Under the Hood of an EKG

When a clinician looks at an EKG, they can depict a STEMI, arrhythmias, and so much more. However, as a non-clinician, when I look at an EKG, I see an electrical circuit built up of many components where the heart is central power unit.  

For many years, I helped develop and build data acquisition systems for a neuro-focused company.  I've found that this experience has given me a slightly different perspective of what is going on under the hood of an EKG than your average layperson or even clinician.

Although there are many different types of EKG systems out there, the basic concepts are relatively the same.  You connect a couple of electrodes to the body and BAM, you get a readout ... but what is happening on the inside of the machine?

Glad you asked. Every acquisition system works with the same basic principles.  Each electrode has a specific impedance.  The impedance of the electrode roughly depicts the surface area of the contact.  Impedance is a resistance value measured at a specific frequency. Knowing this allows the designers of the system to calibrate the input impedance of the circuit.  The electrical activity of the heart is transmitted through the electrode into the wire directly connected to the system. This signal is run through an amp or a buffer, and then run against a common signal, like the ground.  The remaining signal is then processed through some filters, potentially more amplifiers and then ultimately through A/D converters.  And voila ... a signal is presented on the screen or printed to paper.

With technology expanding everyday, these devices are getting smaller and smaller.  What used to take a large, dedicated piece of equipment can now be done with your cell phone or with even a business card!  If you are interested in how these new machines work, read up on FPGA and ASIC (or maybe just stay tuned for a future Pulsara Blog).  

Regardless of the device used to obtain the EKG, Pulsara helps you get it (or an image of the patient's facial droop, medication list, or driver's license) to the hospital as quickly as possible. 

And, all of you neuro folks don’t feel left out - these same principles can be correlated to both invasive and non-invasive neural recording too!