Paper

1. A Wearable ECG-recording System for Continuous Arrhythmia
Monitoring in a Wireless Tele-Home-Care Situation
Rune Fensli Einar Gunnarson Torstein Gundersen
Agder University College, Hospital of Buskerud, Sørlandet Sykehus HF,
Faculty of Engineering Department of acute Medical department,
and Science, Grimstad, medicine, Drammen, Arendal, Norway
Norway Norway
rune.fensli@hia.no
Abstract
New wireless technology for tele-home-care purposes gives new possibilities for
monitoring of vital parameters with wearable biomedical sensors, and will give the patient
the freedom to be mobile and still be under continuously monitoring and thereby to better
quality of patient care. This paper describes a new concept for wireless and wearable
electrocardiogram (ECG) sensor transmitting signals to a diagnostic station at the hospital,
and this concept is intended for detecting rarely occurrences of cardiac arrhythmias and to
follow up critical patients from their home while they are carrying out daily activities.
1. Introduction
Advanced monitoring solutions using telecommunicating technologies are used for remote
ECG diagnosis, and The American College of Cardiology (ACC) and The American Heart
Association (AHA) have published guidelines for ambulatory electrocardiography[1]. The use
of telecommunications for remote diagnosis is growing rapidly, and there are several products
and projects within mobile ECG recording using Internet solutions, Bluetooth technology,
cellular phones, WAP-based implementations and wireless local area networks, WLAN. A
remote diagnosis system integrating digital telemetry has been developed, using a wireless
patient module, a homecare station and a remote clinical station[2]. Traditionally 24/72 h
ECG-recording systems like “Holter-monitoring” can today use built-in mobile telephones to
send information to the hospital[3], but is mostly used with a recording unit that physically
has to be carried to the hospital for analyzes.
Several ongoing international projects where wireless sensors are used within the
framework of a standardized Body Area Network (BAN) are focusing on improving the
patient’s ability to freely move around in a daily situation while being monitored by a
wearable system. Sachpazidis et al[4] are trying to develop a robust platform for real-time
monitoring of patients staying in their home transmitting data to doctors working at the
hospital. This @HOME concept aims at measuring several vital parameters, within a BAN-
framework. Several authors describe solutions based on sensors using a wireless Bluetooth
communication protocol and a standard PDA[5], [6]. Jovanov et al.[7] propose the use of a
Personal Area Network (PAN) with wireless intelligent sensors to perform data acquisition,
and Kong et al. suggested a broadcast of the ECG signals over the Internet[8].
Proceedings of the 18th IEEE Symposium on Computer-Based Medical Systems (CBMS’05)
1063-7125/05 $20.00 © 2005 IEEE

2. Our new concept has several advantages compared to existing solutions. It is easy to use
and requires no technical skills to operate. The ECG-sensor is a compact electronic electrode
which easily can be replaced by the patient himself; just stick it to the chest. The ECG is
continuously recorded with a built-in automatic alarm detection system, and the system can
give early alarm signals even if the patient is unconscious or unaware of cardiac arrhythmias.
With this solution, only one lead is required for the ECG recording. This is accomplished
by using a compact “double-electrode” with no wires connected, as this electrode is equipped
with a wireless transmitter and battery supply for several days of continuous usage. This new
concept was developed as an arrhythmia detection system for long-time ECG-monitoring, and
ambulatory electrocardiography, designed as an alternative to the conventional Holter
monitoring systems. The solution can be described as a continuous event recorder[9],[10].
With the use of this system, it is possible to make an easier and more cost efficient
ambulatory ECG recording compared to existing solutions on the market, and the patient can
be continuously monitored in his home-situation doing daily activities. This paper describes
the implementation of and experiences with this new system for wireless monitoring.
2. Methodology
Our concept for a wireless, continuous event recorder for ECG-signals is based on the
construction of a new ECG sensor. The sensor includes two electrical contact points applied
directly to the patient’s skin with the use of sticky, conducting hydrogel, and they are directly
connected to electronic circuits for amplifying the signal and with a wireless transmission of
the recordings to a receiver integrated as a component within a Hand Held Device (HHD).
The HHD will be the “intelligent” unit for analyzing and temporarily saving the recorded
signals. This unit uses a standard telecommunication facility, GPRS (General Packet Radio
Service), for sending an alarm signal together with the measured ECG-recordings to a remote
WPR Internet connected server. The doctor at the hospital uses a special remote WPR client
installed on a standard PC as a Clinical Diagnostic Station (CDS). Trained personnel will thus
be able to evaluate the ECG-recordings and for diagnosing the conditions detected, and
follow up the patients accordingly.
2.1. System configuration
The wireless sensor is sticky and attached to the patient’s chest. It will continuously
measure and wirelessly transmit sampled ECG-recordings by the use of a built-in RF-radio
transmitter. The RF-radio receiver converts the ECG-samples by the use of a microcontroller
before transmitting the ECG-samples to a standard personal digital assistant (PDA) with a
RS232 connector. It is used a small plastic enclosure for the receiver with the same size as the
PDA which is a Fujitsu-Siemens Pocket LOOX 700 using Microsoft Windows Mobile
Software 2003 for Pocket PC. It is programmed in C# based on .net compiler for Smart
Device Applications. The PDA is equipped with a CF-slot GSM/GPRS module RTM-8000
from Audiovox, and controlled by the software the PDA will automatically connect to the
GPRS mobile network and transmit necessary data to an Internet connected server, which is
shown in Fig. 1.
Proceedings of the 18th IEEE Symposium on Computer-Based Medical Systems (CBMS’05)
1063-7125/05 $20.00 © 2005 IEEE

3. Base station for
Mobile telephone
INTERNET
Wireless WPR Internet
transfer of connected server
encountered GPRS/ Remote WPR
ECG-alarm GSM Client at the
situations
hospital
The Hand-Held device
receives ECG-signals The patient can use a The Doctor at the Hospital can
The patient is wearing and uses automatic web-based system to make diagnositc evaluations
the WPR wireless arrhythmia detection contact the doctor and of the recorded ECG-signals
ECG-sensor algorithms read the encountered
ECG-findings
Figure 1. The figure shows the principal components of the wireless ECG-system.
2.1. Wireless ECG sensor functionality
The sensor measures ECG-signals with a sampling frequency of 500 Hz. The signal is
digitalized with 10 bit resolution, and continuously transmitted to a receiver-module in the
HHD, with the use of a modulated RF-radio link where we use the RF-transmitter CC1050
from ChipCon, operating at 869.700 MHz.
2.1. The HHD with RF-receiver and arrhythmia algorithms
The HHD has implemented an arrhythmia algorithm based on the non-linear
transformation for R-wave detection with adaptive threshold published by Sun et al.[11], with
a documented true detection rate of 99, 2%. In order to compensate for a higher sampling
frequency than used by Sun el al., we have based the detector on a 6-point detection and use
the average of 2 points in the 3-power non-linear transformation.
It is implemented several alarm criteria where the doctor in a setup configuration can
define the actual alarm limits; this includes bradycardia, tachycardia, and arrhythmia defined
as variations in RR intervals.
If an abnormal ECG activity is encountered, the HHD will store 1 minute of the ECG-
recordings and then transmit the recordings to the WPR server by the use of GPRS-
communication. In addition the HHD will calculate Heart Rate (HR) and variations in the R-
R interval, and averaged values together with maximum and minimum values are calculated
every one minute. These values are stored in a status-file which regularly is transmitted to the
WPR server as an XML-file. The wireless sensor and the HHD are shown in Fig. 2.
2.3. CDS with a web-based client
The WPR server consists of a Microsoft Server 2003 with an SQL-database and a web-
based application developed on a Microsoft .net platform. The server is placed in a secure
Proceedings of the 18th IEEE Symposium on Computer-Based Medical Systems (CBMS’05)
1063-7125/05 $20.00 © 2005 IEEE

4. zone in a local area network (LAN). The signals from the HHD are transmitted using a file-
transfer-protocol (FTP), and the recorded data are stored in the database. In order to access
the web-application for the clinician, it is established an encrypted Virtual Private Network
(VPN) tunnel between the server and the Firewall at the perimeter of the hospitals LAN as
shown in Fig. 1. A standard PC with a browser can be used for the CDS. In order to store the
actual ECG-recordings in a standardized format, we have implemented the Medical
Waveform Format, an open standard proposed by Hirai et al.[12].
2.4. Patient application
A survey study showed that the patients wants a quick feedback from the doctor at the
hospital[13], and it is therefore developed a web-based patient application which the patient
from his home can access by the use of a standard Internet browser and an encrypted VPN-
tunnel. The patient can thus read messages and necessary drug prescriptions from the doctor
and can send messages to the doctor questioning the actual follow-up.
Figure 2. Pictures shows to the left the sensor applied to a test person’s chest while
holding the assembled HHD. To the right the different parts of the HHD, the printed
circuit with the receiver unit and battery, connected to the PDA with an RS232 cable.
3. Results
Figure 3. The picture show a typical ECG-recording from the receiver unit connected
to the PDA, and with a sensor position corresponding to V2-V3 on the left side of the
chest to a test person. The figure capture is from a PC connected to the receiver unit.
Proceedings of the 18th IEEE Symposium on Computer-Based Medical Systems (CBMS’05)
1063-7125/05 $20.00 © 2005 IEEE

5. Technical test of the system design is performed during March 2005, and the Fig 3 shows
the ECG-signal recorded at the HHD. The actual curve shape will be dependant on the exact
position of the sensor, and in the figure this position is similar to the standard ECG-positions
V2-V3 on the left side of the chest.
The screenshots in Fig.4 shows the clinical application on the CDS. To the left the doctor
can overview the latest alarm recordings and what time they occurred. To the right a typical
alarm recording is shown. The doctor is able to change the scale-factor for the ECG-curves
both in timescale direction (X-axis) and in amplification (Y-axis). Information from the
regular status-information is retrieved from the database and processed as a trend-analyze for
24 hours variations of RR-interval. The doctor can choose the desired time-interval, and the
graphs can be printed out for documentation. In a separate text-box the doctor can make his
comments to the actual recorded curves and to the alarm-conditions detected by the system.
Figure 4. The pictures show screenshots from the clinical application on the CDS. To
the left is a tabulated overview of the latest alarm recordings, and to the right is
displayed an ECG-curve where the doctor can scroll to the right for viewing the
whole sequence of 1 minute of ECG-recordings. The curve can be enlarged for better
viewing the curve details. The point of alarm is given with the actual time indication.
The system is under implementation at the hospital for the first clinical trials during spring
2005. Preliminary informal assessments indicate that the functionality from the cardiologist’s
point of view is very useful. A study of the functionality and benefits from the patient’s point
of view is carried out as a part of the system trials.
4. Discussion and Conclusion
The ECG-signal obtained differs in some ways from a standard lead-I recording as it only
use two electrodes that are placed close to each other. It is therefore, necessary to further
investigate the use of this recording principle for arrhythmia diagnostic purposes. On the
other hand, the recordings in our system are supposed to be comparable to the recordings
from an implantable loop recorder used by Krahn et al [14] who used the Medtronic ILR, and
Proceedings of the 18th IEEE Symposium on Computer-Based Medical Systems (CBMS’05)
1063-7125/05 $20.00 © 2005 IEEE

6. found that this technology is a powerful tool in arrhythmia diagnosis. Even though proper
clinical trials are clearly needed to verify our hypothesis, it therefore seems reasonable to
assume that our new ECG-monitoring system will be able to, reliably, detect rarely
occurrences of cardiac arrhythmias, and thus make correct diagnosis even under situations
where the patient has the ability to carry out daily activity including physical exercise, body
wash and normal work.
5. Acknowledgement
The study is supported from Norwegian Research Council as a MEDKAP-project, and is
done in close cooperation with WPR medical AS, Norway.
6. References
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Proceedings of the 18th IEEE Symposium on Computer-Based Medical Systems (CBMS’05)
1063-7125/05 $20.00 © 2005 IEEE