A Portable Cardiac Monitor with an MCU at its Heart

Silicon Labs microprocessors are at the heart of a new type of ambulatory cardiac monitor designed for continuous operation for up to 14 days, which requires high performance with relatively low power consumption. Cardiac monitors have been available for more than a century. Yet, Dr. Gust H. Bardy, a cardiac electrophysiologist, had low confidence in their ability to accurately capture arrhythmias. When his wife, Lorene, became ill with heart rhythm problems, his skepticism increased. It was not possible to get clear and precise recordings of her various rhythm disorders. She died April 26, 2012, from cardiac arrest that was the result of broader cardiac and vascular abnormalities. Exactly one year later, Dr. Bardy began a journey to improve both the signal quality and the diagnostic accuracy of ambulatory heart rhythm monitors both as a public health mission and to honor Lorene. It was at this time that he launched Bardy Diagnostics and engaged a small team of engineers to translate the goal of cardiac rhythm diagnostic precision into the circuit board of the device that monitors the heart. Much of this work revolved around showing more nuance in the recorded ECG, educating the team on the diversity and complexity of cardiac rhythm disorders, and significantly altering and improving the software routinely used with ambulatory ECG monitors.

Today, the WHO estimates that cardiovascular diseases (CVDs) are the leading cause of death globally, taking an estimated 17.9 million lives each year. Heart rhythm disorders account for a large proportion of these deaths. Accurately and rapidly identifying those at the highest risk of arrhythmias and ensuring they receive appropriate and timely treatment can prevent premature deaths. New technologies offer the chance to increase the accuracy and efficacy of traditional ECG monitoring devices by resolving smaller signals and finer details in the cardiac waveform leading to more specific diagnoses.1 2


Creating a Smarter Niche with CAM, an Ambulatory Cardiac Monitor

Accurate diagnosis starts with an accurate ECG tracing. The better-known electrocardiogram – or ECG/EKG – is a device designed to record the electrical activity of the heart. This device is non-invasive, usually involving electrodes placed on the skin of the chest and limbs to measure electrical activity from the heart. The output signal can be used to determine or detect abnormal heart rhythms (i.e., arrhythmias) that may cause cardiac arrest, stroke, or loss of consciousness. These monitors, known as long-term ECG (LT-ECG) monitors, are worn 24/7 for up to 14 days without a change of monitoring electrodes, allowing patients to shower, sleep comfortably, and engage in exercise. This is in stark contrast to the historical Holter monitor, worn for just 1-2 days with multiple dangling wires and simplistic engineering and heart rhythm analysis. Dr. Bardy’s invention, the CAM™ Patch, is an LT-ECG device offering exceptional comfort and compliance.

“While a traditional monitor is excellent at detecting R-waves (the largest electrical signal from the heart), and certainly an important part of the cardiac waveform, the R-wave alone is insufficient to diagnose many abnormal heart rhythms," says Gabriel. "There is just so much other information buried in low amplitude shifts of the other waves. What appears to be a small shift in waveform shape can prove critical for helping people get the specific treatment they need to improve their health and manage serious disease.”

The CAM system at all levels of the design needed to be optimized to capture these tiny and delicate signals. And yet, human factors were of utmost importance as the device needed to be minimally intrusive to the patient’s daily activities. 

“Let’s be honest, when you have an octopus of cables and sensors wrapped around your body, as has been the case with typical cardiac monitors, about the only place you are going to be is hiding in your bedroom.” 

From Dr. Bardy’s perspective, if you want to practice good medicine and revolutionize a field absolutely, every aspect of the design is critical. Every piece must be made with love, from the packaging to the training of those who do the overreading of the ECG. And yet, everything pivots around the key feature of the Bardy monitor: the ability to sense very fine, nuanced electrical signals from the heart. This is an electrical design challenge as much as it is mechanical, biological, and chemical. Size, weight, and comfort are absolutely critical for success. But without the subtle details of the ECG, all else has little value.

Reflecting the company’s unwavering dedication to quality and clarity, as well as its patient-first ethos, Gabriel doesn’t mince his words. “Having the gumption to try something different is key. What was state-of-the-art 50 years ago is bad medicine today. The CAM is very much like a flower, the petals being the different aspects of the design: chemical, mechanical, electrical, firmware, software, hardware, algorithms, and especially the humans that make the final overreading decisions. If just one petal is removed, the beauty of the flower is greatly diminished.

Silicon Labs MCU is the Heart of the Portable Cardiac Monitor

Silicon Labs has spent more than two decades honing its wireless communication technology so that companies like Bardy Diagnostics can drive innovation in their fields. There are three fundamental engineering challenges related to developing wireless medical devices. You must guarantee the delivery of accurate measurements with precision and speed, you need to supercharge your medical device’s wireless security with robust technology, and you must maximize your battery life with robust technology by design and low power consumption.

Bardy Diagnostics’ small and lightweight CAM patch is based on the Silicon Lab EFM32 architecture. The patient interface sensor connects to the heart of the system, the EFM32TG210 MCU. This device provides the integrated peripherals (ADC, SPI, ASYNC serial interface and timer functions) and operates with very little power to make the CAM patch effective at “seeing” those minute cardiac details that distinguish the CAM Patch from other available monitors.

“First, the ADC offers the resolution and filtering options to ensure that they can get the raw data acquisitions they need, while keeping within the power budget. Second, the EFM32TG microcontroller’s power management offers exceptional power savings compared to other architectures. Thanks to extremely fast sleep and awake transitions, automous operation of peripherals, and low-power clock generation the EFM32TG exceeds system requirements and enables up to 14 days of continuous ECG recording using a standard CR1225 battery,” explains Silicon Labs’ Brian Blum.

Gabriel also notes that the EFM32TG210’s performance and power modes allowed them to design and build the CAM Patch to specification and ultimately achieve the anticipated results. He maintains that when designing a device, having an MCU that meets performance expectations is key to keeping on schedule and within budget for the project. “The EFM32 architecture was so good that up to 14 days of full disclosure recording was possible with just a 48 mAh CR1225 battery. The signals that were being captured can be as low as 150 uVpp, and even at that range, the clarity of the analog waveform’s fine detail is preserved. The EFM32 architecture contains high-performance ADCs that allow capture of those details while keeping an electromagnetically quiet emissions profile so that small details are not obstructed by interference. Integrated oversampling and exceptionally robust and configurable ADC features were a lifesaver. The EFM32 architecture was absolutely revolutionary at the time, and most chip suppliers are still playing catch-up.”

When asked about the journey from design to market, Gabriel explains that there were many technical challenges that needed to be overcome. “We have not found anyone who has produced an ambulatory system with such low power consumption. Often in the medical industry, things are done in the same way for decades, ECG is no exception to that. The CAM Patch at the time featured a completely new front end designed from the ground up to be low noise and low power. It was hard to find people who were comfortable working with something like that, so our engineering team was trained straight out of (or while in) college. To this day, we believe the topology is unmatched and is seeing adoption in more devices, replacing legacy front end topologies.” 

Post-regulatory certification is another challenge to gaining the confidence of physicians and institutions to embrace a new product. New technologies in mission-critical environments often face adoption resistance, slow decision-making across larger institutions, and inertia through the perceived risk of adoption. Thankfully it’s taken little convincing as the CAM Patch speaks for itself by virtue of the clarity of the cardiac electrical signal that is recorded. 

Mark Willcox, Clinical Cardiac Electrophysiologist at the Alaska Heart and Vascular Institute, came forward as an advocate for the technology saying, “I am one of more than 30 cardiologists at the largest cardiologist practice in Alaska. We rely heavily on Bardy Dx CAM monitors for day-to-day patient care. That care would be compromised in the absence of these monitors. We greatly appreciate Bardy Diagnostics’ efforts to facilitate continued production on behalf of our patients.”

What Does the Future Hold for Bardy Diagnostics?

“The most obvious targets for the platform are to be smaller, lighter, longer running and better connected. We have our eye on the new generation of Silicon Labs EFM32 devices such as the Pearl Gecko and Bluetooth-enabled BG22 for future improvements in this area,” states Gabriel.

Bluetooth is the leading choice for connectivity because it offers a well-tested and mature wireless solution that is also low power, offers interoperability with patients’ mobile devices or other Bluetooth-enabled gateways, and has significant flexibility baked into the protocol to tradeoff throughput, latency, and energy consumption. Bluetooth security offers excellent protection, including secure pairing, 128-bit encryption, data privacy, anti-tracking, and more. 

“We have a couple of teams of engineers that work very hard to create the next state-of-the-art devices. The body is a beautiful electronic symphony with a wide variety of vital signs that can indicate important details about a person’s health. Perhaps in the future, we will see more sensitive instruments or ones that simultaneously capture more vital signs to provide better-connected care."

As the CAM patch continues to advance ambulatory cardiac monitoring and diagnostics, it’s remarkably heartwarming to see how Dr. Bardy’s vision, which was largely built on his personal experience, is helping patients around the world.

1Rho R., et al. Comparison of two ambulatory patch ECG monitors: The benefit of the P- wave and signal clarity. American Heart Journal. March 2018.

2Smith WM., et al. Comparison of diagnostic value using a small, single-channel, P-wave centric sternal ECG monitoring patch with a standard 3-lead Holter system over 24 hours. American Heart Journal. March 2017.

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