The Role of Implantable Cardiac Monitors in Atrial Fibrillation Management

Comparison of Electrocardiogram Characteristics of Two Commercially Available Implantable Loop Monitors: Impact of These Characteristics in the Correct Adjudication of Recorded Events and Minimized Undersensing and Oversensing of Events

Implantable cardiac monitors (ICMs) are useful in the detection of tachycardias, bradycardias, and atrial fibrillation. Undersensing and oversensing of events occur despite complex algorithms. The devices available have subtle differences, which may account for a difference in recorded characteristics. The electrocardiogram (ECG) characteristics of different monitors may influence their ability to correctly identify the events recorded. The objective is to compare the ECG characteristics of two commercially available implantable loop monitors and the ability to improve diagnostic accuracy. Two cohorts of patients were examined. Cohort 1 consisted of 30 patients with a Reveal LINQ I (Medtronic, Minneapolis, MN, USA) implanted, which was replaced with a BIOMONITOR III (Biotronik, Berlin, Germany) when the former had reached end of life. The new monitor was implanted at the same site in all patients. This provided a unique opportunity to compare ECGs obtained by both devices with no other confounding variable. Cohort 2 consisted of patients who had undergone implantation of either device at the discretion of the physician. This was therefore a retrospective analysis of 106 patients who had been implanted with one of the devices within a 2-year period. In both cohorts, we compared R-wave amplitude, the ability to accurately detect P-waves, and the frequency of undersensing and oversensing of events. In cohort 1, the mean R-wave was 0.35 ± 0.2 mV with the LINQ I as compared to 0.98 ± 0.4 with the BIOMONITOR III (P = .001). A P-wave in sinus rhythm was present in 19 (63%) subjects with the LINQ I implants versus 28 (93%) with the BIOMONITOR III implants (P = .004). Undersensing of events was noted in five (16%) patients with the LINQ I versus five (16%) with the BIOMONITOR III (P > .5). Oversensing was seen in 4 patients (13.33%) with the LINQ I versus 0 with the BIOMONITOR III (P = .012). In cohort 2, the mean R-wave with the BIOMONITOR III was significantly greater than with the LINQ I (0.65 ± 0.37 vs. 0.48 ± 0.38; P = .02). A visible P-wave was seen in 33 of 53 patients with the BIOMONITOR III as compared to 16 of 536 patients with the LINQ I monitor (P = .01). The number of patients identified as having under- or oversensing was, however, not significantly different (P = .08) in this cohort. In both patient cohorts, the BIOMONITOR III was noted to have significantly greater R-wave amplitude as compared with the LINQ I. A visible P-wave was also more commonly seen in patients with a BIOMONITOR III. In the paired cohort, but not in the unpaired cohort, the BIOMONITOR III was less likely to oversense R-waves. There was no significant difference in undersensing between the devices.

A Comprehensive Review of Cryptogenic Stroke and Atrial Fibrillation: Real-World Insights Into the Role of Insertable Cardiac Monitors

Cryptogenic stroke, a subtype of ischemic stroke with no identifiable cause after comprehensive evaluation, presents a unique challenge in stroke prevention. Atrial fibrillation (AF), a common risk factor for ischemic stroke, is often underdiagnosed in these patients due to its intermittent, asymptomatic nature. Early detection of AF is critical, as anticoagulation therapy significantly reduces the risk of recurrent stroke in AF patients. However, traditional short-term monitoring methods frequently fail to identify paroxysmal AF. Insertable cardiac monitors (ICMs) offer a novel solution by providing continuous, long-term heart rhythm monitoring, which has proven effective in detecting occult AF. Real-world data further support the clinical value of ICMs in guiding the initiation of anticoagulation therapy, ultimately improving stroke prevention strategies. Despite some limitations, such as false positives and the invasive nature of the device, ICMs have emerged as a critical tool in modern stroke management. As technology evolves, future advancements may further enhance AF detection by integrating artificial intelligence and wearable devices. This review provides a comprehensive overview of the role of AF in cryptogenic stroke, the importance of early detection, and the growing significance of ICMs in clinical practice.

Incidental and anticipated arrhythmic diagnoses in patients with an implantable cardiac monitor

AIMS

In this study, we investigated a cohort of unselected patients with various indications for an implantable cardiac monitor (ICM). Our main objectives were to determine the incidence of arrhythmic diagnoses, both anticipated and incidental in relation to the ICM indication, and to assess their clinical relevance.

METHODS

We examined remote monitoring transmissions from patients with an ICM at four Italian sites to identify occurrences of cardiac arrhythmias. Concurrently, we collected data on medical actions taken in response to arrhythmic findings.

RESULTS

The study included 119 patients, with a median follow-up period of 371 days. ICM indications were syncope/presyncope (46.2%), atrial fibrillation management (31.1%), and cryptogenic stroke (22.7%). In the atrial fibrillation management group, atrial fibrillation was the most common finding, with an incidence of 36% [95% confidence interval (CI) 22-55%] at 18 months. Rates of atrial fibrillation were not significantly different between patients with cryptogenic stroke and syncope/presyncope [17% (95% CI 7-40%) vs. 8% (95% CI 3-19%), P  = 0.229].For patients with cryptogenic stroke, the incidence of asystole and bradyarrhythmias at 18 months was 23% (95% CI 11-45%) and 42% (95% CI 24-65%), respectively, similar to estimates obtained for patients implanted for syncope/presyncope ( P  = 0.277 vs. P  = 0.836).Overall, 30 patients (25.2%) required medical intervention following ICM-detected arrhythmias, predominantly involving atrial fibrillation ablation (10.9%) and medication therapy changes (10.1%).

CONCLUSION

In a real-life population with heterogeneous insertion indications, approximately 25% of patients received ICM-guided medical interventions within a short timeframe, including treatments for incidental findings. Common incidental arrhythmic diagnoses were bradyarrhythmias in patients with cryptogenic stroke and atrial fibrillation in patients with unexplained syncope.

Strategic reprogramming of implantable cardiac monitors reduces the false-positive remote alert burden in a nurse-led service

AIMS

Implantable cardiac monitors (ICMs) can generate false-positive (FP) alerts. Although these devices have an extended programmability, there are no recommendations on their optimization to reduce not-relevant activations.We tested a strategic programming optimization guide based on the type of FP and investigated the safety and feasibility of the nurse-led insertion of ICMs with a long-sensing vector.

METHODS AND RESULTS

Consecutive patients implanted by trained nurses with long-sensing vector ICM were enrolled in a 1-month observational stage (Phase A). Patients who had ≥10 FP episodes underwent ICM reprogramming based on the predefined guide and were followed for an additional month (Phase B). A total of 78 patients had successful ICM insertion by nurses with a mean R wave amplitude of 0.96 ± 0.43 mV and an 86% P wave visibility. Only one patient reported a significant device-related issue, and nurse-delivered ICM was generally well accepted by the patients. During Phase A, 11 patients (14%) generated most of FP (3,627/3,849; 94%) and underwent ICM reprogramming. In the following month (Phase B), five patients (45%) were free from FP and six (55%) transmitted 57 FP alerts (98% reduction compared with Phase A). The median number of FP per patient was significantly reduced after reprogramming [195 (interquartile range, 50-311) vs. one (0-10), P = 0.0002].

CONCLUSION

A strategic reprogramming of ICM in those patients with a high FP alert burden reduces the volume of erroneous activations with potential benefits for the remote monitoring service. No concerns were raised regarding nurse-led insertion of ICMs with a long-sensing vector.

Diagnostic yield of an insertable cardiac monitor in a large patient population

Background

Insertable cardiac monitors (ICMs) are increasingly used for cardiac rhythm diagnosis with expanding indications. Little has been reported about their use and efficacy.

Objective

The study sought to evaluate the clinical utility of a novel ICM (Biotronik BIOMONITOR III) including the time to diagnosis in unselected patients with different ICM indications.

Methods

Patients from 2 prospective clinical studies were included to determine the diagnostic yield of the ICM. The primary endpoint was time to clinical diagnosis per implant indication or to the first change in atrial fibrillation (AF) therapy.

Results

A total of 632 patients were included with a mean follow-up of 233 ± 168 days. Of 384 patients with (pre)syncope, 34.2% had a diagnosis at 1 year. The most frequent therapy was permanent pacemaker implantation. Of 133 patients with cryptogenic stroke, 16.6% had an AF diagnosis at 1 year, resulting in oral anticoagulation. Of 49 patients with an indication for AF monitoring, 41.0% had a relevant change in AF therapy based on ICM data at 1 year. Of 66 patients with other indications, 35.4% received a rhythm diagnosis at 1 year. Moreover, 6.5% of the cohort had additional diagnoses: 26 of 384 patients with syncope, 8 of 133 patients with cryptogenic stroke, and 7 of 49 patients with AF monitoring.

Conclusion

In a large unselected patient population with heterogeneous ICM indications, the primary endpoint of rhythm diagnosis was achieved in ∼1 in 4, and additional clinically relevant findings was achieved in 6.5% of patients at short-term follow-up.

Insertable cardiac monitor with a long sensing vector: Impact of obesity on sensing quality and safety

Background

Fat layers in obese patients can impair R-wave detection and diagnostic performance of a subcutaneous insertable cardiac monitor (ICM). We compared safety and ICM sensing quality between obese patients [body mass index (BMI) ≥ 30 kg/m²] and normal-weight controls (BMI <30 kg/m²) in terms of R-wave amplitude and time in noise mode (noise burden) detected by a long-sensing-vector ICM.

Materials and methods

Patients from two multicentre, non-randomized clinical registries are included in the present analysis on January 31, 2022 (data freeze), if the follow-up period was at least 90 days after ICM insertion, including daily remote monitoring. The R-wave amplitudes and daily noise burden averaged intraindividually for days 61-90 and days 1-90, respectively, were compared between obese patients (n = 104) and unmatched (n = 268) and a nearest-neighbour propensity score (PS) matched (n = 69) normal-weight controls.

Results

The average R-wave amplitude was significantly lower in obese (median 0.46 mV) than in normal-weight unmatched (0.70 mV, P < 0.0001) or PS-matched (0.60 mV, P = 0.003) patients. The median noise burden was 1.0% in obese patients, which was not significantly higher than in unmatched (0.7%; P = 0.056) or PS-matched (0.8%; P = 0.133) controls. The rate of adverse device effects during the first 90 days did not differ significantly between groups.

Conclusion

Although increased BMI was associated with reduced signal amplitude, also in obese patients the median R-wave amplitude was >0.3 mV, a value which is generally accepted as the minimum level for adequate R-wave detection. The noise burden and adverse event rates did not differ significantly between obese and normal-weight patients.Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT04075084 and NCT04198220.

Atrial fibrillation: focus on monitoring strategies after cryptogenic stroke

Atrial fibrillation (AF) is responsible for up to one-third of ischemic strokes, with stroke potentially being the first manifestation of a previously undetected AF. Given the efficacy of oral anticoagulants in preventing AF-related ischemic events, searching for unknown AF after stroke requires a comprehensive diagnostic workup. Prospective data have demonstrated the benefits of long-term cardiac monitoring to identify AF in association with cryptogenic stroke, as most strokes are presumed to result from AF. However, strategies of empirical anticoagulation using oral anticoagulants following cryptogenic stroke failed to improve outcomes. We herein summarize contemporary evidence and knowledge gaps on searching for AF after a stroke and the potential secondary prevention strategies to prevent further recurrences.

Programming Optimization in Implantable Cardiac Monitors to Reduce False-Positive Arrhythmia Alerts: A Call for Research

No studies have investigated whether optimizing implantable cardiac monitors (ICM) programming can reduce false-positive (FP) alerts. We identified patients implanted with an ICM (BIOMONITOR III) who had more than 10 FP alerts in a 1-month retrospective period. Uniform adjustments of settings were performed based on the mechanism of FP triggers and assessed at 1 month. Eight patients (mean age 57.5 ± 23.2 years; 37% female) were enrolled. In 4 patients, FPs were caused by undersensing of low-amplitude premature ventricular contractions (PVCs). No further false bradycardia was observed with a more aggressive decay of the dynamic sensing threshold. Furthermore, false atrial fibrillation (AF) alerts decreased in 2 of 3 patients. Two patients had undersensing of R waves after high-amplitude PVCs; false bradycardia episodes disappeared or were significantly reduced by limiting the initial value of the sensing threshold. Finally, the presence of atrial ectopic activity or irregular sinus rhythm generated false alerts of AF in 2 patients that were reduced by increasing the R-R variability limit and the confirmation time. In conclusion, adjustments to nominal settings can reduce the number of FP episodes in ICM patients. More research is needed to provide practical recommendations and assess the value of extended ICM programmability.

Use of a smartphone electrocardiogram to diagnose arrhythmias during exercise in athletes: a case series

Background

While athletes are generally very fit, intense exercise can increase the risk of atrial fibrillation. Moreover, other arrhythmias such as atrial flutter or supraventricular tachycardia can cause distressing, exercise-related symptoms. Given symptoms are infrequent and may occur during intense exertion, traditional monitoring devices are often impractical to use during exercise. Smartphone electrocardiograms (ECGs) such as the Alivecor Kardia device may be the portable and reliable tool required to help identify arrhythmias in this challenging population. This case series highlights the use of such devices in aiding the diagnosis of arrhythmias in the setting of exercise-related symptoms in athletes.

Case summary

The six cases in this series included one elite non-endurance athlete, two elite cricketers, one amateur middle-distance runner, and two semi-elite ultra-endurance runners, with an age range of 16-48 years. An accurate diagnosis of an arrhythmia was obtained in five cases (atrial fibrillation/flutter and supraventricular tachycardias) using the smartphone ECG, which helped guide definitive treatment. No arrhythmia was identified in the final case despite using the device during multiple symptomatic events.

Discussion

The smartphone ECG was able to accurately detect arrhythmias and provide a diagnosis in cases where traditional monitoring had not. The utility of detecting no arrhythmia during symptoms in one case was also highlighted, providing the athlete with the confidence to continue exercising. This reassurance and confidence across all cases is perhaps the most valuable aspect of this device, where clinicians and athletes can be more certain of reaching a diagnosis and undertaking appropriate management.

Reducing the Electrogram Review Burden Imposed by Insertable Cardiac Monitors

BACKGROUND

Insertable cardiac monitors (ICMs) are essential for ambulatory arrhythmia diagnosis. However, definitive diagnoses still require time-consuming, manual adjudication of electrograms (EGMs).

OBJECTIVE

To evaluate the clinical impact of selecting only key EGMs for review.

METHODS

Retrospective analyses of randomly selected Abbott Confirm Rx^TM devices with ≥90 days of remote transmission history was performed, with each EGM adjudicated as true or false positive (TP, FP). For each device, up to 3 "key EGMs" per arrhythmia type per day were prioritized for review based on ventricular rate and episode duration. The reduction in EGMs and TP days (patient-days with at least 1 TP EGM), and any diagnostic delay (from the first TP), were calculated vs. reviewing all EGMs.

RESULTS

In 1,000 ICMs over a median duration of 8.1 months, at least one atrial fibrillation (AF), tachycardia, bradycardia, or pause EGM was transmitted by 424, 343, 190, and 325 devices, respectively, with a total of 95716 EGMs. Approximately 90% of episodes were contributed by 25% of patients. Key EGM selection reduced EGM review burden by 43%, 66%, 77%, and 50% (55% overall), while reducing TP days by 0.8%, 2.1%, 0.2%, and 0.0%, respectively. Despite reviewing fewer EGMs, 99% of devices with a TP EGM were ultimately diagnosed on the same day vs. reviewing all EGMs.

CONCLUSIONS

Key EGM selection reduced the EGM review substantially with no delay-to-diagnosis in 99% of patients exhibiting true arrhythmias. Implementing these rules in the Abbott patient care network may accelerate clinical workflow without compromising diagnostic timelines. This article is protected by copyright. All rights reserved.

New Generation Miniaturized Insertable Cardiac Monitor with a Long Sensing Vector: Insertion Procedure, Sensing Performance, and Home Monitoring Transmission Success in a Real-World Population

Background

Objective

Methods

Results

Conclusion

Remote assessment of QT interval: A new perspective for implantable cardiac monitors

BACKGROUND

There is an unmet need for simple tools for monitoring QT intervals. The feasibility of measuring the QT interval on the single‑lead subcutaneous electrocardiogram (subECG) recorded and transmitted by implantable cardiac monitors (ICMs) has never been tested.

METHODS

We performed a standard ECG in patients who had already been implanted with a long sensing vector ICM (BIOMONITOR, Biotronik SE&Co.) to calculate the corrected QT interval in lead II (QTc ECG). The QTc was then evaluated on the subECG provided by ICM both by using the programmer printout (QTc subECG) and the snapshot transmitted via home monitoring (QTc HM). Values were compared with Bland-Altman analyses.

RESULTS

The study cohort consisted of 23 ICM recipients (age 58 ± 19 years, 35% female) implanted mainly for unexplained syncope (78%). The mean QTc ECG interval was 404 ± 31 ms. The T-wave was visible and QTc could be calculated in all patients using the ICM programmer printout and in 21 (91%) patients remotely. The QTc subECG and QTc HM were 405 ± 34 and 406 ± 32 ms. Compared to the QTc ECG, Bland-Altman analyses revealed a bias of -0.9 (95% confidence interval: -6.8/4.9) ms and 0.1 (-12.7/12.9) ms for QTc subECG and QTc HM, respectively.

CONCLUSIONS

The QTc interval can be reliably estimated on in-person and remote subECG in most patients without bias compared to the ECG lead II assessment. This technology has the potential to facilitate remote QT interval monitoring.

Subcutaneouscardiac Rhythm Monitors: A Comprehensive Review

Subcutaneous loop recorders (SCRMs) are subcutaneous electronic devices which have revolutionized the field of arrhythmia detection. They have become increasingly appealing due to advances such as miniaturization of device, longer battery life, bluetooth capabilities and relatively simple implantation technique without the need for complex surgical suites. They can be implanted in the office, patient bedside without the need to go to the operating room. One of the most common indications for their implantation is detection of atrial fibrillation (AF) after a cryptogenic stroke. They have also been utilized for assessing the success of rhythm control strategies such post pulmonary venous isolation. More recently studies have assessed the utility of SCRMs for detecting silent AF in at risk populations such as patients with sleep apnea or those on hemodialysis. In this paper, we review the evolution of SCRMs, the clinical studies assessing their value for different indications, their role incurrent clinical practice and future avenues in the era of smart wearable devices like apple watch etc.

R-wave amplitude changes with posture and physical activity over time in an insertable cardiac monitor

Background

Insertable cardiac monitors (ICMs) are accepted tools in cardiac arrhythmia management. Consistent R-wave amplitude (RWA) is essential for optimal detection.

Objectives

Assess RWAs with posture/activities at insertion and at 30 days.

Methods

Participants (n = 90) with Confirm Rx™ ICM had RWAs measured in different postures (supine, right-side [RS], left-side [LS], sitting, and standing) and defined physical activities (including isometric push [IPUSH] and pull) at 2 time points. ICMs were inserted in 45° to sternum and parasternal orientations.

Results

There were significant reductions at insertion with RS, LS, sitting, or standing vs supine (reference position) (all P < .05). At 30 days, significant changes only occurred with LS and sitting (P < .05). Sex had an effect on RWAs, with females having significant variability at insertion (supine vs RS, LS, sitting, standing, and IPUSH; all P < .05). Males showed large RWA interpatient variabilities but minimal differences between positions vs supine. At 30 days, RS, LS, and sitting positions remained significant for females (P < .05), while in males RWAs were higher than at insertion for most postures and activities. The orientation 45° to sternum had consistently higher RWAs vs parasternal orientation at both time points (P < .0001). In females, ICM orientation had no significant effect on RWAs; however, in males the 45° to sternum produced higher RWAs. ICM movement from the insertion site showed no correlation with RWA changes.

Conclusion

The mean RWAs were higher at 30 days with less interparticipant and interpostural variability; males had higher RWAs compared to females; 45° to sternum orientation had higher RWAs; and ICM migration from the insertion site did not affect RWAs.

Factors affecting signal quality in implantable cardiac monitors with long sensing vector

PURPOSE

Electrical artefacts are frequent in implantable cardiac monitors (ICMs). We analyzed the subcutaneous electrogram (sECG) provided by an ICM with a long sensing vector and factors potentially affecting its quality.

METHODS

Consecutive ICM recipients underwent a follow-up where demographics, body mass index (BMI), implant location, and surface ECG were collected. The sECG was then analyzed in terms of R-wave amplitude and P-wave visibility.

RESULTS

A total of 84 patients (43% female, median age 68 [58-76] years) were enrolled at 3 sites. ICMs were positioned with intermediate inclination (n = 44, 52%), parallel (n = 35, 43%), or perpendicular (n = 5, 6%) to the sternum. The median R-wave amplitude was 1.10 (0.72-1.48) mV with P waves readily visible in 69.2% (95% confidence interval, CI: 57.8%-79.2%), partially visible in 23.1% [95% CI: 14.3%-34.0%], and never visible in 7.7% [95% CI: 2.9%-16.0%] of patients. Men had higher R-wave amplitudes compared to women (1.40 [0.96-1.80] mV vs 1.00 [0.60-1.20] mV, P = .001), while obese people tended to have lower values (0.80 [0.62-1.28] mV vs 1.10 [0.90-1.50] mV, P = .074). The P-wave visibility reached 86.2% [95% CI: 68.3%-96.1%] in patients with high-voltage P waves (≥0.2 mV) at surface ECG. The sECG quality was not affected by implant site.

CONCLUSION

In ordinary clinical practice, ICMs with long sensing vector provided median R-wave amplitude above 1 mV and reliable P-wave visibility of nearly 70%, regardless of the position of the device. Women and obese patients showed lower but still very good signal quality.

Over- and undersensing-pitfalls of arrhythmia detection with implantable devices and wearables

Cardiac implantable electronic devices (CIEDs) are a cornerstone of arrhythmia and heart failure detection as well as management. In recent years new kinds of devices have emerged which can be used subcutaneously or worn on the skin. In particular for large-scale arrhythmia monitoring, small, unobtrusive gadgets seem positioned to upend paradigms and care delivery. However, the performance of CIEDs and wearables is only as good as their sensing and detection capacities. Whether for pacing, defibrillation or diagnostic monitoring, the device must be able to process and filter the sensed signal to reduce noise and to exclude irrelevant physiological signals. The demands on sensing and detection quality will differ depending on how the information is applied. With a pacemaker or implantable cardioverter/defibrillator, withheld or erroneous therapy can have severe consequences and accurate and reliable detection of cardiac function is crucial. Monitoring devices are usually used in risk assessment and management, with greater tolerance for isolated artefacts or lower quality of readings. This review discusses sensing and detection and the performance to date by CIEDs as well as subcutaneous and wearable devices.

Miniaturized implantable cardiac monitor with a long sensing vector (BIOMONITOR III): Insertion procedure assessment, sensing performance, and home monitoring transmission success

BACKGROUND

Implantable Cardiac Monitors (ICMs) are used for long-term monitoring of arrhythmias. BIOMONITOR III is a novel ICM with a miniaturized profile, long sensing vector due to a flexible antenna, simplified implantation with a dedicated insertion tool for pocket formation and ICM placement in a single step, and daily automatic Home Monitoring (HM) function.

METHODS

In 47 patients undergoing BIOMONITOR III insertion for any ICM indication, 16 investigators at 10 Australian sites assessed handling characteristics of the insertion tool, R-wave amplitudes, noise burden, P-wave visibility, and HM transmission success. Patients were followed for 1 month.

RESULTS

All 47 attempted insertions were successful. Median time from skin incision to removal of the insertion tool after ICM insertion was 39 s (IQR 19-65) and to wound closure and cleaning was 4.7 min (IQR 3.5-7.8). All aspects of the insertion tool were rated as "good" or "excellent" in ≥97.9% and "fair" in ≤2.1% of patients, except for "force needed for tunnelling" (91.5% good/excellent, 8.5% fair). Based on HM data, R-waves in the first month were stable at 0.70 ± 0.37 mV. Median noise burden (disabling automatic rhythm evaluation) was 0.19% (IQR 0.00-0.93), equivalent to 2.7 min (IQR 0.0-13.4) per day. In HM-transmitted ECG strips with regular sinus rhythm, P-waves were visible in 89 ± 24% of heart cycles. Patient-individual automatic Home Monitoring transmission success was 98.0% ± 5.5%.

CONCLUSIONS

The novel ICM performed well in all aspects studied, including fast insertion, reliable R-wave sensing, good P-wave visibility, and highly successful HM transmissions.

Are implantable cardiac monitors reliable tools for cardiac arrhythmias detection? An intra-patient comparison with permanent pacemakers

INTRODUCTION

Implantable cardiac monitor (ICM) is an established tool for the management of unexplained syncope and atrial fibrillation (AF) even if its accuracy of arrhythmia detection may be suboptimal. The aim of this study was to perform an intra-patient comparison of the diagnostic capability of ICM with a dual-chamber PM as a gold standard.

METHODS

We included 19 patients with a previously implanted ICM (BioMonitor 2 Biotronik, Berlin, Germany), who received a dual-chamber PM for standard indications. ICM-detected arrhythmic events in a 6-month follow-up were compared with those detected by the PM and classified by visual inspection of intracardiac electrograms.

RESULTS

During follow up, ICMs generated 15 false asystole and 39 false bradycardia detections in 5 patients (26.3%) due to recurrent premature ventricular contractions. A total of 34 true high ventricular rate (HVR) episodes were detected by the PM. Of them, 30 (88%) events were also recorded by the ICM, which further detected 14 false HVR snapshots, leading to a sensitivity and positive predictive value of 88% and 68%, respectively. In addition, PM identified 234 true AF episodes. Of them, 225 (96%) events were also detected by the ICM, while 8 (42%) ICMs stored 50 AF episodes classified as false positives. The ICM sensitivity for AF was 96% with a positive predictive value of 82%.

CONCLUSION

Our intra-patient comparison with permanent PM confirmed that ICM is an effective tool for cardiac arrhythmias detection. ICM algorithms for AF and HVR detection were highly sensitive with an acceptable rate of false positive episodes.

Use of insertable cardiac monitors for the detection of atrial fibrillation in patients with cryptogenic stroke in the United States is cost-effective

Objectives: Atrial fibrillation (AF) is the most common arrhythmia and a major marker of ischemic stroke risk. Early detection is crucial and, once diagnosed, anticoagulation therapy can be initiated to reduce stroke risk. The aim of this study was to assess the cost-effectiveness of employing an insertable cardiac monitor (ICM), BIOMONITOR, for the detection of AF compared to standard of care (SoC) ECG and Holter monitoring in patients with cryptogenic stroke, that is, stroke of unknown origin and where paroxysmal, silent AF is suspected. Materials and methods: A Markov model was developed which consisted of five main health states reflecting the potential lifetime evolution of the AF disease: post cryptogenic stroke (index event), subsequent mild, moderate and severe stroke, and death. Sub-states were included to track a patient's AF diagnostic status and the use of antiplatelet or anticoagulant therapy. AF detection was assumed to result in a treatment switch from aspirin to anticoagulants, except among those with a history of major bleeding. Detection yield and accuracy, clinical actions and treatment effects were derived from the literature and validated by an expert clinician. All relevant costs from a US Medicare perspective were included. Results and conclusions: An ICM-based strategy was associated with a reduction of 37 secondary ischemic strokes per 1000 patients monitored compared with SoC. Total per-patient costs with an ICM were higher (US$90,052 vs. US$85,157) although stroke-related costs were reduced. The use of an ICM was associated with a base-case incremental cost-effectiveness ratio of US$18,487 per life year gained compared with SoC and US$25,098 per quality-adjusted life year gained, below established willingness-to-pay thresholds. The conclusions were found to be robust over a range of input values. From a US Medicare perspective the use of a BIOMONITOR ICM represents a cost-effective diagnostic strategy for patients with cryptogenic stroke and suspected AF.

Transmission and loss of ECG snapshots: Remote monitoring in implantable cardiac monitors

INTRODUCTION

Remote monitoring including transmission of electrocardiogram (ECG) strips has been implemented in implantable cardiac monitors (ICM). We appraise whether the physician can rely on remote monitoring to be informed of all possibly significant arrhythmias.

METHODS

We analyzed remote monitoring transmissions of patients in the ongoing BIO|GUARD-MI study, in which Biotronik devices are used. Once per day, the devices automatically transmit messages with up to six ECG snapshots to the Home Monitoring Service Center. If more than one type of arrhythmia is recorded during a day, at least one ECG of each arrhythmia type is transmitted.

RESULTS

212 study patients were registered at the service center. The mean age of the patients was 70 ± 8 years, and 74% were male. Patients were followed for an average of 13 months. The median time from device implantation until the first message receipt in the service center was 2 days. The median patient-individual transmission success was 98.0% (IQR 93.6-99.8) and remained stable in the second and third year. The most frequent arrhythmias were atrial fibrillation, bradycardia and high ventricular rate. 17.3% of the messages with ECG snapshots contained more than one arrhythmia type.

DISCUSSION

Our analysis confirms that the physician can rely on Home Monitoring to be informed of all possibly significant arrhythmias during long-term follow-up. We have found hints that the transmission of only one episode per day may lead to the loss of clinically relevant information if patients with ICMs are followed by remote monitoring only.

Long-term rhythm monitoring with an implantable loop recorder in patients after the first clinical atrial fibrillation episode. Towards an individualized management

Although atrial fibrillation (AF) is an arrhythmia with a variable clinical profile (symptomatic and asymptomatic episodes), the first symptomatic episode leads to its initial diagnosis in most cases. Nowadays, continuous and remote long-term cardiac rhythm monitoring is feasible by the use of implantable loop recorders. The data concerning the AF recurrences and progression after the first electrocardiographic-documented clinical AF episode demonstrates that a high percentage of patients may not suffer any other AF recurrence, or may present a low recurrence rate of the arrhythmia in the future. The AF burden may play a key role in the management of the arrhythmia as far as the decision-making for anticoagulation, rate and/or rhythm control therapy is concerned. There is evidence that a higher AF burden is associated with a higher risk of ischemic stroke. Non-vitamin K antagonists (NOACs) anticoagulants are increasingly used in the management of AF, providing a more predictable effect with rapid onset and offset of their action. The use of these agents in combination with devices that provide a continuous remote rhythm monitoring capability has encouraged anticoagulation strategies based on the AF burden. Data from tailored anticoagulation studies in AF are in favor of the long-term rhythm monitoring, ensuring a patient-centered approach with a better evaluation and more individualized management of AF, especially in patients with intermediate thromboembolic risk and high bleeding risk. Further large randomized trials are needed, not only to evaluate such strategies but also to elucidate the long-term cardiac rhythm monitoring in the AF management.

Implantable loop recorder in clinical practice

The implantable loop recorder (ILR), also known as insertable cardiac monitor (ICM) is a subcutaneous device used for diagnosing heart rhythm disorders. These devices have been strongly improved and miniaturized during the last years showing several reliable features along with the availability of remote monitoring which improves the diagnostic timing and the follow-up strategy with a potential reduction of costs for health care. The recent advent of injectable ILRs makes the procedure even easier and more tolerated by patients. ILR allows the investigation of unexplained recurrent syncope with uncertain diagnosis, revealing a possible relationship with cardiac arrhythmias. In addition, it has recently been equipped with sophisticated algorithms able to detect atrial fibrillation episodes. This new opportunity may provide to the physicians systematic heart rhythm screening with possible effects on patient antiarrhythmic and anticoagulant therapy management. The use of such devices will surely increase, since they may be helpful to diagnose a wide range of disorders and pathologies. Indeed, further studies should be performed in order to identify all the potentialities of these tools.

Noninvasive Assessment of Atrial Fibrillation Complexity in Relation to Ablation Characteristics and Outcome

Background: The use of surface recordings to assess atrial fibrillation (AF) complexity is still limited in clinical practice. We propose a noninvasive tool to quantify AF complexity from body surface potential maps (BSPMs) that could be used to choose patients who are eligible for AF ablation and assess therapy impact.

Methods: BSPMs (mean duration: 7 ± 4 s) were recorded with a 252-lead vest in 97 persistent AF patients (80 male, 64 ± 11 years, duration 9.6 ± 10.4 months) before undergoing catheter ablation. Baseline cycle length (CL) was measured in the left atrial appendage. The procedural endpoint was AF termination. The ablation strategy impact was defined in terms of number of regions ablated, radiofrequency delivery time to achieve AF termination, and acute outcome. The atrial fibrillatory wave signal extracted from BSPMs was divided in 0.5-s consecutive segments, each projected on a 3D subspace determined through principal component analysis (PCA) in the current frame. We introduced the nondipolar component index (NDI) that quantifies the fraction of energy retained after subtracting an equivalent PCA dipolar approximation of heart electrical activity. AF complexity was assessed by the NDI averaged over the entire recording and compared to ablation strategy.

Results: AF terminated in 77 patients (79%), whose baseline AF CL was 177 ± 40 ms, whereas it was 157 ± 26 ms in patients with unsuccessful ablation outcome (p = 0.0586). Mean radiofrequency emission duration was 35 ± 21 min; 4 ± 2 regions were targeted. Long-lasting AF patients (≥12 months) exhibited higher complexity, with higher NDI values (≥12 months: 0.12 ± 0.04 vs. <12 months: 0.09 ± 0.03, p < 0.01) and short CLs (<160 ms: 0.12 ± 0.03 vs. between 160 and 180 ms: 0.10 ± 0.03 vs. >180 ms: 0.09 ± 0.03, p < 0.01). More organized AF as measured by lower NDI was associated with successful ablation outcome (termination: 0.10 ± 0.03 vs. no termination: 0.12 ± 0.04, p < 0.01), shorter procedures (<30 min: 0.09 ± 0.04 vs. ≥30 min: 0.11 ± 0.03, p < 0.001) and fewer ablation targets (<4: 0.09 ± 0.03 vs. ≥4: 0.11 ± 0.04, p < 0.01).

Conclusions: AF complexity can be noninvasively quantified by PCA in BSPMs and correlates with ablation outcome and AF pathophysiology.