The rate of implantable
cardioverter defibrillator (ICD) implantation has gone up as primary
and secondary prevention trials have relatively consistently shown
significant improvement in mortality and morbidity. Most patients with
ICDs are followed routinely at intervals ranging from 3 to 6 months.
Many patients require additional non-scheduled visits to investigate
symptoms that may or may not relate to their cardiac disease or device.
Appropriate and inappropriate therapies of implantable cardioverter
defibrillators have a major impact on morbidity and quality of life in
ICD recipients. Remote monitoring systems can substitute for routine
follow-up visits and/ or deliver continuous diagnostic and device
status information. Remote monitoring of ICDs can decrease the need for
many patient visits and, thereby, probably reduce expense.
Remote Monitoring
In the early
1970s, the concept of trans telephonic monitoring (TTM) was introduced
to monitor the longevity of pacemakers
1.
This modality was identified as a useful method for tracking the basic
function of pacemaker systems; particularly in the early era of
pacemaker development when both lead and pulse generator longevities
were unpredictable. In the late 1970s and 1980s, the usefulness of TTM
as a diagnostic tool expanded to other problems including sensing,
capture, lead malfunction, and arrhythmias. As the sophistication of
pacemakers increased, the modes of follow up also inevitably
changed. Most pacemaker manufacturers now have systems in place that
facilitate remote pacemaker follow-up. Transmissions can be made
totally trans-telephonically or, more recently, by using web-based
networks. Implanted devices can be interrogated by using easy-to-use
equipment in patients' homes (or elsewhere) that communicates stored
and real-time information trans-telephonically to a secure server where
the data are available to the pacemaker/heart rhythm professional.
Just as for
pacemakers, there are currently several systems either available or in
development for the remote interrogation and monitoring of ICDs. Each
system can only be used with devices manufactured by the same company.
Cardiomessenger & Home Monitoring
from Biotronik uses diagnostic data transmitted from pacemakers, ICDs
and heart failure devices to a mobile phone-like unit, then, in turn
via cellular phone network, to a secure, remote monitoring center, and
then further forwarded on to patients' clinical teams. Data is
generated and transmitted at set times, following an event, or with
patient-triggering. Similar in concept,
CareLink from Medtronic,
Housecall Plus from St. Jude
Medical, and
Latitude from
Boston Scientific/Guidant are remote monitoring systems that use
standard telephone lines to communicate with clinicians and/or secure
computer servers which can be accessed by clinicians. Depending on the
system, comprehensive device information including electrograms can be
collected from the implanted device and transmitted and stored for
clinician access and use.
Usefulness
By diminishing
the frequency of clinic visits, remote monitoring may reduce health
care costs and patients' inconvenience. Diagnostic data from devices
such as the numbers of aborted and delivered ICD therapies are an
indicator of the total incidence of tachyarrhythmia. Frequently
recurring episodes of ventricular tachyarrhythmias in patients may
indicate increasing instability and progression of cardiac disease
2. Inappropriate ICD therapy, typically
related to sinus tachycardia or other superventricular tachycardia can
be elucidated remotely as well as in clinic
3.
In one study, 59 patients completed 119 transmissions. Clinician review
of data transmissions revealed several clinically significant findings,
including silent AF discovery, assessment of antiarrhythmic drug
efficacy in a previously diagnosed AF patient, previously unobserved
atrial undersensing, and ventricular tachycardia. Clinicians were
satisfied with the performance of the network and the quality of the
web-accessed data, and found it comparable to an in-office device
interrogation
4. In
another prospective evaluation, 124 patients with single chamber ICDs
were monitored by remote interrogation and monitoring for a total of
570 transmissions. The investigators demonstrated a high degree
of patient satisfaction with the convenience and ease of use of remote
ICD monitoring
5.
Intracardiac electrograms (IEGMs) stored in the ICD can be essential
for differentiating appropriate and inappropriate ICD therapies. High
quality IEGMs are increasingly available with implanted devices and the
remote monitoring systems. Validation of adequacy of remotely
acquired IEGMs is under study
6
Remote
monitoring can be especially useful for monitoring patients with CRT-D
devices. A prospective, longitudinal, multicenter home monitoring trial
was conducted in 123 patients with clinical indications for CRT. In a
mean follow-up period of 3 months, 11 unplanned re-hospitalizations for
cardiovascular causes and 9 deaths occurred. In 70% of the
re-hospitalization events, the retrospective analysis of remotely
acquired data revealed an increase in mean heart rate at rest and in
mean heart rate over 24 h within 7 days preceding hospitalization.
These interim findings suggest that remotely acquired data may predict
events leading to hospitalization and encourage further research
7. Other implantable devices using
transthoracic impedance sensing in ICDs, and RV pressure parameter
monitoring have been used with remote monitoring to assist in caring
for patients with heart failure.
An important
and untapped potential utility for remotely monitored devices in which
data is collected in large databases involves the capacity to predict
device performance problems.
Cost Effectiveness
In a cost
effectiveness study conducted among 502 patients, costs of conventional
follow-up of ICDs were calculated without and compared with the
expected cost of follow up with remote monitoring. It was concluded
that the remote monitoring may considerably reduce the overall costs of
ICD follow up by saving on transportation cost, particularly when the
distance between home and medical facility is >100 km
8. Patient satisfaction with the
convenience and reliability of the remote monitoring system ranged from
93 to 97% in SF-36 surveys
9
Conclusion
Remote
interrogation provides frequent, convenient, safe and comprehensive
monitoring of ICDs. Device and patient related problems can be reliably
detected and reduce the frequency of outpatient visits. Patients are
highly satisfied with the convenience and ease of use of the systems.
Surveillance of device performance is a potentially important future
capability. In the future an exponential growth in implementation of
remote monitoring is likely to occur in the field of implanted devices
including ICDs, pacemakers, and implantable disease monitors.
