Wireless, flexible and stretchable ECG patch

Wearable, wire free and easy to set up do not usually describe devices that monitor heart rate and cardiac activity. However, IMEC, an independent research centre in nanoelectronics and nanotechnology, has developed an ECG (electrocardiography) patch that is all of these things.

The patch is a hybrid system combining electronic assemblies on a flexible polyimide substrate that is integrated into a textile. This allows flexibility and the use of standard ECG electrodes.

The device weighs about 15 g, can fit body curves and can be used to monitor cardiac activity 'on the move' in normal-life conditions.

The core of the wireless patch consists of a miniaturised sensor node integrated into the substrate. It uses IMEC's single-channel, ultra-low-power biopotential ASIC for monitoring the ECG signal.

It also includes a commercial microprocessor enabling local digital signal processing, a 2.4 GHz radio link and a miniaturised rechargeable Lithium-Ion battery.

The battery is placed under the electronic components to ensure the local rigidity required for long-term functioning of the electronic components. In addition, the sensor node features a fork-antenna and a snap-on connector. The total size of the flexible core part is 60x20 mm2.

Two additional snap-on connectors are coupled to the central part to form the complete system.

The patch can work in continuous monitoring mode, in which the data is continuously transmitted to the receiver (sample frequency between 250 and 1000 Hz).

It contains a transceiver type Nordic nRF2401 with a range of between 1 and 30 m depending on the channel conditions, output power and data rates used. Typically, it has a range of 10 m.

Where only the heart rate is required, this can be computed locally on the node and sent to the receiver.

The rechargeable battery has a capacity of 175 mAh, which allows use from one day with continuous monitoring to several days for heart rate monitoring.

"The heart activity is sent to a PC or to a PDA which records the pulses. The data is analysed by a doctor or trainer because the patch does not contain data storage," said Katrien Marent for IMEC.

"The wearable sensor can be used for cardiac monitoring - useful for medical and sport applications. Placed on the arm, trunk or leg, the patch can monitor muscle activity. These multiple applications are made possible by the ultra-low-power biopotential ASIC which can be used to read out both ECG and EMG signals."

So far the device has been tested at IMEC on five healthy volunteers.

"We will now start more rigorous tests on a larger population of healthy volunteers and validate the system against a golden reference for ambulatory cardiac monitoring such as a commercial Holter monitor. We are looking for partners to perform these validations," said Marent.

IMEC will not itself develop and sell products and it is developing and validating the technology and looking for partners to commercialise the final result.

"The current system is definitely cost effective. Produced in large quantities the cost of a wireless patch would be about 10&128;," Marent said.

Technically, devices can become available on the market within one year, according to Marent. Although it may be a few years more before the technology is available in saleable products.