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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. S2 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 S3 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 January 2007, Supplement 1 PACE, Vol. 30 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. PACE, Vol. 30 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 S5 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 January 2007, Supplement 1 PACE, Vol. 30 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. PACE, Vol. 30 January 2007, Supplement 1 S7 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 PACE, Vol. 30 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 S9 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 PACE, Vol. 30 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. References 1. Gregoratos G, Abrams J, Epstein AE, Freedman RA, Hayes DL, Hiatky MA, Kerber RE, et al.. American College of Cardiology/American Heart Association Task Force on Practice Guidelines/North American Society for Pacing and Electrophysiol- PACE, Vol. 30 ogy Committee to Update the 1998 Pacemaker Guidelines. ACC/AHA/NASPE 2002 guideline update for implantation of cardiac pacemakers and antiarrhythmia devices: Summary article: A report of the American College of Cardiology/American Heart January 2007, Supplement 1 S11 LAZARUS 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. Association Task Force on Practice Guidelines (ACC/AHA/NASPE Committee to Update the 1998 Pacemaker Guidelines). Circulation 2002; 106:2145–2161. 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