Use of the implantable loop recorder in evaluation of patients with unexplained syncope

Single Position ECG Detection System Based on Charge Induction

With the growing incidence of cardiovascular disease (CVD) in recent decades, the demand for out-of-hospital real-time ECG monitoring is increasing day by day, which promotes the research and development of portable ECG monitoring equipment. At present, two main categories of ECG monitoring devices are "limb lead ECG recording devices" and "chest lead ECG recording devices", which both require at least two electrodes. The former needs to complete the detection by means of a two-hand lap joint. This will seriously affect the normal activities of users. The electrodes used by the latter also need to be kept at a certain distance, usually more than 10 cm, to ensure the accuracy of the detection results. Decreasing the electrode spacing of the existing ECG detection equipment or reducing the area required for detection will be more conducive to improving the integration of the out-of-hospital portable ECG technologies. Therefore, a single-position ECG system based on charge induction is proposed to realize ECG detection on the surface of the human body with only one electrode with a diameter of less than 2 cm. Firstly, the ECG waveform detected in a single location is simulated by analyzing the electrophysiological activities of the human heart on the human body surface with COMSOL Multiphysics 5.4 software. Then, the hardware circuit design of the system and the host computer are developed and the test is performed. Finally, experiments for static and dynamic ECG monitoring are carried out and the heart rate correlation coefficients are 0.9698 and 0.9802, respectively, which proves the reliability and data accuracy of the system.

BioMonitor 2 Pilot Study: Early Experience With Implantation of the Biotronik BioMonitor 2 Implantable Cardiac Monitor

BACKGROUND

The BioMonitor 2 Pilot Study assessed the implantation procedure, the sensing amplitude and the remote monitoring transmission success rate of the second generation implantable cardiac monitor, the BioMonitor 2 (Biotronik, Berlin, Germany).

METHODS

This was a prospective, multi-centre, single-arm, non-randomised study involving seven operators in five sites across Australia. Data were collected at implantation, during clinic visits at 1 week and 1 month post-implantation, and through wireless remote monitoring.

RESULTS

Thirty patients with indications for long-term cardiac monitoring underwent successful insertion of a study device. The median implantation time was 9 minutes (interquartile range (IQR) 5-14 mins). The mean R-wave amplitude at 1 week was 0.75±0.39mV and remained stable over the follow-up period. Within 1 day, 97% of the patients connected to the remote monitoring network and daily messages were transmitted on 93.8% of all study days. Seventy-six per cent of patients transmitted at least one subcutaneous ECG (sECG), with a median number of sECGs per patient of seven (IQR 3-37) within 28 days.

CONCLUSIONS

The results of the BioMonitor 2 Pilot study confirm the excellent sensing amplitudes afforded by this new device and the utility of the implantation tools and technique. Patient compliance with and the transmission success rate of the home monitoring system were excellent.

P- and R-wave Amplitude Sensed by Reveal LINQ™ Loop Recorder in Pediatric Patients

Implantable loop recorders are commonly used to sense arrhythmias. The purpose of this study is to assess the P- and R-wave amplitudes at implantation (I) and follow-up (F) following insertion of the Reveal LINQ™ Insertable Cardiac Monitor (Medtronic, Minneapolis, MN) in an institutional review board-approved, multicenter study performed on pediatric patients younger than 18 years old. Collected data included demographics, presence of congenital heart disease (CHD), P- and R-wave-sensed amplitude at I and F, and the method of implant (i.e. mapping or standard.) P waves were manually measured and R-wave sensing was recorded by the device. A total of 87 patients had a Reveal LINQ™ (Medtronic, Minneapolis, MN) device implanted; the mean patient age was 11.8 years (0.5 years to 18 years) with 48% of patients being female and 19% of patients having CHD; mapping was used in 43% of patients. The Reveal LINQ™ (Medtronic, Minneapolis, MN) experienced no change in average sensed R-wave amplitude at either I or F (1.28 mV vs 1.26 mV, p = NS). There was no difference in sensed R-wave amplitude noted with or without mapping used at I (1.29 mV vs 1.26 mV, p = NS) or F (1.48 mV vs 1.18 mV, p = NS). Additionally, no difference could be found in R-wave sensing of patients with CHD or without CHD at I (1.26 mV vs 1.4 mV, p = NS) or F (1.32 mV vs 1.32 mV, p = NS). R-wave sensing trended towards being inversely proportional to patient body surface area (BSA) (p = NS). P waves were detected on 48% of tracings in all patients at I and/or F, irrespective of whether the Reveal LINQ™ (Medtronic, Minneapolis, MN) device was placed with mapping. The R wave was (0.37–3.5 mV) at I and (0.3–3 mV) (p = NS) at F when P waves were detected. From these results, it can be said that the Reveal LINQ™ Insertable Cardiac Monitor (Medtronic, Minneapolis, MN) has an excellent ability to sense R-wave amplitude in pediatric patients. No significant difference in the sensing ability of the device could be identified with respect to the presence of CHD, use of mapping or BSA. P waves tended to be identified when there was a higher baseline R-wave amplitude.

Performance of an Implantable Cardiac Monitor to Detect Atrial Fibrillation: Results of the DETECT AF Study

INTRODUCTION

Reliable detection and monitoring of atrial fibrillation (AF) is essential for accurate clinical decision making, which can now be done continuously with the introduction of implantable cardiac monitors (ICM) The DETECT AF study evaluated the performance of the Confirm DM2102 ICM (St. Jude Medical, St. Paul, MN, USA) to accurately detect and monitor AF.

METHODS

Ninety patients previously implanted with the ICM and with either suspected or known paroxysmal AF were enrolled at 12 centers in Germany and The Netherlands. At least 2 weeks after ICM implant, patients wore a Holter monitor for 4 days, while the ICM monitored for AF episodes lasting at least 2 minutes. Holter monitor data was analyzed by a blinded, independent core laboratory and compared to the ICM AF detections. Patient and episode sensitivity (SE), specificity (SP), positive predictive value (PPV), and negative predictive (NPV) were calculated using standard analysis and a generalized estimation equation method where appropriate.

RESULTS

A total of 79/90 subjects (61% male, 65.7 ± 9.6 years old) were included in the analysis, totaling 6,894 hours of Holter monitoring. Using a per patient analysis SE was 100%, PPV was 64.0%, SP was 85.7%, and NPV was 100%. Using a per episode analysis, SE was 94.0% and PPV was 64.0%. With an AF duration analysis, the SE was 83.9%, PPV was 97.3%, SP was 99.4% with an NPV of 98.5%.

CONCLUSION

The SJM Confirm DM2102 can accurately and repeatedly detect paroxysmal AF episodes of at least 2 minutes in length.

R-wave sensing in an implantable cardiac monitor without ECG-based preimplant mapping: results from a multicenter clinical trial

INTRODUCTION

Reducing the form factor of an implantable cardiac monitor (ICM) may simplify device implant. This study evaluated R-wave sensing at a range of electrode distances and a preferred device implant location without mapping.

METHODS

Patients scheduled for a Medtronic Reveal® ICM implant (Medtronic Inc., Minneapolis, MN, USA) underwent a preimplant pocket recording using a diagnostic recording catheter. The ICM implant location was left to the discretion of the implanting physician, but a "recommended" position spanned the V2 -V3 electrocardiogram electrode location in an oblique 45° angle. R-wave amplitudes were analyzed from ICM follow-up.

RESULTS

Seventeen of 41 subjects (15 male, age 57 ± 16 years) had the maximum surface-filtered R-wave at the recommended location. Fourteen patients underwent diagnostic recording across the range of electrode spacing. There was a strong correlation between the R-wave amplitude and electrode distance (r(2) = 0.97, P < 0.001) with an increase of 29 μV per 2.5 mm. Comparing normalized R-wave distributions between the recommended ICM implant group (Group 1, n = 19) and the remaining patients (Group 2, n = 7), the proportion of ICM R-wave counts of amplitude 0.25-1.2 mV was higher (79% vs 46%, P < 0.05). Of 17 patients in Group 1 who had ≥ 1-month ICM follow-up (79 ± 45 days), no sensing-related false arrhythmia detection was found in 16 (93%) patients.

CONCLUSIONS

The subcutaneous R-wave amplitude correlates with electrode spacing in the implant zone of ICM patients. Implant locations at the V2 -V3 position at a 45° angle offer an adequate R wave for sensing. Preimplant mapping to achieve acceptable R-wave amplitude may not be necessary.

A retrospective study of the clinical experience of the implantable loop recorder in a paediatric setting

The implantable loop recorder (ILR) has proved highly efficacious in the management of syncope, presyncope and palpitations in selected populations. Limited information regarding patient selection and diagnostic yield exists in the paediatric setting. A retrospective evaluation of patients who underwent ILR implantation over a 66-month period, in a tertiary paediatric cardiology unit was conducted. Twenty-three patients (10 male, 13 female) following initial assessment and investigation, were referred for device implantation. The mean age at time of ILR insertion was 11.39 +/- 4.34 (range, 2.0-16.8) years. The indications for ILR were recurrent syncope (n = 11), presyncope (n = 3) or palpitations (n = 9). Four (17.4%) patients had structural heart disease, three (13%) had a positive family history of sudden cardiac death and one (4%) had perinatal arrhythmia. One patient required ILR repositioning, and pocket infection necessitated explantation in one further patient. Minimum follow-up was 7.8 months during which symptoms were reported in 15 (65.2%) patients post-ILR insertion. Eight (34.7%) remained asymptomatic. Of the 15 who experienced symptom recurrence, eight (53.3%) had an arrhythmia recorded. Tachycardias recorded were polymorphic ventricular tachycardia (n = 1) and supraventricular tachycardia (n = 5). Clinically significant bradycardias documented, included sinus arrest (n = 1) and Mobitz type II second degree atrioventricular block (n = 1). The ILR had a high diagnostic yield, enabling an arrhythmic or non-arrhythmic diagnosis in 65.2% of patients with recurrent syncope, presyncope or palpitations in a selected paediatric population.

Sudden Cardiac Death in the Young: A Strategy for Prevention by Targeted Evaluation

The annual incidence of sudden cardiac death (SCD) in the general population is estimated as 1 in a 1,000. Since survival rates from out-of-hospital cardiac arrests are poor, primary prevention is key to reducing the burden of SCD in the community. Prominent causes of SCD include ischaemic heart disease, anomalous coronary arteries, and the primary myocardial diseases: hypertrophic cardiomyopathy, dilated cardiomyopathy, and ar rhythmogenic right ventricular cardiomyopathy (ARVC). In 4% of sudden deaths in the 16-64 age group, post-mortem examination fails to identify a cause, yielding a default diagnosis of sudden arrhythmic death syndrome (SADS). The inherited arrhythmia syndromes (long QT, short QT, and Brugada syndromes, and familial catecholaminergic polymorphic ventricular tachycardia) may be implicated in SADS, owing to their propensity for producing ventricular tachyarrhythmia in the structurally normal heart. Monogenic disorders therefore predominate as causes of SCD in the young. The advent of effective therapies for these diseases, particularly implantable cardioverter defibrillators, has prompted calls for universal screening to enable timely diagnosis of occult cardiac disease. Since prospective cardiac assessment of the general population is not feasible, the solution may be to target high-risk subgroups, namely, patients with cardiac symptoms, relatives of SCD victims, and competitive athletes. The recommended preliminary work-up includes a 12-lead ECG, signal-averaged ECG, transthoracic echocardiogram, exercise test, and ambulatory ECG monitoring. Cardiovascular magnetic resonance is a useful adjunct in patients with suspected ARVC or anomalous coronary arteries. Provocative challenge with a sodium challenge blocker may be of value in unmasking the Brugada syndrome. Identification of disease-causing mutations in affected individuals facilitates cascade screening of families.

Long-term continuous external electrocardiographic recording: a review

Ambulatory electrocardiographic (AECG) monitoring is an essential tool in the diagnostic evaluation of patients with cardiac arrhythmias. Recent advances in solid-state technology have improved the quality of the ECG signals and new dedicated algorithms have expanded the clinical application of software-based AECG analysis systems. These advances, in addition to the availability of inexpensive large storage capacities, and very long-term continuous high-quality AECG monitoring, have opened new potential uses for AECG. New digital recorders have the capability of multichannel simultaneous recordings (from 3 to 12 leads) and for telemetred signal transduction. These possibilities will expand the traditional uses of AECG for arrhythmia detection, as arrhythmia monitoring to assess drug and device efficacies has been further defined by new studies. The analysis of transient ST-segment deviation still remains controversial, but considerably more data are now available, especially about the prognostic value of detecting asymptomatic ischaemia. Heart rate variability analysis has shown promise for predicting mortality rates in cardiac patients at high risk. We review recent advances in this field of non-invasive cardiac testing.

An implantable loop recorder study of highly symptomatic vasovagal patients: the heart rhythm observed during a spontaneous syncope is identical to the recurrent syncope but not correlated with the head-up tilt test or adenosine triphosphate test

OBJECTIVES

The aim of this study was to analyze the heart rhythm during spontaneous vasovagal syncope (VVS) in highly symptomatic patients with implantable loop recorders (ILR) and to correlate this rhythm with the heart rhythm observed during head-up tilt test (HUT).

BACKGROUND

Heart rhythm obtained during provocative condition is often used to guide therapy in VVS. To date there is no conclusive evidence that the heart rhythm observed during a positive HUT can predict heart rhythm during VVS or that the heart rhythm observed during a spontaneous syncope will be identical to the recurrent syncope.

METHODS

Twenty-five consecutive VVS patients (age 60.2 +/- 17.1 years; 14 women,) presenting with frequent syncopes (6.9 +/- 4.6 episodes/year) and a positive HUT (cardioinhibitory in 8 patients) were implanted with an ILR. Seven of them also had a positive adenosine triphosphate (ATP) test.

RESULTS

Follow-up was 17.0 +/- 3.6 months. Thirty VVS were observed in 12 patients. Nine episodes showed bradycardia of <40 beats/min or asystole; progressive sinus bradycardia preceding sinus arrest was the most frequent electrocardiographic finding. Twenty-one syncopes occurred without severe bradycardia. The heart rhythm observed during the first syncope was identical to the recurrence. No correlation was found between slow heart rate at the ILR interrogation and a cardioinhibitory HUT response (p = 1.0) or a positive ATP test (p = 1.0).

CONCLUSIONS

In highly symptomatic patients with VVS, the heart rhythm observed during spontaneous syncope does not correlate with the HUT. The heart rhythm during the first spontaneous syncope is identical to the recurrent syncope.

Infrequent Syncope in a Heavy Vehicle Driver

We present a case study of a truck driver with sinus node dysfunction diagnosed with the help of an implantable loop recorder more than 18 months after implantation. This case emphasizes that cardiogenic syncope may be very infrequent and its diagnosis can be elusive despite extensive testing.

Abdominal Implantation of Loop Recorders in Infants and Children

Implantable loop recorders have an important role in establishing symptom-rhythm correlation in adults with recurrent syncope or palpitations. The standard location of these devices is in a subcutaneous prepectoral pocket. As the device is bulky, this is not an ideal location in young patients. We report a technique of abdominal implantation of this device in 10 consecutive infants and children, achieving an excellent cosmetic result and diagnostic-quality electrograms at follow-up.

Feasibility of the Inframammary Location for Insertable Loop Recorders in Young Women and Girls

The parasternal location for the insertable loop recorder (ILR) has potential for erosion in small patients, and can be aesthetically unappealing, especially for young women. We assessed the feasibility of the inframammary location in nine patients, utilizing a 2 cm transverse incision at the inferior and medial border of the left or right breast. Signal quality was adequate with clearly discernable atrial and ventricular electrograms. No complications involving the surgical site were observed. Cosmetically, placement of the scar in the natural breast crease has been favorably accepted. Inframammary implantation of the ILR is feasible, and is the preferred method in young women and girls at our center.