Explain about Wilson's Central Terminal.
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Wilson central terminal ECG reference electrode explanation
Wilson's central terminal (WCT) is a reference electrode used to record the six unipolar chest, or precordial, ECG leads: V1 to V6.
How it is made
The ECG machine connects the three limb electrodes:
- Right arm (RA)
- Left arm (LA)
- Left leg (LL)
through three equal high-value resistors, classically about 5 kΩ, to one common point. Its voltage is approximately the average of the three limb potentials:
[
\text{WCT} \approx \frac{RA+LA+LL}{3}
]
Purpose
In a precordial lead, the chest electrode is the positive, exploring electrode, while WCT acts as the negative, relatively indifferent reference.
For example:
[
V_1 = \text{potential at V1 chest electrode} - \text{WCT}
]
The same principle applies to V2 through V6.
Why it is called “indifferent”
WCT is designed to have little net variation from the heart's electrical activity, so it provides a near-neutral baseline against which electrical activity under each chest electrode can be measured. It is not perfectly electrically silent, so “indifferent” is an approximation.
Clinical significance
The precordial leads formed using WCT view cardiac electrical activity in the horizontal plane, helping localize abnormalities such as:
- Septal changes: V1-V2
- Anterior changes: V3-V4
- Lateral changes: V5-V6
This differs from the standard bipolar limb leads I, II, and III, which compare the potential between two actual limb electrodes. The ECG lead-system explanation describes WCT as the averaged limb-electrode reference used for chest leads.
Textbook description: WCT combines right arm, left arm, and left leg potentials through equal resistances, and serves as the reference for unipolar precordial leads. Guyton and Hall Textbook of Medical Physiology, “Precordial Leads”; Goldman-Cecil Medicine, “Electrocardiographic Leads.”
Explain how Wilson’s terminal differs from Goldberger’s terminal
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electrocardiography augmented limb leads
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Goldberger terminal Wilson central terminal augmented unipolar limb leads explanation
| Feature | Wilson’s central terminal (WCT) | Goldberger’s terminal (GCT) |
|---|---|---|
| Reference formed from | Average of all three limb electrodes: RA, LA, LL | Average of the other two limb electrodes, excluding the exploring limb |
| Example | (\text{WCT} = (RA + LA + LL)/3) | For aVR: ((LA + LL)/2) |
| Leads produced | Mainly the precordial chest leads: V1-V6. It was also used for the original unaugmented limb leads, VR, VL, VF. | Augmented limb leads: aVR, aVL, aVF |
| Exploring electrode | A chest electrode for V1-V6 | One limb electrode: RA for aVR, LA for aVL, LL/foot for aVF |
| Voltage amplitude | Smaller for limb-lead recordings | Produces a signal 50% larger than the corresponding Wilson unipolar limb lead |
| Why “a” in aVR/aVL/aVF? | Not applicable | “a” means augmented |
Mathematical example: aVR
Let the limb potentials be (RA), (LA), and (LL).
Wilson-type right-arm lead:
[
VR = RA - \frac{RA+LA+LL}{3}
]
Goldberger augmented right-arm lead:
[
aVR = RA - \frac{LA+LL}{2}
]
This gives:
[
aVR = \frac{3}{2}VR
]
So, the Goldberger lead is 1.5 times, or 50%, larger in voltage.
Key concept
- Wilson’s terminal includes the electrode being explored in the reference average. This partly reduces the recorded voltage.
- Goldberger’s terminal disconnects the exploring limb electrode from the reference and uses only the other two limbs. The reference is therefore farther electrically from the exploring electrode, giving a larger, more readable signal.
Thus, modern 12-lead ECGs use:
- WCT for V1-V6: chest electrode versus average of RA + LA + LL
- GCT for aVR, aVL, aVF: one limb electrode versus average of the other two limb electrodes
Neither terminal is truly at zero potential, so these “unipolar” leads are more accurately considered leads using a low-potential constructed reference. This distinction is reviewed in this ECG terminal comparison. Guyton and Hall Textbook of Medical Physiology, “Augmented Limb Leads.”
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