Understanding 3 Lead ECGs and AEDs

Introduction to ECGs and AEDs

In this section, we shall explore 3 Lead ECGs and AEDs, commonly referred to as defibs. These devices usually exist in two primary forms:

• A simple AED: suitable for delivering a shock when necessary.
• A combined AED with a 3 Lead monitor: ideal for monitoring a patient's heart's electrical activity.

3 Lead ECG Application and Basic Rhythms

For the purpose of our demonstration, the ECG will be applied to the patient's legs. In practical situations, it's advised against placing it on the legs. Instead, the ECG would be typically found in the ambulance's rear or next to the patient on the floor.

Attachment and Placement

With certain brands and models, ECG dots are separate units, linked via Bluetooth to the main device. This offers the flexibility that the device needn't follow the patient too closely. The device can lag by a meter or so, ensuring it remains connected. The dots are positioned as follows:

• Red for right: Usually on the patient's right arm.
• Yellow: Typically on the patient's left arm.
• Green: Generally on the patient's left leg.

Understanding Different Lead Versions

The one described above is a 3 Lead ECG. However, some machines feature a 4 Lead version. Although the basic principles remain the same, the fourth black lead is an earth lead. It's not typically used for monitoring, serving more for consistency in labelling and placement.

Monitoring Heart Rhythms with ECG

Once the device is switched on, it runs a quick system check. By default, these machines start in defib mode but can be shifted to monitor mode. The exact method might vary depending on the device's brand and model.

Upon monitoring, some common rhythms can be observed:

1. Normal Sinus Rhythm

It displays a regular rhythm at approximately 72 beats per minute.

2. Ventricular Fibrillation (VF)

This reflects the heart muscles' chaotic movements, causing them to lose their rhythm and hamper blood circulation. Fortunately, a defib can typically rectify this by delivering an electrical charge across the heart.

3. Ventricular Tachycardia (VT)

Here, the heart's ventricles beat excessively fast, allowing inadequate time for blood refill, resulting in ineffective blood pumping. A defib can usually reset this to a normal sinus rhythm.

4. Asystole or Flatline

This shows the heart's complete electrical inactivity. Notably, a defib will not correct asystole.