Evolution of Technology to Meet the Need
Haran Burri
Nicolas Dayal
KEY POINTS
Remote cardiovascular implantable electronic device (CIED) monitoring has evolved from transtelephonic electrocardiographic monitoring of pacemakers (PMs) in the 1970s to automatic wireless full device data transmission launched by Biotronik in 2001.
All major CIED companies currently offer remote device management.
Opportunities offered by remote device management, other than fewer in-office visits and shorter delays to actionable events, are online data processing, integration of device data with hospital electronic health records, and tracking of product performance.
Some challenges remain, such as battery consumption and cybersecurity.
Low-energy Bluetooth technology dispenses of the requirement for a dedicated transmitter by using the patient’s cellphone for this purpose. There are several advantages, such as reductions in cost for industries and empowerment of the patient who has access to data on an app, and also potential concerns regarding energy consumption, security, reliability, and increased workload resulting from more patient-initiated transmissions.
INTRODUCTION
This chapter deals with the technical aspects of remote surveillance of patients with cardiovascular implantable electronic devices (CIEDs). Currently, these include pacemakers (PMs), implantable cardioverter-defibrillators (ICDs), cardiac resynchronization therapy (CRT) devices, implantable loop recorders (ILRs), and implantable cardiac monitors (ICMs).1
Remote surveillance of CIEDs in general involves the transmission of data from the patient’s location over a network via a central database to a hospital or physician’s office. The data include functional status of the device, device-monitored patient variables, and sometimes additional disease-related data collected by the
patient or caregiver.2 The general goals are to reduce the number of time-consuming office visits and to increase the speed of action in case of abnormal device function or patient status.
patient or caregiver.2 The general goals are to reduce the number of time-consuming office visits and to increase the speed of action in case of abnormal device function or patient status.
DEFINITIONS
When dealing with remote management of CIEDs, a review of the medical literature exposes a certain lack of standardization, with a variety of terms used to describe different aspects of the technology.3 To avoid confusion, the International Society for Holter and Noninvasive Electrocardiology (ISHNE) and the European Heart Rhythm Association (EHRA) published a consensus paper clarifying the different terminologies of remote management4:
Remote follow-up involves programmed scheduled device interrogation and transmission from home, enabling data collection similar to in-office visits (eg, battery status, thresholds, and sensing). The interrogations can be performed either automatically in patients implanted with modern wireless devices or manually using induction technology-wanded home transmitters.
Remote monitoring (RM) involves automatic unscheduled transmission of prespecified alert events (eg, atrial arrhythmias and abnormal lead impedance). It is a continuous form of surveillance, does not require any patient collaboration (apart from setting up the device), and is only possible in modern wireless devices.
Patient-initiated interrogations are nonscheduled follow-ups initiated manually by the patient as a result of a real or perceived clinical event. The interrogation can be made either wirelessly or using induction.
HISTORY OF REMOTE MANAGEMENT TECHNOLOGY FOR CARDIOVASCULAR IMPLANTABLE ELECTRONIC DEVICE
Pacemakers and Transtelephonic Transmission
The concept of remote management of CIEDs was born in the early 1970s.5 At that time, the transition from zinc-mercuric oxide to lithium iodide batteries thanks to Wilson Greatbatch in 19726 prolonged the longevity of CIEDs and reduced the risk of very premature battery depletion (weeks or months) of earlier models.7 Nevertheless, the longevity of PMs was still considerably less than today, with up to 50% of PMs being explanted for battery failures within 4 years.8,9 This was a significant problem, causing 83% of all PM failures.10 Under these circumstances, follow-up of PMs had to be undertaken very frequently, with a recommended visit every 2 months for the first 6 months after implantation, then shortening of the intervals to once a month until the 18th or 24th month when weekly office visits were recommended until battery depletion. This could mean between 30 and 60 in-office visits for a PM with a mean battery duration of 28 months! This reality led to the development of transtelephonic monitoring (TTM) of CIEDs by Furman and his colleagues in order to reduce the burden of in-office visits.
The earliest and simplest approach to TTM was to provide RM of the paced heart rate to analyze battery level. Once the first battery cell was depleted, there was a sharp drop in PM rate, thus signifying impending battery failure (Figure 1.1). For heart rate analysis of TTM to work, the PM had to be equipped with a magnetic switch to convert to an asynchronous mode upon application of a magnet or for pacing stimuli to be frequent enough to analyze rate. This system did not allow verification of ventricular capture.
 FIGURE 1.1 Chart of heart rate (y-axis, beats per minute) plotted against time (x-axis, months from implant) from a patient followed by transtelephonic monitoring. Beginning of battery depletion is illustrated by declining heart rate, then pacemaker end-of-life is signified by a rapid rate drop of around 7 beats/min in 1 week (arrow). The pacemaker was replaced during the 35th month of operation. Reproduced with permission from Furman S, Escher DJ. Transtelephone pacemaker monitoring: five years later. Ann Thorac Surg. 1975;20:326-338. |
The first technique that allowed remote determination of ventricular capture was digital plethysmography, which was coupled to rate analysis. However, the technique had obvious flaws, with substantial false-positive and false-negative rates (even though no statistical analysis was published), and was replaced by electrocardiographic (ECG) monitoring. The technology used a base carrier frequency that was then modulated by the ECG, providing a tone that wavered acoustically coupled to a telephone. The reconstructed tracings allowed analysis of PM capture and sensing.
Although the advent of TTM ECG was a huge advance in the follow-up of CIED patients, the system had its flaws. First, the use of a single-lead system, usually lead I, raised the possibility of an isoelectric or microvolt signal that was insufficient for diagnostic purposes. Second, telephone noise linked either to continuous interference or to electrical transients frequently caused artifacts, although they were easily recognizable. Other sources of artifacts were motion, accidental movement of the magnet, and respiration.
Obviously, the sporadic nature of TTM meant that intermittent PM dysfunction could be missed.
A few years after the implementation of TTM and spurred by the advent of automatic sensing and capture check within a PM circuit,11 Federico et al described the addition of a logic circuit to a TTM receiver featuring ECG analysis,7 thus allowing automatic evaluation of PM sensing and capture, and providing this information to the patient via colored lights (Figure 1.2). With this system, the patient could verify
the correct PM function in between office visits and contact his/her physician while transmitting their ECG in case of malfunction.
the correct PM function in between office visits and contact his/her physician while transmitting their ECG in case of malfunction.
 FIGURE 1.2 Transtelephonic monitoring device with self-check functionality. (A) Watch-band electrodes for electrocardiogram. (B) On-off switch. (C) Lead connectors. (D) Green light. (E) Yellow light. (F) Battery compartment. (G) Speaker compartment of telephone transmitter. (H) Hidden switch to check on adequacy of QRS detection. Reproduced with permission from Federico AJ, Giori F, Bhayana JN, et al. Instrumentation for the follow-up of pacemaker patients. Telephone transmission of the electrocardiogram and self-check by the patient on pacemaker function and capture. Pacing Clin Electrophysiol. 1979;2:315-324. |
One limitation was that the device was dependent on the reliable presence of ventricular capture and absence of fusion or functional noncapture during magnet application, and thus worked best with PMs programmed with a high magnet rate of 100 beats/min.
In the initial 5-year experience of Dr Furman from 1969 to 1974, 619 patients were followed up, with 280 battery failures detected before complete end-of-life or symptoms. Of these, there was a 0.7% rate of errors concerning only two patients, one because of failure of recognition of lack of capture during rate-only monitoring, and the other linked to intermittent lack of capture outside of the periods of TTM transmission.12 In a later study of TTM performance among 269 patients, this technique was found to have a sensitivity of 94.6% and a specificity of 98.5% in diagnosing PM malfunction.13
The PM has evolved from a device providing basic heart rate support to one offering a myriad of diagnostic information. TTM technology does not allow remote access to all these data, which is therefore only available during in-office visits (ie, 1-2 times/y for PMs). The need for more advanced remote management tools has become evident in order to access all these data. Transmitters with wands that allow patient-initiated full device interrogation followed by PMs with wireless technology allowing automatic transmission resulted in TTM becoming obsolete.
IMPLANTABLE CARDIOVERTER-DEFIBRILLATOR DEVELOPMENT AND THE ADVENT OF REMOTE FOLLOW-UP AND MONITORING
Although TTM has proven to be a reliable and useful tool in the management of PM patients, its utility in the follow-up of ICD patients is reduced in its basic form: many of these patients do not require bradycardia support, and the main function of the ICD, that is, diagnosing and treating life-threatening arrhythmias, cannot be evaluated with basic TTM. Thus, the transfer of remote surveillance to ICDs was delayed until more sophisticated forms of remote management were developed.
The exponential growth in ICD population following the publication of the landmark primary and secondary prevention trials14,15,16 drastically increased the workload of physicians and CIED clinics, especially as ICD follow-up was initially
recommended every 3 months before automatic capacitor reformation was implemented in these devices. Even after implementation of this technology, follow-up is still recommended every 3-6 months according to the HRS/EHRA guidelines,1 mainly because of the high risk of clinical events and system dysfunction in ICD recipients. The advent of ICDs coupled with CRT brought along devices capable of providing a large amount of clinically relevant data to aid heart failure management (atrial and ventricular arrhythmia burden, biventricular pacing rates, transthoracic impedance measurement, etc), increasing the demand for remote management even more. The nonnegligible burden of device and/or lead dysfunction in this population, along with increasingly sophisticated algorithms allowing timely diagnosis and action in case of dysfunction, augmented the value of remote follow-up significantly. Finally, the search for more cost-effective solutions to follow-up ICD patients also drove the development of remote management.
recommended every 3 months before automatic capacitor reformation was implemented in these devices. Even after implementation of this technology, follow-up is still recommended every 3-6 months according to the HRS/EHRA guidelines,1 mainly because of the high risk of clinical events and system dysfunction in ICD recipients. The advent of ICDs coupled with CRT brought along devices capable of providing a large amount of clinically relevant data to aid heart failure management (atrial and ventricular arrhythmia burden, biventricular pacing rates, transthoracic impedance measurement, etc), increasing the demand for remote management even more. The nonnegligible burden of device and/or lead dysfunction in this population, along with increasingly sophisticated algorithms allowing timely diagnosis and action in case of dysfunction, augmented the value of remote follow-up significantly. Finally, the search for more cost-effective solutions to follow-up ICD patients also drove the development of remote management.
All these aspects, coupled with the fact that only a small proportion (<10%) of in-office visits lead to a specific course of action (reprogramming, medication change, or system revision)17 and that remote surveillance can potentially diagnose 99.5% of arrhythmia- or device-related issues, have made the development of remote management an important goal in CIED development.18
Perhaps the first application of remote management in ICDs was the use of event recorders coupled with a remote transmission device in ICD patients.19 The aim was to provide the physician with ECG documentation of rhythm before ICD discharge, as most ICDs did not feature electrogram (EGM) storage facilities. Several studies evaluated this basic technology, either in patients newly implanted with ICDs20 or in those who had recently experienced an ICD discharge.21 The patients had to manually “capture” the stored rhythm corresponding to the ICD discharge and remotely transmit it to their health care providers. Interestingly, the results from the study of Porterfield et al illustrated the high rate of patient-perceived events in this population, as the 20 patients initiated 54 transmissions in a 2.5-month period, with only 9 of them corresponding to ICD discharges and almost half for symptoms not associated with arrhythmias. This study also exposed another limitation of a fully patient-initiated monitoring system: 5 of the 20 patients had received ICD discharges unknown to them.
Another early application of remote surveillance was linked to a safety condition concerning premature capacitor failure of the original Ventritex Cadence V-100 ICD. The rudimentary system that was provided effectively only reported battery voltage, but was deemed extremely useful in preventing morbidity linked to the safety condition, and this proved that remote follow-up of ICDs could be undertaken.22
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