How Do Skin Electrodes Detect Heart Depolarization?

[Master Wayne]

I'm reading a book about electrocardiograms. In one page, the author says that when a wave of depolarization (positively charged sodium ions enter the muscle cells of the heart, causing contraction) moves through the heart toward an electrode placed on the skin, an upward deflection is registered on the ECG record.

That got me wondering about the physics of it. A wave of depolarization is not exactly an electric current, since there's no net movement of charges, right? What exactly does this wave of depolarization do to the electrode? And what would a possible mechanism be by which that is recorded as an upward deflection?

 

[UltrafastPED]

A quick search found: https://www.khanacademy.org/science...epolarization-waves-flowing-through-the-heart

and http://www.sh.lsuhsc.edu/fammed/outpatientmanual/basicecg.htm

 

[Master Wayne]

A quick search found: https://www.khanacademy.org/science...epolarization-waves-flowing-through-the-heart

and http://www.sh.lsuhsc.edu/fammed/outpatientmanual/basicecg.htm

Thanks for the reply! But what I'm really interested in knowing is not about ECGs themselves, it's about electrodes. How do they work?

 

[UltrafastPED]

Thanks for the reply! But what I'm really interested in knowing is not about ECGs themselves, it's about electrodes. How do they work?

They measures small changes in voltages between the various contacts:
https://en.wikipedia.org/wiki/Electrocardiography#Principles

 

[sardar]

Skin electrodes work by detecting the electrical activity of the heart. When the heart muscle cells undergo depolarization, positively charged sodium ions enter the cells causing them to contract. This movement of ions generates an electrical signal that travels through the heart and can be detected by electrodes placed on the skin.

The electrodes are designed to pick up the small electrical signals produced by the heart and amplify them for recording. These signals are then displayed as a graph on an electrocardiogram (ECG) machine. The upward deflection on the ECG record represents the depolarization wave moving towards the electrode.

While a wave of depolarization is not exactly an electric current, it does create an electrical field that can be detected by the electrodes. This is because the movement of positively charged ions creates a difference in electrical potential between the inside and outside of the heart cells. This difference in potential can be measured by the electrodes, which then convert it into a visible signal on the ECG.

As for the mechanism by which the upward deflection is recorded, it is a combination of the electrical properties of the heart and the design of the electrodes. The electrodes are placed strategically on the skin to detect the electrical activity of the heart in a specific direction and at a specific depth. This information is then used to create the ECG graph.

In summary, skin electrodes work by detecting the electrical signals produced by the heart during depolarization. This is achieved through the use of strategically placed electrodes and their ability to convert the electrical signals into a visible record on an ECG.