Download Lazarus A. Remote, wireless, ambulatory monitoring of implantable

Remote, Wireless, Ambulatory Monitoring
of Implantable Pacemakers, Cardioverter Defibrillators,
and Cardiac Resynchronization Therapy Systems:
Analysis of a Worldwide Database
ARNAUD LAZARUS, M.D.
From the InParys Clinical Research Group, Paris, France
Study Objective: To describe the daily routine application of a new telemonitoring system in a large
population of cardiac device recipients.
Methods: Data transmitted daily and automatically by a remote, wireless Home MonitoringTM system
(HM) were analyzed. The average time gained in the detection of events using HM versus standard practice and the impact of HM on physician workload were examined. The mean interval between device
interrogations was used to compare the rates of follow-up visits versus that recommended in guidelines.
Results: 3,004,763 transmissions were made by 11,624 recipients of pacemakers (n = 4,631), defibrillators (ICD; n = 6,548), and combined ICD + cardiac resynchronization therapy (CRT-D) systems (n = 445)
worldwide. The duration of monitoring/patient ranged from 1 to 49 months, representing 10,057 years.
The vast majority (86%) of events were disease-related. The mean interval between last follow-up and
occurrence of events notified by HM was 26 days, representing a putative temporal gain of 154 and 64
days in patients usually followed at 6- and 3-month intervals, respectively. The mean numbers of events
per patient per month reported to the caregivers for the overall population was 0.6. On average, 47.6%
of the patients were event-free. The mean interval between follow-up visits in patients with pacemakers,
single-chamber ICDs, dual chamber ICDs, and CRT-D systems were 5.9 ± 2.1, 3.6 ± 3.3, 3.3 ± 3.5, and
1.9 ± 2.9 months, respectively.
Conclusions: This broad clinical application of a new monitoring system strongly supports its capability
to improve the care of cardiac device recipients, enhance their safety, and optimize the allocation of health
resources. (PACE 2007; 30:S2–S12)
ambulatory monitoring, remote consultation, implantable cardiac device
Introduction
The exponential growth rate of cardiac devices implantation calls for new methods of longterm surveillance with a view to optimize patient
safety and care, alleviate the burden of caregivers,
lower health care cost, and address regulatory and
legal issues. In parallel with their increasing use,
devices are also incorporating more refined and
complex features, which, unless regularly interrogated and reset, lose their diagnostic or therapeutic usefulness and pertinence. In addition, a
high proportion of remediable adverse events are
undetected because they are asymptomatic, or become apparent only after persisting long enough to
cause marked deterioration of the clinical status.
Finally, even when symptomatic, patients might
be reluctant or unable to report the occurrence of
adverse health changes. These considerations have
This analysis was supported by Biotronik GmbH, Berlin,
Germany. Arnaud Lazarus, M.D., is a medical consultant for
Biotronik France.
Address for reprints: Arnaud Lazarus, M.D., InParys Clinical
Research Group, 12 rue Pasteur, 92210-Saint-Cloud, France.
Fax: +33-1-41-12-07-15; e-mail: [email protected]
prompted the design of new monitoring systems
with a view to (a) facilitate the regular access to upto-date information stored in the devices’ memories, (b) allow the early detection of adverse events
and prompt corrective measures, (c) minimize the
participation of patients in the process, and (d)
assess the effects of treatment interventions. One
of the strategies being actively pursued to fulfill
these goals is based on remote monitoring, which
minimizes the need for frequent and close interactions between patients and caregivers. This report
is an analysis of a wide application in daily routine practice of new technology incorporated in
implantable cardiac rhythm management devices,
which enables the daily, remote, wireless, patientindependent ambulatory monitoring of multiple
medical and technical data.
Methods
Characteristics of the Monitoring System
The pacemakers, defibrillator cardioverters
(ICD), and cardiac resynchronization therapy
(CRT) systems implanted in our study population
are embedded with an antenna enabling the wireless, automatic, patient-independent transmission
C 2007, The Authors. Journal compilation C 2007, Blackwell Publishing, Inc.
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January 2007, Supplement 1
PACE, Vol. 30
REMOTE MONITORING OF CARDIAC DEVICES
Table I.
Triggers of Events Reported by the Monitoring System Included in this Analysis
Event Trigger
Programmable
on the
Internet
Platform
General device status
Elective replacement indicator
No
Abnormal device status
No
Lead function
Atrial and right and left ventricular pacing lead impedance ()
Low
Yes*
High
Yes*
Shock lead impedance
Yes
Ineffective 30 J shock delivery
Yes
<50% in P or R sensing safety margin
Yes
P sensing (mV)
Yes
R sensing (mV)
Yes
Ventricular capture control disabled
Yes
Ventricular capture threshold >4.8 V
Yes
≥1 V change in ventricular pacing
Yes
threshold vs. last measurement
Rhythm monitoring
First automatic mode switch since last
Yes
follow-up
First automatic mode switch per each
Yes
24 hours
Duration of automatic mode switch
Yes
episode, hours
Sensed supraventricular tachycardia
Yes
Number of premature ventricular
Yes
events/hours
Sensed ventricular tachycardia
Yes
Sensed ventricular fibrillation
Yes
Ventricular resynchronization function
Upper mean resting heart rate limit,
Yes
bpm
Lower percent ventricular
Yes
resynchronization limit
Default
Range
On
On
–
–
250
1500
<25 or >110
On
On
0.5
1.5
Off
On
Off
200–500
1000–3000
–
–
–
0.1–3.0
0.5–3.0
–
–
–
Off
–
Off
–
2.5
2.5–18
Off
50
–
10–250
Off
On
–
–
90
70–120
90
50–95
All event triggers are not applicable to all devices (see Table II).
*Limited to ICDs and CRT-D.
of diagnostic information stored in the device
memory. The event information transmitted by the
various types of implantable devices included in
this analysis is presented in Table I. When activated, Home MonitoringTM (HM, Biotronik GmbH
& Co. KG, Berlin, Germany) transmits data systematically on a daily basis, at a fixed time of day (usually nocturnal), via a special cell phone-like instrument (CardioMessengerTM , Biotronik) kept within
2 m from the implanted device. The transmission utilizes state-of-the-art encrypted SMS technology to transfer worldwide data to a dedicated
PACE, Vol. 30
service center located in Berlin, Germany, where it
is anonymously analyzed and archived, as well as
posted on a secured Internet platform permanently
accessible to the attending physician. The occurrence of abnormal events, previously selected for
individual patients (Tables I and II), are reported
to the user physician via e-mail, SMS, and/or
facsimile singly or combined, as preferred. The
data transmission following interrogation of a device includes a marker used to track the occurrence of scheduled or unscheduled patient followups.
January 2007, Supplement 1
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LAZARUS
Table II.
Events Transmitted by the Home Monitoring System
Among Implanted Devices Included in this Analysis
Transmitted Event
Medical events monitoring
Atrial arrhythmias
First automatic mode switch since
last follow-up
First automatic mode switch per
each 24 hours
Duration of automatic mode
switch episode > X hours
Sensed supraventricular
tachycardia
Ventricular arrhythmias
>X premature ventricular
complexes/hours
Sensed ventricular tachycardia
Sensed ventricular fibrillation
Others
Mean resting heart rate above
programmable value
Percent ventricular
resynchronization below
programmable value
System status
Elective replacement indicator
Atrial and/or ventricular lead(s)
impedance outside specified
range
High voltage lead impedance
outside specified range
Abnormal device status
Configuration monitoring
Ventricular capture control
algorithm and critical change in
pacing threshold
<50% in P or R sensing safety
margin
P or R amplitude below
programmable mV
Ineffective 30 J shock delivery
PM ICD CRT-D
+
–
+
+
–
+
+
–
+
–
+
+
–
+
+
–
–
+
+
+
+
–
–
+
–
–
+
+
+
+
+
+
+
Events Classification
The types of events detected and transmitted during the study period were classified
(Table I), according to the information they contained, as (a) medical (disease-related), (b) system status-related (e.g. battery status or inactive
ventricular arrhythmia detection), and (c) configuration monitoring (sensing/pacing functions, ineffective high voltage shock delivery). The mean
time interval (X) between first report of a type of
event and the last device interrogation was calculated. Assuming a twice yearly follow-up schedule
for pacemaker surveillance and quarterly followups for ICDs and CRT systems, the average time
gained in the detection of asymptomatic events using HM versus standard medical practice was calculated as 180 – X days for pacemakers, and 90 –
X for other devices.
Rates of Events Reported
–
+
+
–
+
+
+
–
–
+
–
–
The impact of HM on physician workload was
examined by counting the average number of event
reports received per patient per month according
to each type of device (PM vs ICD vs CRT) implanted. It is noteworthy that the type and quantity of information arriving to the service center is
not identical to that forwarded to the caregivers,
since the latter preselect the events to be reported
according to their individual patients.
–
–
+
Rates of Follow-Up Visits
–
+
+
PM = dual chamber pacemakers; ICD = single and dual
chamber cardioverter defibrillators; CRT-D = combined cardiac
resynchronization therapy system and cardioverter defibrillator.
Data Collection and Management
This retrospective analysis utilized data collected by HM in daily routine practice. It is noteworthy that between the beginning of the data
collection and 2006, the number of patients monitored increased markedly, and that the quantity
and type of information increased and changed,
S4
respectively, among the several types and generations of implanted devices. No attempt, however,
was made to analyze the data according to particular devices. In addition, since the data storage
does not include demographic or clinical information, this report does not correlate HM reporting
and occurrence of a clinical or device-related event
confirmed during patient follow-up. Finally, no information was available pertaining to the actions
taken by caregivers in response to the reporting of
events.
The mean interval between markers of device interrogation was used to compare the rates
of follow-up visits in this population versus that
recommended in guidelines issued by professional
societies.1
The analyses were performed with OracleTM
version 9i software (Oracle Corporation, Redwood
Shores, CA, USA) and other analytical software
custom-developed for this database. The results
are presented as means ± standard deviation, or
medians, when appropriate.
Results
Between January 2002 and February 2006,
3,004,763 transmissions were made by 11,624
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REMOTE MONITORING OF CARDIAC DEVICES
Figure 1. Percentages of patients with events transmitted to the HM service center in 4,631 pacemaker recipients during a mean follow-up of 8.5 ± 8.1 months. ERI = elective replacement indicator; VImp = ventricular lead impedance out of range; AImp = atrial lead impedance out of
range; VThr = ventricular threshold >4.8 V; VACC = ventricular active capture control disabled;
LowR ≤ 50% R-wave sensing safety margin; LowP ≤50% P-wave sensing safety margin; VThrin
≥1 V increase in ventricular capture threshold; VThrDe ≥1 V decrease in ventricular capture
threshold; AF = atrial fibrillation; FU = follow-up; and Dur = duration.
recipients of various models of Biotronik pacemakers (n = 4,631), ICDs (n = 6,548), and CRT systems
(n = 445) in 23 countries. The overall duration of
monitoring of individual patients ranged from 1 to
49 months (mean = 10.5 ± 9.4 months), representing a total of 10,057 years.
Event Rates
Pacemakers
The percentages of patients with specific
events transmitted to the service center during a
mean follow-up of 8.5 ± 8.1 months (range 1–49)
among 4,631 pacemaker recipients are shown in
Figure 1. It is noteworthy that the overwhelming
majority of events were prompted by episodes of
atrial fibrillation, detected on the basis of automatic pacing mode switches. In >10% of patients,
the episode of mode switch lasted >2.5 hours per
day, the shortest programmable duration of sustained episodes prompting an alert.
Single Chamber ICDs
The percentages of patients with specific
events transmitted to the service center during a
mean follow-up of 12.4 ± 10.6 months (range 1–
46) among 3,509 recipients of single chamber ICDs
are shown in Figure 2A. As expected, the majority
of events were related to episodes of ventricular
tachyarrhythmias. The relatively low rate of VT2
events is attributable to the frequent programming
of a single VT detection zone, or of VF detection
only.
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Dual Chamber ICDs
The percentages of patients with specific
events transmitted to the service center by HM in
3,039 recipients of dual chamber ICDs during a
mean follow-up of 11.7 ± 9.3 months (range 1–49)
are shown in Figure 2B, and are similar to those observed with single chamber ICDs, except for the detection of supraventricular tachycardia enabled by
the presence of an atrial lead and use of a dedicated
tachycardia discrimination algorithm. Of particular importance and interest was the observation,
among all ICD recipients, of 66 alerts from 40 devices for abnormal function status, indicating either inactivation of the device (n = 63 in 38 devices), or a random anomaly of device function
(n = 3 alerts in two devices). In addition, 271 devices (4.1%) delivered ≥1 ineffective 30 J shock.
CRT-D
Finally, the percentages of patients with specific events transmitted to the service center in 445
recipients of CRT-D systems during a mean followup of 7.2 ± 4.9 months (range 1–19) are shown in
Figure 3. As a result of the increasing complexity
of the system and greater severity of illness of their
recipients, the list, as well as the absolute number
of events, were markedly greater than in the other
patient groups, and prominently represented by
medically related alerts. The 46.7% incidence of
CRT delivery below, and 23.8% incidence of rise
in mean resting heart rate above the programmed
thresholds, are particularly noteworthy.
January 2007, Supplement 1
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LAZARUS
Figure 2. (A) Percentages of patients with events transmitted to the HM service center in 3,509
recipients of single chamber ICDs during a mean follow-up of 12.4 ± 10.6 months. (B) Percentages
of patients with events transmitted to the HM service center in 30,39 recipients of dual chamber
ICDs during a mean follow-up of 11.7 ± 9.3 months. SImp = shocking lead impedance out of
range; Status = abnormal device status; In30J = ineffective 30 J shock delivery; VT1 = ventricular
tachycardia zone 1; VT2 = ventricular tachycardia zone 2; VF = ventricular fibrillation; SVT =
supraventricular tachycardia; see Figure 1 for other abbreviations.
In the overall analysis, in contrast to the high
proportion of disease-related alerts (86%), those
related to abnormal device status (3%) and to system configuration (11%) were low (Fig. 4). The proportion of disease-related alerts was prominently
highest among CRT systems recipients (97.6%).
patients. The putative temporal gain represented
by these early event detections were 154 days
in patients usually followed at 6-month intervals
(pacemaker recipients), and 64 days in patients
usually followed at 3-month intervals (other patients).
Putative Average Temporal Gain in Detection
of Asymptomatic Events
Workload-Related Observations
The mean ± SD time intervals between last
follow-up and occurrence of events and their notification by HM in pacemaker, single and dual
chamber ICDs, and CRT-D recipients were 26 ± 51,
33 ± 45, 28 ± 41, and 17 ± 24 days, respectively.
Regrouping the recipients of devices capable of
cardioversion/defibrillation, the mean ± SD time
interval was 26 ± 45 days, the same as in paced
S6
Rates of Events Reported
The mean numbers of events per patient per
month reported by HM to the caregivers for pacemaker, ICD, and CRT-D recipients, and for the overall population, are presented in Figure 4. The lowest numbers of alerts were observed in the ICD population (approximately 1 event per quarter), and
highest in the CRT-D population (approximately
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REMOTE MONITORING OF CARDIAC DEVICES
Figure 3. Percentages of patients with events transmitted to the HM service center in 445 recipients of CRT-D systems during a mean follow-up of 7.2 ± 4.9 months . RVImp = right ventricular
lead impedance out of range; CRT = cardiac resynchronization therapy = percentage of biventricular paced events below programmed value; mHRR >X = mean resting heart rate above
programmed value; VES/hour = number of ventricular extrasystoles above programmed value;
see Figures 1 and 2 for other abbreviations.
2 events/month). The percentages of eventfree pacemaker, ICD, and CRT-D patients were
54.8%, 43.5%, and 28.3%, respectively, with an
overall average of 47.6 %.
Rates of Follow-Up Visits
The average ± SD time interval between
follow-up visits in patients with pacemakers,
single-chamber ICDs, dual chamber ICDs, and
CRT-D systems were 5.9 ± 5.5, 3.6 ± 3.3, 3.3 ±
3.5, and 1.9 ± 1.8 months, respectively.
Illustrative Examples
An illustrative example of early arrhythmia
detection by HM is presented in Figure 5. At
7 weeks after the previous follow-up, automatic
mode switch triggered by episodes of atrial fibrillation was detected by HM. The event transmission was triggered by a cumulative duration >2.5
hours (default cut-off for this event). When contacted in response to this transmission, the patient retrospectively admitted to feeling ill the day
before, which was not reported. Changes in drug
Figure 4. Mean number of events/month (above each bar) reported by HM to the caregivers
among recipients of pacemakers (IPG), single chamber ICDs (ICD-VR), dual chamber ICDs (ICDDR), combined cardiac resynchronization and ICD systems (CRT-D), and overall (ALL) population.
The system status- (black fill), configuration- (hatched fill), and medically related (unfilled) events
are also shown.
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January 2007, Supplement 1
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LAZARUS
Figure 5. Illustrative example of early arrhythmia detection by HM. Diamonds = cumulative duration of
mode switch expressed in % of time/24 hours (right vertical axis). Cumulative mode switch lasting longer than
programmed duration (>2.5 hours/24 hours) occurs on
04/24/06. Filled circles indicates the number of mode
switch episodes/24 hours (left vertical axis). CMDur =
cumulative duration of automatic mode switch. See text
for further explanations.
therapy were followed by no further event during subsequent follow-up. An example of early
detection of sustained ventricular tachycardia is
shown in Figure 6. The ventricular cycle length
fluctuates around the programmed tachycardia detection cut-off (400 ms). The event was reported
and confirmed remotely by examination of stored
electrograms transmitted by HM, along with the
alert. Atrioventricular dissociation was evident.
The episode was terminated by a single burst of
antitachycardia pacing (not shown). Figure 7 illustrates the early detection of a critical rise in pacing
impedance occurring within 24 hours after the last
normal measurement, consistent with ventricular
lead failure in the ICD recipient. The patient was
hospitalized in response to the alert, and further
impedance measurements remained out of range
until replacement of the fractured lead confirmed
roentgenographically.
Discussion
Main Study Findings
This is the first report of long-term, “real-life”
application of a new means of remote, day-to-day,
wireless, automatic monitoring of a large population of cardiac device recipients. While our analysis did not confirm a correlation between the transmission and the occurrence of events, and did not
examine the impact of HM on overall patient care,
it strongly suggests that it is a dependable new
method of surveillance of patients with a variety of implanted devices. The detection of asymp-
S8
tomatic adverse clinical events, anomalous device
behavior, or untoward interaction between devices
and their recipients by standard follow-up methods mandates either physical contact, or the establishment of an intermittent, deliberate communication, requiring active participation of both patients and caregivers. However, a growing patient
population, combined with increasing budgetary
constraints, are confronting the health care system
with staggering challenges with respect to the longterm surveillance of complex, device-based therapies. The early, automatic detection of undesirable
changes in delivery of ventricular resynchronization in nearly 50%, and inappropriate increase in
resting heart rate in nearly 1/4 of our population
with CRT-D devices, or of ineffective 30 J shock
or elective replacement indicator detection in a
small percentage of ICD recipients, prominently
illustrate the life-saving potential of HM. It is particularly noteworthy that the huge amount of data
acquired in this large population, followed for a
mean of 10.5 months, imposed a minimal putative
additional burden on the professional activities of
caregivers, since the warnings issued by HM were
limited to critical events partially defined by its
users. One might even hypothesize that it could
become a time- and resources-saving tool, as a proportion of systematic follow-ups recommended by
current practice guidelines could be replaced by
the information available remotely and automatically. There is, indeed, little medical value in the
one-time download of data stored in the memory
of a device, only to find that it is operating flawlessly. There is, on the other hand, considerable
return in the early, automatic detection of partial
or complete loss of ventricular resynchronization.
This hypothesis warrants to be examined in a controlled study.
Several recent incidents pertaining to the
long-term reliability of implanted devices have
positioned HM in a new perspective.2–4 The announcement of a potential device failure, albeit
rare, places both the caregivers and patients in
front of an unsettling situation. The economic and
emotional cost, and risk/benefit ratio of systematic
replacements are prohibitive, while a “wait-andsee” strategy is hardly acceptable to most. One of
the functions incorporated in HM, though not included in this report since its use would apply to
the specific concern of impending device failure,
consists of sending a warning when the system remains silent for a programmable period of time,
for any reason (e.g. separation of the patient from
the transmitter). This feature would allow the detection of rapid loss of function of an implanted
device. Thus, a day-to-day, automatic surveillance
of devices at risk, as enabled by HM, seems a
most attractive alternative, since it should detect as
January 2007, Supplement 1
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REMOTE MONITORING OF CARDIAC DEVICES
Figure 6. Illustrative example of early detection of successfully treated sustained ventricular
tachycardia (VT1 detected). Shown are the A (As) and V (Vs) marker chains with measurements of
respective consecutive cycle lengths (upper tracing) and corresponding ventricular electrograms
(lower tracing). See text for further explanations.
promptly as currently possible the small numbers
of actual device failures, eliminate the need to proceed with large numbers of unnecessary replacements, obviate the recommended acceleration of
follow-ups in huge patient populations,2 and provide patients with the highest level of reassurance
and comfort. However, the timely and appropriate
exploitation of the information offered by HM on
an ongoing basis requires new, dedicated resources
to support its activities.
Our analysis suggests that HM offers information that might allow the detection of adverse
events on average 2 and 5 months earlier than feasible by standard care in patients followed quarterly
and biannually, respectively. It is, however, noteworthy that, in this study of a population reflecting routine medical practice, HM had no impact on
the rate of formal follow-up visits. This might be
partially the product of a balance between shorter
follow-up intervals following an alert and a postponement of the next visit. The short intervisit intervals observed in the group of CRT-D recipients
was probably due to (1) the greater severity of disease of these patients, and (2) the more recent implantation of this kind of system, followed by a
first visit at 1 month after the procedure.
This study in the Context of Prior Related
Observations
HM has been the object of few earlier reports.
In a feasibility study, using the first implantable
device embedded with HM, Varma et al. examined
the reliability of the system in the United States,
PACE, Vol. 30
in 107 patients (22,356 scheduled transmissions)
with class I or II pacing indications.5 All transmissions were received within <10 hours, and >90%
within 4 minutes. In an analysis of a subgroup of
45 patients, a comparison of 4,200 variables transmitted by HM versus data stored by the pulse generator memory confirmed a 100% concordance. In
a European study of 43 patients, Stellbrink et al.
observed a 92% transmission success rate.6 The
time interval between pulse generator and delivery of 2,334 messages to the caregivers was <3
minutes in 97% of transmissions. The results of
a single study of the clinical applications of HM
in 271 patients with ICDs have been published
recently.7 Comparing the information yielded by
HM before a formal patient visit with that gathered
during the visit in over 1,000 follow-ups, the author developed a follow-up management scheme
suggesting that approximately 50% of encounters
could have been omitted. In a hypothetical analysis of the economic implications of eliminating up
to two visits per year over the 5 years of expected
life of an ICD, the decrease in costs for follow-up
visits was estimated at 2,149 dollars.8 Other studies are in progress to examine the potential clinical benefits of HM in various patient populations
and distinct disease entities and presentations.9,10
Their results, however, will probably not be known
for months or years.
A single report has been published describing the use of another remote monitoring system
in a small patient population of ICD recipients.11
Using standard telephone lines, large amounts of
January 2007, Supplement 1
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LAZARUS
Figure 7. Illustrative example of early detection of >3,000 rise in pacing impedance (bottom
panel). The last normal measurement was made on 09/15/2004. The report (top panel), accessible
on the Internet, highlights and details the triggering event, as well as recommends action (orange
highlight). See text for further explanations.
data stored in the devices’ memories can be transferred, including electrograms, that are accessible
by users on an Internet site. However, unlike HM,
the transmissions are neither automatic nor daily,
and require active patient participation. No system, including HM, currently allows the remote
reprogramming of implanted devices.
Potential Applications of HM
Medical Monitoring
HM was originally conceived as a tool to monitor the patients’ clinical status. As illustrated in
this analysis, the overwhelming majority of alerts
are disease-related, prompted by atrial fibrillation,
S10
ventricular arrhythmias, and ICD or CRT therapy,
in particular. With respect to atrial fibrillation, the
merit of the system is supported by the known
high rates of asymptomatic episodes, as high as
70% after successful cardioversion or ablation attempts.12–17 Early detection of asymptomatic atrial
fibrillation (a) facilitates the timely introduction of
protective interventions against thromboembolic
events, (b) limits inappropriate therapy delivery in
ICD recipients, and (c) anticipates adverse hemodynamic effects, notably loss of resynchronization,
in patients treated with CRT. In addition, dayto-day monitoring subsequently offers a reliable
means of confirming the success of rate or rhythm
January 2007, Supplement 1
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REMOTE MONITORING OF CARDIAC DEVICES
control. Furthermore, in ICD or CRT-D recipients,
HM enables (1) the systematic and remote evaluation of (a) ventricular tachyarrhythmias, (b) appropriateness of diagnosis and therapy delivery,
and (c) effectiveness of high energy shocks, and
(2) the correlation between perceived disease manifestations and presence versus absence of event
(e.g. absence of reported shock). The recent inclusion of stored electrograms in the HM message
has further enhanced its diagnostic power, particularly with respect to the confirmation of the
appropriateness of therapy delivery by ICDs. Finally, frequent aborted ICD shocks, with their consequences on battery charge, is another major adverse event in need of early detection to preserve
device longevity.
The potential benefits of telephone-based
monitoring in the management of patients suffering from chronic heart failure has been highlighted
in several publications.18–22 While the most reliable variables indicative of changes in patients’
clinical status have yet to be clearly defined, abnormal vital signs, including accelerated heart rate,
are simple predictors that have been identified
in prospective studies.23–25 However, further controlled investigations are warranted to confirm its
value in a broad-based patient population of device recipients.10
Monitoring of Device Function
In contrast to alerts emitted for disease-related
events, messages associated with changes in device function were relatively few. It is, however,
predictable that, in the long-term, an increasing
rate of alerts will be transmitted to warn of impending elective replacement indicator. Uncomplicated
battery depletion can be easily and safely identified by standard device surveillance, though mandates the shortening of follow-up intervals in order
to minimize the risk of patient exposure to an inactive device.2 This time- and resource-consuming
acceleration of the rate of ambulatory visits could
be obviated by remote daily monitoring. In addition, the detection of sudden unexpected battery
failure, a life-threatening emergency that is likely
to remain undetected until formal device interrogation, could be similarly diagnosed in a timely
fashion.
Study Limitations
The database utilized for this analysis included no systematic clinical information. There-
fore, no attempt was made to validate the clinical utility of HM or measure the adverse eventfree survival, and no conclusions could be drawn
with respect to the effects of HM on patient outcomes. A study is in progress to examine its impact on the long-term efficacy of antiarrhythmic
management in patients with atrial fibrillation.9
Furthermore, the workload imposed on caregivers
was estimated, instead of quantified on the basis
of a prospective data collection, and their response
to the information provided by HM could not be
assessed.
Since the events reported were not confirmed,
the rates of false positive events could not be
calculated. Similarly, this study was not designed
to measure the incidence of false negative information. However, a previous analysis in a small
group of ICD recipients reported a 14% rate of false
negative and 3% rate of false positive events over
a follow-up of 1 year.7 These results need to be
reassessed in prospective studies including larger
number of unselected recipients of state-of-the-art
devices.
HM is a patient- though not caregiver-independent system. Therefore, one might hypothesize that the day-to-day availability of information
provided by HM prompts diagnostic and therapeutic interventions that might have been otherwise omitted, perhaps unnecessary or harmful.
Although unlikely, this potential effect of remote
monitoring could only be properly studied in a
randomized controlled trial.
Conclusions
A new, powerful, remote, wireless, patientindependent monitoring system has been applied
in a large population of cardiac device recipients followed for up to 4 years. This experience suggests that the system, if intelligently
utilized, is capable of improving the care and enhance the safety of these patients, as well as optimize the allocation of human and financial health
resources.
Acknowledgments: Dr. Hans-Juergen Wildau, Biotronik
GmbH & Co. KG, was responsible for the design and development of HM, and for organizing the acquisition and management of the data, to which the author had access. The author
thanks Jacques Clementy, MD, University of Bordeaux, France,
for providing the records shown in Figures 6 and 7, and all
physicians who contributed to the database.
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