From delayed detection to early intervention: Innovating cardiac monitoring with e-tattoos

Fortunately, a group of scientists from the University of Texas at Austin has made significant progress in this area. They have developed a new device that is wireless, comfortable, and can measure multiple cardiac time intervals.

The team has been working on this technology since 2019 when they first published a study about the e-tattoo. But they have made a lot of progress since then.

IE spoke to the lead author of the study, Dr. Nanshu Lu, holder of the Frank and Kay Reese Endowed Professorship in Engineering, and Sarnab Bhattacharya, Ph.D. candidate, both from the Cockrell School of Engineering at the University of Texas at Austin.

"Heart disease is the deadliest disease in the U.S., accounting for 1 in every 5 deaths. Additionally, it is important to note that 20% of heart attacks are considered silent, meaning that damage occurs without apparent symptoms. However, there is hope, as 80% of heart disease and strokes can be prevented through early diagnosis and preemptive interventions," said Lu, emphasizing the importance of early diagnosis and preemptive interventions for heart diseases.

Wearable e-tattoo for cardiac measurements 

The development of devices that can monitor cardiac measurements is essential to the early diagnosis and treatment of heart diseases. 

"My parents are in their late 60s [and live] across the Pacific Ocean. Although I have bought them many wearables on the market, none of them is a medical grade which can reliably monitor their health or make a diagnosis," said Lu, discussing the team's motivation behind developing this innovative device.

"Biomedical research has always been a topic of interest for me, especially because both my parents are practicing medical doctors. Apart from that, my grandfather suffered a heart attack, and there was a delay in taking him to the hospital as it was detected late. Fortunately, he made a full recovery. However, recall my father expressing regret over the lack of readily available early monitoring devices that could have significantly improved the ease of detection, treatment, and recovery. This makes me particularly interested in cardiovascular monitoring research," added Bhattacharya.

Cardiac monitoring is generally carried out using electrocardiography, a non-invasive process that records the heart's electrical activity, called an electrocardiogram (ECG). 

An ECG is a graphical representation of the heart's electrical activity over time. It is measured using electrodes which can detect and measure the electrical signals produced during each heartbeat, making it easy for doctors to pick up any fluctuations. 

However, as mentioned earlier, these are not suitable for long-term wear.

The team led by Lu and Bhattacharya has developed an e-tattoo, a device that can do everything a cardiac monitor can but has the advantage of being easy to wear long-term. 

"E-tattoos are wearable electronics in the form of a temporary tattoo sticker which is ultra-thin, ultra-soft, well-conformed to the curvature of our skin surface and conducting biometric sensing and wireless data transmission," explained Lu. 

The technology behind the e-tattoo

The e-tattoo is a micro-thin device with a thickness of only 200 micrometers, just two to three times thicker than a strand of human hair! It weighs only 2.5 grams, and its design allows it to stretch up to 20% of its original size when worn.

It has two modes of sensing: electrocardiography and seismocardiography, which measures the mechanical vibrations produced by the heart's contraction and ejection of blood.

The e-tattoo is made of a flexible printed circuit (FCP) with traces of copper on it. Copper is an excellent conductor of electricity and provides electrical conductivity for the circuit components. This is then encapsulated with additional layers to prevent unintentional electrical contact.

The electrode for the ECG is made of a stretchable graphite film that sits on top of a medical dressing. This acts as a substrate for the electrode, allowing it to adjust to the shape of the body and maintain contact with the skin.

A unique adhesive called anisotropic conductive film (ACF) is used to make the electrical connections. The ACF contains silver-coated glass beads and forms an electrical connection between the electrodes and the ECG front end when pressure is applied.

The e-tattoo can be worn on various parts of the body, including the chest, where it is generally placed for cardiac monitoring. However, the versatility of the e-tattoo design allows for potential applications on other body locations, such as the limbs or torso, depending on the monitoring needs and desired physiological measurements.

Validating the e-tattoo technology

The testing and validation process for the e-tattoo involved several steps to ensure its accuracy and reliability in measuring physiological parameters. The primary goal of the researchers was to compute parameters needed for assessing and diagnosing heart diseases, pre-ejection period (PEP), and left ventricular ejection time (LVET) using an ECG and seismocardiogram (SCG).

The collected data, including the ECG and SCG, were wirelessly transmitted in real-time to a mobile device using Bluetooth low energy (BLE) technology. This allowed for convenient storage and analysis of the streamed data.

Six patients were used to test the validity of the e-tattoo. The researchers evaluated the tattoo based on its performance and accuracy in computing PEP and LVET values. This was then validated against standard clinical apparatus and instruments.

The results showed high accuracies for PEP and LVAT values while consuming low power. Additionally, the e-tattoo detected heart rate (HR) and LVET during exercise recovery with minimal errors.

The tattoo's performance was on par with standard clinical apparatus and instruments. Furthermore, the e-tattoo demonstrated its capability for long-term, continuous cardiac sensing. It maintained excellent wearability, conforming to the chest and enabling high-fidelity SCG measurements.

In addition to its remarkable testing and validation results, the e-tattoo offers several advantages over conventional wearable heart monitoring systems.

"Conventional wearable heart monitoring systems like Holter and other emerging patch-like devices are much heavier and thicker than our e-tattoos, [and] are uncomfortable to wear. Moreover, they only monitor ECG, but our e-tattoo simultaneously and synchronously monitors ECG and SCG," said Lu, explaining how the e-tattoo is different from other cardiac monitors.

"Additionally, the e-tattoo can be worn under normal clothing, making it suitable for use during social gatherings as well, whereas traditional obtrusive bulky monitors might be uncomfortable," added Bhattacharya.

Exploring the future of e-tattoo technology

"High-risk patients can wear the e-tattoo and live a normal life because it is mechanically imperceptible to wear and can provide high-fidelity sensing of ECG even under motion," said Lu explaining how the tattoo could help patients with heart disease.

The researchers shared their insights on further developments and validation of the e-tattoo technology.

"We have already validated our e-tattoos against FDA-cleared patient monitors in our lab on healthy subjects. Next, we are going to validate the e-tattoos on post-operative patients with congenital heart disease at Cleveland Clinic in collaboration with their cardiologist, Dr. Aashoo Tandon," explained Lu.

"We also want to test the e-tattoo under extreme conditions, including challenging environments such as firefighting, as well as high-motion scenarios like jogging," added Bhattacharya. These tests will help evaluate the robustness and reliability of the e-tattoo under challenging circumstances, ensuring its suitability for a wide range of applications.

When discussing the challenges to the widespread availability and accessibility of e-tattoos, Lu emphasized the need for rigorous multi-stage clinical validations to ensure safety and efficacy. "We also need to partner with Cardio Data Management to store and process the data and form reports for cardiologists to confirm and make a diagnosis," she concluded.

By continuing to push the boundaries of exploring diverse usage scenarios, the researchers aim to enhance the capabilities and versatility of e-tattoo technology. These future steps will contribute to the ongoing advancement of wearable healthcare devices and pave the way for their widespread adoption in clinical and everyday settings.