Development and validation of a dual sensing scheme to improve accuracy of bradycardia and pause detection in an insertable cardiac monitor

Novel algorithms improve arrhythmia detection accuracy in insertable cardiac monitors

INTRODUCTION

Insertable cardiac monitors (ICMs) are commonly used to diagnose cardiac arrhythmias. False detections in the latest ICM systems remain an issue, primarily due to inaccurate R-wave sensing. New discrimination algorithms were developed and tested to reduce false detections of atrial fibrillation (AF), pause, and tachycardia episodes in ICMs.

METHODS

Stored electrograms (EGMs) of AF, pause, and tachycardia episodes detected by Abbott Confirm Rx™ ICMs were extracted from the Merlin.net™ Patient Care Network, and manually adjudicated to establish independent training and testing datasets. New discrimination algorithms were developed to reject false episodes due to inaccurate R-wave sensing, P-wave identification, and R-R interval patterns. The performance of these new algorithms was quantified by false positive reduction (FPR) and true positive maintenance (TPM), relative to the existing algorithms.

RESULTS

The new AF detection algorithm was trained on 5911 EGMs from 744 devices, resulting in 66.9% FPR and 97.8% TPM. In the testing data set of 1354 EGMs from 119 devices, this algorithm achieved 45.8% FPR and 97.0% TPM. The new pause algorithm was trained on 7178 EGMs from 1490 devices, resulting in 70.9% FPR and 98.7% TPM. In the testing data set of 1442 EGMs from 340 devices, this algorithm achieved 74.4% FPR and 99.3% TPM. The new tachycardia algorithm was trained on 520 EGMs from 204 devices, resulting in 57.0% FPR and 96.6% TPM. In the testing data set of 459 EGMs from 237 devices, this algorithm achieved 57.9% FPR and 96.5% TPM.

CONCLUSION

The new algorithms substantially reduced false AF, pause, and tachycardia episodes while maintaining the majority of true arrhythmia episodes detected by the Abbott ICM algorithms that exist today. Implementing these algorithms in the next-generation ICM systems may lead to improved detection accuracy, in-clinic efficiency, and device battery longevity.

Diagnostic sensitivity and cost per diagnosis of ambulatory cardiac monitoring strategies in unexplained syncope patients

Diagnosing cardiac pauses that could produce syncopal episodes is important to guide appropriate therapy. However, the infrequent nature of these episodes can make detection challenging with conventional monitoring (CM) strategies with short-term ECG monitors. Insertable cardiac monitors (ICMs) continuously monitor for arrhythmias but present a higher up-front cost. It is not well understood whether these higher costs are offset by the costs of repeat evaluation in CM strategies. We simulated the likelihood of diagnostic success and cost-per-diagnosis of pause arrhythmias with CM strategies compared to ICM monitoring. ICM device data from syncope patients diagnosed with pause arrhythmias was utilized to simulate patient pathways and diagnostic success with CM. We assumed that detected true pause episodes (≥5 seconds) were symptomatic and prompted a hospital encounter and further evaluation with CM. Subsequent true pause episodes in yet-undiagnosed patients triggered additional rounds of CM. Costs of monitoring were accrued at each encounter and represent the U.S. payer perspective. Cost per diagnosed patient was calculated as the total costs accrued for all patients divided by the number of patients diagnosed, across 1,000 simulations. During a mean 505±333 days of monitoring ICM detected 2.4±2.7 pause events per patient, with an average of 109±94 days until the first event. CM was projected to diagnose between 13.8% (24-hour Holter) and 30.2% (two 30-day monitors) of the ICM-diagnosed patients. Total diagnostic costs per ICM-diagnosed patient averaged $7,847, whereas in the CM strategies average cost-per-diagnosis ranged from $12,950±2,589 with 24-hour Holter to $32,977±14,749 for two 30-day monitors. Relative to patients diagnosed with pause arrhythmias via ICM, CM strategies diagnose fewer patients and incur higher costs per diagnosed patient.

Effectiveness of SharpSense™ algorithms in reducing bradycardia and pause detection: real-world performance in Confirm Rx™ insertable cardiac monitor

PURPOSE

SharpSense™ technology is an upgradable software enhancement introduced to the Abbott Confirm Rx™ insertable cardiac monitor (ICM). This study aims to characterize the real-world performance of SharpSense algorithms by comparing device detected pause and bradycardia episodes before and after the SharpSense upgrade.

METHODS

Confirm Rx devices with at least 90 days monitoring each before and after SharpSense upgrade were included in the study. Bradycardia and pause detections and subcutaneous electrocardiograms (SECGs) within 90 days before and after the upgrade were extracted from Merlin.net™ patient care network for evaluation and adjudicated by expert adjudicators.

RESULTS

A total of 197 devices were included in the analysis. Devices were implanted for syncope (35.0%), atrial fibrillation (32.5%), cryptogenic stroke (16.8%), and other indications including palpitations (15.7%). The SharpSense upgrade significantly reduced the number of bradycardia detections by 86.8% and pause detections by 93.1%. In adjudicated SECGs, the upgrade significantly reduced false positive (FP) bradycardia episodes by 91.5% and FP pause episodes by 82.8%. The percentage of devices with at least one FP episode was reduced from 39 to 20% for bradycardia and from 52 to 35% for pause. The number of devices with FP rate greater than 1 episode per week was reduced from 23 to 8% for bradycardia and from 39 to 20% for pause.

CONCLUSIONS

In this real-world performance evaluation, the algorithms incorporated in SharpSense software upgrade in Confirm Rx ICMs substantially reduced false positive bradycardia and pause detections and the number of transmitted SECGs for clinic review.

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.

Performance of implantable loop recorders. Role of R vector and detection algorithms

INTRODUCTION

We evaluated the performance of implantable loop recorders (ILRs) with different detection algorithms and looked for artifacts and therapeutic consequences and their dependence on patient factors.

METHODS AND RESULTS

586 RevealLinq™ ILRs (first generation (NT): n = 335; second generation with TruRhythm™ (TR): n = 251) were implanted during 2014-2021 (syncope n = 206; embolic stroke of unknown source (ESUS) n = 380). Automatically detected EGM episodes (n = 18,650) were classified as correct or incorrect for asystole (AS), atrial fibrillation (AF) or tachycardia (TA). Incorrect episodes were caused by loss of signal (LO), noise (NO), extrasystole (ES) and T-wave oversensing (TWO). Left directed R axes, lower R-amplitudes and older age were related to artifacts. Results were separated by indication. In ESUS patients TR reduced total median artifact episodes: 0.6 (0-7) vs 0 (0-5) (p < 0.03) and median artifact examination time: 0.3 (0-3.5) vs 0 (0-2.5) (p = 0.03) per patient-year. This benefit is caused by significant reductions in total AS and ES-AS artifacts. The total positive predictive value (PPV) improved only in syncope patients (45 vs 71%, p = 0.002). Accordingly in syncope patients with TR more therapeutic consequences could be established (log rank 0.003).

DISCUSSION

Patients R-axis and measured R-amplitudes during implantation predicted artifacts. This should be taken into account during ILR implantation. Total artifacts, AS artifacts and time spent for artifact analysis was reduced by the new TR detection algorithm in ESUS patients, whereas total artifacts remained unchanged in syncope patients despite reduction of AS artifacts. However TR had no effect on AF and TA episode detection and therefore has to be improved.

[Implantable ECG monitors]

Implantable loop recorders are a diagnostic tool for detecting cardiac arrhythmias and are independent of the patient's compliance. Automatic algorithms lead to a preselection of arrhythmic events that are transferred by telemonitoring to the cardiac specialists. This article describes the available loop recorders on the market, the respective implantation techniques, the indication, and reimbursement.

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.

Clinical evaluation of a small implantable cardiac monitor with a long sensing vector

Introduction

We conducted this study to show the safety and efficacy of a new implantable cardiac monitor (ICM), the BioMonitor 2 (Biotronik SE & Co. KG; Berlin, Germany), and to describe the arrhythmia detection performance.

Methods

The BioMonitor 2 has an extended sensing vector and is implanted close to the heart. It can transmit up to six subcutaneous electrocardiogram strips by Home Monitoring each day. We enrolled 92 patients with a standard device indication for an ICM in a single‐arm, multicenter prospective trial. Patients were followed for 3 months, and 48‐h Holter recordings were used to evaluate the arrhythmia detection performance.

Results

One patient withdrew consent and in one patient, the implantation failed. Two study device‐related serious adverse events were reported, satisfying the primary safety hypothesis. Implantations took 7.4 ± 4.4 min from skin cut to suture. At 1 week, the R‐wave amplitude was 0.75 ± 0.53 mV. In the 82 patients with completed Holter recordings, all patients with arrhythmias were correctly identified. False positive detections of arrhythmia were mostly irregular rhythms wrongly detected as atrial fibrillation (episode‐based positive predictive value 72.5%). Daily Home Monitoring transmission was 94.9% successful.

Conclusion

Safety and efficacy of the new device has been demonstrated. The detected R‐wave amplitudes are large, leading to a low level of inappropriate detections due to over‐ or undersensing.

Insertable cardiac monitors: current indications and devices

INTRODUCTION

Recurrent unexplained syncope is a well-established indication for an insertable cardiac monitor (ICM). Recently, the indications for an ICM have been expanded.

AREAS COVERED

This review article discusses the current indications for ICMs and gives an overview of the latest generation of commercially available ICMs.

EXPERT COMMENTARY

The 2018 ESC Syncope guidelines have expanded the indications for an ICM to patients with inherited cardiomyopathy, inherited channelopathy, suspected unproven epilepsy, and unexplained falls. ICMs are also increasingly used for the detection of subclinical atrial fibrillation (AF) in patients with cryptogenic stroke. Whether treatment of subclinical AF (SCAF) with oral anticoagulation prevents recurrent stroke is yet unknown. The current generation of ICMs are smaller, easier to implant, have better diagnostics, and are capable of remote monitoring. The Reveal LINQ (Medtronic) is the smallest ICM and has the most extensive performance and clinical data. The BioMonitor 2 (Biotronik) is the largest ICM but has excellent R-wave amplitudes, longest longevity, and reliable remote monitoring. The Confirm Rx (Abbott) is capable to provide mobile data transmission enabled by a smartphone app. Future generation of ICMs will incorporate heart failures indices to facilitate remote monitoring of heart failure patients.

Investigation of Key Variables Impacting ICM Sensing Using Computer Simulations

The insertable cardiac monitors (ICMs) used for diagnosing and managing abnormal heart activities can falsely detect heart rhythms due to respiration, device rotation/orientation, device position, device flipping, and body mass that alter the amplitudes and morphologies. The objective of this paper is to investigate the effects of these key variables on ICM sensing by using computer simulations and virtual human family. We observed in these simulations that sensing amplitudes can vary greatly depending on device flipping, orientation/rotation, and migration; change significantly due to respiration effect; and are most sensitive to it when body mass is large. Those findings support identification of the key variables impacting clinical false detections.

Trends in Subcutaneous Cardiac Monitoring Technology

Ambulatory cardiac monitoring is a rapidly expanding field and one that is likely to progress beyond electrocardiographic (ECG) and blood pressure recordings. To date, the primary cardiac monitoring focus has been ambulatory ECG (AECG) monitoring. In this setting, AECG monitoring has become a diagnostic tool used daily by physicians of many specialties. In this regard, both wearable and subcutaneous ECG monitoring technologies are now widely available, with the appropriate choice for a given patient being best determined by the frequency with which the patient’s symptom recurrences are expected. In other words, the less frequent the symptomatic events, then the longer the monitoring duration requirement should be. However, multiple factors other than the technology used impact success. For example, wearable AECG systems are only capable of monitoring patients for a period of a few days to several weeks due to limited battery longevity, patient intolerance to cutaneous ECG electrodes, the cumbersome nature of the device, or a combination of these factors. Current-generation insertable cardiac monitors (ICMs), on the other hand, offer three years of monitoring and infrequent skin irritation. Additionally, automatic remote download, a valuable feature in many cases, is only offered by certain wearable technologies, but is an option in all currently available ICMs. This report focuses on the current status of subcutaneous ICMs and their indications and limitations. The goal is to highlight the variety of utility of current ICM technologies and to provide insight into potential future subcutaneous ICM applications.

A single center experience on the clinical utility evaluation of an insertable cardiac monitor

BACKGROUND

The evaluation of insertable cardiac monitor (ICM) has been largely on the device performance and safety with only limited studies on the clinical utility. The aim of this study was to evaluate the clinical utility of ICM in patients with a variety of clinical presentations.

METHODS

A single-center retrospective study on the clinical utility, as measured by both expected and unexpected clinical useful ICM findings and the initiation of therapeutic interventions, was conducted.

RESULTS

Ninety-five consecutive patients (median age 68 years) received ICM Reveal LINQ™ for clinical indications of unexplained syncope (53), cryptogenic stroke (19), unexplained infrequent palpitations (14) and AF management (9). During a median follow-up of 414 days, the causes for unexplained syncope were arrhythmia-related (11.3%), arrhythmia-unrelated (32%) and undetermined (56.6%). Atrial fibrillation in patients with cryptogenic stroke was detected in 31.6% (6/19). The clinical utility occurrence was 48.4% with the expected and incidental (unexpected) clinical utility of 41% and 7.4% patients respectively. Of these, therapeutic interventions based on ICM diagnoses were initiated in 18.9% (18/95) of patients.

CONCLUSIONS

ICM (Reveal LINQ™) offers substantial expected and unexpected clinical utility in patients with a variety of clinical presentations. The causes of nearly one third of patients receiving ICM for unexplained syncope were unrelated to cardiac arrhythmia. Nearly one fifth of patients with newly diagnosed arrhythmia from ICM received therapeutic interventions.

Sensing performance, safety, and patient acceptability of long-dipole cardiac monitor: An innovative axillary insertion

BACKGROUND

The recommended location for implantable cardiac monitor (ICM) insertion is the left pectoral region. We tested whether an innovative left axillary implantation approach could be applicable for a new ICM, characterized by a long sensing dipole.

METHODS

We considered a series of 55 patients consecutively implanted with a long-dipole ICM (BioMonitor 2); the first 30 subjects underwent prepectoral location insertion, while the subsequent 25 received the ICM in the axillary region. Sensing performances collected at 1-month follow-up were compared between the two groups. During the visit, each patient was also asked to fill in a brief questionnaire to assess patient acceptability of the device.

RESULTS

All patients had a successful insertion of ICM. Mean R-wave amplitude was 0.87 ± 0.44 mV in the prepectoral group and 1.00 ± 0.45 mV in the axillary one, without any significant difference. The percentage of patients with visible P wave was also comparable between the two approaches (65.5% vs 68.2%, P = 0.84). None of the patients reported device-related issues or discomfort, and ICM was generally well accepted and tolerated by all the involved patients.

CONCLUSION

Axillary insertion may represent a valid alternative to the standard one for long-dipole ICM technology providing not only patient acceptability but also high-quality sensing performances.