the Practice of Biomedical Engineering
and Director of Duke Engineering World Health.

Introduction

Disposable ECG electrodes have become the standard for modern cardiac monitoring units in the United States. These electrodes cost an average of $0.65 and are meant only for single-use monitoring of one patient. However, the lack of availability and cost associated with these disposable electrodes present challenges to effective and safe ECG monitoring in hospitals in the developing world.

This document describes the construction of a semi-permanent ECG electrode that can be manufactured using materials locally available in large cities in sub-Saharan Africa. The electrodes are very cheap, easy to manufacture, easy to clean, reusable for 100 patients, and provide an accurate ECG trace when attached via standard ECG lead wires from patient to monitoring unit.

Electrode gels do not need to be used for non-ambulatory patients, but locally available materials have been tested to work with this electrode, including shower gel, aloe, and body moisturizing lotion.

Directions for Use:

These electrodes should be used for patient cardiac monitoring in conjunction with a standard 3-lead ECG unit and accompanying 3 or 4 ECG lead wires. Monitoring and interpretation of ECG traces should only be performed by medical professionals.

The electrodes should have been cleaned with an alcohol solution, mild detergent, diluted bleach or autoclave (just the metallic snap element) before use.

1) Attaching the electrode to the patient
The patient’s skin should be cleaned thoroughly before application of electrodes. Light abrasion with a cotton gauze aids recording.

Use four 7 cm strips of medical adhesive tape in a square configuration to attach the electrode to the patient. When placing the tape, try to get the tape as close to the center of the electrode as possible without covering up any of the metal snap that can be seen through the plastic. This will insure that the tape is holding the electrode securely in place while making sure the ECG lead wire can still connect to the electrode.




2) Attach the ECG lead wire to the electrode
Make sure the lead wire snaps into the electrode. Also, notice how the ECG lead wire does not contact any of the medical tape. If the lead wire contacts the tape, the connection between the sewing snap and the lead wire is probably not as secure as it should be. In this case, reapply the tape in a way that you can see the entire snap after all tape has been applied.

Non-ambulatory patients do not require ECG gel. Ambulatory or restless patients can show improved recordings with electrode gel. If the hospital does not have gel, these electrodes have been used with a very thin layer of shower gel, aloe, and body moisturizing lotion.

Directions for Cleaning

To clean the pad, disconnect the LDPE disc from the sewing snap, and wipe both parts with an alcohol swab.

The sewing snap can be autoclaved, if desired.

The LDPE disc should NOT be autoclaved.

Reassemble the electrode after the parts have dried.




DO NOT AUTOCLAVE THE PLASTIC

Directions for Construction

Materials List:

1) Exacto Knife or small cutting tool – used to puncture small x in center of LDPE cap seal to push snap head through

2) Cap from a plastic Coke Bottle (20 oz size preferred) – LDPE seal will be removed from inside of this cap. If unable to find a plastic bottle, a glass bottle cap will also have a seal (although more force is required to remove form the interior of the cap).


3) Ni-plated sewing snap (Standard Size 3) – this will serve as the electrode and connection to the lead ECG wire. Sewing snaps can be bought from local fabric stores (sold at Jo-Ann? Fabrics for four snaps for $0.91). Any tailor or seamstress will have standard snaps for clothing. If standard size is not found, bring ECG lead wire with you when shopping for snap to be sure it fits the connection.



Assembly of materials needed to construct electrodes

Directions for Assembly, use, and cleaning

1) Obtaining the LDPE disc
The LDPE disc can be obtained from numerous varieties of bottle caps, including plastic Coke bottles and beer bottles. The disc on the Coke bottles is slightly thicker and more durable than the ones from glass beer bottles, but either one will work fine. The disk is located on the inside of the cap and in the case of a Coke bottle can be easily removed because there is no glue holding it in place. Glass bottles tend to glue the LDPE disc to the metal cap, so more effort is required to remove the cap.



Notice the concavity associated with the disc. We want the disc to eventually be placed concave down on the patient (i.e. it should look like a dome, not a bowl sitting on the patient’s arm).



2) Cut an “X” in the disk to allow the snap to come through
Using an Exacto knife or other sharp cutting object, make a small (no more than a few millimeters) incision in the center of the LDPE disc. Turn the disc 90 degrees and repeat to form an “X” in the center.



It is important not to make the incisions too big, as the snap will not fit as snugly in the disc with a larger hole.

3) Find a package of “Size 3” sewing snaps from a local fabric store
“Size 3” sewing snaps specify the size of the knob in the middle of the snap. If “Size 3” sewing snaps are not available, find a snap with the knob diameter of 3.6 mm at the top and 3.20 mm at the bottom. The approximate diameter of the base of the snap is 11.95 mm. Sewing snaps come in two pieces, a top and a bottom. For this design, we only want the bottom piece, as the knob on the top piece is too big to fit into a standard ECG lead wire.



4) Push the snap from the bottom of the LDPE disc through the hole
Make sure that the snap comes through the “inside of the dome” and the knob of the snap comes out of the top. In other words, make sure that the LDPE disc is oriented to look like a dome and place it over the sewing snap.



5) Remove excess LDPE from the sides of the knob
After you push the snap through the LDPE disc, some LDPE will ride up the sides of the snap. Take the Exacto knife or other sharp cutting device and carefully trim around the sides of the snap in order to maximize the surface area of the snap that pokes through. A finished electrode is shown below.

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