Augmented Limbs on ECG Machines
A Quinton Brand Review of ECG Machines


When you heard of “Leads aVR, aVL, and aVF”, these are the so-called 'augmented limb leads'. They are derived from the same three electrodes as leads I, II, and III. However, they view the heart from different angles (or vectors) because the negative electrode for these leads is a modification of 'Wilson's central terminal', which is derived by adding leads I, II, and III together and plugging them into the negative terminal of ECG machines.

This zeroes out the negative electrode and allows the positive electrode to become the "exploring electrode" or a unipolar lead. This is possible because Einthoven's Law states that I + (-II) + III = 0. The equation can also be written I + III = II. It is written this way (instead of I - II + III = 0) because Einthoven reversed the polarity of lead II in Einthoven's triangle, possibly because he liked to view upright QRS complexes. Wilson's central terminal paved the way for the development of the augmented limb leads aVR, aVL, aVF and the precordial leads V1, V2, V3, V4, V5, and V6.

• Lead aVR or "augmented vector right" has the positive electrode (white) on the right arm. The negative electrode is a combination of the left arm (black) electrode and the left leg (red) electrode, which "augments" the signal strength of the positive electrode on the right arm.
• Lead aVL or "augmented vector left" has the positive (black) electrode on the left arm. The negative electrode is a combination of the right arm (white) electrode and the left leg (red) electrode, which "augments" the signal strength of the positive electrode on the left arm.
• Lead aVF or "augmented vector foot" has the positive (red) electrode on the left leg. The negative electrode is a combination of the right arm (white) electrode and the left arm (black) electrode, which "augments" the signal of the positive electrode on the left leg.

The augmented limb leads aVR, aVL, and aVF are amplified in this way because the signal is too small to be useful when the negative electrode is Wilson's central terminal. Together with leads I, II, and III, augmented limb leads aVR, aVL, and aVF form the basis of the hexaxial reference system, which is used to calculate the heart's electrical axis in the frontal plane.

In modern digital equipment, the augmented leads are derived from the limb leads by simple calculation:

aVR = -(I + II)/2

aVL = I - II/2

aVF = II - I/2.

Too much information overload? Well, then, let’s leave it on the backseat and discuss this interesting brand and its featured products included in the EKGShop.Com listing: the Quinton brand of ECG machines.

Quinton Q-Stress™ Exercise ECG System - Windows based operating system. Combines Quinton algorithms, unique baseline wander and muscle artifact filters, and 8000 samples per second to provide the highest ECG fidelity in the industry. Leads can be displayed in 3, 6, or 12-lead views. Standard protocols are preloaded for routine exercise testing. Easily add and customize protocols to meet specific testing needs such as Stress-Echo, Stress Adenosine, and Persantine.

Quinton 4500 Stress Test System Complete with Q-4500 controller & Treadmill - This machine pays for itself after 60 tests. Freeze half of the screen while the other half displays live ECG data. Up to 7 user-definable ergometer protocols, each with a resting stage and up to 99 exercise stages. High-resolution thermal chart recorder produces quality reports ready for signature. Menu, entry and control functions are easily accessible on the removable PC-compatible keyboard.

Quinton Cardiology has a well-earned reputation for solid product engineering, excellent technical support and superior customer service. In fact, it's common to find early versions of our products working reliably in the field, long after their production has been discontinued. Quinton is particularly proud of their team of support personnel - all are dedicated to the complete satisfaction of their customers.