Europace Advance Access originally published online on April 22, 2008
Europace 2008 10(6):729-735; doi:10.1093/europace/eun099
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ICDs
Automatic home monitoring of implantable cardioverter defibrillators
1 Cardiology Department, Heart Center, University of Leipzig, Leipzig, Germany; 2 Department of Cardiology B, Skejby Hospital, Brendstrupgaardsvej, DK-8200 Aarhus N, Denmark; 3 Department of Cardiology and Pneumology, Heart Center, Goettingen, Germany; 4 CHU de Nancy Brabois, Vandoeuvre les Nancy, Nancy, France; 5 Cardiology Department, Carl-Thiem Clinic, Cottbus, Germany; 6 Clinic for Internal Medicine III, Department of Cardiology, Angiology and Pneumology, University Clinic Heidelberg, Germany; 7 Friedrich-Ebert-Hospital, Neumuenster, Germany; 8 Cardiology Department, Center of Cardiovascular Medicine, Bad Neustadt, Germany; 9 Cardiology Department, Medical University Vienna, Austria; 10 Service de Cardiologie E, Hopital Cardiologique du Haut-Leveque, Pessac, France; 11 Center for Clinical Research and Scientific Studies, Biotronik GmbH & Co. KG, Erlangen, Germany
Manuscript submitted 12 January 2008. Accepted after revision 24 March 2008.
* Corresponding author. Tel: +45 89 49 55 66; fax: +45 89 49 60 02.E-mail address: cosedis{at}dadlnet.dk
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Abstract |
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Aims: With the expanding indications for implantable cardioverter defibrillator (ICD) and reports of unexpected ICD failures, home monitoring (HM) was proposed to decrease follow-up workload and increase patient safety. Home monitoring implantable cardioverter defibrillators offer wireless, everyday transfer of ICD status and therapy data to a central HM Service Center, which notifies the attending physician of relevant HM events. We evaluated functionality and safety of HM ICDs.
Methods and results: A total of 260 patients with HM ICDs were monitored for a mean of 10 ± 5 months. Time to HM events [medical (ventricular tachycardia/ventricular fibrillation) and technical (ICD system integrity)] since ICD implantation and since the latest in-clinic follow-up was analysed. Mean number of HM events per 100 patients per day was calculated, without and with a 2-day blanking period for re-notifying the same type of event. About 41.2% of the patients had HM events (38.1% medical, 0.8% technical, and 2.3% both types). Probability of any HM event after 1.5 years was 0.50 (95% confidence interval: 0.42–0.58). More than 60% of new HM event types occurred within the first month after follow-up. A mean of 0.86 event notifications was received per 100 patients per day or 0.45 with the 2-day blanking period.
Conclusion: Home monitoring is feasible and associated with an early detection of medical and technical events.
Key Words: Implantable cardioverter defibrillator, Fibrillation, Defibrillation, Tachycardia, Follow-up, Home monitoring
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Introduction |
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Several new indications for the implantable cardioverter defibrillator (ICD) have been established in recent years.1
–6 If all patients eligible for ICD implantation actually receive them, the cardiology workforce performing ICD controls will face massive additional workload with insufficient resources.7 Moreover, unexpected ICD failures because of electronic or lead defects remain to be a serious and potentially fatal problem.8–13
Remote ICD monitoring concept has been proposed to optimize medical management of the patients and to decrease the follow-up workload.14,15 Implantable cardioverter defibrillator devices should be empowered to remotely alert the referring clinic to the impaired functional integrity of the implanted system as well as to key arrhythmic and therapeutic events. To avoid setbacks because of incompliance, patients should preferably play no active role in the monitoring process.
Implantable cardioverter defibrillator devices with an integrated home monitoring (HM) capability were introduced in 2001. The HM ICDs enable wireless, everyday transfer of the essential status and ICD therapy data to a central HM Service Center. An automated analysis of HM data is performed there to identify important technical and medical events and to generate the corresponding ‘event notifications’ for delivery to the referring clinics per SMS, e-mail, fax, or combined. Despite the clinical application of HM ICDs for more than 6 years, little has been published to date. The aim of the present study was to analyse and present our experience with HM technology in a cohort of 260 ICD patients.
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Methods |
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Patient population
We analysed HM messages in patients prospectively enrolled in a Belos-T Registry. To be enrolled in this registry, the patient had to have an ICD indication and be judged as capable of keeping the CardioMessenger® device operational by appropriate device positioning, as will be described in the following sections. Exclusion criteria were HM use over a period of less than 3 months or pause in the HM coverage longer than 30 consecutive days. The patients underwent regular in-clinic ICD follow-up visits every 3–6 months. All patients had given informed consent for the HM use before this feature was activated.
Home monitoring technology
The physician could activate or deactivate the HM function at any time after implantation of a dual-chamber ICD (Belos DR-T or Lexos DR-T, Biotronik, Berlin, Germany) or their single-chamber counterparts (Belos VR-T or Lexos VR-T, Biotronik, Berlin, Germany). A cell-phone-like device named CardioMessenger (Biotronik, Berlin, Germany) was assigned to each patient. Every day at a time preset by the physician, the ICD attempts automatic wireless transmission of therapy and status data to the CardioMessenger, which has to be located <2 m away from the ICD. The recommended transmission time is 2:00 a.m., when the patient is supposed to be in bed, with the CardioMessenger placed at the patient’s bedside cabinet. To raise the probability of data capture by the CardioMessenger, ICD repeats data transmission at 1.5, 3.0, and 4.5 h after the assigned time. The CardioMessenger relays captured ICD data in the form of encrypted SMS via mobile phone links to the Biotronik HM Service Center in Berlin, where HM messages incoming from all countries are archived and decoded. Patients are not required to actively support data transfer, except for keeping the CardioMessenger in the vicinity of their beds during the night, placed in a console that allows recharging of the CardioMessenger battery.
An automated analysis of HM messages is performed in the HM Service Center to recognize events listed in Table 1 and promptly send succinct statements, called event notifications, to the attending physicians. Several event notification types are related to lead defects that can jeopardize patient safety.1,8–13 Other technical events alert to impending battery depletion or impaired device functionality for other reasons, such may be deactivated therapy delivery because of exposure to electromagnetic interference or prior to elective surgery or catheter ablation, with subsequent failure to reactivate the device.12 Medical events are related to major arrhythmia recurrences (Table 1). In dual-chamber ICDs, supraventricular tachycardia can be differentiated from ventricular tachyarrhythmia by the SMART algorithm.16,17 Atrial arrhythmias associated with normal ventricular rhythm are not indicated in HM messages generated by ICDs.
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The system is devised to preserve information pertinent to event notifications irrespective of the number of ICD messages failing to reach the HM Service Center. This is achieved by automated comparison of the cumulative ICD counters of arrhythmic and therapeutic episodes in the incoming and the previously received messages for the given patient.
Implantable cardioverter defibrillators can instantaneously alert ventricular tachyarrhythmia or abnormal shock coil impedance by sending unscheduled HM messages (Table 1). They basically duplicate the information from regular HM messages but may disclose events some hours earlier. The latest ICD follow-up control date (i.e. ICD programmer head application) is included in all HM messages.
Using the allotted username and password, the physician can access the HM Service Center website to allow or disallow generation of event notifications unrelated to device status and to redefine the method of event notification delivery to him/her (e-mail, fax, or/and SMS). House monitoring data for own patients can be reviewed in greater detail online, including the number of tachyarrhythmia episodes and delivered, successful or aborted anti-tachycardia pacing sequences or shock therapies, lead impedance values, battery voltage, and percentage of pacing in any chamber. The values can also be displayed as trends over several months.
Data evaluation
To determine the occurrence of HM events from Table 1, we evaluated the data in the HM Service Center database for the 260 Belos-T Registry patients who met the inclusion/exclusion criteria for the current analysis. Time of HM activation and time to HM event notifications since ICD implantation and since the ICD follow-up control preceding the event were studied. It was assumed that the date of an HM event was the date of the HM message disclosing the event. Duplicative notifications of the same HM event were eliminated.
In order to evaluate the time to detect a new clinical problem, we calculated temporal distribution of new HM events since previous ICD follow-up control. Recurrences of the same HM event type were eliminated before the next patient visit to the ICD follow-up clinic. To calculate normalized distribution, we divided the number of HM events during the given week since the last ICD follow-up by the total number of HM events.
The mean number of HM event notifications per 100 patients per day was calculated, without and with a blanking period of 2 days for the same type of event since its latest notification. We computed the approximate latency of an event capture in the HM Service Center (the time between an HM event and its disclosure to the HM Service Center) as the time interval between the HM message revealing an event and the immediately preceding event-free HM message, divided by two, to follow the probability law for events distribution between successive HM messages.
The number of unplanned in-clinic ICD follow-up visits within the first year after ICD implantation was recorded. For each unplanned visit, we determined whether it was initiated by an HM event or not.
The HM Service Center database for the Belos-T Registry is the property of Biotronik. The analysis of data was done by Biotronik (D.D.) in cooperation with the first author.
Statistical methods
Unless stated otherwise, study results are presented as mean ± standard deviation for normally distributed values or as median and inter-quartile range for non-normal distributions. Cumulative probability for a patient to have any HM event, a ventricular fibrillation (VF) event or a ventricular tachycardia (VT) event was computed according to the Kaplan–Meier method, and the relative risk with 95% confidence intervals (CIs) was calculated using the Cox regression models. We also performed the Cox regression analysis to study the predictive value of the following baseline parameters for the occurrence of any HM event type: gender, age, history of atrial fibrillation or flutter, history of coronary heart disease, New York Heart Association (NYHA) functional class, indication for ICD (VF, VT, and prophylactic), and implantation of single- or dual-chamber ICD.
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Patient characteristics at baseline
One-hundred and seventy-eight (68%) patients received a single-chamber ICD and 82 (32%) patients a dual-chamber ICD. The mean age was 64 ± 12 years (range: 21–85 years) and 82% were male. Indication for ICD implantation was VF (29%), sustained VT (53%), and prophylactic use (18%). One-quarter of the patients had a history of atrial fibrillation or atrial flutter, 7% exhibited bradyarrhythmia, and 3% had left bundle branch block. History of coronary artery disease was reported in 53%, hypertension in 20%, and diabetes in 17% of the patients. The mean ejection fraction recorded in 74% of the patients was 37 ± 15% (range: 10–84%). The NYHA class was reported in two-thirds of patients, of whom 8% had class I, 68% class II, 22% class III, and 2% class IV.
Home monitoring data
The HM Service Center received a total of 74 778 messages from the 260 patients who were monitored remotely for 80 082 days or, on average, 10.1 months per patient. At least, one HM event occurred in 41.2% of the patients. The vast majority of HM events were medical events (Table 2). The incidence of different HM event types and their temporal distance from the latest ICD follow-up control are shown in Table 3. For instance, VF affected 25.4% of the patients and recurred at a median of 15 days after the previous follow-up control. Division of VT into VT zones 1 and 2 was disregarded. Technical HM events included invalid shock coil impedance in three patients, invalid ventricular lead impedance in five patients, and special implant status in one patient (deactivation of VF detection).
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The distribution of HM events during the follow-up period is illustrated in Figure 1. Most new HM events were detected early between two standard clinical visits: more than 30% of the events occurred within the first week and more than 60% during the first month after the previous follow-up control (Figure 1, lower panel). A mean of 0.86 event notifications was generated per 100 patients per day, or 0.45 per 100 patients per day if the 2-day blanking period was used for notifying the same type of event after its latest notification. Probability of having any HM event after 1.5 years was 0.50, with a 95% CI of 0.42–0.58 (Figure 2A). The risk of a VF HM event and a VT HM event was 0.35 (95% CI: 0.27–0.46) and 0.26 (95% CI: 0.21–0.33), respectively (Figure 2). The mean and median approximated times between an HM event and its disclosure to the HM Service Center were computed to be 22 and 12 h, respectively. Using the univariate analysis, none of the evaluated baseline parameters was predictive of any HM event during follow-up (P > 0.1 for all).
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There were 54 unplanned in-clinic ICD follow-up visits within the first year in 47 patients. Fourteen (26%) of the visits were initiated by a HM message. Three patients died from advanced heart failure at 118, 276, and 420 days after ICD implantation.
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Discussion |
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Early detection of relevant events by home monitoring
Home monitoring is feasible and allows individualized therapy control by shortening physicians’ reaction time to arrhythmias and technical problems. In standard clinical practice, ICD patients undergo regular follow-up every 3–6 months. The majority of important HM events occur within the first month after a follow-up visit (Figure 1).18
Although HM is aimed at early detection of key clinical events, it is not an emergency system. We calculated the median approximate time duration between event occurrence and physician notification to be 12 h.19 Comparison with the values measured or interrogated using an ICD programmer raised no concerns with respect to the HM data accuracy.20,21 No risks seem to be imposed to the patient by the surveillance process.22
Defibrillation leads are the most vulnerable components of ICD systems. Some models have a failure rate of up to 38% after 8 years.8–13 Abnormal lead impedance trends may reflect lead degradation several weeks before the clinical presentation of lead failure.23,24 Atrial and ventricular pacing impedances and the shock coil impedance are among technical events in Table 1. Several cases of potentially lethal lead problems detected by HM data are described in the literatures.23,25,26 As pacing and sensing thresholds are not monitored remotely, standard ICD follow-up scheduling is indispensable during post-operative lead maturation. In the present study, deactivated detection of VF was reported in one patient.12,13 As our data refer to the initial follow-up years, no impending ICD battery depletion was encountered. A study group that followed their 87 HM ICD patients for a mean of 17 ± 14 months received the appropriate elective replacement event notification in two patients after a mean of 45 months of ICD implantation.27
Home monitoring data allow us to monitor the frequency of arrhythmic events and therapeutic outcomes. Benefits reported to date include the discovery of clinically relevant but minimally symptomatic incessant VT in several cases; detection of inadequate shock and anti-tachycardia pacing therapies because of sinus tachycardia; supraventricular tachycardia or T-wave over-sensing; tracking of the episodes of recurrent slow VT, which were in some cases eliminated by modified drug therapy or catheter ablation; unfolding pro-arrhythmic effects of medications; and reassuring concerned patients that no VT or VF therapy was delivered.20,21,28–33 These exceptional situations frequently required an additional clinical follow-up visit to change drug therapy or reprogram the ICD, whereas the outcome could be followed remotely using HM.29,31 In the present study, 39% of the patients had a ventricular tachyarrhythmia episode reported by HM, whereas 58.8% were free of any HM event.
Home monitoring influence on the implantable cardioverter defibrillator follow-up burden and costs
Home monitoring bears the potential to reduce the need for routine in-clinic ICD follow-up, in which the majority of cases reveal no need for interference,34 but cumulatively require significant personal and financial resources. The current practice of regular ICD controls has to be reconsidered in view of the growing ICD population.2,7,35,36 Remote access to the most relevant ICD data will probably allow extension of 3–6-month intervals between routine in-clinic controls to 12-month intervals. Reducing the expenditure for uneventful regular controls in patients with stable clinical conditions can spare more resources to treat patients with a high arrhythmic burden or technical problems. The goal is to use HM data as a triage tool for an individualized follow-up schedule that would improve management of arrhythmia patients, but containing health costs and workload for cardiologists.28,36–40
Although longer intervals between routine in-clinic follow-up visits spare resources, reviewing HM messages on the Internet or in the fax form and combining these data with patient files is time-consuming. According to the experience of the Heart Center in Leipzig, the physician needs 5 min on average to evaluate an HM event notification and to decide on the consequence for the patient. The reception of a mean of 0.86 event notifications per 100 HM ICD patients per day thus corresponds to a total of 26 working hours per year. If a blanking period of 2 days is used for notifying the same type of event after its latest notification, only 0.45 HM messages per 100 patients per day would require 14 working hours per year. Such blanking period is clinically reasonable for ICD patients with frequent recurrent episodes of supraventricular tachycardia or slow, well-tolerated VT and may be used in all patients to save physicians working hours with the cost of <2-day delay in re-notification of HM events. In the present study, HM messages led to a minor increase in the number of unscheduled in-clinic follow-up visits.
The economic consequences of the use of HM remain to be scrutinized. The therapeutic outcome as well as patient satisfaction and quality of life with HM have to be evaluated in randomized trials before generally extending the intervals between in-clinic follow-up visits. Many ICD patients have a significant heart disease requiring medical treatment and regular evaluation by a cardiologist.
Several ongoing studies, including remote follow-up for ICD-therapy in patients meeting MADIT II criteria (REFORM)38,39 initiated in January 2004 and influence of home monitoring on the clinical status of heart failure patients (IN-TIME)41 started in July 2007, to investigate whether HM data reduce the follow-up burden and associated costs, while improving clinical outcome and quality of life of the patients in comparison with the standard ICD follow-up scheme. According to the preliminary REFORM findings, all HM-induced follow-ups were highly effective.38 The concept of ‘evaluation of visit necessity using HM data’ allows a saving of 712
per patient and year when regular 3-month controls without HM are replaced by 12-month visits or shorter follow-up intervals if HM data indicate the need for this.38 The number of visits was reduced by 63.2%, where a 3.9% increase in visits through HM-induced effects and a 7.9% increase through patient-initiated visits were subtracted from the initial reduction of 75% through protocol-related effects. As no significant difference in patients’ hospitalization and mortality was seen between the two arms, Elsner et al.38 interpreted the overall results as a preliminary proof of a high cost-effectiveness of HM for at least equal quality of care.
Rapidly evolving home monitoring features
The recent Home CARE study has indicated that HM has a potential for detecting clinical changes, predicting unplanned hospitalization,42 and atrial fibrillation increasing the risk of stroke.43
To enable the physician to judge on the appropriateness of ICD discharges, the intracardiac electrogram strips are included in HM messages of newer generation ICDs.44–46 The latter also offer an array of new event notifications that may be enabled, disabled, or adjusted regarding their cut-off values, and include: atrial and ventricular sensing amplitudes below a programmable limit (e.g. <0.5 and <2 mV, respectively), daily shock lead impedance outside a pre-specified range, and various events related to individual ventricular arrhythmia episodes (unsuccessful or long-period anti-tachycardia pacing, an episode with acceleration of ventricular rhythm, an episode with multiple started shocks, etc.). As sudden malfunction of ICDs due to component failure may occur and is life-threatening,12,13,47,48 a dedicated HM event has been introduced to alert to the interruption of HM transmission for a period longer than 2 weeks. A significant increase in pacing threshold and more than six aborted ICD shocks are potential new types of HM events for the future. Biventricular ICDs additionally send notifications of too high mean heart rate at rest (e.g. >90 bpm), too high mean ventricular rate, excessive number of ventricular extrasystoles per hour (e.g. >50), a low percentage of left ventricular pacing (e.g. <80%), and high atrial arrhythmia burden (e.g. >25%).
However, it must be kept in mind that the inclusion of more ICD data in HM messages and broadening of event notification types will result in additional burden to the physician, nursing, and technical personnel. Furthermore, at the dawn of the era of evolving medical records, there are appeals to establish common approaches to transmission and storage of data generated by ICDs of different manufacturers.35,44
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Study limitations |
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This study was retrospective in nature, with all of its inherent limitations. Patient characteristics at baseline data were incomplete. We were merely able to present the maximum possible number of HM event notifications that could be generated in the HM Service Center based on remotely attained ICD data. The number of HM event notifications that were actually sent to the referring clinics is low because of the opportunity to deactivate undesired notifications and occasional embracing of multiple concomitant HM events in a single notification. Owing to a lack of systematic information, we were not able to describe measures undertaken by the physicians in response to HM event notifications.
The patients included in this analysis were selected on the basis of their ability to perform HM, and therefore the data cannot necessarily be extrapolated to all patients with an implantable defibrillator.
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Conclusion |
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Home monitoring allows an early detection of medical and technical events in ICD patients. It may improve an individualized therapy control and shorten physicians’ reaction time to arrhythmias and technical problems. Studies investigating whether HM may reduce the burden of regular ICD follow-up and decrease medical costs are underway, with promising preliminary data.
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Data collection were sponsored by research grant of Biotronik GmbH & Co. KG, Berlin, Germany. J.C.N. is supported by grants from the Research Initiative of Århus University Hospital, Helga and Peter Kornings Foundation, August H Jensen and wife’s Foundation, Elin Holms Foundation, the Danish Society of Cardiology and the Association of Young Cardiologists. M.Z. received research grant from Biotronik.
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Acknowledgements |
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The authors thank Georg Stowasser for performing queries of the HM Service Center database, Michael Kraus for coordinating this process, and Simone Böhm for assistance in technology-related questions during manuscript preparation.
Conflict of interest: B.S. is currently conducting research sponsored by Biotronik. J.C. is consultant of Biotronik. D.D. is full-time employee of Biotronik. M.Z. and G.H. are both conucting research with Biotronik and are also members of the speaker's bureau.
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References |
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