A range of treatments have been developed for the management of cardiac arrhythmias. These include antiarrhythmic drugs, artificial pacemakers, implanted cardiac defibrillators and ablation of damaged or malfunctioning cardiac tissue. However, to allow a physician to choose the most suitable course of treatment for a patient, it is important that the correct diagnosis be made in an appropriate period of time. Cardiac monitors can provide the physician with electrocardiogram (ECG) data that can either confirm or rule out the presence of an arrhythmia.
The symptoms described by the patient should allow the physician to decide which method of cardiac monitoring is most suitable in order to maximise the outcome of a successful diagnosis. For many patients, the symptoms of an arrhythmia may arise infrequently or unpredictably, while others may not feel any obvious indication at all. The current standard of cardiac monitoring is the Holter monitor, which provides 24–48 hours of continuous ECG recording. In many cases, the arrhythmia may not occur during this time period, leading to the monitoring being repeated. This approach puts pressure on medical resources and increases the time before a successful diagnosis can be made and treatment administered.
Newer cardiac monitors and recorders are increasingly being used to provide patients with more selective ECG recording. Data can also be sent directly to the physician should the patient experience a cardiac event during the monitoring period. Advances in device and electrode design and on-board analysis and technology are providing patients with much more sophisticated methods of diagnosing cardiac conditions and managing chronic heart disease, while maintaining patient freedom and quality of life. This short article outlines the current methods of cardiac monitoring and describes the Remote Event Monitor (REM) that is being developed by Sensor, Technology & Devices Ltd, Belfast, UK.
Background
Coronary heart disease (CHD) is the most common cause of death in Europe, accounting for 1.92 million deaths each year, 741,000 of which occur in the EU. This amounts to one in six men and over one in seven women in the EU dying from the disease;1 however, these statistics do not reflect the number of people living with the disease. The American Heart Association (AHA) has estimated that while chronic heart disease accounted for 42% of American deaths in 1997, the number of patients surviving acute cardiac attacks is steadily increasing. In 1997, there were 60 million people living with some form of cardiovascular disease (CVD),2 a statistic attributable to the advances made in the diagnostic and monitoring facilities available to patients.
It has also been estimated that the worldwide population over 65 years of age will increase from 357 million in 1990 to 761 million in 2025. In the US, healthcare expenditure reached US$1.8 trillion in 2004.3 With patients living longer and healthcare costs continuously rising, healthcare systems are facing new challenges that require more scalable and affordable solutions. Focusing on the prevention and early detection of disease, and a shift towards the proactive management of wellness rather than illness, is vital to ensure a sustainable and cost-effective healthcare system. In particular, moving the point of care from the hospital to the home can address healthcare costs, as well as improving the quality of life of patients.
Ambulatory heart monitoring can provide a safe and effective means of evaluating or monitoring patients who experience symptoms suggestive of a cardiac arrhythmia. These symptoms can include syncope, palpitations and dizziness. The rate of recurrence of the symptoms should dictate to clinicians the method of monitoring that is suitable for that patient.4 Most guidelines will recommend 24–48 hours of Holter monitoring for patients with suspected or known arrhythmias that occur every day.5 The Holter monitor was first introduced in 1957 and since then it has been continually developed in terms of data acquisition and storage capacity.6 Holter monitoring is an uncomplicated technology that facilitates the continuous monitoring and recording of asymptomatic arrhythmias or arrhythmias associated with loss of consciousness without requiring patient activation. However, the physical dimensions of the device may impede the patient’s normal daily activities, such as exercise, which may be the cause of the arrhythmia.7 The use of this device for patients who experience infrequent arrhythmias is not recommended due to the insufficient timescale for the monitoring period. Alternative monitoring methods have been developed in order to facilitate this. Intermittent ambulatory monitoring can be used for diagnosing a suspected arrhythmia and establishing its frequency and related symptoms experienced by the patient to the arrhythmia. It is suitable for patients who experience sporadic symptoms that include palpitations, dizziness, light-headedness or syncope.5
Current Standards in Ambulatory Cardiac Monitoring
Currently, several types of device are used to remotely assess cardiac rhythm abnormalities in ambulatory patients. The largest category of devices includes patient- and event-activated intermittent recorders. These devices may be pre-symptom continuous-loop or post-symptom recorders, and can be worn externally or implanted into the body. Continuous realtime remote cardiac monitoring is the newest category with four devices commercially available.8 These devices can transmit ECG data to a central, attended monitoring station.
Patient- and Event-activated Intermittent Recorders
Thesed devices can continuously monitor a patient’s ECG without constantly recording the data. The data that are recorded can be transmitted to a doctor’s office or hospital via the telephone or can be uploaded to a PC. Monitoring can take place over a period of weeks or months, as opposed to the maximum of 48 hours available using a Holter monitor.7 Once transmitted, technicians or medical personnel can monitor the ECG data from a remote monitoring centre (i.e. attended monitoring).
External Loop Recorders Pre-symptom Memory Loop Cardiac Event Recorders
Standard external loop recorders (ELRs) can be worn for 20–30 days and utilise memory loop recording, i.e. they record several minutes of activity at a time and then start over. When patients experience symptoms, they must hold the device next to their chest and activate the device to begin recording ECG data.7 Only data associated with symptomatic events will be recorded using these devices, allowing the physician to determine whether the symptom is a result of a cardiac arrhythmia. However, the patient may not be aware of asymptomatic events that occur, and so this information cannot be included when the physician is making his or her diagnosis.
Auto-trigger External Loop Recorders
These also utilise memory-loop recording but differ from standard ERLs by having on-board software to automatically detect events that are asymptomatic as well as symptomatic, providing the physician with a clearer picture of the patient’s condition. This technology relies on the patient calling to transmit the data via telephone to the physician or technician at the hospital or monitoring centre.8
Implantable or Insertable Loop Recorders Pre-symptom Memory Loop Cardiac Event Recorders
Implantable or insertable loop recorders (ILRs) carry out the same function as ELRs, but are implanted subcutaneously in the left or right chest region. ILRs can be used for 14–20 months before being surgically removed. Currently, only Reveal Plus (Medtronic) and Sleuth (Transoma Medical) are commercially available. Each of these devices can be programmed for both automatic and patient activation. Reveal Plus cannot transmit data from the patient’s home. Should an episode of syncope occur, the patient must visit the doctor’s office for assessment of the recorded data. However, Sleuth can wirelessly transmit ECG data to a remote monitoring centre for analysis.8–10
Post-symptom Event Recorders
These hand-held devices do not use chest electrodes to monitor ECG data, but the device can be placed on the precordium when symptoms occur to record a few minutes of ECG data. Memory loop recording is not used, so only ECG data after patient activation is recorded. These devices will not generally have automatic activation when asymptomatic arrhythmias occur.8
Continuous Realtime Attended Remote Cardiac Monitors
These will automatically record and transmit event data to personnel monitoring or attending the monitor at the hospital or clinic. To date, the only commercially marketed systems are the CardioNet system,11 the HEARTLink II system (Cardiac Telecom Corp),12 the Vital Signs Transmitter (Biowatch Medical)13 and the CG-6108 Lifestar Ambulatory Cardiac Telemetry (ACT) system (Card Guard Scientific Survival Ltd).14 These devices provide automatic wireless transmission of abnormal ECG waveforms at the time of event, from the patient’s home to an attended monitoring centre.
Mobile Cardiac Outpatient Telemetry System (CardioNet)
The CardioNet mobile cardiac outpatient telemetry (MCOT) system can automatically detect and transmit a patient’s ECG data when an arrhythmic event occurs. Patients using this device are monitored for up to 21 days.15 The system uses a sensor (see Figure 1) worn around the patient’s neck or on their belt to continuously detect and transmit ECG data to the monitor. The monitor enables realtime analysis of the patient’s ECG. If an arrhythmia is detected, the data are sent to the CardioNet Monitoring Centre to be reviewed by trained technicians.16
If the patient is aware of the symptoms, they can be recorded (along with patient activities) using the touch screen on the monitor.17 When the monitor is in its base, a telephone line transmits the ECG data to the monitoring centre. If the patient is away from home, a mobile phone embedded in the device is used. Should a cardiac emergency arise, an urgent report is sent to the physician and emergency services are contacted if required. Physicians will receive daily updates on any significant cardiac events or symptoms experienced by the patient via fax or the Internet.16
Heartlink II ‘Telemetry @ Home’ (Cardiac Telecom)
The Heartlink II system is available as a ‘Telemetry @ Home’ service that is designed to monitor and automatically identify abnormalities in a patient’s ECG rhythm using 16 diagnostic algorithms. When an arrhythmia is detected, the data are transmitted to a central monitoring station and viewed by trained personnel within 15 seconds. The system has four operational modes in which: arrhythmias are automatically detected and transmitted to the monitoring station; the patient activates transmission should symptoms arise; ECG data can be viewed in realtime by the physician; and a ‘Help Request’ issued for use in non-cardiac emergencies.18 The patient transmitter sends ECG data to a Tele-Link computer box (see Figure 2) that monitors, analyses, stores and transmits pre-determined cardiac events to a surveillance laboratory via the patient’s telephone line. The arrhythmia data transmitted are merged with trend data gathered during monitoring in order to provide continuous ECG recordings for a given 24-hour period.18
Vital Signs Transmitter (Biowatch Medical)
Biowatch Medical’s Vital Signs Transmitter (VST) (see Figure 3) is a belt-like device that uses interpretative, self-adaptive algorithms to continuously monitor and analyse a patient’s ECG. The device is designed for short- and long-term monitoring. Positioned around the patient’s chest, the VST uses built-in dry electrodes, while other sensors provide two-lead ECG, temperature and respiration readings. Future designs of the device will provide information on oxygen saturation, non-invasive blood pressure (NIBP) and patient weight via radiofrequency transmission.19 The VST has an event button that the patient presses when symptoms arise, and can record up to two weeks’ worth of data at a time. ECG data are sent in realtime to the company’s control centre, which is monitored 24/7 by trained staff.
Should the patient experience a cardiac problem requiring attention, control-centre staff contact the patient via an in-built mobile phone. If the patient is unresponsive, emergency services can be contacted and the patient’s location identified via global positioning system (GPS). The patient’s ECG data are also securely available online for analysis by his or her physician.19 The VST can never come into contact with water, preventing the patient from being monitored during showering or any other activity that may involve the device becoming wet.20
Lifestar ACT Ambulatory Cardiac Telemetry System (Card Guard)
This device, shown in Figure 4, uses a in-built mobile phone or land-line to transmit ECG data to a healthcare provider once an arrhythmia is automatically detected. Atrial fibrillation (AF) (any rate), bradycardia, tachycardia and a pause in the normal sinus rhythm are listed as the arrhythmias that can be automatically detected, identified and transmitted. There is also a manual activation button that allows the patient to transmit data if he or she feels unwell.21,22 The Lifestar ACT provides the physician with a patented, variable and full 24-hour disclosure report and histogram data, which enables better management of patients with chronic AF. The system also incorporates a smart phone that sends ECG data to the physician and provides a communication link between the patient, the service provider and the physician.23
Limitations of Current Remote Cardiac Monitoring Systems
Patient-activated devices will only record what the patient perceives to be symptomatic events. Patients may also have difficulty activating the recorder while symptoms are being experienced, which may lead to the event being partially recorded.24–26 A report into patient-activated devices suggested extensive and continued patient education could improve the diagnostic yield of patient-activated monitors.26 These limitations will not apply to automatic event-activated recorders as they can record both symptomatic and asymptomatic arrhythmias.7,26 However, depending on the programming used, the device may activate unnecessarily (i.e. false event) or may not record during some symptomatic events.
This would be a result of pre-programmed rhythm specification that causes the device to activate and record. Limited device memory could also lead to a false event erasing a previously recorded true event.27 Less memory will also mean that more frequent downloads or transmissions will be required for multiple recorded events. Post-symptom looping devices are limited in that the arrhythmia may have ended before the recorder is activated post-event.
ELRs require patch electrodes to be attached to skin on a daily basis, and so have been reported to be less comfortable to wear than the post-event recorders.7 Therefore, patients can be less compliant with the wear and maintenance required in order to gather sufficient information regarding the patient’s condition. A higher number of electrodes will also increase patient discomfort during the monitoring period.
Internal looping recorders are invasive, requiring a surgical procedure to insert the implant with the concomitant risks associated with surgery, such as infection or the implant being dislodged. While ELRs and post-event recorders will usually allow ECG transmission trans-telephonically, ILR data can only be assessed during office visits (with the exception of the Sleuth system, which allows home transmission).
A New Approach – The Remote Event Monitor
The REM, shown in Figures 5 and 6, comprises a flexible three-lead ECG electrode patch, a body-worn device and a hand-held/belt-worn device. The electrode can comfortably and unobtrusively facilitate continuous ECG monitoring via the attached body-worn device for up to seven days. If the patient experiences symptoms, an ‘event’ button on the monitor can be quickly and easily pressed to activate recording. The body-worn device uses memory loop recording to capture the patient’s ECG prior to, during and after the event has taken place. A short-range wireless link sends the data to the hand-held device, which then uses wireless technology (such as general packet radio service [GPRS] or WiFi) to transmit the ECG data to a receiving station, which can be securely accessed by the clinician from any location via the Internet. With 10 arrhythmia detection algorithms included in the on-board software, the REM system allows ECG data during asymptomatic events to be recorded and transmitted to the clinician in near realtime. In the case of the patient being unable to activate the device, the REM system can automatically detect and transmit data during bradyarrhthmia, ventricular tachycardia (VT), supaventricualar tachyarrhythmia (SVT), self-terminating ventricular fibrillation (VF), asytole, atrial flutter, AF and first-, second- and third-degree heart block. A continuous Holter monitor can also be incorporated into the system. This will provide continuous ECG recording for 24 hours to ensure any frequent asymptomatic arrhythmias are recorded, which may be outside the diagnosis of those mentioned above.
The REM system can be remotely reconfigured at any time before or during the monitoring period. Pre- and post-event recording time can be specified for each patient, as can the type of event to be automatically detected. The data recorded by the system are immediately transmitted for analysis by the clinician to ensure the patient is receiving the best care. The system also has the facility to send alerts to the physician via SMS or email.
The REM system will allow the patient to successfully carry out their normal daily activities during monitoring. The device is discrete, compact and unobtrusive, and can be worn during the night and while the patient is showering. The freedom enjoyed by the patient while wearing the REM device, combined with the reassurance felt as a result of continuous monitoring, can help to improve the patient’s quality of life and reduce stress, therefore contributing to good cardiac health. Additionally, it is during these everyday activities that the patient’s arrhythmia may arise. The flexible design of the electrode patch allows it to be easily applied to both men and women as a ‘second skin’ in order to maximise comfort and ease of wear and minimise noise and motion artefact. The patch design enables easy application without jeopardising the quality of the ECG signals recorded. The REM can be extended to record more ECG leads and will also have the capability to wirelessly monitor blood oxygen levels, respiration and body temperature. A tri-axial accelerometer can also be incorporated into the system in order to monitor a patient’s posture and motion. This additional information, combined with high-quality ECG, provides physicians with an excellent range of physiological data on which to build a detailed health analysis of the patient.
Conclusion
Continuous cardiac monitoring allows early detection and therefore appropriate intervention for patients with cardiac arrhythmias. The data recorded enable clinicians to accurately determine whether an arrhythmia is the cause of the symptoms presented by the patient. An accurate diagnosis will ensure the most appropriate treatment is administered, providing effective management of the cardiac condition. The latest cardiac monitors provide more efficient data capture, where the physician will be presented only with relevant ECG data that contain irregular waveforms, or when the patient actually experiences symptoms. Ambulatory cardiac monitoring offers patients independence and improved quality of life in comparison with in-hospital monitoring. It also allows patients living in remote areas to be continually monitored without having to stay in hospital. The cost-effectiveness of this method of cardiac monitoring is underlined when lower transportation and accommodation costs, as well as earlier diagnosis and therefore treatment times, are combined.