Easy to Make ECG

Problem Statement: The goal of this project is to design, fabricate, and test an ECG device that amplified the signal, attenuates noise, and displays and interprets raw data with an output of a readable ECG wave form and a numerical reading for heart rate in beats per minute.

In May of 1887, Augustus Waller collected the first ever successful electrocardiogram (ECG) from a live heart. The initial readings were primitive and twisted by artifact, but they were the beginnings of a technology that has now evolved into a staple of modern medicine[1].

Electrocardiograms, which measure the difference in electric potential across the heart, provide critical information to medical professionals regarding the electric signaling within the heart pacing system and muscle tissue[2]. However, it does not provide information regarding the contraction or the mechanical performance of the heart.

As the ECG has further developed, numerous complexities have been added to it allowing it to translate more complex information from the human body to data which medical professionals can use to diagnose patients. Much of this progress has come in the form of adding leads to the ECG to take measurements between different points surrounding the heart. To date researchers have performed ECG’s with as many as twenty-four leads; however, twelve leads has become the highest number of leads typically used in a clinical setting as this setup provides doctors with the necessary information to adequately diagnose and treat patients[3], [4].

 Although the ability to collect information from multiple leads has greatly improved the state of the art for ECGs, the information they collect would not be useful if not for the advancements made in amplifying and filtering. While initial ECGs were displayed using Einthoven’s String Galvanometer, since these devices were large and cumbersome and since they did not have filtering capacity, they were eventually replaced with compact electronic devices to increase their utility within the clinical setting[5]. However, these devices brought their own set of problems, as they introduced high frequency interference from power sources and electronics[6]. Additionally, as 60 Hz power became standardized, this increasingly became an issue as 60 Hz lies within the range of frequencies of the typical of a heart rate, which is 0.05-150 Hz[7], [8]. Thus, the need arose to eliminate artifact at 60 Hz and at high frequencies.

While twelve leads are typically used by doctors to diagnose electrocardial pathologies, this study will focus on the design and fabrication of the amplifier and filters for single lead ECG. While single lead ECG’s do not provide the abundance of information that those with twelve leads do, they still are used today within specific applications. For instance, single lead ECGs are used for extended heart studies lasting fourteen or more days because they reduce the number of points of contact with the patient while still providing information regarding how the heart functions over an extended period. Additionally, single lead ECGs are commonly packaged as portable, easy to use devices. While these devices do not provide sufficient information regarding heart function to diagnose specific pathologies, abnormalities in these readings can indicate that further investigation at a medical establishment is necessary.

For this study the ECG lead were placed at the wrist and ankles of the test subject. Since these locations do not have much underlying muscle, these provide ideal testing locations as interference from myoelectric signaling in skeletal muscles will be minimized.

References:

[1]      S. S. Barold, “Willem Einthoven and the birth of clinical electrocardiography a hundred years ago,” Card Electrophysiol Rev, vol. 7, no. 1, pp. 99–104, Jan. 2003, doi: 10.1023/A:1023667812925.

[2]      “Electrocardiogram | Johns Hopkins Medicine.” https://www.hopkinsmedicine.org/health/treatment-tests-and-therapies/electrocardiogram (accessed Apr. 26, 2022).

[3]      “Lead systems – how an ECG works | CardioSecur.” https://www.cardiosecur.com/magazine/specialist-articles-on-the-heart/lead-systems-how-an-ecg-works (accessed Apr. 26, 2022).

[4]      U. Pahlm, O. Pahlm, and G. S. Wagner, “The 24-lead ECG display for enhanced recognition of STEMI-equivalent patterns in the 12-lead ECG,” Journal of Electrocardiology, vol. 47, no. 4, pp. 425–429, Jul. 2014, doi: 10.1016/J.JELECTROCARD.2014.04.007.

[5]      M. Rivera-Ruiz, C. Cajavilca, and J. Varon, “Einthoven’s String Galvanometer: The First Electrocardiograph,” Texas Heart Institute Journal, vol. 35, no. 2, p. 174, 2008, Accessed: Apr. 26, 2022. [Online]. Available: /pmc/articles/PMC2435435/

[6]      C. H. Chang, H. J. Ko, and K. M. Chang, “Cancellation of high-frequency noise in ECG signals using adaptive filter without external reference,” Proceedings - 2010 3rd International Conference on Biomedical Engineering and Informatics, BMEI 2010, vol. 2, pp. 787–790, 2010, doi: 10.1109/BMEI.2010.5639953.

[7]      E. Trägårdh and T. T. Schlegel, “High-frequency ECG”.

[8]      “List of Voltages & Frequencies (Hz) by Country - Electric Power Around the Globe.” https://www.generatorsource.com/Voltages_and_Hz_by_Country.aspx (accessed Apr. 26, 2022).

Resources for ECG Connection to Human Test Subject

• 3x ECG electrodes
• 3x ECG electrode connection cables
• 3x aligator clip wires

Resources for Arduino Connection

• 1x Arduino
• 1x Arduino to USB (or USB-c) connector
• Computer

Follow the provided schematics in order to create the desires Instrumental Amplifier Circuit.

Some tips for creating the circuit:

• Don't add extra wires
• Try to make the circuit look like the circuit diagram so that it is easier to read and debug

Follow the provided schematics in order to create the desires Notch Filter Circuit.

Follow the provided schematics in order to create the desires Instrumental Low Pass Filter Circuit.

Now that you have created each circuit independently, combine them on the same breadboard, such that the output of the amplifier is the input of the Notch filter, and the output of the notch filter is the input for the Low pass filter.

Now that you have a complete circuit, follow these steps in order to complete the project and see you ECG:

To physically connect the Arduino to the circuit:

1. connect the output of the ECG circuit that you have created to PIN A0 of the Arduino UNO
2. connect the group of the circuit to the group of the arduino

To run the ECG program:

1. copy and past the provided code into the Arduino IDE
2. select upload at the top left of the user interface

You have now uploaded the code to the Arduino; it is currently running the code.

In order to see the results of your project:

1. Navigate to "tools" in the toolbar at the top of the screen
2. Select "Serial Monitor" to view voltage output and BPM
3. Select "Serial Ploter" to view a plot of voltage output; this will present you ECG waveform

Congratulations!!! You have now made an ECG!