Insertable loop recorder use for detection of intermittent arrhythmias

Perioperative management of patients with cardiac implantable electronic devices

The use of cardiac implantable electronic devices (CIEDs) has increased significantly in recent years. Consequently, more patients with CIEDs will undergo surgery during their lifetime, and thus the involvement of anesthesiologists in the perioperative management of CIEDs is increasing. With ongoing advancements in technology, many types of CIEDs have been developed, including permanent pacemakers, leadless pacemakers, implantable cardioverter defibrillators, cardiac resynchronization therapy-pacemakers/defibrillators, and implantable loop recorders. The functioning of CIEDs exposed to an electromagnetic field can be affected by electromagnetic interference, potential sources of which can be found in the operating room. Thus, to prevent potential adverse events caused by electromagnetic interference in the operating room, anesthesiologists must have knowledge of CIEDs and be able to identify each type. This review focuses on the perioperative management of patients with CIEDs, including indications for CIED implantation to determine the baseline cardiovascular status of patients; concerns associated with CIEDs before and during surgery; perioperative management of CIEDs, including magnet application and device reprogramming; and additional perioperative provisions for patients with CIEDs. As issues such as variations in programming capabilities and responses to magnet application according to device can be challenging, this review provides essential information for the safe perioperative management of patients with CIEDs.

Validation of Adhesive Single-Lead ECG Device Compared with Holter Monitoring among Non-Atrial Fibrillation Patients

There are few reports on head-to-head comparisons of electrocardiogram (ECG) monitoring between adhesive single-lead and Holter devices for arrhythmias other than atrial fibrillation (AF). This study aimed to compare 24 h ECG monitoring between the two devices in patients with general arrhythmia. Twenty-nine non-AF patients with a workup of pre-diagnosed arrhythmias or suspicious arrhythmic episodes were evaluated. Each participant wore both devices simultaneously, and the cardiac rhythm was monitored for 24 h. Selective ECG parameters were compared between the two devices. Two cardiologists independently compared the diagnoses of each device. The two most frequent monitoring indications were workup of premature atrial contractions (41.4%) and suspicious arrhythmia-related symptoms (37.9%). The single-lead device had a higher noise burden than the Holter device (0.04 ± 0.05% vs. 0.01 ± 0.01%, p = 0.024). The number of total QRS complexes, ventricular ectopic beats, and supraventricular ectopic beats showed an excellent degree of agreement between the two devices (intraclass correlation coefficients = 0.991, 1.000, and 0.987, respectively). In addition, the minimum/average/maximum heart rates showed an excellent degree of agreement. The two cardiologists made coherent diagnoses for all 29 participants using both monitoring methods. In conclusion, the single-lead adhesive device could be an acceptable alternative for ambulatory ECG monitoring in patients with general arrhythmia.

A new era in electroencephalographic monitoring? Subscalp devices for ultra-long-term recordings

Inaccurate subjective seizure counting poses treatment and diagnostic challenges and thus suboptimal quality in epilepsy management. The limitations of existing hospital- and home-based monitoring solutions are motivating the development of minimally invasive, subscalp, implantable electroencephalography (EEG) systems with accompanying cloud-based software. This new generation of ultra-long-term brain monitoring systems is setting expectations for a sea change in the field of clinical epilepsy. From definitive diagnoses and reliable seizure logs to treatment optimization and presurgical seizure foci localization, the clinical need for continuous monitoring of brain electrophysiological activity in epilepsy patients is evident. This paper presents the converging solutions developed independently by researchers and organizations working at the forefront of next generation EEG monitoring. The immediate value of these devices is discussed as well as the potential drivers and hurdles to adoption. Additionally, this paper discusses what the expected value of ultra-long-term EEG data might be in the future with respect to alarms for especially focal seizures, seizure forecasting, and treatment personalization.

Arm-ECG Wireless Sensor System for Wearable Long-Term Surveillance of Heart Arrhythmias

This article presents the devising, development, prototyping and assessment of a wearable arm-ECG sensor system (WAMECG1) for long-term non-invasive heart rhythm monitoring, and functionalities for acquiring, storing, visualizing and transmitting high-quality far-field electrocardiographic signals. The system integrates the main building blocks present in a typical ECG monitoring device such as the skin surface electrodes, front-end amplifiers, analog and digital signal conditioning filters, flash memory and wireless communication capability. These are integrated into a comfortable, easy to wear, and ergonomically designed arm-band ECG sensor system which can acquire a bipolar ECG signal from the upper arm of the user over a period of 72 h. The small-amplitude bipolar arm-ECG signal is sensed by a reusable, long-lasting, Ag–AgCl based dry electrode pair, then digitized using a programmable sampling rate in the range of 125 to 500 Hz and transmitted via Wi-Fi. The prototype comparative performance assessment results showed a cross-correlation value of 99.7% and an error of less than 0.75% when compared to a reference high-resolution medical-grade ECG system. Also, the quality of the recorded far-field bipolar arm-ECG signal was validated in a pilot trial with volunteer subjects from within the research team, by wearing the prototype device while: (a) resting in a chair; and (b) doing minor physical activities. The R-peak detection average sensibilities were 99.66% and 94.64%, while the positive predictive values achieved 99.1% and 92.68%, respectively. Without using any additional algorithm for signal enhancement, the average signal-to-noise ratio (SNR) values were 21.71 and 18.25 for physical activity conditions (a) and (b) respectively. Therefore, the performance assessment results suggest that the wearable arm-band prototype device is a suitable, self-contained, unobtrusive platform for comfortable cardiac electrical activity and heart rhythm logging and monitoring.

Implantable loop recorder versus conventional diagnostic workup for unexplained recurrent syncope

BACKGROUND

The most recent syncope guideline recommends that implantable loop recorders (ILRs) are implanted in the early phase of evaluation of people with recurrent syncope of uncertain origin in the absence of high-risk criteria, and in high-risk patients after a negative evaluation. Observational and case-control studies have shown that loop recorders lead to earlier diagnosis and reduce the rate of unexplained syncopes, justifying their use in clinical practice. However, only randomised clinical trials with an emphasis on a primary outcome of specific ILR-guided diagnosis and therapy, rather than simply electrocardiogram (ECG) diagnosis, might change clinical practice.

OBJECTIVES

To assess the incidence of mortality, quality of life, adverse events and costs of ILRs versus conventional diagnostic workup in people with unexplained syncope.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL, Issue 3, 2015), MEDLINE, EMBASE, ClinicalTrials.gov and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) Search Portal in April 2015. No language restriction was applied.

SELECTION CRITERIA

We included all randomised controlled trials of adult participants (i.e. ≥ 18 years old) with a diagnosis of unexplained syncope comparing ILR with standard diagnostic workup.

DATA COLLECTION AND ANALYSIS

Two independent review authors screened titles and abstracts of all potential studies we identified as a result of the literature search, extracted study characteristics and outcome data from included studies and assessed risk of bias for each study using the criteria outlined in the Cochrane Handbook for Systematic Reviews of Interventions. We contacted authors of trials for missing data. We analysed dichotomous data (all-cause mortality and aetiologic diagnosis) as risk ratios (RR) with 95% confidence intervals (CI). We used the Chi(2) test to assess statistical heterogeneity (with P < 0.1) and the I² statistic to measure heterogeneity among the trials. We created a 'Summary of findings' table using the five GRADE considerations (study limitations, consistency of effect, imprecision, indirectness and publication bias) to assess the quality of a body of evidence as it relates to the studies which contribute data to the meta-analyses for the prespecified outcomes.

MAIN RESULTS

We included four trials involving a total of 579 participants. With the limitation that only two studies reported data on mortality and none of them had considered death as a primary endpoint, the meta-analysis showed no evidence of a difference in the risk of long-term mortality between participants who received ILR and those who were managed conventionally at follow-up (RR 0.97, 95% CI 0.41 to 2.30; participants = 255; studies = 2; very low quality evidence) with no evidence of heterogeneity. No data on short term mortality were available. Two studies reported data on adverse events after ILR implant. Due to the lack of data on adverse events in one of the studies' arms, a formal meta-analysis was not performed for this outcome.Data from two trials seemed to show no difference in quality of life, although this finding was not supported by a formal analysis due to the differences in both the scores used and the way the data were reported. Data from two studies seemed to show a trend towards a reduction in syncope relapses after diagnosis in participants implanted with ILR. Cost analyses from two studies showed higher overall mean costs in the ILR group, if the costs incurred by the ILR implant were counted. The mean cost per diagnosis and the mean cost per arrhythmic diagnosis were lower for participants randomised to ILR implant.Participants who underwent ILR implantation experienced higher rates of diagnosis (RR (in favour of ILR) 0.61, 95% CI 0.54 to 0.68; participants = 579; studies = 4; moderate quality evidence), as compared to participants in the standard assessment group, with no evidence of heterogeneity.

AUTHORS' CONCLUSIONS

Our systematic review shows that there is no evidence that an ILR-based diagnostic strategy reduces long-term mortality as compared to a standard diagnostic assessment (very low quality evidence). No data were available for short-term all-cause mortality. Moderate quality evidence shows that an ILR-based diagnostic strategy increases the rate of aetiologic diagnosis as compared to a standard diagnostic pathway. No conclusive data were available on the other end-points analysed.Further trials evaluating the effect of ILRs in the diagnostic strategy of people with recurrent unexplained syncope are warranted. Future research should focus on the assessment of the ability of ILRs to change clinically relevant outcomes, such as quality of life, syncope relapse and costs.

Sudden cardiac death risk stratification

Arrhythmic sudden cardiac death (SCD) may be caused by ventricular tachycardia/fibrillation or pulseless electric activity/asystole. Effective risk stratification to identify patients at risk of arrhythmic SCD is essential for targeting our healthcare and research resources to tackle this important public health issue. Although our understanding of SCD because of pulseless electric activity/asystole is growing, the overwhelming majority of research in risk stratification has focused on SCD-ventricular tachycardia/ventricular fibrillation. This review focuses on existing and novel risk stratification tools for SCD-ventricular tachycardia/ventricular fibrillation. For patients with left ventricular dysfunction or myocardial infarction, advances in imaging, measures of cardiac autonomic function, and measures of repolarization have shown considerable promise in refining risk. Yet the majority of SCD-ventricular tachycardia/ventricular fibrillation occurs in patients without known cardiac disease. Biomarkers and novel imaging techniques may provide further risk stratification in the general population beyond traditional risk stratification for coronary artery disease alone. Despite these advances, significant challenges in risk stratification remain that must be overcome before a meaningful impact on SCD can be realized.

Experimental Path Loss Models for In-Body Communications Within 2.36-2.5 GHz

Biomedical implantable sensors transmitting a variety of physiological signals have been proven very useful in the management of chronic diseases. Currently, the vast majority of these in-body wireless sensors communicate in frequencies below 1 GHz. Although the radio propagation losses through biological tissues may be lower in such frequencies, e.g., the medical implant communication services band of 402 to 405 MHz, the maximal channel bandwidths allowed therein constrain the implantable devices to low data rate transmissions. Novel and more sophisticated wireless in-body sensors and actuators may require higher data rate communication interfaces. Therefore, the radio spectrum above 1 GHz for the use of wearable medical sensing applications should be considered for in-body applications too. Wider channel bandwidths and smaller antenna sizes may be obtained in frequency bands above 1 GHz at the expense of larger propagation losses. Therefore, in this paper, we present a phantom-based radio propagation study for the frequency bands of 2360 to 2400 MHz, which has been set aside for wearable body area network nodes, and the industrial, scientific, medical band of 2400 to 2483.5 MHz. Three different channel scenarios were considered for the propagation measurements: in-body to in-body, in-body to on-body, and in-body to off-body. We provide for the first time path loss formulas for all these cases.

[Long term results of implantable loop recorder in patients with syncope: results of a French survey]

BACKGROUND AND OBJECTIVE

A first publication of our group demonstrated that implantation of a loop recorder in 30 patients experiencing an unexplained syncope (Medtronic Reveal DX or XT) definitively determined that an arrhythmia was the cause of symptoms in 10 patients (32%). However, we lack the results of a survey evaluating the results of long term follow-up after a loop recorder implantation and the results in case of wider indications of implantation of loop recorders.

METHODS AND RESULTS

A device (Medtronic Reveal DX or XT) was implanted in 97 patients between january 2009 and june 2014. During a mean follow-up of 21±19 months, loop recording determined that an arrhythmia was the cause of symptoms in 34 patients (35%). For the management of these arrhythmias, treatments received by patients were a pacemaker implantation in 18 patients (53%), an implantable cardioverter-defibrillator in four patients (12%) and a supraventricular tachycardia ablation (cryo or radiofrequency ablation) in three patients (9%). For nine patients (26%), the arrhythmic events were asymptomatic and didn't justify a specific treatment. The final positive rate of loop monitoring implantation was of 25/97 (26%). The study demonstrated that the positivity of the follow-up was demonstrated after two years of follow-up in 26% of the cases.

CONCLUSION

Long-term follow-up of 97 patients implanted by a loop monitor leaded to an interventional rythmology procedure in 26% of the cases. In 26% of patients, loop-monitoring follow-up was positive after a duration of more than two years.

Clinical utility of implantable loop recorders

Implantable loop recorders provide the highest sensitivity and accuracy of diagnosing cardiac arrhythmia that results in cardiac syncope. When bradyarrhythmia or tachyarrhythmia, including atrial fibrillation, is detected, appropriate secondary prevention therapy will be implemented, which will impact the long-term clinical outcome. An implantable loop recorder enables the clinician to record for a longer period of time, which increases the likelihood of detecting cardiac arrhythmia. Currently, this technology is being evaluated to diagnose a cardiac etiology of ischemic stroke and to optimize atrial fibrillation management that will predict the success of rhythm control and prevent thromboembolic events. This article reviews implantable loop recorder technology, and discusses the current indications, the outcomes of clinical studies and ongoing current studies, and future technological improvements.

AF Detected on Implanted Cardiac Implantable Electronic Devices: Is There a Threshold for Thromboembolic Risk?

OPINION STATEMENT

Atrial fibrillation (AF) is a common cardiac arrhythmia that is associated with elevated thromboembolism risk caused by multiple pathophysiologies, including a hypercoagulable state, structural heart changes, left atrial appendage stasis, inflammation, and endothelial dysfunction. With the exception of lone AF, most other categories of AF, whether paroxysmal or persistent, have been shown to share a high thromboembolism risk. Risk stratification schemes such as CHADS2 and CHA2DS2-VASc scores help to identify the level at which anticoagulation may mitigate thromboembolism risk. AF may be episodic and asymptomatic; therefore, AF diagnosis that depends entirely on office electrocardiogram (ECG) may be easily missed. With the increasing use of pacemakers, implantable cardioverter defibrillators (ICDs), and insertable loop recorders (ILRs) for diagnosis and treatment of arrhythmias, AF has been incidentally detected with increasing frequency. However, the sensitivity and specificity for detection of AF, especially brief episodes, vary from one type of device to another, and rhythm confirmation should be considered. Several recent studies have examined device-detected AF and have tried to follow associated clinical outcomes. In this paper, we review studies that have addressed device-detected AF and associated thromboembolism risk to try to identify the burden of AF that is associated with an elevated risk of thromboembolism and may therefore warrant anticoagulation therapy.

[Long-term follow-up after implantable loop recorder in patients with syncope: results of a French general hospital survey]

BACKGROUND AND OBJECTIVE

Despite recent advances in diagnostic procedures, syncope remains unexplained in 15 to 35% of patients. If implantable loop recorder is a validated diagnostic tool for unexplained syncope, results of this strategy are largely issued from randomized studies. We lack the results of surveys. The aim of this study was to report a single center experience with implantable loop recorders, in patients with unexplained syncope.

METHODS AND RESULTS

A device (Medtronic Reveal DX or XT) was implanted in 31 patients between January 2009 and January 2012. During a mean follow-up of 10.5±8.5 months, loop recording definitively determined that an arrhythmia was the cause of symptoms in 10 patients (32%). Fourteen patients (45%) experienced syncope or pre-syncope. In eight of the 14 patients with syncope, during follow-up, no arrhythmic diagnosis could be made (one patient has been diagnosed as presenting epilepsy and seven as having hypotensive vasovagal syncope). In six patients, the ILR showed an arrhythmic aetiology. Four other patients presented an abnormal ILR result without symptoms. Diagnosis included sinusal arrest in four patients, bradycardia in one patient, advanced atrioventricular block in two patients, ventricular arrythmias in two patients, and supraventricular tachycardia of 180/min in one patient. Therapy was instituted in all patients, in whom an arrhythmic cause was found except one who refused the therapy (six pacemaker, two implantable cardioverter-defibrillator implantations, and one cryoablation of atrioventricular nodal reentrant tachycardia confirmed by an invasive exploration).

CONCLUSION

In this survey, implantable loop recorder implantation led to the diagnosis of an arrhythmic cause in 32% of patients and excluded an arrhythmic cause in 26% of patient with a mean follow-up of 10.5 months.

Wireless distributed functional electrical stimulation system

Background

The control of movement in humans is hierarchical and distributed and uses feedback. An assistive system could be best integrated into the therapy of a human with a central nervous system lesion if the system is controlled in a similar manner. Here, we present a novel wireless architecture and routing protocol for a distributed functional electrical stimulation system that enables control of movement.

Methods

The new system comprises a set of miniature battery-powered devices with stimulating and sensing functionality mounted on the body of the subject. The devices communicate wirelessly with one coordinator device, which is connected to a host computer. The control algorithm runs on the computer in open- or closed-loop form. A prototype of the system was designed using commercial, off-the-shelf components. The propagation characteristics of electromagnetic waves and the distributed nature of the system were considered during the development of a two-hop routing protocol, which was implemented in the prototype’s software.

Results

The outcomes of this research include a novel system architecture and routing protocol and a functional prototype based on commercial, off-the-shelf components. A proof-of-concept study was performed on a hemiplegic subject with paresis of the right arm. The subject was tasked with generating a fully functional palmar grasp (closing of the fingers). One node was used to provide this movement, while a second node controlled the activation of extensor muscles to eliminate undesired wrist flexion. The system was tested with the open- and closed-loop control algorithms.

Conclusions

The system fulfilled technical and application requirements. The novel communication protocol enabled reliable real-time use of the system in both closed- and open-loop forms. The testing on a patient showed that the multi-node system could operate effectively to generate functional movement.

New real-time loop recorder diagnosis of symptomatic arrhythmia via telemedicine

BACKGROUND

One disadvantage of current loop recorders is the long interval between recording an electrocardiogram (ECG), establishing a diagnosis, and taking appropriate medical measures. The Cardio R loop recorder transmits cardiac recordings by cellular communication at the push of a button. Users can concomitantly relay symptoms, thereby providing a symptom/cardio-rhythm correlation.

HYPOTHESIS

The Cardio R is capable of early detection of cardio-electrical events that could account for patients' symptoms.

METHODS

This observational study was designed to evaluate patients who were referred from community physicians/cardiologists for evaluation of various cardiac symptoms that were not observed by regular office ECGs or traditional 24-hour Holter cardiac monitoring. Transmitted recordings were instantly displayed on a monitor for immediate diagnosis by the on-duty medical team at SHL-Telemedicine's call center. Abnormal tracings, especially when accompanied by symptoms selected from the prepared list, enabled the staff to instruct the subscriber, notify their physician, and/or dispatch a mobile intensive care unit to the scene.

RESULTS

Between January 2009 and August 2010, there were 17 622 ECG transmissions received from 604 patients (age range, 10-95 years) who completed a 1-month trial with the Cardio R device. Palpitation, presyncope, and chest pain were the leading complaints. A disturbance in rhythm that could account for symptoms occurred during recording in 49% cases and was displayed within 7 minutes in 93% of them. No longer than 2 days elapsed from recording onset to diagnosis.

CONCLUSIONS

The Cardio R device enables prompt ECG confirmation/exclusion of a probable arrhythmic cause of symptoms, enabling rapid intervention for cardiac-relevant complaints.

Efficacy of diagnostic tools for detecting cardiac arrhythmias: systematic literature search

BACKGROUND/OBJECTIVES

Symptoms suggestive of cardiac arrhythmias are a challenge to the diagnosis. Physical examination and a 12-lead ECG are of limited value, as rhythm disturbances are frequently of a paroxysmal nature. New technologies facilitate a more accurate diagnosis. The objective of this study was to review the medical literature in an effort to define a guide to rational diagnostic testing.

METHODS

Primary studies on the use of a diagnostic tool in the evaluation of palpitations were searched in MEDLINE, and EMBASE with an additional reference check.

RESULTS

TWO TYPES OF STUDIES WERE FOUND: descriptive and experimental studies, which compared the yield of two or more devices or diagnostic strategies. Holter monitors seemed to have less diagnostic yield (33 to 35%) than event recorders. Automatically triggered recorders detect more arrhythmias (72 to 80%) than patient-triggered devices (17 to 75%). Implantable devices are used for prolonged monitoring periods in patients with infrequent symptoms or unexplained syncope.

CONCLUSION

The choice of the device depends on the characteristics of the symptoms and the patient. Due to methodological shortcomings of the included studies no evidence-based diagnostic strategy can be proposed. (Neth Heart J 2010;18:543-51.).

Unexpected low prevalence of atrial fibrillation in cryptogenic ischemic stroke: a prospective study

Purpose

Ischemic stroke is a frequent pathology with high rate of recurrence and significant morbidity and mortality. There are several causes of stroke, affecting prognosis, outcomes, and management, but in many cases, the etiology remains undetermined. We hypothesized that atrial fibrillation was involved in this pathology but underdiagnosed by standard methods. The aim of the study was to determine the incidence of atrial fibrillation in cryptogenic ischemic stroke by using continuous monitoring of the heart rate over several months. The secondary objective was to test the value of atrial vulnerability assessment in predicting spontaneous atrial fibrillation.

Methods and results

We prospectively enrolled 24 patients under 75 years of age, 15 men and 9 women of mean age 49 years, who within the last 4 months had experienced cryptogenic stroke diagnosed by clinical presentation and brain imaging and presumed to be of cardioembolic mechanism. All causes of stroke were excluded by normal 12-lead ECG, 24-h Holter monitoring, echocardiography, cervical Doppler, hematological, and inflammatory tests. All patients underwent electrophysiological study. Of the patients, 37.5% had latent atrial vulnerability, and 33.3% had inducible sustained arrhythmia. Patients were secondarily implanted with an implantable loop recorder to look for spontaneous atrial fibrillation over a mean follow-up interval of 14.5 months. No sustained arrhythmia was found. Only one patient had non-significant episodes of atrial fibrillation.

Conclusion

In this study, symptomatic atrial fibrillation or AF with fast ventricular rate has not been demonstrated by the implantable loop recorder in patients under 75 years with unexplained cerebral ischemia. The use of this device should not be generalized in the systematic evaluation of these patients. In addition, this study attests that the assessment of atrial vulnerability is poor at predicting spontaneous arrhythmia in such patients.

Change point analysis for longitudinal physiological data: detection of cardio-respiratory changes preceding panic attacks

Statistical methods for detecting changes in longitudinal time series of psychophysiological data are limited. ANOVA and mixed models are not designed to detect the existence, timing, or duration of unknown changes in such data. Change point (CP) analysis was developed to detect distinct changes in time series data. Preliminary reports using CP analysis for fMRI data are promising. Here, we illustrate the application of CP analysis for detecting discrete changes in ambulatory, peripheral physiological data leading up to naturally occurring panic attacks (PAs). The CP method was successful in detecting cardio-respiratory changes that preceded the onset of reported PAs. Furthermore, the changes were unique to the pre-PA period, and were not detected in matched non-PA control periods. The efficacy of our CP method was further validated by detecting patterns of change that were consistent with prominent respiratory theories of panic positing a relation between aberrant respiration and panic etiology.

Implantable loop recorders: a viable diagnostic tool in veterinary medicine

OBJECTIVE

The purpose of this study was to investigate whether implantable loop recorders could be used in the diagnosis of unexplained collapse in dogs.

METHODS

The medical records of six dogs presented to the University of Liverpool Small Animal Teaching Hospital between May 2003 and October 2006 for further evaluation of intermittent syncopal episodes, collapse or episodic weakness, were reviewed. All these dogs underwent standard investigations and had implantable loop recorders placed.

RESULTS

A provisional diagnosis of supraventricular tachycardia was made in one dog, and diagnoses of exclusion of arrhythmogenic right ventricular cardiomyopathy and idiopathic epilepsy was made in two dogs. One dog suffered no further syncopal episodes, a diagnosis was not reached in another dog and the final dog was lost to follow-up.

CLINICAL SIGNIFICANCE

The implantable loop recorder can be used successfully for the diagnosis of unexplained collapse in dogs.

Ambulatory cardiac rhythm monitoring

Cardiac arrhythmias may cause palpitations, dyspnoea, angina pectoris, dizziness or even syncope and sudden death. This article will review the indications for investigation, the novel devices that are available for investigating patients with suspected cardiac dysrhythmias and the new technology available for analysis and reporting.

Implications of mechanism of bradycardia on response to pacing in patients with unexplained syncope

AIM

Asystole >3 s or sinus bradycardia with a ventricular rate <40 in association with complete heart block or sinus node dysfunction are considered to be Class 1 indications for permanent cardiac pacing. Nevertheless, these phenomena may be observed in symptomatic patients with neurocardiogenic syncope, who may not respond to pacing therapy. We hypothesized that the pattern of spontaneous bradycardia in symptomatic patients would distinguish patients with sinus node dysfunction or conduction system disease who would benefit from pacing from patients with neurally-mediated syncope who would derive lesser benefit.

METHODS AND RESULTS

Patients with symptomatic spontaneous bradycardia during long-term monitoring for unexplained syncope who underwent pacemaker implantation were classified according to the ISSUE classification system and followed for recurrent syncope. Follow-up included review of medical records, pacemaker clinic visits, and telephone interviews. Loop recorder tracings were reviewed to identify characteristics potentially predicting a favourable response to pacing. Thirty-three patients (21 male; age, 70 +/- 14) were followed for 3.56 +/- 1.71 years. Six patients had a recurrence of syncope during the follow-up. All patients with recurrent syncope despite pacing demonstrated a Type 1A (n = 5) or 1B (n = 1) pattern with gradual onset of bradycardia at baseline, suggesting a neurocardiogenic mechanism. There was no difference in the severity of bradycardia or duration of asystole in baseline loop recorded events in responding and non-responding patients. Multivariate analysis using stepwise logistic regression revealed that the ISSUE classification and the absence of structural heart disease were the only independent predictors of treatment failure of cardiac pacing in patients with spontaneous symptomatic bradycardia.

CONCLUSION

Patients with syncope associated with abrupt bradycardia displayed a better response to cardiac pacing therapy than those with gradual onset bradycardia.

Risk of cellular phone interference with an implantable loop recorder

This study examined the risk of cellular phone ringing interference with implantable loop recorders (ILR). The technical manual of ILR warns of potential interference by cellular phone in close proximity to the implanted device, corrupting the data stored in memory or causing inappropriate device operation. The ringing phase of a digital Global System for Mobile Communication (GSM) or Personal Communication Services (PCS) cellular phone includes a brief burst of peak emitted power. To obviate the risk of dysfunction in recipients of implanted ILRs, the testing was performed with externally applied devices. The ILR was positioned in the left parasternal region and the telemetry wand removed after regular programming. Digital cellular telephones were placed over the device at a 1-cm distance and calls were placed. The phone systems tested were single- or dual-band receivers. The GSM used a maximal power output of 2 W, operating on a 900 MHz carrier frequency, and the PCS a maximal output of 1 W, operating on a 1800 MHz carrier frequency. The device activator was used to store the episodes encompassing the tests. Sixty nine tests were performed in 45 patients. In 61 tests, high-frequency polymorphic artifacts were visible on manually activated recordings, beginning a few seconds before the first audible ringing tone and persisting throughout the ringing phase. Cellular phone ringing in close proximity to an externally applied ILR caused bursts of high-frequency signals during electrocardiogram monitoring, without causing permanent device dysfunction or reprogramming. Cellular telephones are a potential source of electrocardiographic artifacts on ILR recordings.

Syncope: case studies

In this series of clinical vignettes, the authors have attempted to provide a "feel" for the varied causes of syncope. The neurologist should be able to diagnose most causes of syncope using a simple algorithmic approach. Initial evaluation includes detailed clinical history, physical examination, and 12-lead ECG. Following initial evaluation, the cause of syncope is usually immediately apparent (typical story for vasovagal syncope, clinically demonstrable autonomic failure, long QT), strongly suspected (syncope preceded by chest pain or palpitations), or uncertain. In the latter group of patients, further workup will depend on the suspicion or documented presence of heart disease. In those with a single episode of syncope and no evidence of heart disease, further workup may not be necessary. In patients over 60 years of age with recurrent episodes and no cardiac history or abnormal ECG, tilt-table testing and carotid sinus massage may be diagnostic. If no diagnosis is found, an implantable loop monitor may be needed. Patients with heart disease will need the most comprehensive evaluations, possibly including exercise testing, cardiac electrophysiology, and tilt-table testing. As better understanding of pathophysiology and epidemiology emerge, under-standing of the diagnosis and treatment of syncope will improve. In the meantime, there is no substitute for astute clinical acumen.

Safe scanning, but frequent artifacts mimicking bradycardia and tachycardia during magnetic resonance imaging (MRI) in patients with an implantable loop recorder (ILR)

BACKGROUND

Patients with implantable devices are generally not permitted to undergo magnetic resonance imaging (MRI) because of potentially deleterious interactions. Little has been reported regarding the safety and effects of MRI scanning of patients with implantable loop recorders (ILRs). We evaluated the safety of scanning patients with ILRs and the output of the ILR after undergoing MRI.

METHODS

Ten patients underwent 11 MRI scanning events. All patients had Reveal Plus (Medtronic, Minneapolis, MN) ILRs. Seven cranial, two lumbar-spine, one shoulder, and one knee MRI were performed. All of the MRIs were performed with the understanding that the patient had an ILR. In each patient, the ILR was cleared moments before the scan and the integrity of the signal and time date stamp were verified. The devices were reinterrogated immediately after MRI in 10 patients and two days post MR scanning in one patient. Each patient was questioned post MRI regarding any symptoms experienced during the scan.

RESULTS

Both tachy and bradyarrhythmias appeared as artifacts as a result of ILR exposure to MRI. Post MRI, none of the ILRs showed diminished signal integrity, altered programmed parameters, diminished battery status, inability to communicate or be reprogrammed. No sensations of tugging or warmth at the implant site were noted.

CONCLUSION

MRI was performed in ILR patients without harm to the patient or permanent damage to the ILR. MRI scanning of the Reveal appears safe. Artifact mimicking an arrhythmia was common, however, and must be excluded in any ILR patient undergoing MRI to avoid mistakenly attributing a syncopal episode, or palpitations to the artifacts produced from MRI exposure.

Medical devices of the chest

Chest devices are encountered on a daily basis by almost all radiologists. A multitude of extrathoracic materials, from intravenous catheters to oxygen tubing and electrocardiographic leads, frequently overlie the chest, neck, and abdomen. Chest tubes, central venous catheters, endotracheal tubes, and feeding tubes are very common. Cardiac surgery involves the use of many sophisticated devices and procedures, ranging from valve replacement to repair of complex congenital anomalies. Coronary artery bypass surgery is no longer considered unusual, and in many large medical centers, ventricular assist devices and total artificial hearts are frequently encountered. Breast implants are visible at standard chest radiography, and many ancillary devices not intended for treatment of cardiac or thoracic diseases are visible on chest radiographs. New devices are constantly being introduced, but most of them are variations on a previous theme. Knowing the specific name of a device is not important. It is important to recognize the presence of a device and to have an understanding of its function, as well as to recognize the complications associated with its use.

Comparison of autotriggered memory loop recorders versus standard loop recorders versus 24-hour Holter monitors for arrhythmia detection

To determine the relative yields of Holter monitoring (HM), memory loop recording (MLR), and autotriggered MLR (AT-MLR), we retrospectively interrogated the very large database of Lifewatch (a Card Guard company and a commercial monitoring company) and compared the results obtained by each method. From among a total database of approximately 100,000 patients, records of 1,800 patients from 2003 were randomly selected and examined, 600 from each of the 3 different monitoring groups. Each session of MLR and AT-MLR was applied for 30 days. For each patient we determined the symptomatic and asymptomatic events that were documented, including those that met predefined immediate physician notification criteria and the time to first notification event. The groups were identical in age and symptoms that necessitated monitoring; fewer women had HM. Information on the type of underlying structural heart disease, if present, and medications taken, if any, was not available to us in this database. The AT-MLR approach provided a higher yield of diagnostic events (e.g., 37, 108, and 216 total patients who had events; 37, 212, and 524 total events; and 6.2%, 17%, and 36% with a diagnostic yield for HM, MLR, and AT-MLR, respectively) and an earlier diagnosis. AT-MLR was also the most effective technique for capturing asymptomatic significant events, such as atrial fibrillation (52 with AT-MLR vs 1 for standard MLR). AT-MLR detected more than half as many asymptomatic episodes of atrial fibrillation (n = 52) as the total number of symptomatic episodes detected by patient activated recording (n = 94), thus confirming the common presence of asymptomatic atrial fibrillation. AT-MLR provided electrocardiographic documentation of tachyarrhythmias (n = 392) more often than MLR (n = 47) or HM (n = 44) and bradyarrhythmias/pauses/atrioventricular block (n = 38) more often than MLR (n = 13) or HM (n = 18). Thus, MLR and AT-MLR provide a diagnosis more often than does HM, thus confirming the benefit of prolonged monitoring. Further, the higher yield of AT-MLR versus MLR demonstrates the significantly enhanced benefit of autotriggered programmable recording.