Assessment of the clinical benefits of remote monitoring of cardiac-implanted devices: A single-center study in Japan

Abstract

Introduction

The clinical benefits of remote monitoring (RM) of cardiac-implanted devices have not been fully evaluated in Japan. We investigated the clinical benefits of RM in a single center in Japan.

Methods

Patients with pacemakers, implantable cardioverter-defibrillators (ICD), or cardiac resynchronization therapy with defibrillators (CRT-D) were assigned to RM and non-RM groups. The outpatient wait times and times to notification of EVENTS that we defined sustained ventricular tachyarrhythmias, worsening heart failure, and inappropriate therapy for supraventricular tachyarrhythmias in this study, were compared between the 2 groups.

Results

A total of 416 patients (RM: 61; non-RM: 355) were evaluated. The outpatient wait time was 17.6±22.1 min for the RM group and 35.6±25.2 min for the non-RM group (P<0.001). Seventy-seven and 306 EVENTS were observed in 38 and 256 patients during mean follow-up periods of 360±22 days and 429±10 days in the RM and non-RM groups, respectively. The times to notification of EVENTS were 8.1±16.2 days for the RM group and 38.7±33.2 days for the non-RM group (P<0.001).

Conclusions

RM significantly shortened outpatient wait times and times to notification of EVENTS. Therefore, RM was clinically beneficial in a single center in Japan.

1 Introduction

Cardiac-implanted devices offer multiple programmable features and can store large amounts of diagnostic information related to the device function, arrhythmia frequency, hemodynamic or physiologic parameters, and patient activity. Traditional device follow-up requires direct interrogation of the device in order to view the programmed parameters and stored diagnostic data, identify and correct possible malfunctions, and optimize therapy by reprogramming the device [1]. As the use of implanted cardiac devices has expanded, the number of patients consulting device clinics has increased each year, extending the wait times at the clinic.

Remote monitoring (RM) systems for cardiac-implanted devices that transmit data from the implanted device from remote locations to the medical institution through analog or wireless telephones have recently been introduced in Japan. The transmitters are able to interrogate the device, either manually by the patient's use of a telemetry wand or automatically using wireless technology [2].

RM systems consist of data acquisition by the device on a scheduled basis followed by transmission of predefined alerts to the physician as necessary [1]. RM has been widely used in the U.S. and in European countries. Recent studies from these countries have demonstrated positive effects of RM [3–6], but the benefits of RM have not been fully evaluated in Japan. The objective of the present study was to investigate the clinical benefits of RM, particularly with respect to outpatient wait times and times to detection of EVENTS that we defined sustained ventricular tachyarrhythmic events, worsening heart failure, and inappropriate therapy for supraventricular tachyarrhythmias (SVT), in a single center in Japan.

2 Methods 2.1 Patients

This study was designed as a prospective evaluation of RM in patients with cardiac-implanted devices. All of the patients in the study population had had pacemakers, implantable cardioverter-defibrillators (ICD), or cardiac resynchronization therapy with defibrillators (CRT-D) implanted at our institution. Patients divided into either the RM (using RM) or the non-RM (without RM) group. Either the CareLink system (Medtronic, Inc., Minneapolis, MN, USA; for pacemakers, ICDs, and CRT-Ds) or the Merlin.net system (St. Jude Medical, Inc., St. Paul, MN, USA; for ICDs and CRT-Ds) was used in RM patients. The 2 RM systems are compared in Table 1. The RM system was explained to all patients using newly implanted or generator-exchanged ICDs or pacemakers from Medtronic or St. Jude Medical. Patients from whom written informed consent could be obtained were enrolled in the RM group, while other patients with ICDs and pacemakers were assigned to the non-RM group.

1 Comparison of the RM systems.

	CareLink system (Medtronic, Inc.)	Merlin.net system (St. Jude Medical, Inc.)
Device	pacemakers, ICD, CRT-D	ICD, CRT-D
Characteristic	stationary	stationary
Data transmission	analog phone line	wireless, analog phone line
Transmission range	3m	3m
Home telemetry	pacemakers: wand ICD, CRT-D: Wirelessa	wireless
Frequency of transmissions	scheduled follow-up, alert events	scheduled follow-up, alert events
Scheduled follow-up	at 3:00 a.m.	between 2 a.m. and 4 a.m.
Response to events	immediate transmission	immediate transmission
Retransmission	every 3h for 3 days	every 2h for 24h
Physician notification	SMS, e-mail, smartphone	fax, e-mail, SMS text, smartphone
IEGM (arrhythmic episodes)	all recorded episodes	all recorded episodes
Special features	automatic RA, RV and LV pacing thresholds	alerts fully configurable online
	OptiVol Fluid Status Monitoring

SMS: short message service, IEGM: intracardiac electrocardiogram, RA: right atrium.

RV: right ventricle, LV: left ventricle.

a

Except for the first transmission using wand-operated transmitters.

The physician decided whether each patient was assigned to the CareLink system or Merlin.net system based on the patient's medical condition. The patients with history of congestive heart failure were generally given Medtronic devices due to the availability of OptiVol Monitoring. OptiVol Fluid Status Monitoring, which is available only in the CareLink system, measures the intrathoracic impedance between the implanted lead in the right ventricle (RV) and the device generator and provides early detection of worsening heart failure [7–9].

This study was approved by the ethics committees of Osaka City University. A written informed consent to participate was obtained from all patients.

2.2 Evaluation

The outpatient wait times and times to notification of EVENTS were compared between RM and non-RM patients. At our institution, patients with cardiac devices undergo medical examinations after their devices have been checked in another room. However, the patients using the CareLink system can skip the device check. Outpatient wait time was defined as the interval from the time of the appointment for the device check to the start of the medical examination.

The time to EVENTS notification was defined as the time from the onset of the EVENTS to the notification of the physician. The rates of EVENTS and emergency visits and data confirmation times (device check time or RM data confirmation time) were also compared between the RM and the non-RM groups. The precise day and time at which the alert events occurred could be identified only for EVENTS (alert events due to increased OptiVol index, shock therapy, or ATP [anti-tachycardia pacing] delivered for sustained VT or VF, including inappropriate therapy). Therefore, the times to notification of the EVENTS were evaluated and compared between the RM and non-RM groups. Patients were diagnosed with worsening heart failure based on their general conditions, including symptoms, chest radiography findings, blood test parameters, and OptiVol findings (OptiVol index >60 (ohm-days)).

The device check time in non-RM patients was defined as the interval from the interrogation of the implanted device using the programmer to the printing of all of the data at the clinic. The RM data confirmation time was defined as the interval from clicking on the web site to transmit the data to the printing of the data at the clinic. The transmitted alert data were checked at the clinic every weekday at 9 a.m., while the scheduled transmitted data were checked at the clinic a day before each scheduled visit.

2.3 Patient follow-up and data collection

Patients with pacemakers: both RM and non-RM patients were followed up at office visits every 6 months. The RM patients' device data were transmitted every 6 months on a scheduled basis.

Patients with ICDs or CRT-Ds: both RM and non-RM patients were followed up at office visits every 3 months. The RM patients' device data were transmitted every 3 months on a scheduled basis.

In addition, the contents of any inquiries to the RM call center for troubleshooting of the RM system and of the alert data were evaluated during the follow-up examinations of RM patients. The alert settings of the RM group are shown in Tables 2 and 3.

2 Event trigger settings (CareLink system).

Electrical reset	Active can off
Excessive charge time End of Service	OptiVol index >60
Charge circuit timeout (30seconds)	RV lead integrity
VF detection/therapy off	RV lead noise
RV pacing impedance <200Ω, >2500Ω	ERI
RV defibrillation impedance <20Ω, >200Ω	RA pacing impedance <200Ω, >2500Ω
SVC defibrillation impedance <20Ω, >200Ω	LV pacing impedance <200Ω, >2500Ω
All therapies in a zone exhausted	Number of shocks delivered in an episode
Pacing mode DOO, VOO or AOO	AT/AF daily burden >6hours
Average ventricular rate during AT/AF >100bpm (>6hours)

VF: ventricular fibrillation, RV: right ventricle, AT: atrial tachycardia, SVC: superior vena cava, LV: left ventricle, RA: right atrium, ERI: elective replacement indicator, AF: atrial fibrillation, bpm: beats per minute.

3 Event trigger settings (Merlin.net system).

ST episode detected	RA pacing lead impedance out of range
Tachycardia therapy disabled	RV percent pacing greater than limit
Device programed to emergency pacing	LV pacing lead impedance out of range
Charge time limit reached	AT/AF episode duration >threshold
Possible HV circuit damage	AT/AF burden >threshold
Longevity analysis	Average RV rate during AT/AF >threshold
Device reset	HV therapy delivered
Back-up VVI mode	Successful ATP pacing delivered
Device at ERI	Therapy accelerated rhythm
Device at end of service	RV pacing lead impedance out of range
Possible HV lead issue	BiV percent pacing less than limit
HV pacing lead impedance out of range	Episode with alert conditions

HV: high voltage, ATP: anti-tachycardia pacing, BiV: biventricular.

2.4 Statistical analysis

Outpatient wait times and times to notification of EVENTS were compared between the RM and the non-RM groups using a Student's t-test or Aspin-Welch t-test. All data are shown as the mean±standard deviation. P-values less than 0.05 were considered significant. All events from the day after enrollment to patient death were included.

3 Results 3.1 Patient characteristics

A total of 416 patients (66 in the RM group and 350 in the non-RM group) were enrolled from November 2009 to September 2011. However, 5 patients in the RM group were excluded because they lacked access to an analog telephone (n=2), were unwilling to conduct CareLink or Merlin.net follow-up visits (n=2), or were found to have dementia (n=1). These 5 patients were reassigned to the non-RM group. Therefore, the final data evaluated came from 61 patients in the RM group and 355 in the non-RM group. The numbers of patients with pacemakers, ICDs, and CRT-Ds were 256, 140, and 20, respectively. A total of 1,460 visits for the non-RM group and 125 visits for the RM group were analyzed, with an average number of visits per patient of 3±2 (range, 1 to 10 visits) over a mean follow-up period of 419±9 days (range, 6 to 698 day). The mean age of all patients at the time of implantation was 69.7±13.7 years, and 239 (57%) were male. The characteristics of the patients in this study are shown in Table 4. The patients with pacemakers were younger in the RM group than in the non-RM group, while the characteristics of patients with ICDs or CRT-Ds were similar between the RM and non-RM groups. The 41 patients in the RM group using the CareLink system were younger than the 189 patients in the non-RM group using Medtronic devices. The patients in the RM group using the CareLink system and the Merlin.net system had similar characteristics.

4 Patient characteristics.

(a)	PM	RM (n=18)		non RM (n=238)	P value
Age		65.3±11.4		75.0±11.6	0.0005
Male		6 (33%)		102 (43%)	0.05
Heart disease	SSS	7 (39%)		111 (47%)	0.58
	AV block	11 (61%)		127 (53%)	0.51
(b)	ICD/CRT-D	RM (n=43)		non RM (n=117)	P value
Age		62.0±14.4		62.2±12.6	0.91
Male		38 (88.3%)		93 (79.4%)	0.15
LVEF (%)		42.8±15.6		43.0±16.2	0.94
		CareLink (n=23)	Merlin.net (n=20)	non RM (n=117)
	OMI	4	9	36	0.56
	DCM	5	2	15	0.37
	HCM	6	2	12	0.13
	ARVC	0	1	3	0.71
Heart disease	Sarcoidosis	1	1	6	0.77
	Brugada	4	1	29	0.05
	LQT	0	0	1	0.60
	IVF/IVT	3	2	8	0.41
	Valuvlar disease	0	2	5	0.74
	HHD	0	0	2	0.53

OMI: old myocardial infarction, LQT: long QT syndrome, DCM: dilated cardiomyopathy, HCM: hypertrophic cardiomyopathy.

ARVC: arrhythmogenic right ventricular cardiomyopathy, IVF: idiopathic ventricular fibrillation, IVT: idiopathic ventricular tachycardia.

HHD: hypertensive heart disease.

3.2 Scheduled data transmission in RM patients

In total, 125 scheduled data transmissions were performed successfully; these consisted of 22, 79, and 24 data transmissions in patients with pacemakers, ICDs, and CRT-Ds, respectively. Eighty-seven data transmissions using the CareLink system and 38 data transmissions using the Merlin.net system were analyzed.

The 125 scheduled transmissions during the mean follow-up period of 360±22 days in the RM group contained the following 15 alert events (12%): 14 incidents of sustained ventricular tachycardia (VT) and 1 of ventricular fibrillation (VF). All of the 15 alert events were EVENTS. The average number of EVENTS per transmission with alert events was 0.1 (0–8 EVENTS).

All of the 14 VT EVENTS were treated by ATP therapy in patients with the CareLink system. However, these events were included in scheduled transmissions rather than transmitted as unscheduled alerts because it was impossible to set ATP therapy for VT as an alert event in the CareLink system.

The 1 VF event in the scheduled transmissions from the CareLink system involved shock delivery to treat the VF. This did not triggered an alert event even though the alert was triggered for EVENTS because the CareLink system does not trigger again until it is reset by an in-office interrogation [10].

The automatic transmissions of 8 events by the CareLink system were unsuccessful because the transmitter was not set up and initiated to send out transmissions (n=3), inappropriate circumstances occurred in which the patient was away from the transmitter (n=3), the transmitter was disconnected from the analog phone line (n=1), or technical problems occurred with the telephone line (the analog telephone line was too old to transmit) (n=1). The automatic transmissions of 8 events by the Merlin.net system were unsuccessful because inappropriate circumstances occurred in which the patient was away from the transmitter (n=1), a cellular adapter card did not fit in the transmitter (n=1), or technical errors occurred (the capacity of the data communication card was exceeded) (n=6).

The contents of the troubleshooting calls are shown in Table 5. Eight calls for the CareLink system and 4 calls for the Merlin.net system were requests for physicians to set the transmitters.

5 Troubleshooting calls.

	CareLink	Merlin.net
Transmission	8	6
Confirmation of data arrival	9	0
Transmitter setting	8	0
Others	4	0
Total	29	6

3.3 Unscheduled transmitted alert data for RM patients during the follow-up period

A total of 65 unscheduled transmissions were successfully transmitted; 46 and 19 transmissions occurred in patients with ICD and CRT-D, respectively.

The 65 unscheduled transmissions that occurred during the follow-up period contained 202 alert events. The average number of alert events per transmission was 3.1 (1–13 events). The contents of the alert events were as follows: OptiVol fluid index exceeding the threshold in the CareLink system (n=25), VT (n=114), VF (n=6), atrial fibrillation (AF) burden (n=16), AF episode of long duration (n=15), ventricular high rate during AF (n=8), ventricular pacing rate in CRT-D less than 90% (n=5), ventricular pacing rate in ICD over 40% (n=2), significant ST deviation (n=2), and inappropriate therapy for SVT (n=9; 2 sinus tachycardia, 5 AF, and 2 atrial tachycardia events).

The 202 alert events contained the following 62 EVENTS: OptiVol fluid index over threshold (n=25), VT (n=22), VF (n=6), and inappropriate therapy for SVT (n=9). The average number of EVENTS per transmission with alert events was 0.95 (0–13 EVENTS). Transmission of alerts prompted unscheduled contacts performed by phone. These phone calls resulted in 15 unscheduled office visits for the following reasons: OptiVol fluid index exceeding the threshold (n=7), delivered shock (n=7), and ventricular pace rate in CRT-D less than 90% (n=1). Of the 15 unscheduled visits, 5 determined that reprogramming of the device was required and 3 that hospitalization was needed.

3.4 Alert events in non-RM patients

At the clinic, we found the following 376 alert events in non-RM patients during the mean follow-up period of 429±10 days: OptiVol fluid index exceeding the threshold according to the Medtronic device (n=101), VT (n=141), VF (n=20), device at Elective replacement indicator (n=18), RV lead noise (n=2), right atrium (RA) pacing lead impedance out of range (n=2), possible high-voltage lead issue (n=2), ventricular pace rate in ICD over 40% (n=43), and ventricular pace rate in CRT-D less than 90% (n=3). Inappropriate therapy for SVT was included in the following 44 alert events (12%): sinus tachycardia (n=18), AF (n=21), and atrial tachycardia (n=5). The 376 alert events included 306 EVENTS. These were OptiVol fluid index over the threshold (n=101), VT (n=141), VF (n=20), and inappropriate therapy for SVT (n=44).

Sixty-eight unscheduled visits were made by patients in the non-RM group during the follow-up period because of heart failure (n=43), delivered shock (n=8), palpitation (n=12), syncope (n=3), and alert sound from the device (n=2). Reprogramming of the device was needed at 9 visits, and hospitalization was needed at 26 visits. The rate of hospitalization was significantly higher at the unscheduled visits (38%) than at the scheduled visits (5 visits, 0.003%) (P<0.001).

3.5 Outpatient wait times

The outpatient wait times at the clinic were 17.6±22.1 min for the RM group and 35.6±25.2 min for the non-RM group in all patients (P<0.001), 6.6±23.6 min for the RM group and 32.6±22.0 min for the non-RM group for patients with pacemakers (P<0.001), and 19.4±25.6 min for the RM group and 41.2±25.5 min for the non-RM group for patients with ICDs or CRT-Ds (P<0.001) (Fig. 1). For patients with Medtronic ICDs or CRT-Ds, the outpatient wait times were significantly shorter for the RM group (14.2±20.9 min, n=44) than for the non-RM group (42.7±24.5 min, n=162) (P<0.001). However, for patients with St. Jude Medical ICDs or CRT-Ds, the outpatient wait time did not differ significantly between the RM group (28.7±13.0 min, n=20) and the non-RM group (38.1±27.9 min, n=70) (P=0.14). The wait time was significantly shorter for patients using the CareLink system than for patients using the Merlin.net system (P<0.001).

Fig. 1. Distribution of the outpatient wait times. The black box and bar represent the mean time in min±SD. Blue plots indicate the RM group and green plots the non-RM group. All: distribution in all patients, PM: pacemakers.

3.6 Data confirmation time

The average device check time at the outpatient clinic was 4.9±3.2 min at scheduled visits (n=1,460). The RM data confirmation time per patient was 4.3±2.9 min (n=125). The RM data confirmation time was significantly shorter than the device check time at the outpatient clinic (P<0.001).

3.7 Time to notification of EVENTS

The study included 383 EVENTS (77 in the RM group and 306 in the non-RM group). The average time to notification of EVENTS was 8.1±16.2 days for the RM group and 38.7±33.2 days for the non-RM group (P<0.001). The time to notification was 14.3±20.8 days for patients using the CareLink system (n=42) and 2.1±1.3 days for patients using the Merlin.net system (n=35). The time to notification was significantly shorter for patients using the Merlin.net system than for patients using the CareLink system (P<0.001). The time to notification of sustained ventricular tachyarrhythmias was 26.6±23.1 days for patients using the CareLink system (n=21) and 2.5±1.2 days for patients using the Merlin.net system (n=22) (P<0.001). However, when we excluded ATP therapy in patients using the CareLink system from the EVENTS, the time to notification of EVENTS was 1.1±0.4 days for patients using the CareLink system (n=27). Therefore, the difference in time to notification of EVENTS between the 2 systems is due mainly to the inability of the CareLink system to transmit ATP therapy for VT as an alert.

4 Discussion 4.1 Main study findings

This study revealed that the use of RM significantly shortened outpatient wait times, times to notification of EVENTS, and data confirmation times at the clinic in patients with implanted cardiac devices at a single Japanese center. The monitoring of implanted cardiac devices through RM technology may provide benefits for the clinical management of patients in Japan.

4.2 Scheduled data transmission in RM patients

In the RM patients, 125 scheduled data transmissions (89%) were performed successfully. This result confirms the previously reported feasibility, reliability, and availability of RM of implanted devices in most cases [11,12]. Of the remaining 16 scheduled data transmissions (11%) that were not transmitted, 8 data transmissions by the CareLink system were not successfully transmitted because the transmitter was not set up and initiated to send out transmissions or inappropriate circumstances occurred in which the patient was away from the transmitter, the transmitter was not connected to an analog phone line, or technical problems occurred with the phone line. These reasons for unsuccessful transmission by the CareLink system were similar to those in a previous report from the U.S. and European countries [10]. In a Japanese multicenter study, Ando et al. reported that a total of 470 transmissions were attempted, of which 385 (81.9%) were successful [13]. Although the proportion of patients with pacemakers who had to transmit data by wand-operated transmission was higher in their study (53.2%) than in ours (36.1%), the rates of successful transmissions were similar. Eight data transmissions by the Merlin.net system were not successfully transmitted because inappropriate circumstances occurred in which the patient was away from the transmitter, a cellular adapter card did not fit in the transmitter, or technical errors occurred (the capacity of the data communication card was exceeded). Such technical errors associated with the Merlin.net system were peculiar to Japan and were due to the unstable mobile phone signals and the small number of mobile phone operating stations in Japan.

Twenty-five of the 125 transmissions (20%) required outside assistance. Schoenfeld et al. reported that patients did not require outside assistance in 91% of 110 transmissions and that 93% of second transmissions were unassisted [14]. In our study, the rate of outside assistance was slightly higher than previously reported. However, most of the requests for outside assistance were only for confirmation of transmission despite the successful transmission of all data.

4.3 Unscheduled transmitted alert data in RM patients during the follow-up period

Lazarus et al. reported that most of the alert data transmitted by RM were related to heart failure, progression of AF, or ICD treatment for VF. In our study, 92% of the alert events in RM patients were related to signs of heart failure, AF, or shocks delivered for treatment of VT or VF, much as in a previous report [15]. Most of the alert events (128 events, 59%) in the RM group in our study were related to VT. After phone calls, 7 unscheduled visits were made because the physicians judged that examinations at the clinic were warranted, as an increase in the OptiVol fluid index over the threshold is indicative of heart failure. Of these 7 patients, 1 was emergently admitted. RM thus enabled the early detection and treatment of heart failure, AF, VT or VF events, and inappropriate shock treatment for VT or VF.

4.4 Alert events in non-RM patients

Of the 376 alert events in our non-RM patients, we found 306 EVENTS (81.4%). Sixty-eight unscheduled visits were made due to the patients' symptoms. Unfortunately, the rate of hospitalization at these unscheduled visits was very high (38%). Senges-Becker et al. reported that only 34% of complications related to cardiac implanted devices were detected during routine follow-up [16]. The use of RM in these non-RM patients might have called attention to events before the patients became symptomatic and could have reduced the rate of hospitalization.

4.5 Outpatient wait times

The outpatient wait times were significantly shorter for the RM group than for the non-RM group. However, the wait times for patients using the Merlin.net system did not differ significantly from those of the non-RM group. As the Merlin.net system used did not have an automatic threshold-measurement function, it was necessary to check the pacing threshold at the outpatient clinic. We considered this to be a reason for the lack of significant difference between the RM and non-RM groups for patients using the Merlin.net system. Use of the latest model (not currently available in Japan) in which the threshold measurement and adjustment are performed automatically [17] might result in shorter outpatient wait times even for the Merlin.net system. In this study, the outpatient wait time for the RM group was 17.6±22.1 min. The outpatient wait time did not include the time required to travel to and from the clinic or for the actual medical procedure. Some of our patients required prescriptions and/or other examinations, such as chest radiographs or blood examinations, at their follow-up office visits. The actual medical procedure times may have been prolonged for these patients. Therefore, we evaluated only the actual time spent waiting in this study.

4.6 Data confirmation time

In our study, the RM data confirmation time (4.3±2.9 min per patient) was shorter than the device check time at the outpatient clinic, as was shown in previous reports [13,17]. In our study, the RM data confirmation time was defined as the time from clicking on the web site to transmit data to the printing of the data. Ando et al. reported that physicians spent an average of 6.4±5.1 min to evaluate the data over the internet [13], while Raatikainen et al. reported that physicians required 8.4±4.5 min to review device data on the secure website [17]. Although the RM data confirmation time depends on the performance of the computer, internet speed, and personal analytical ability, which follows a learning curve [12], the RM data confirmation time was shorter in this study than in the previous studies.

4.7 The time to notification of EVENTS

In this study, the time to notification of EVENTS was significantly shorter in the RM group than in the non-RM group. The clinical benefits of RM for the early detection and treatment of heart failure, VT or VF events, and inappropriate therapy for VT or VF were clearly evident. Such monitoring and notification can enable more rapid adjustment of therapy that would otherwise be delayed until the next scheduled follow-up visit, as previously reported [18].

The time to notification was significantly shorter for patients using the Merlin.net system (2.1±1.3 days) than for those using the CareLink system (14.3±20.8 days). Once alert data were transmitted by the CareLink system, the next similar alert data were not transmitted until the system was reset by in-office interrogation at the clinic. Moreover, the CareLink system did not transmit ATP therapy for VT as an alert. We speculate that these defects in the CareLink system were responsible for the different times to notification of the 2 systems. Crossley et al. reported that the median time per patient from the occurrence of an event to a clinical decision was 4.6 days in RM patients using the CareLink system and 22 days in non-RM patients [10]. Both intervals were shorter than those in this study. Notably, Crossley et al. did not include incidents of ATP therapy for VT as EVENTS; we, however, included the administration of ATP for VT, which was communicated only at the follow-up office visits. This difference probably explains why the time to notification in patients using the CareLink system was longer in this study than in that of Crossley et al.

4.8 Limitations

In this study, the outpatient wait time was defined as the interval from the time of the appointment for the device check to the start of the medical examination. This time may be influenced by the device check time and by the number of patients with appointments for medical examinations. The device check time may be affected by the number and severity of alert events relayed at that time. The RM confirmation time may be affected by the performance of the computer, internet speed, and personal analytical ability. These factors may not have been uniform in our study. We checked all of the alert data from 9 a.m. through 5 p.m. on weekdays. Therefore, the time to notification of EVENTS may have been longer when the EVENTS occurred on weekends or holidays. Moreover, we could not evaluate the times to notification for alert events other than EVENTS because the date and time of onset were unclear. This study also included a relatively small number of patients in the RM group, especially those using the Merlin.net system.

5 Conclusions

The use of RM significantly shortened outpatient wait times and times to notification of EVENTS. Early detection and treatment of arrhythmia events, worsening heart failure, and abnormal device performance were possible. The clinical benefits of RM were evident at a single center in Japan. Further prospective randomized studies may be needed to identify the patients who would benefit most from RM of cardiac-implanted devices in Japan.

Conflict of interest statement

No conflict of interest declared.