ECG Patch Monitors for Assessment of Cardiac Rhythm Abnormalities

PR O GRE S S I N C ARDI O VAS CU L AR D I S EAS E S 5 6 ( 2 0 13 ) 22 4–2 29
Available online at www.sciencedirect.com
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ECG Patch Monitors for Assessment of Cardiac
Rhythm Abnormalities
S. Suave Lobodzinski⁎
Department of Electrical and Biomedical Engineering, California State University, Long Beach, CA, USA
A R T I C LE I N FO
AB S T R A C T
Keywords:
The primary goal of long-term monitoring is the improvement of diagnostic yield. Despite
ECG patch monitors
the clear utility of Holter monitoring in clinical cardiology, issues of relatively low
Cardiac rhythm abnormalities
diagnostic yield, cost and inconvenience have motivated the development of ultra-
Atrial fibrillation
portable devices referred to as ECG patch monitors. Although the “gold standard” for
assessing cardiac rhythm abnormalities remains a 12-lead Holter, there is an increasing
interest in portable monitoring devices that provide the opportunity for evaluating cardiac
rhythm in real-world environments such as the workplace or home. To facilitate patient
acceptance these monitors underwent a radical miniaturization and redesign to include
wireless communication, water proofing and a patch carrier for attaching devices directly to
the skin. We review recent developments in the field of “patch” devices primarily designed
for very long-term monitoring of cardiac arrhythmic events. As the body of supporting
clinical validation data grows, these devices hold promise for a variety of cardiac
monitoring applications. From a clinical and research standpoint, the capacity to obtain
longitudinal cardiac activity data by patch devices may have significant implications for
device selection, monitoring duration, and care pathways for arrhythmia evaluation and
atrial fibrillation surveillance. From a research standpoint, the new devices may allow for
the development of novel diagnostic algorithms with the goal of finding patterns and
correlations with exercise and drug regimens.
© 2013 Elsevier Inc. All rights reserved.
Indications for monitoring
2. Autonomic cardiac neuropathy associated with diabetes mellitus; or
Cardiac monitoring may be necessary for diagnostic evaluation of patients with any of the following symptoms or
conditions1:
3. Idiopathic hypertrophic or dilated cardiomyopathy.
1. The need to assess treatment effectiveness in individuals
with baseline high frequency, reproducible, sustained,
symptomatic premature ventricular complexes, supraventricular arrhythmias or ventricular tachycardia.
4. In individuals with pacemakers. a need to assess paroxysmal symptoms, myopotential inhibition, pacemaker
medicated tachycardia, anti-tachycardia pacing device
functioning, rate-responsive physiologic pacing function.
5. Symptoms suggestive of Prinzmetal's angina.
6. Post-myocardial
dysfunction.
infarction
with
left
ventricular
Statement of Conflict of Interest: see page 229.
⁎ Address reprint requests S. Suave Lobodzinski, PhD, Department of Electrical and Biomedical Engineering, California State University,
Long Beach, CA 90840.
E-mail address: suavelobodzinski@gmail.com.
0033-0620/$ – see front matter © 2013 Elsevier Inc. All rights reserved.
http://dx.doi.org/10.1016/j.pcad.2013.08.006
PR O G RE S S I N C ARDI O V A S CU L A R D I S EA S E S 5 6 (2 0 1 3) 22 4–2 2 9
Abbreviations and Acronyms
ADC = Analog to Digital
Converter
AF = atrial fibrillation
AFE = Analog Front-End
ASIC = Application Specific Integrated Circuit
BLE = Bluetooth Low Energy
DSP = Digital Signal Processing
ECG = electrocardiogram
EPM = ECG patch monitor
FDA = Federal Drug Agency
Li-Pro = lithium polymer
MCT = Mobile Cardiac Telemetry
SoC = System on a Chip
SPI = Peripheral Interface Data
Bus
ZEUS = Zio ECG Utilization
Service
7. Symptoms consistent
with
rhythm disturbances (e.g., frequent palpitation, syncope,
unexplained
dizziness).
Typically if any of
the above conditions is
encountered,
Holter
monitoring is used.
However intermittent
cardiac event monitors
(i.e., external loop recorders) and external
intermittent
cardiac
event monitors with
real-time data transmission and analysis
are considered medically necessary for
any of the following
conditions:
1. To document an
arrhythmia in persons with a non-diagnostic Holter
monitor, or in persons whose symptoms occur infrequently (less frequently than daily) such that the
arrhythmia is unlikely to be diagnosed by Holter
monitoring.
2. To document ST-segment depression for suspected
ischemia.
3. To document the impact of initiating drug therapy for
an arrhythmia.
4. To document the recurrence of an arrhythmia after
discontinuation of drug therapy.
5. To document the results after an ablation procedure for
arrhythmia.
6. To evaluate syncope and lightheadedness in persons
with a non-diagnostic Holter monitor, or in persons
whose symptoms occur infrequently (less frequently
than daily) such that the arrhythmia is unlikely to be
diagnosed by Holter monitoring.
Current state of the art ECG patch monitoring
technologies for assessment of cardiac
rhythm abnormalities
Ideally ECG path monitor (EPM) devices would combine the
features of the present-day Holter and event/loop recorders
with real-time data transmission and analysis capabilities. This
is however not yet technologically possible. The present-day
mix of FDA cleared EPMs are limited by their data acquisition
capabilities (typically single-channel electrogram), adhesive
materials that limit the device on-skin longevity and communication capabilities. Some EPM can be categorizes as a single-
225
lead “Holter-like devices,” exemplified by Zio Patch,2 some as
post-symptom event recorders with data transmission and yet
another as event/loop recorders with pre-symptom capabilities
in addition to data transmission such as NUVANT.3 An
overview of a typical EPM system architecture illustrates the
technologies used in patch monitor designs.
A typical ECG patch monitor (EPM) architecture is shown in
Fig 1. The EPM be functionally divided into two subsystems.
The first subsystem is responsible for processing of both
analog and digital ECG data. It is implemented as a System on
a Chip (SoC) self-contained processor, that has three primary
constituents: an Analog Front-End (AFE) for ECG signal
acquisition, amplification and filtering, a 12-bit Analog to
Digital Converter (ADC) that converts the analog ECG signal
into a digital format, and a custom Digital Signal Processing
(DSP). DSP is responsible for various ECG processing tasks
such as signal filtering, feature extraction, waveform analysis
and motion artifact removal. The artifact removal is aided by
an accelerometer, which provides time-dependent data on
the patient's movements. Typically, fast and excessive
motion triggers ECG measurement artifacts, often rendering
the signal unreadable. DSP either ignores or heavily filters
unreadable ECG segments when excessive motion is encountered. The second, SoC, is dedicated to wireless data transmission and features a low-power Bluetooth Low Energy (BLE)
processor, which is responsible for transmitting the data from
the. ECG SoC and accelerometer to a remote BLE enabled
device, such as a smart phone, tablet or notebook computer.
The two SoC subsystems are interconnected through a Serial
Peripheral Interface Data Bus (SPI). Other EPM sensors that
include three-axis accelerometer for patient activity monitoring and a MicroSD memory card for data logging are
interfaced to the BLE SoC through a second SPI interface.
The system is powered by two 3.7-V coin lithium polymer (LiPo) batteries with a total capacity of 400 mAh.
ECG patch monitor data processing
The ECG SoC is a sophisticated processor capable of real-time
data processing tasks such as QRS and optimized R-wave
detection. The QRS complex is detected using an algorithm
based on derivative or band-power extraction. The accurate R
peak value detection is accomplished by a continuous wavelet
transform algorithm optimized for reduction of the motion
artifacts. The data from the sensors can be sampled individually or simultaneously depending on the mode of operation.
The power consumption of the EPM has been estimated to be
1 mA at 3.7 V during streaming of ECG data, heart rate and
acceleration data simultaneously.
Patient interface
EPM electronics is attached to the skin via an adhesive carrier
with embedded wet gel electrodes. In a typical present-day
configuration, EPM may feature up to three ECG leads. The
electrodes within the patch are closely spaced (about 80 mm)
to facilitate the placement of the adhesive patch on the body
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PR O GRE S S I N C ARDI O VAS CU L AR D I S EAS E S 5 6 ( 2 0 13 ) 22 4–2 29
Fig 1 – Hardware architecture of the ECG patch monitor4.
surface as shown in Fig 3. The adhesive carrier is typically
optimized to last up to 14 days on the skin.
Clinical EPM devices
A number of new EPM devices have recently been announced in
various news releases, engineering conference proceedings or
Web pages. We have restricted our review to two most
representative examples—a ZIO Patch Recorder 2, which could
be best categorized as a single-lead Holter and NUVANT/PiiX
event recorder with a data transmission capability 3. Zio Patch
can only continuously record the ECG data, while NUVANT/PiiX
performs ECG analysis in real time, stores only the arrhythmic
events and transmits some to the caregivers. Both devices that
received FDA clearance are now commercially available to the
healthcare providers worldwide. Unlike traditional ECG devices, the electrograms acquired from closely spaced EPM
electrodes cannot be directly compared to any of the ECG
leads in either standard 12-, Mason–Likar or EASI lead
configurations5,6 commonly used in Holter monitoring. Rather,
typical EPM signals from the left pectoral region closely
resemble the data obtained by implantable devices, such as
insertable loop recorder (Reveal Plus, Medtronic Corporation) as
shown in Fig 2 and characterized by the narrower QRS
complexes and suppressed signal morphology.
response of Zio Patch is 0.15–34 Hz, input impedance is
greater than 3 MOhm, differential range is ± 1.65 mV and the
resolution is 10 bits.
The Zio Patch uses a patch carrier that is placed on the left
pectoral region. The patch does not require patient activation.
However, a button on the patch can be pressed by the patient
to mark a symptomatic episode. The manufacturer states that
it is indicated for use in patients who may be asymptomatic or
who may suffer from transient symptoms (e.g., anxiety,
dizziness, fatigue, light headedness, palpitations, presyncope, shortness of breath, and syncope). At the end of
the recording period, the patient mails back the patch in a
prepaid envelope to a central monitoring station.8 A report is
provided to the ordering physician within a few days.
The Zio ECG Utilization Service (ZEUS) system is a
comprehensive system that processes and analyzes received
ECG data captured by long duration, single-lead, continuous
recording diagnostic devices, such as the Zio Patch. The ZEUS
Zio patch recorder
According to the manufacturer (Zio Patch from iRhythm
Technologies of San Francisco, CA7), it is a waterproof
single-use, long-term cardiac rhythm monitor that provides
continuous monitoring for up to 14 days (Fig 3).
The Zio Patch is a single-channel EPM recorder with a
memory of up to 14 days of stored rhythms. The frequency
Fig 2 – A typical single-lead electrogram recording from the
left pectoral region. The middle electrode is an equivalent to
RL (body potential reference).
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227
Fig 3 – ZIO Patch assembly and Company recommended placement on the body.
system uses beat-by-beat QRS detection and a sophisticated
rhythm analysis algorithm to detect up to 10 categories of
rhythms. ZEUS runs on a cloud-computing platform and can
be used to analyze up to 14 days of ECG data more rapidly and
accurately than traditional systems. The data processed by
the ZEUS algorithm are reviewed by a certified cardiographic
technician to help ensure high accuracy and quality. iRhythm
has received Food and Drug Administration (FDA) 510(k)
clearance for both the Zio Patch, and the companion ZEUS
algorithm and software system.9
NUVANT Mobile Cardiac Telemetry (MCT)
system—system overview
The NUVANT® Mobile Cardiac Telemetry (MCT) System is
a patient-friendly, wireless-enabled arrhythmia monitor
designed to support more effective and timely assessment
of suspected non-lethal cardiac arrhythmias, such as atrial
fibrillation, in ambulatory patients. It consists primarily of
the PiiX® wearable monitoring device, the zLink® portable
data transmission device and a Patient Trigger Magnet to
enable on-demand collection of ECGs (recordings of heart
rhythm). In combination with interpretation services
provided by the Corventis Monitoring Center, as well as
secure online access to data (for prescribing physicians
only), NUVANT MCT enables patient- and physicianfriendly arrhythmia detection for up to 30 days at a time
(Fig 4).
NUVANT MCT utilizes the water-resistant, wireless and
low-profile PiiX sensor to collect data and identify non-lethal
cardiac arrhythmias. The sensor samples the ECG Signal at
200 Hz with a resolution of 10 bits. Each PiiX device lasts for
up to 7.5 days. Patients in need of longer monitoring
Fig 4 – An overview of the Corventis NUVANT/PiiX system.
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PR O GRE S S I N C ARDI O VAS CU L AR D I S EAS E S 5 6 ( 2 0 13 ) 22 4–2 29
durations utilize multiple PiiX devices, in sequence (for up to
30 days).
Once applied to the body, the PiiX sensor automatically
activates, begins collecting data and starts monitoring for
rhythm abnormalities.10 The device continuously monitors
the heart and automatically transmits ECGs (single-lead)
when the following rhythm abnormalities are detected:
• Bradycardia ≤ 40 bpm
• Pause ≥ 3 seconds
• Atrial fibrillation
• Ventricular tachycardia/ventricular fibrillation
• Tachycardia HR > 130 bpm
• A-Fib/A-Flutter (all rates)
• Heart block—all degrees
• Fall-associated arrhythmia capture
Patients can also trigger collection and transmission of
ECGs when they experience cardiac symptoms by using the
Patient Trigger Magnet.11
Data collected by the PiiX device are automatically transmitted from the PiiX to the zLink using Bluetooth communication. The zLink, in turn, then automatically transmits the data
to a secure, cloud-based application using cellular communication, from multiple geographical locations around the world.
Certified cardiographic technicians at the Corventis Monitoring Center review received data using cloud-based application and document symptoms reported by patients. Clinical
reports containing heart rate trends, Atrial fibrillation burden
and ECGs are prepared by the Corventis Monitoring Center
and delivered to provide data to prescribing physicians for
assistance with the diagnosis and identification of various
clinical conditions, events and/or trends. Prescribing physicians may also be contacted by the Corventis Monitoring
Center directly when arrhythmias that meet certain predefined criteria are detected. The NUVANT Mobile Cardiac
Telemetry System, Corventis, Inc. has been cleared by FDA
under 510(k)12 and CE Mark. Other EPM devices currently in
existence that include IMEC, V-Patch, CardioLeaf, Novosense
and similar have been reviewed by Lobodzinski et al.13
Clinical experience with ECG patch monitors
So far, the clinical outcomes and cost-effectiveness of extended
cardiac monitoring by means of the Zio Patch, the ZEUS,
NUVANT systems and similar devices have not been shown to
be superior to other available approaches. Mittal et al.8 noted
that “clinical experience [with the Zio Patch] is currently
lacking.” The author stated that it is not known how well
patients can tolerate the patch for 1 to 2 weeks, and whether
the patch can yield a high-quality artifact-free ECG recording
through the entire recording period. The authors stated,
furthermore, that “the clinical implications of not having
access to ECG information within the recording period need to
be determined.” Documented clinical experience in the scientific literature with NUVANT is lacking at the present time.
Rosenberg et al.14 compared the Zio Patch with a 24-hour
Holter monitor in 74 consecutive patients with paroxysmal
atrial fibrillation (AF) referred for Holter monitoring for
detection of arrhythmias. The Zio Patch was well tolerated,
with a mean monitoring period of 10.8 ± 2.8 days (range,
4–14 days). Over a 24-hour period, there was excellent
agreement between the Zio Patch and Holter for identifying
AF events and estimating AF burden. Although there was no
difference in AF burden estimated by the Zio Patch and the
Holter monitor, AF events were identified in 18 additional
individuals, and the documented pattern of AF (persistent or
paroxysmal) changed in 21 patients after Zio Patch monitoring. Other clinically relevant cardiac events recorded on the
Zio Patch after the first 24 hours of monitoring, including
symptomatic ventricular pauses, prompted referrals for
pacemaker placement or changes in medications. As a result
of the findings from the Zio Patch, 28.4% of patients had a
change in their clinical management. The authors concluded
that the Zio Patch was well tolerated, and allowed significantly longer continuous monitoring than a Holter, resulting
in an improvement in clinical accuracy, the detection of
potentially malignant arrhythmias, and a meaningful change
in clinical management. Moreover, they stated that further
studies are necessary to examine the long-term impact of the
use of the Zio Patch in AF management. The study concluded
that the promising data from this pilot study suggest that the
Zio Patch device may represent a more convenient and
efficient method of outpatient arrhythmia detection than
current methods using Holter monitors, event recorders, or
mobile cardiac outpatient telemetry. A second head-to-head
randomized comparison for all symptomatic indications has
just been completed, with results expected in late 2013.
In another study, Turakhia et al.15 evaluated compliance,
analyzable signal time, interval to arrhythmia detection, and
diagnostic yield of the Zio Patch, in 26,751 consecutive patients.
The mean wear time was 7.6 ± 3.6 days, and the median
analyzable time was 99% of the total wear time. Among the
patients with detected arrhythmias (60.3% of all patients), 29.9%
had their first arrhythmia and 51.1% had their first symptomtriggered arrhythmia occur after the initial 48-hour period.
Compared with the first 48 hours of monitoring, the overall
diagnostic yield was greater when data from the entire Zio Patch
wear duration were included for any arrhythmia (62.2% vs 43.9%,
p < 0.0001) and for any symptomatic arrhythmia (9.7% vs 4.4%,
p < 0.0001). For paroxysmal atrial fibrillation (AF), the mean
interval to the first detection of AF was inversely proportional to
the total AF burden, with an increasing proportion occurring
after 48 hours (11.2%, 10.5%, 20.8%, and 38.0% for an AF burden of
51% to 75%, 26% to 50%, 1% to 25%, and <1%, respectively). The
authors concluded that, extended monitoring with the Zio Patch
for ≤14 days is feasible, with high patient compliance, a high
analyzable signal time, and an incremental diagnostic yield
beyond 48 hours for all arrhythmia types.
Conclusions
Although still considered experimental by some, long-term
monitoring with the EPM for ≤ 14 days is feasible. Patch ECG
Monitors offer patient-friendly, well-tolerated non-obtrusive,
electrode and lead wire-free very long-term recording
PR O G RE S S I N C ARDI O V A S CU L A R D I S EA S E S 5 6 (2 0 1 3) 22 4–2 2 9
capabilities. These new devices allowed significantly longer
continuous monitoring than a Holter, resulting in an improvement in clinical accuracy, the detection of potentially
malignant arrhythmias, and a meaningful change in clinical
management. Further studies are necessary to examine the
long-term impact of the use of EPM in AF and other
arrhythmia management. As EPM devices get more popular
in the market place, we can expect the improvements in their
functionality and capabilities.
Statement of Conflict of Interest
The author declare that there are no conflicts of interest.
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