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Available online at www.sciencedirect.com
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Ambulatory ECG Monitoring in Atrial Fibrillation Management Spencer Z. Roseroa, 1 , Valentina Kutyifaa, 1 , Brian Olshanskyb , Wojciech Zarebaa,⁎ a
Cardiology Division, University of Rochester Medical Center, Rochester, NY, USA University of Iowa, Iowa City, IA, USA
b
A R T I C LE I N F O
AB ST R A C T
Keywords:
Ambulatory ECG monitoring technology has rapidly evolved over the last few decades and
Atrial fibrillation
has been shown to identify life-threatening and non-life threatening arrhythmias and
Ambulatory
provide actionable data to guide clinical decision making. Atrial fibrillation episodes can
ECG monitoring
often be asymptomatic, even after catheter ablation for atrial fibrillation, creating a
Atrial fibrillation ablation
disconnect between symptoms and actual arrhythmia burden which may alter clinical
Holter monitor
management. In this review, we aim to provide a comprehensive overview of invasive and
Event monitor
non-invasive ECG monitoring strategies in patients with atrial fibrillation, with a special
Implanted loop recorder
focus on the diagnosis of atrial fibrillation, and on follow-up of patients after catheter
Pacemaker
ablation for atrial fibrillation ablation.
Implantable cardioverter
© 2013 Elsevier Inc. All rights reserved.
defibrillator Cardiac resynchronization therapy
Recent technological advancements have facilitated ambulatory electrocardiogram (ECG) monitoring in the outpatient environment providing continuous, high resolution ECG data streams ranging from days to months at a time. Wireless communication has permitted the transfer of relevant ECG data in real-time encouraging rapid analysis and timely clinical intervention. The rapid commercialization and competitive market for managing patients with atrial fibrillation (AF) have produced a large menu from which clinicians must now carefully choose to meet the needs of their patients. Atrial fibrillation is the most common arrhythmia, especially in hypertensive patients, in the elderly1–5 and in those with heart failure (HF).6–8 The incidence and prevalence of atrial fibrillation are constantly growing.9 A recent study suggested that the incidence of atrial fibrillation will double
by the year of 2030, and the prevalence of the disease will reach 12.1 million cases in the United States.10 Furthermore, AF may have significant clinical consequences. It is known to be associated with a significant increase in the risk of stroke, HF hospitalization and related health care costs.11 Catheter ablation for atrial fibrillation ablation has become an established method to provide efficient rhythm control in patients with atrial fibrillation and has been claimed as a “cure” for the disease. However, longterm success data are still lacking, and success also depends on the ECG modality that is used to monitor AF episodes.12 This review article will provide an overview on the invasive and non-invasive ECG monitoring tools in atrial fibrillation with a focus on atrial fibrillation diagnosis, and follow-up in patients undergoing catheter ablation. Furthermore, we present data on new methods to be investigated in this rapidly evolving field.
Statement of Conflict of Interest: see page 150. ⁎ Address reprint requests to Wojciech Zareba, MD, PhD, Heart Research Follow-up Program Cardiology Division, University of Rochester Medical Center, 265 Crittenden Blvd., Box 653, Rochester, NY 14642. E-mail address: [email protected] (W. Zareba). 1 S.Z.R. and V.K. contributed equally to the work. 0033-0620/$ – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.pcad.2013.10.001
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Abbreviations and Acronyms AF = atrial fibrillation
General considerations
AT = atrial tachycardia In patients with atrial fibrillation, initial diagnosis has been most ECG = electrocardiogram often made utilizing a 12-lead ECG or Holter ELEM = event loop monitoring monitoring. Therapy efHF = heart failure ficacy has been evaluated by patient-reported ICD = implantable cardioverter symptoms, repeated 12defibrillator lead ECG recordings or ILR = implanted loop recorder Holter monitoring. However, several studies MCOT = mobile cardiac outpasuggested that episodes tient telemetry of AF occur without PM = implanted pacemaker symptoms.13–15 These events may carry significant risk of stroke, and thromboembolic events and falsify the success rate of catheter ablation for atrial fibrillation. Therefore, the identification of AF episodes and recurrences is relevant. Long-term Holter recording and event monitors were proven to have a superior diagnostic yield compared to 12lead ECG or 24/48-hour Holter monitoring; however, the complexity of these devices, patient compliance, need of a CRT = cardiac resynchronization therapy
transmitter device, and in some cases the relatively slow review of the records limit every-day clinical applicability. Newer techniques using patch-type monitors that provide real time feedback to the care provider or to the patient itself are more useful in clinical practice and may drive immediate changes in medical therapy or patient care to improve clinical outcome. These new methods need to be not only simple, but reliable, with sufficient capability to store and to transmit episodes. However, the most optimal devices are those that provide continuous long-term monitoring, 24 hours, 7 days a week, with immediate feedback. Implanted loop recorders (ILR), and implanted pacemakers (PM), defibrillators (ICD), or cardiac resynchronization therapy devices (CRT) are able to do continuous monitoring and produce output of the recorded rhythm abnormalities. However, necessity of the invasive procedure restricts their wide applicability. The key points in current ambulatory ECG monitoring are 1) long-term monitoring capabilities, 2) instant feedback, 3) simplicity, 4) every-day use, 5) non-invasive nature. A summary of ambulatory ECG monitoring tools with respected ranges of diagnostic accuracy is listed in Fig 1 and discussed in details in the chapters below. However, the requirements for diagnosing AF and for follow-up of patients after catheter ablation for AF are somewhat different. Suggested schemes for diagnosing AF and evaluating the success rate of catheter ablation are depicted in Figs 2 and 3 and will be discussed later.
Fig 1 – Summary of ambulatory ECG monitoring tools with respected ranges of diagnostic accuracy.
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Fig 2 – Diagnosing atrial fibrillation using ECG monitoring tools.
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Fig 3 – Evaluating the success of catheter ablation for atrial fibrillation using ECG monitoring tools.
ECG monitoring and transtelephonic ECG The traditional 12-lead ECG may easily confirm the diagnosis of atrial fibrillation. In some cases, however, it depicts the electrical activity of the heart for only a very limited amount
of time. Its main advantage is that it is simple, easy to perform, widely available, and it is relatively easy and fast to interpret the findings. However, the ECG diagnosis of AF might be still challenging in primary care; the SAFE (Screening for Atrial Fibrillation in the Elderly) trial showed 80% sensitivity and 95% specificity in identifying AF among
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general practitioners.16 Furthermore, since it only presents information on few beats, it is often not sufficient to detect atrial fibrillation. Transtelephonic ECG recording, consisting of 10 seconds up to 1–2 minutes continuous recordings, is more efficient in diagnosing AF and follow-up patients after catheter ablation for AF. Senatore et al.17 evaluated the role of 12-lead ECG performed one, and four months after catheter ablation for atrial fibrillation and compared it to transtelephonic ECG monitoring performed daily, and when symptoms occurred, combined with a 24-hour Holter monitoring in 72 consecutive patients. They found that transtelephonic ECG was able to identify a higher number of recurrent AF events (27.8% of the total patient cohort) compared to 12-lead ECG performed at one, and four months after catheter ablation combined with a 24-hour Holter recording (13.9% of the total patient cohort). A most recent study suggested that transtelephonic ECG is more sensitive than 24-hour Holter monitoring.18 This group evaluated 22 patients with diagnosed atrial fibrillation who had a 24-hour Holter once within the first 30 days, and transtelephonic ECG was recorded twice a day for 10 seconds. AF episodes were detected in 82% of the patients using transtelephonic ECG compared to a 32% event rate when analyzed by 24-hour Holter monitoring. Others suggested that transtelephonic ECG yields similar accuracy as does a 7-day Holter monitoring. Thirty patients were evaluated by Piorkowski et al.19 following catheter ablation for atrial fibrillation. They performed transtelephonic ECG every second day for six months, and a 7-day Holter at 3 and 6-month post-ablation. Patient-reported symptoms were also collected. In this study, 7-day Holter and transtelephonic yielded comparable diagnostic accuracy, with a success rate of 50% with 7-day Holter, and 45% with transtelephonic ECG.
Holter monitoring Holter monitoring has been the gold standard of ambulatory ECG monitoring available since 1961, introduced by Norman Holter.20 It is usually recorded for 24, or 48 hours with 3-lead or 12-lead ECG configuration. It provides comprehensive information in AF patients on recurrence, AF burden expressed in number of minutes in AF, and on the minimum, maximum, and mean ventricular rate during sinus rhythm or AF. Additionally, it produces an output including the number of atrial and ventricular ectopic beats, and the presence of sustained ventricular tachyarrhythmias with or without AF. Holter monitoring has been an essential tool in the diagnosis of AF, because of the non-sustained nature of this arrhythmia. Often it is helpful utilizing the patient event markers to relate clinical symptoms to the occurrence of the arrhythmia. In patients with infrequent symptoms, 24–48-hour Holter monitoring may provide a better diagnostic yield, however prolonged Holter recordings or other methods with long-term monitoring may increase related health care costs. The advantages of Holter monitoring are the relative simplicity of the technique and the detailed information about the initiation and termination of the AF episode. However, the electrodes and leads are uncomfortable to wear for most patients, especially in
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case of multi-day recordings, and some patients have allergy to the electrodes making the recording impossible. Holter needs time-consuming evaluation by trained health care personnel, although improved algorithms for AF detection may significantly shorten evaluation time. Some of the recordings may have substantial artifacts, noise and need to be repeated. Arrhythmias with rare occurrence may be often missed by 24–48-hour Holter and multiday recording might be necessary. However, Holter monitoring is still playing a key role in monitoring drug effects of rate control.21 Average heart rate in AF from 24-hour (or longer) Holter monitoring is an important tool in guiding optimal rate control therapy and helps in titration of drug dosage. Botto et al.22 evaluated the diagnostic accuracy of detecting AF episodes by Holter monitoring. He found that the mean sensitivity to detect a more than 5 minutes long AF event was 44.4%, 50.4% and 65.1% for 24-hour, 1-week, and 1month Holter monitoring. The clinical applicability of 1month Holter however is very ambiguous. Hindricks et al.23 assessed the applicability of 7-day Holter in patients after catheter ablation for atrial fibrillation. They suggested that the incidence of asymptomatic AF recurrences after catheter ablation is high, and therefore more intense monitoring is warranted in this patient group. They prospectively evaluated 114 consecutive patients following catheter ablation for AF utilizing 7-day Holter immediately after, and 3, 6, 12 months after catheter ablation and collected data on symptoms. They showed that the incidence of asymptomatic AF recurrences after ablation increased to 37% from 5% at baseline indicating that the symptom-based follow-up in this group may not be sufficient. Other groups also investigated the role of one-week Holter monitoring to detect AF recurrences after ablation compared to 24-hour Holter monitoring. Kottkamp et al.24 showed that in 100 patients following catheter ablation for AF, there was a higher incidence (26%) detected with 7 day Holter monitoring at 12 months compared to 12% detected with classical 24 hour Holter monitoring. Dagres et al.25 evaluated 215 patients who underwent 7-day Holter monitoring following catheter ablation for AF. They explored the incremental value of days of Holter monitoring in the diagnosis of recurrences. They found that the Holter monitoring with duration of less than or equal to 5 days detected significantly less AF recurrences compared to the 7day monitoring. There was a linear relationship between the ability of detecting recurrences and increasing monitoring time. The classical 24-hour Holter would have detected 59%, a 48-hour recording 67%, 72-hour recording 80%, 4-day recording 91% of the AF recurrences of those that were detected during the 7-day Holter monitoring. It is clear from these studies that the more aggressive the monitoring procedure is, the more episodes will be revealed during follow-up.26
Event monitors Event monitors are small leadless devices that are applied to the chest and record the ECG for a short period of time. The life span of these devices is usually up to 30 days. There are
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looping and non-looping monitors, the looping monitors use patient triggered activation, or record events based on the programmed criteria. Data are sent to a data center and physician and patient are notified based on pre-specified alerts. This is the first type of monitor that provides feedback for the physician and the patient immediately. Possible disadvantage of this method is that the patient triggered activation needs compliance, and arrhythmias with sudden onset may disable the patient to activate the device. Event monitors have proven useful in the detection of arrhythmias occurring at least every 21–30 days.27 Several studies suggested superior diagnostic yield of event monitors compared to Holter monitoring in patients with infrequent arrhythmias.27–29 Some of the reports also claimed costeffectiveness of this approach compared to Holter monitoring.29 The detection of atrial fibrillation is feasible using event monitors. Reiffel et al.30 have shown that loop event monitors and auto-triggered loop monitors identify AF more often than Holter monitoring. Furthermore, auto-triggered loop recorder was more sensitive compared to the loop recorder suggesting that there is an additional benefit of symptom-related AF detection. Therefore, use of auto-triggered loop recorders is highly recommended in patients with AF. Joshi et al.31 evaluated AF recurrence in patients in the first three months after catheter ablation for AF. They found that there was a peak in AF recurrences 2 weeks after ablation with an incidence rate of 54% that was lower at 3 months, around 22%. Interestingly, 34% of these episodes were asymptomatic further stressing the importance of continuous ECG monitoring when evaluating the success of catheter ablation. Despite the fact that we are still using 3 months blanking period after catheter ablation for atrial fibrillation, this group suggested that the freedom from AF in the first 2 weeks after ablation highly predicted the long-term success of the procedure.
Long-term ECG monitors Advances in electronics, power supply, wireless communication and data storage have facilitated the use of ECG monitoring devices capable of continuously acquiring data for days, weeks and months at a time. Traditional external loop event monitoring provides short term ECG recordings before and during a symptomatic event but requires the patient to activate the recording at that time. This may be worn for several weeks and the patient may transmit the data manually over the phone or return the device to the office for download. Several of these external loop monitors also have auto-detect features that record arrhythmias detected by proprietary algorithms. Mobile cardiac outpatient telemetry (MCOT) allows for either patient activated time stamping of events, passive automatic event triggering, and/or continuous 24/7 live monitoring using a third party coverage. In the latter system, predefined clinically significant events are communicated to the physician on call. In the current environment of managed care, consolidation among healthcare providers, increased competition and
declining reimbursement rates, the major players in the MCOT and event monitoring space have been increasingly required to compete on the basis of price, value and efficiency. In order to compete effectively, they have accelerated the creation of and/or acquisition of advanced technology. Companies such as BioMedical, CardioNet, LifeWatch, Medicomp, MedNet, ScottCare, and Medicalgorithmics are commonly used in clinical practice and provide distinct “menu” options for the physician to customize their strategy in following patients with recurrent arrhythmias, especially in the post intervention period. The integration of monitoring technology with the internet has improved physicians access to real time data. For example, Medicalgorithmics (Spectocor) offers continuous Holter monitoring for as long as needed with innovative technology providing streaming of full-disclosure ECG recording to central web-based station.32 The recordings could be stopped after 2 days if AF is detected or could be continued for 20–30 days or longer if needed. This system offers superiority over other available systems due to the fact that full disclosure Holter recording is immediately available on the web to the physician who could verify the AF episodes and assess AF burdens. Other long-term monitoring devices rely on algorithms detecting AF and storing only periods when AF was detected without opportunity to visualize continuous ECG in case of AF being missed by the algorithms. The decision process for choosing the most appropriate monitoring for a particular patient requires the provider to address three key questions: 1) Is there interest in only symptomatic events? (i.e. syncope, palpitations, lightheadedness) 2) Will the detection of a specific arrhythmia such as AF, both symptomatic and asymptomatic, be important? 3) Will the detection of certain asymptomatic arrhythmias, such as sinus node dysfunction, ventricular tachycardia, torsade de pointes, AF, atrial flutter, or SVT change the clinical management plan? Rothman et al.33 compared the value of MCOT with a traditional patient activated external loop event monitor in detecting symptomatic arrhythmias. This multicenter prospective trial enrolled 305 patients and randomized them to MCOT or event loop monitoring (ELEM) for 30 days. Their endpoint was the confirmation or exclusion of a probable arrhythmic cause of symptoms. The study demonstrated that 88% of patients randomized to the MCOT group had a diagnosis confirmed compared to 75% of the ELEM subjects. In a sub-study of patients with syncope, there was an 89% diagnostic yield using MCOT compared to 69% in ELEM (p = 0.008). Symptomatic AF was reported by approximately 8% of patients in both groups. However, 17% of the MCOT patients were found to have asymptomatic AF with rapid ventricular rates greater than 150 bpm. The finding of new asymptomatic AF may significantly alter medical decision making because of its association with stroke and the existence of guidelines outlining anticoagulation strategies based on risk. Reiffel et al30 evaluated the yield of continuous monitor with an AF autodetect feature compared to standard event
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monitors and Holter recorders. Table 1 summarizes the results based on a retrospective analysis of a Lifewatch database of 100,000 patients, from which they randomly selected 1,800 patients (600 patients for each recording method). These methods also provide an efficient and quantitative approach for monitoring patients after catheter ablation for AF. Kircher et al.12 addressed the need for long-term, continuous monitoring that can accurately detect AF and its implications for guiding medical therapy. The increased morbidity and mortality associated with AF, regardless of whether symptomatic or asymptomatic, prioritize early detection since its presence or absence directly impacts decisions regarding anticoagulation. In the post ablation period, the requirement for increased sensitivity is critical since false negatives may result in the premature discontinuation of anticoagulation and concomitant increase in stroke risk in this patient population. Specificity is also important and can often be improved with post detection manual confirmation. Current technologies allow for manual analysis of ECG categorized by algorithms as arrhythmia. Vasamreddy et al.34 used MCOT to monitor patients after ablation of AF. The MCOT was used for 5 consecutive days per month for up to 6 months. They demonstrated that while 70% of the patients were free from symptomatic AF episodes, the true success was closer to 50% if asymptomatic episodes were included. Depending on the goal of ablation therapy: cure, control of symptoms, and/or reduction of AF burden, the asymptomatic presence of AF poses a risk to patients if anticoagulation therapy is altered based on symptoms alone.
Implantable loop recorders Implantable loop recorders are semi-invasive, leadless devices that are implanted subcutaneously to record the ECG signals. The device is programmable to detect certain duration of specific type of (atrial or ventricular) arrhythmias. The life span of the device is 2–3 years. The advantage of this technique is the possibility of long recordings that enable the physician to follow the patient for years after the diagnosis or following catheter ablation of atrial fibrillation and therefore, it may be an optimal approach to guide and manage treatment. Possible disadvantage is the semi-invasive nature of the device implantation. Also, every 2–3 years the device needs to be replaced and it has a relatively high cost compared to the short term ECG monitors. This device has been proven as a feasible diagnostic tool to diagnose syncope.35 Compared to intermittent monitoring, there is an advantage of using continuous monitoring, even when compared to more aggressive intermittent monitoring strategies. The socalled temporal AF burden aggregation (AF density) was shown to be directly related to the sensitivity of the intermittent monitoring options.36 Newer studies investigated the role of implanted loop recorders in diagnosing AF, and follow-up of patients with AF. Giada et al.37 evaluated the diagnostic yield of ILR compared to short-term ambulatory ECG recordings and electrophysiological study in patients with recurrent unexplained palpitations. They showed that ILR yielded diagnosis in 73% of the
patients compared to 21% using the conventional strategy. They also suggested that using ILR is cost effective, because it leads to a diagnosis at a lower cost. Another study, the Cardiac Arrhythmias and Risk Stratification After Myocardial Infarction (CARISMA) proposed the feasibility of ILR to record brady- and tachyarrhythmias after myocardial infarction.38,39 A sub-study of the CARISMA trial also showed that new-onset AF detected by ILR predicts the risk of major cardiovascular events in patients with AF events > 30 seconds, but not in those with shorter episodes. In this particular analysis, more than 90% of the detected AF episodes were asymptomatic.40 AF episodes detected by the ILR in CARISMA were also shown to be predictive of ventricular arrhythmias and bradyarrhythmias during the follow-up. This implies the clinical value of long-term cardiac rhythm monitoring in cardiac high risk patients. A novel ILR, Reveal XT was evaluated to detect AF in patients after surgical ablation for atrial fibrillation in 45 patients compared to 24 hour Holter monitoring. Holter monitoring yielded to a 60% sensitivity, and a 64% negative predictive value compared to the loop recorder.41 In a small scale study conducted by Eitel et al.42 on ILR with this specific AF detection algorithm showed a trend towards more sensitive detection of AF by loop recorder compared to serial 7 day Holter assessment. Following this small study, a large multicenter clinical trial, the XPECT trial was launched to assess the performance of the new ILR with AF specific algorithm (Reveal XT). Twenty-four centers participated from Europe, and Canada. A total of 247 patients were enrolled in the study with frequent AF who had undergone catheter ablation for AF due to paroxysmal AF. Patients with persistent or permanent AF were excluded. During the follow-up, 235 of 247 patients had Holter recording suitable for analysis. Only 3.9% of the patients were free of AF during the follow-up. Almost all of the patients, 96.1% had at least one AF episode. The sensitivity for identifying AF episodes was 96.1%. The specificity was 85.4% after adjudication of the episodes. The positive predictive value to detect AF was 79.3%, the negative predictive value was 97.4%. The authors concluded that the new algorithm reliably detects the presence or absence of AF and suggested clinical application of this new implantable loop recorder in patients with atrial fibrillation. The current data on ILR with AF specific algorithm are promising. However, long-term follow-up and future studies assessing clinical outcome are warranted.43
Table 1 – Arrhythmia yield using various modalities. Arrhythmia Yield Using Various Modalities
Patients Diagnostic yield
Holter Monitor
Loop Event Monitor
Autodetect Feature
N = 600
N = 600
N = 600
37 6.2%
108 17%
216 36%
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Implanted devices
New advances in technology
Implanted pacemakers (PM), implantable cardioverter defibrillators (ICD), and cardiac resynchronization therapy (CRT) devices provide proper detection and recording of ventricular and atrial arrhythmias. All of the implanted devices record the date and time of the atrial arrhythmias as well as the duration, and the mean or maximum heart rate in the atrium, and in the ventricle (in case of a dual chamber device). The information stored in the devices is essential for the management of AF patients; it may drive medical therapy, change the dose of medication, e.g. more efficient frequency control, and initiate invasive procedures, e.g. catheter ablation for AF, or AV-node ablation in selected cases with implanted pacemakers. The entry criteria for episode recording, like duration and atrial rate are programmable. However, there is a limit in the storage of the episodes depending on the device type therefore telemetry might be preferred to have a comprehensive overview of each event. The device also stores data on long-term AF burden that is extremely useful for the physician to guide therapy. The advantage of device stored information on AF is the possibility of recording asymptomatic episodes, and long-term follow-up. The first large multicenter trial, Jewel AF showed that dual chamber pacemakers were able to detect 98% of the AF episodes and 88% of the atrial tachycardia/flutter episodes.44 Another group, Israel et al.14 evaluated 110 patients with implanted pacemakers and revealed that 38% of the device stored episodes were asymptomatic. Also, AF was documented by ECG only in 46% of the patients compared to 88% recorded by the device. Notably, long AF episodes > 48 hours were more often asymptomatic, suggesting the importance of continuous monitoring in those with persistent atrial fibrillation. Another study suggested that even in high-risk patients with history of paroxysmal AF, there was only 21% of recurrent AF stored by the device during a mean follow-up of 16 months. Symptoms had only 19% sensitivity and 21% positive predictive value to predict AF episodes.15 Remote monitoring of implanted medical devices is essential to provide feedback to the clinician on patient condition that may help guiding therapy.45 The recently published Subclinical Atrial Fibrillation and the Risk of Stroke (ASSERT) trial found that asymptomatic subclinical AF is present in 10% of patients with no prior history of AF. Asymptomatic AF was highly predictive of subsequent symptomatic AF episodes and predictive of ischemic stroke or systemic embolization.46 This investigation underlies the importance of AF monitoring to guide therapy. They found that the median time to the first episode of AF was 36 days after device implantation suggesting that even a 7-day Holter monitoring may not be sufficient to detect subclinical AF in patients with no prior history of AF. Similar findings were reported in patients with prior history of AF, the device detected atrial arrhythmias predicted stroke or death,47 and thromboembolic events.22,48
The emergence of new long-term ambulatory monitoring technologies will soon make it possible to unobtrusively monitor patients for weeks and months instead of days. One of these upcoming developments is a universal ECG sensor (UES) that combines a standard 12-lead Holter with a telemetry enabled event monitor. The new device has been developed by Lobodzinski et al.49 The UES device is a selfcontained 1.5″ × 4″ “patch” that uses low mass, flexible biopotential fiber sensors instead of traditional wires and electrodes that attach directly to the patients' skin. Special hydrocolloid adhesive material used in UES stays up to 30 days on the skin and does not induce dermatitis as seen in previous patch devices. Custom software is used to analyze the long-term ECG data. The field of wearable computing provides an exciting venue for the testing and development of other novel technologies may be currently underway that the authors are not aware of and therefore did not include in the present review article.
Summary We provided a comprehensive overview on currently available and emerging new methodologies in ambulatory ECG monitoring with a focus on the diagnosis of AF and follow-up of patients after catheter ablation for AF. There is no perfect solution for ECG monitoring in AF patients. All the current technologies present certain advantages and disadvantages. Clinicians need to choose the method that is the most appropriate for the patient and for the clinical scenario. To provide guidance in this process, flowcharts were presented to facilitate decision making (Figs 2 and 3). Please note that individual clinical cases may need further consideration. Also, in developing countries, many of the techniques may not be available, or too costly, and may not be reimbursed. In this article, we did not aim to accommodate such conditions. National guidelines may introduce these additional limits.
Statement of Conflict of Interest All authors declare that there are no conflicts of interest.
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implications for the risk of thromboembolic events. J Cardiovasc Electrophysiol. 2009;20:241-248. Hindricks G, Piorkowski C, Tanner H, et al. Perception of atrial fibrillation before and after radiofrequency catheter ablation: relevance of asymptomatic arrhythmia recurrence. Circulation. 2005;112:307-313. Kottkamp H, Tanner H, Kobza R, et al. Time courses and quantitative analysis of atrial fibrillation episode number and duration after circular plus linear left atrial lesions: trigger elimination or substrate modification: early or delayed cure? J Am Coll Cardiol. 2004;44:869-77. Dagres N, Kottkamp H, Piorkowski C, et al. Influence of the duration of Holter monitoring on the detection of arrhythmia recurrences after catheter ablation of atrial fibrillation: implications for patient follow-up. Int J Cardiol. 2010;139: 305-306. Beukema R, Beukema WP, Sie HT, Misier AR, Delnoy PP, Elvan A. Monitoring of atrial fibrillation burden after surgical ablation: relevancy of end-point criteria after radiofrequency ablation treatment of patients with lone atrial fibrillation. Interact Cardiovasc Thorac Surg. 2009;9:956-959. Gula LJ, Krahn AD, Massel D, Skanes A, Yee R, Klein GJ. External loop recorders: determinants of diagnostic yield in patients with syncope. Am Heart J. 2004;147:644-648. Linzer M, Pritchett EL, Pontinen M, McCarthy E, Divine GW. Incremental diagnostic yield of loop electrocardiographic recorders in unexplained syncope. Am J Cardiol. 1990;66: 214-219. Kinlay S, Leitch JW, Neil A, Chapman BL, Hardy DB, Fletcher PJ. Cardiac event recorders yield more diagnoses and are more cost-effective than 48-hour Holter monitoring in patients with palpitations. A controlled clinical trial. Ann Intern Med. 1996;124:16-20. Reiffel JA, Schwarzberg R, Murry M. Comparison of autotriggered memory loop recorders versus standard loop recorders versus 24-hour Holter monitors for arrhythmia detection. Am J Cardiol. 2005;95:1055-1059. Joshi S, Choi AD, Kamath GS, et al. Prevalence, predictors, and prognosis of atrial fibrillation early after pulmonary vein isolation: findings from 3 months of continuous automatic ECG loop recordings. J Cardiovasc Electrophysiol. 2009;20: 1089-1094. Dziubinski M. PocketECG: a new continuous and real-time ambulatory arrhythmia diagnostic method. Cardiol J. 2011;18: 454-460. Rothman SA, Laughlin JC, Seltzer J, et al. The diagnosis of cardiac arrhythmias: a prospective multi-center randomized study comparing mobile cardiac outpatient telemetry versus standard loop event monitoring. J Cardiovasc Electrophysiol. 2007;18:241-247. Vasamreddy CR, Dalal D, Dong J, et al. Symptomatic and asymptomatic atrial fibrillation in patients undergoing radiofrequency catheter ablation. J Cardiovasc Electrophysiol. 2006;17:134-139. Mason PK, Wood MA, Reese DB, Lobban JH, Mitchell MA, DiMarco JP. Usefulness of implantable loop recorders in office-based practice for evaluation of syncope in patients with and without structural heart disease. Am J Cardiol. 2003;92:1127-1129. Charitos EI, Stierle U, Ziegler PD, et al. A comprehensive evaluation of rhythm monitoring strategies for the detection of atrial fibrillation recurrence: insights from 647 continuously monitored patients and implications for monitoring after therapeutic interventions. Circulation. 2012;126:806-14. Giada F, Gulizia M, Francese M, et al. Recurrent unexplained palpitations (RUP) study comparison of implantable loop
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42.
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recorder versus conventional diagnostic strategy. J Am Coll Cardiol. 2007;49:1951-1956. Huikuri HV, Mahaux V, Bloch-Thomsen PE. Cardiac arrhythmias and risk stratification after myocardial infarction: results of the CARISMA pilot study. Pacing Clin Electrophysiol. 2003;26:416-419. Bloch Thomsen PE, Jons C, Raatikainen MJ, et al. Long-term recording of cardiac arrhythmias with an implantable cardiac monitor in patients with reduced ejection fraction after acute myocardial infarction: the Cardiac Arrhythmias and Risk Stratification After Acute Myocardial Infarction (CARISMA) study. Circulation. 2010;122:1258-1264. Jons C, Jacobsen UG, Joergensen RM, et al. The incidence and prognostic significance of new-onset atrial fibrillation in patients with acute myocardial infarction and left ventricular systolic dysfunction: a CARISMA substudy. Heart Rhythm. 2011;8:342-348. Hanke T, Charitos EI, Stierle U, et al. Twenty-four-hour holter monitor follow-up does not provide accurate heart rhythm status after surgical atrial fibrillation ablation therapy: up to 12 months experience with a novel permanently implantable heart rhythm monitor device. Circulation. 2009;120:S177-S184. Eitel C, Husser D, Hindricks G, et al. Performance of an implantable automatic atrial fibrillation detection device: impact of software adjustments and relevance of manual episode analysis. Europace. 2011;13:480-485.
43. Hindricks G, Pokushalov E, Urban L, et al. Performance of a new leadless implantable cardiac monitor in detecting and quantifying atrial fibrillation: Results of the XPECT trial. Circ Arrhythm Electrophysiol. 2010;3:141-147. 44. Swerdlow CD, Schsls W, Dijkman B, et al. Detection of atrial fibrillation and flutter by a dual-chamber implantable cardioverter-defibrillator. For the Worldwide Jewel AF Investigators. Circulation. 2000;101:878-5. 45. Dubner S, Auricchio A, Steinberg JS, et al. ISHNE/EHRA expert consensus on remote monitoring of cardiovascular implantable electronic devices (CIEDs). Ann Noninvasive Electrocardiol. 2012;17:36-56. 46. Healey JS, Connolly SJ, Gold MR, et al. Subclinical atrial fibrillation and the risk of stroke. N Engl J Med. 2012;366: 120-129. 47. Glotzer TV, Hellkamp AS, Zimmerman J, et al. Atrial high rate episodes detected by pacemaker diagnostics predict death and stroke: report of the Atrial Diagnostics Ancillary Study of the MOde Selection Trial (MOST). Circulation. 2003;107: 1614-1619. 48. Glotzer TV, Daoud EG, Wyse DG, et al. The relationship between daily atrial tachyarrhythmia burden from implantable device diagnostics and stroke risk: the TRENDS study. Circ Arrhythm Electrophysiol. 2009;2:474-480. 49. Lobodzinski SM, Laks MM. Biopotential fiber sensor. J Electrocardiol. 2006;39:S41-S46.
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Ambulatory ECG Monitoring in Atrial Fibrillation Management Spencer Z. Roseroa, 1 , Valentina Kutyifaa, 1 , Brian Olshanskyb , Wojciech Zarebaa,⁎ a
Cardiology Division, University of Rochester Medical Center, Rochester, NY, USA University of Iowa, Iowa City, IA, USA
b
A R T I C LE I N F O
AB ST R A C T
Keywords:
Ambulatory ECG monitoring technology has rapidly evolved over the last few decades and
Atrial fibrillation
has been shown to identify life-threatening and non-life threatening arrhythmias and
Ambulatory
provide actionable data to guide clinical decision making. Atrial fibrillation episodes can
ECG monitoring
often be asymptomatic, even after catheter ablation for atrial fibrillation, creating a
Atrial fibrillation ablation
disconnect between symptoms and actual arrhythmia burden which may alter clinical
Holter monitor
management. In this review, we aim to provide a comprehensive overview of invasive and
Event monitor
non-invasive ECG monitoring strategies in patients with atrial fibrillation, with a special
Implanted loop recorder
focus on the diagnosis of atrial fibrillation, and on follow-up of patients after catheter
Pacemaker
ablation for atrial fibrillation ablation.
Implantable cardioverter
© 2013 Elsevier Inc. All rights reserved.
defibrillator Cardiac resynchronization therapy
Recent technological advancements have facilitated ambulatory electrocardiogram (ECG) monitoring in the outpatient environment providing continuous, high resolution ECG data streams ranging from days to months at a time. Wireless communication has permitted the transfer of relevant ECG data in real-time encouraging rapid analysis and timely clinical intervention. The rapid commercialization and competitive market for managing patients with atrial fibrillation (AF) have produced a large menu from which clinicians must now carefully choose to meet the needs of their patients. Atrial fibrillation is the most common arrhythmia, especially in hypertensive patients, in the elderly1–5 and in those with heart failure (HF).6–8 The incidence and prevalence of atrial fibrillation are constantly growing.9 A recent study suggested that the incidence of atrial fibrillation will double
by the year of 2030, and the prevalence of the disease will reach 12.1 million cases in the United States.10 Furthermore, AF may have significant clinical consequences. It is known to be associated with a significant increase in the risk of stroke, HF hospitalization and related health care costs.11 Catheter ablation for atrial fibrillation ablation has become an established method to provide efficient rhythm control in patients with atrial fibrillation and has been claimed as a “cure” for the disease. However, longterm success data are still lacking, and success also depends on the ECG modality that is used to monitor AF episodes.12 This review article will provide an overview on the invasive and non-invasive ECG monitoring tools in atrial fibrillation with a focus on atrial fibrillation diagnosis, and follow-up in patients undergoing catheter ablation. Furthermore, we present data on new methods to be investigated in this rapidly evolving field.
Statement of Conflict of Interest: see page 150. ⁎ Address reprint requests to Wojciech Zareba, MD, PhD, Heart Research Follow-up Program Cardiology Division, University of Rochester Medical Center, 265 Crittenden Blvd., Box 653, Rochester, NY 14642. E-mail address: [email protected] (W. Zareba). 1 S.Z.R. and V.K. contributed equally to the work. 0033-0620/$ – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.pcad.2013.10.001
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Abbreviations and Acronyms AF = atrial fibrillation
General considerations
AT = atrial tachycardia In patients with atrial fibrillation, initial diagnosis has been most ECG = electrocardiogram often made utilizing a 12-lead ECG or Holter ELEM = event loop monitoring monitoring. Therapy efHF = heart failure ficacy has been evaluated by patient-reported ICD = implantable cardioverter symptoms, repeated 12defibrillator lead ECG recordings or ILR = implanted loop recorder Holter monitoring. However, several studies MCOT = mobile cardiac outpasuggested that episodes tient telemetry of AF occur without PM = implanted pacemaker symptoms.13–15 These events may carry significant risk of stroke, and thromboembolic events and falsify the success rate of catheter ablation for atrial fibrillation. Therefore, the identification of AF episodes and recurrences is relevant. Long-term Holter recording and event monitors were proven to have a superior diagnostic yield compared to 12lead ECG or 24/48-hour Holter monitoring; however, the complexity of these devices, patient compliance, need of a CRT = cardiac resynchronization therapy
transmitter device, and in some cases the relatively slow review of the records limit every-day clinical applicability. Newer techniques using patch-type monitors that provide real time feedback to the care provider or to the patient itself are more useful in clinical practice and may drive immediate changes in medical therapy or patient care to improve clinical outcome. These new methods need to be not only simple, but reliable, with sufficient capability to store and to transmit episodes. However, the most optimal devices are those that provide continuous long-term monitoring, 24 hours, 7 days a week, with immediate feedback. Implanted loop recorders (ILR), and implanted pacemakers (PM), defibrillators (ICD), or cardiac resynchronization therapy devices (CRT) are able to do continuous monitoring and produce output of the recorded rhythm abnormalities. However, necessity of the invasive procedure restricts their wide applicability. The key points in current ambulatory ECG monitoring are 1) long-term monitoring capabilities, 2) instant feedback, 3) simplicity, 4) every-day use, 5) non-invasive nature. A summary of ambulatory ECG monitoring tools with respected ranges of diagnostic accuracy is listed in Fig 1 and discussed in details in the chapters below. However, the requirements for diagnosing AF and for follow-up of patients after catheter ablation for AF are somewhat different. Suggested schemes for diagnosing AF and evaluating the success rate of catheter ablation are depicted in Figs 2 and 3 and will be discussed later.
Fig 1 – Summary of ambulatory ECG monitoring tools with respected ranges of diagnostic accuracy.
PR O G RE S S I N C ARDI O V A S CU L A R D I S EA S E S 5 6 (2 0 1 3) 14 3–1 5 2
Fig 2 – Diagnosing atrial fibrillation using ECG monitoring tools.
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Fig 3 – Evaluating the success of catheter ablation for atrial fibrillation using ECG monitoring tools.
ECG monitoring and transtelephonic ECG The traditional 12-lead ECG may easily confirm the diagnosis of atrial fibrillation. In some cases, however, it depicts the electrical activity of the heart for only a very limited amount
of time. Its main advantage is that it is simple, easy to perform, widely available, and it is relatively easy and fast to interpret the findings. However, the ECG diagnosis of AF might be still challenging in primary care; the SAFE (Screening for Atrial Fibrillation in the Elderly) trial showed 80% sensitivity and 95% specificity in identifying AF among
PR O G RE S S I N C ARDI O V A S CU L A R D I S EA S E S 5 6 (2 0 1 3) 14 3–1 5 2
general practitioners.16 Furthermore, since it only presents information on few beats, it is often not sufficient to detect atrial fibrillation. Transtelephonic ECG recording, consisting of 10 seconds up to 1–2 minutes continuous recordings, is more efficient in diagnosing AF and follow-up patients after catheter ablation for AF. Senatore et al.17 evaluated the role of 12-lead ECG performed one, and four months after catheter ablation for atrial fibrillation and compared it to transtelephonic ECG monitoring performed daily, and when symptoms occurred, combined with a 24-hour Holter monitoring in 72 consecutive patients. They found that transtelephonic ECG was able to identify a higher number of recurrent AF events (27.8% of the total patient cohort) compared to 12-lead ECG performed at one, and four months after catheter ablation combined with a 24-hour Holter recording (13.9% of the total patient cohort). A most recent study suggested that transtelephonic ECG is more sensitive than 24-hour Holter monitoring.18 This group evaluated 22 patients with diagnosed atrial fibrillation who had a 24-hour Holter once within the first 30 days, and transtelephonic ECG was recorded twice a day for 10 seconds. AF episodes were detected in 82% of the patients using transtelephonic ECG compared to a 32% event rate when analyzed by 24-hour Holter monitoring. Others suggested that transtelephonic ECG yields similar accuracy as does a 7-day Holter monitoring. Thirty patients were evaluated by Piorkowski et al.19 following catheter ablation for atrial fibrillation. They performed transtelephonic ECG every second day for six months, and a 7-day Holter at 3 and 6-month post-ablation. Patient-reported symptoms were also collected. In this study, 7-day Holter and transtelephonic yielded comparable diagnostic accuracy, with a success rate of 50% with 7-day Holter, and 45% with transtelephonic ECG.
Holter monitoring Holter monitoring has been the gold standard of ambulatory ECG monitoring available since 1961, introduced by Norman Holter.20 It is usually recorded for 24, or 48 hours with 3-lead or 12-lead ECG configuration. It provides comprehensive information in AF patients on recurrence, AF burden expressed in number of minutes in AF, and on the minimum, maximum, and mean ventricular rate during sinus rhythm or AF. Additionally, it produces an output including the number of atrial and ventricular ectopic beats, and the presence of sustained ventricular tachyarrhythmias with or without AF. Holter monitoring has been an essential tool in the diagnosis of AF, because of the non-sustained nature of this arrhythmia. Often it is helpful utilizing the patient event markers to relate clinical symptoms to the occurrence of the arrhythmia. In patients with infrequent symptoms, 24–48-hour Holter monitoring may provide a better diagnostic yield, however prolonged Holter recordings or other methods with long-term monitoring may increase related health care costs. The advantages of Holter monitoring are the relative simplicity of the technique and the detailed information about the initiation and termination of the AF episode. However, the electrodes and leads are uncomfortable to wear for most patients, especially in
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case of multi-day recordings, and some patients have allergy to the electrodes making the recording impossible. Holter needs time-consuming evaluation by trained health care personnel, although improved algorithms for AF detection may significantly shorten evaluation time. Some of the recordings may have substantial artifacts, noise and need to be repeated. Arrhythmias with rare occurrence may be often missed by 24–48-hour Holter and multiday recording might be necessary. However, Holter monitoring is still playing a key role in monitoring drug effects of rate control.21 Average heart rate in AF from 24-hour (or longer) Holter monitoring is an important tool in guiding optimal rate control therapy and helps in titration of drug dosage. Botto et al.22 evaluated the diagnostic accuracy of detecting AF episodes by Holter monitoring. He found that the mean sensitivity to detect a more than 5 minutes long AF event was 44.4%, 50.4% and 65.1% for 24-hour, 1-week, and 1month Holter monitoring. The clinical applicability of 1month Holter however is very ambiguous. Hindricks et al.23 assessed the applicability of 7-day Holter in patients after catheter ablation for atrial fibrillation. They suggested that the incidence of asymptomatic AF recurrences after catheter ablation is high, and therefore more intense monitoring is warranted in this patient group. They prospectively evaluated 114 consecutive patients following catheter ablation for AF utilizing 7-day Holter immediately after, and 3, 6, 12 months after catheter ablation and collected data on symptoms. They showed that the incidence of asymptomatic AF recurrences after ablation increased to 37% from 5% at baseline indicating that the symptom-based follow-up in this group may not be sufficient. Other groups also investigated the role of one-week Holter monitoring to detect AF recurrences after ablation compared to 24-hour Holter monitoring. Kottkamp et al.24 showed that in 100 patients following catheter ablation for AF, there was a higher incidence (26%) detected with 7 day Holter monitoring at 12 months compared to 12% detected with classical 24 hour Holter monitoring. Dagres et al.25 evaluated 215 patients who underwent 7-day Holter monitoring following catheter ablation for AF. They explored the incremental value of days of Holter monitoring in the diagnosis of recurrences. They found that the Holter monitoring with duration of less than or equal to 5 days detected significantly less AF recurrences compared to the 7day monitoring. There was a linear relationship between the ability of detecting recurrences and increasing monitoring time. The classical 24-hour Holter would have detected 59%, a 48-hour recording 67%, 72-hour recording 80%, 4-day recording 91% of the AF recurrences of those that were detected during the 7-day Holter monitoring. It is clear from these studies that the more aggressive the monitoring procedure is, the more episodes will be revealed during follow-up.26
Event monitors Event monitors are small leadless devices that are applied to the chest and record the ECG for a short period of time. The life span of these devices is usually up to 30 days. There are
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looping and non-looping monitors, the looping monitors use patient triggered activation, or record events based on the programmed criteria. Data are sent to a data center and physician and patient are notified based on pre-specified alerts. This is the first type of monitor that provides feedback for the physician and the patient immediately. Possible disadvantage of this method is that the patient triggered activation needs compliance, and arrhythmias with sudden onset may disable the patient to activate the device. Event monitors have proven useful in the detection of arrhythmias occurring at least every 21–30 days.27 Several studies suggested superior diagnostic yield of event monitors compared to Holter monitoring in patients with infrequent arrhythmias.27–29 Some of the reports also claimed costeffectiveness of this approach compared to Holter monitoring.29 The detection of atrial fibrillation is feasible using event monitors. Reiffel et al.30 have shown that loop event monitors and auto-triggered loop monitors identify AF more often than Holter monitoring. Furthermore, auto-triggered loop recorder was more sensitive compared to the loop recorder suggesting that there is an additional benefit of symptom-related AF detection. Therefore, use of auto-triggered loop recorders is highly recommended in patients with AF. Joshi et al.31 evaluated AF recurrence in patients in the first three months after catheter ablation for AF. They found that there was a peak in AF recurrences 2 weeks after ablation with an incidence rate of 54% that was lower at 3 months, around 22%. Interestingly, 34% of these episodes were asymptomatic further stressing the importance of continuous ECG monitoring when evaluating the success of catheter ablation. Despite the fact that we are still using 3 months blanking period after catheter ablation for atrial fibrillation, this group suggested that the freedom from AF in the first 2 weeks after ablation highly predicted the long-term success of the procedure.
Long-term ECG monitors Advances in electronics, power supply, wireless communication and data storage have facilitated the use of ECG monitoring devices capable of continuously acquiring data for days, weeks and months at a time. Traditional external loop event monitoring provides short term ECG recordings before and during a symptomatic event but requires the patient to activate the recording at that time. This may be worn for several weeks and the patient may transmit the data manually over the phone or return the device to the office for download. Several of these external loop monitors also have auto-detect features that record arrhythmias detected by proprietary algorithms. Mobile cardiac outpatient telemetry (MCOT) allows for either patient activated time stamping of events, passive automatic event triggering, and/or continuous 24/7 live monitoring using a third party coverage. In the latter system, predefined clinically significant events are communicated to the physician on call. In the current environment of managed care, consolidation among healthcare providers, increased competition and
declining reimbursement rates, the major players in the MCOT and event monitoring space have been increasingly required to compete on the basis of price, value and efficiency. In order to compete effectively, they have accelerated the creation of and/or acquisition of advanced technology. Companies such as BioMedical, CardioNet, LifeWatch, Medicomp, MedNet, ScottCare, and Medicalgorithmics are commonly used in clinical practice and provide distinct “menu” options for the physician to customize their strategy in following patients with recurrent arrhythmias, especially in the post intervention period. The integration of monitoring technology with the internet has improved physicians access to real time data. For example, Medicalgorithmics (Spectocor) offers continuous Holter monitoring for as long as needed with innovative technology providing streaming of full-disclosure ECG recording to central web-based station.32 The recordings could be stopped after 2 days if AF is detected or could be continued for 20–30 days or longer if needed. This system offers superiority over other available systems due to the fact that full disclosure Holter recording is immediately available on the web to the physician who could verify the AF episodes and assess AF burdens. Other long-term monitoring devices rely on algorithms detecting AF and storing only periods when AF was detected without opportunity to visualize continuous ECG in case of AF being missed by the algorithms. The decision process for choosing the most appropriate monitoring for a particular patient requires the provider to address three key questions: 1) Is there interest in only symptomatic events? (i.e. syncope, palpitations, lightheadedness) 2) Will the detection of a specific arrhythmia such as AF, both symptomatic and asymptomatic, be important? 3) Will the detection of certain asymptomatic arrhythmias, such as sinus node dysfunction, ventricular tachycardia, torsade de pointes, AF, atrial flutter, or SVT change the clinical management plan? Rothman et al.33 compared the value of MCOT with a traditional patient activated external loop event monitor in detecting symptomatic arrhythmias. This multicenter prospective trial enrolled 305 patients and randomized them to MCOT or event loop monitoring (ELEM) for 30 days. Their endpoint was the confirmation or exclusion of a probable arrhythmic cause of symptoms. The study demonstrated that 88% of patients randomized to the MCOT group had a diagnosis confirmed compared to 75% of the ELEM subjects. In a sub-study of patients with syncope, there was an 89% diagnostic yield using MCOT compared to 69% in ELEM (p = 0.008). Symptomatic AF was reported by approximately 8% of patients in both groups. However, 17% of the MCOT patients were found to have asymptomatic AF with rapid ventricular rates greater than 150 bpm. The finding of new asymptomatic AF may significantly alter medical decision making because of its association with stroke and the existence of guidelines outlining anticoagulation strategies based on risk. Reiffel et al30 evaluated the yield of continuous monitor with an AF autodetect feature compared to standard event
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monitors and Holter recorders. Table 1 summarizes the results based on a retrospective analysis of a Lifewatch database of 100,000 patients, from which they randomly selected 1,800 patients (600 patients for each recording method). These methods also provide an efficient and quantitative approach for monitoring patients after catheter ablation for AF. Kircher et al.12 addressed the need for long-term, continuous monitoring that can accurately detect AF and its implications for guiding medical therapy. The increased morbidity and mortality associated with AF, regardless of whether symptomatic or asymptomatic, prioritize early detection since its presence or absence directly impacts decisions regarding anticoagulation. In the post ablation period, the requirement for increased sensitivity is critical since false negatives may result in the premature discontinuation of anticoagulation and concomitant increase in stroke risk in this patient population. Specificity is also important and can often be improved with post detection manual confirmation. Current technologies allow for manual analysis of ECG categorized by algorithms as arrhythmia. Vasamreddy et al.34 used MCOT to monitor patients after ablation of AF. The MCOT was used for 5 consecutive days per month for up to 6 months. They demonstrated that while 70% of the patients were free from symptomatic AF episodes, the true success was closer to 50% if asymptomatic episodes were included. Depending on the goal of ablation therapy: cure, control of symptoms, and/or reduction of AF burden, the asymptomatic presence of AF poses a risk to patients if anticoagulation therapy is altered based on symptoms alone.
Implantable loop recorders Implantable loop recorders are semi-invasive, leadless devices that are implanted subcutaneously to record the ECG signals. The device is programmable to detect certain duration of specific type of (atrial or ventricular) arrhythmias. The life span of the device is 2–3 years. The advantage of this technique is the possibility of long recordings that enable the physician to follow the patient for years after the diagnosis or following catheter ablation of atrial fibrillation and therefore, it may be an optimal approach to guide and manage treatment. Possible disadvantage is the semi-invasive nature of the device implantation. Also, every 2–3 years the device needs to be replaced and it has a relatively high cost compared to the short term ECG monitors. This device has been proven as a feasible diagnostic tool to diagnose syncope.35 Compared to intermittent monitoring, there is an advantage of using continuous monitoring, even when compared to more aggressive intermittent monitoring strategies. The socalled temporal AF burden aggregation (AF density) was shown to be directly related to the sensitivity of the intermittent monitoring options.36 Newer studies investigated the role of implanted loop recorders in diagnosing AF, and follow-up of patients with AF. Giada et al.37 evaluated the diagnostic yield of ILR compared to short-term ambulatory ECG recordings and electrophysiological study in patients with recurrent unexplained palpitations. They showed that ILR yielded diagnosis in 73% of the
patients compared to 21% using the conventional strategy. They also suggested that using ILR is cost effective, because it leads to a diagnosis at a lower cost. Another study, the Cardiac Arrhythmias and Risk Stratification After Myocardial Infarction (CARISMA) proposed the feasibility of ILR to record brady- and tachyarrhythmias after myocardial infarction.38,39 A sub-study of the CARISMA trial also showed that new-onset AF detected by ILR predicts the risk of major cardiovascular events in patients with AF events > 30 seconds, but not in those with shorter episodes. In this particular analysis, more than 90% of the detected AF episodes were asymptomatic.40 AF episodes detected by the ILR in CARISMA were also shown to be predictive of ventricular arrhythmias and bradyarrhythmias during the follow-up. This implies the clinical value of long-term cardiac rhythm monitoring in cardiac high risk patients. A novel ILR, Reveal XT was evaluated to detect AF in patients after surgical ablation for atrial fibrillation in 45 patients compared to 24 hour Holter monitoring. Holter monitoring yielded to a 60% sensitivity, and a 64% negative predictive value compared to the loop recorder.41 In a small scale study conducted by Eitel et al.42 on ILR with this specific AF detection algorithm showed a trend towards more sensitive detection of AF by loop recorder compared to serial 7 day Holter assessment. Following this small study, a large multicenter clinical trial, the XPECT trial was launched to assess the performance of the new ILR with AF specific algorithm (Reveal XT). Twenty-four centers participated from Europe, and Canada. A total of 247 patients were enrolled in the study with frequent AF who had undergone catheter ablation for AF due to paroxysmal AF. Patients with persistent or permanent AF were excluded. During the follow-up, 235 of 247 patients had Holter recording suitable for analysis. Only 3.9% of the patients were free of AF during the follow-up. Almost all of the patients, 96.1% had at least one AF episode. The sensitivity for identifying AF episodes was 96.1%. The specificity was 85.4% after adjudication of the episodes. The positive predictive value to detect AF was 79.3%, the negative predictive value was 97.4%. The authors concluded that the new algorithm reliably detects the presence or absence of AF and suggested clinical application of this new implantable loop recorder in patients with atrial fibrillation. The current data on ILR with AF specific algorithm are promising. However, long-term follow-up and future studies assessing clinical outcome are warranted.43
Table 1 – Arrhythmia yield using various modalities. Arrhythmia Yield Using Various Modalities
Patients Diagnostic yield
Holter Monitor
Loop Event Monitor
Autodetect Feature
N = 600
N = 600
N = 600
37 6.2%
108 17%
216 36%
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Implanted devices
New advances in technology
Implanted pacemakers (PM), implantable cardioverter defibrillators (ICD), and cardiac resynchronization therapy (CRT) devices provide proper detection and recording of ventricular and atrial arrhythmias. All of the implanted devices record the date and time of the atrial arrhythmias as well as the duration, and the mean or maximum heart rate in the atrium, and in the ventricle (in case of a dual chamber device). The information stored in the devices is essential for the management of AF patients; it may drive medical therapy, change the dose of medication, e.g. more efficient frequency control, and initiate invasive procedures, e.g. catheter ablation for AF, or AV-node ablation in selected cases with implanted pacemakers. The entry criteria for episode recording, like duration and atrial rate are programmable. However, there is a limit in the storage of the episodes depending on the device type therefore telemetry might be preferred to have a comprehensive overview of each event. The device also stores data on long-term AF burden that is extremely useful for the physician to guide therapy. The advantage of device stored information on AF is the possibility of recording asymptomatic episodes, and long-term follow-up. The first large multicenter trial, Jewel AF showed that dual chamber pacemakers were able to detect 98% of the AF episodes and 88% of the atrial tachycardia/flutter episodes.44 Another group, Israel et al.14 evaluated 110 patients with implanted pacemakers and revealed that 38% of the device stored episodes were asymptomatic. Also, AF was documented by ECG only in 46% of the patients compared to 88% recorded by the device. Notably, long AF episodes > 48 hours were more often asymptomatic, suggesting the importance of continuous monitoring in those with persistent atrial fibrillation. Another study suggested that even in high-risk patients with history of paroxysmal AF, there was only 21% of recurrent AF stored by the device during a mean follow-up of 16 months. Symptoms had only 19% sensitivity and 21% positive predictive value to predict AF episodes.15 Remote monitoring of implanted medical devices is essential to provide feedback to the clinician on patient condition that may help guiding therapy.45 The recently published Subclinical Atrial Fibrillation and the Risk of Stroke (ASSERT) trial found that asymptomatic subclinical AF is present in 10% of patients with no prior history of AF. Asymptomatic AF was highly predictive of subsequent symptomatic AF episodes and predictive of ischemic stroke or systemic embolization.46 This investigation underlies the importance of AF monitoring to guide therapy. They found that the median time to the first episode of AF was 36 days after device implantation suggesting that even a 7-day Holter monitoring may not be sufficient to detect subclinical AF in patients with no prior history of AF. Similar findings were reported in patients with prior history of AF, the device detected atrial arrhythmias predicted stroke or death,47 and thromboembolic events.22,48
The emergence of new long-term ambulatory monitoring technologies will soon make it possible to unobtrusively monitor patients for weeks and months instead of days. One of these upcoming developments is a universal ECG sensor (UES) that combines a standard 12-lead Holter with a telemetry enabled event monitor. The new device has been developed by Lobodzinski et al.49 The UES device is a selfcontained 1.5″ × 4″ “patch” that uses low mass, flexible biopotential fiber sensors instead of traditional wires and electrodes that attach directly to the patients' skin. Special hydrocolloid adhesive material used in UES stays up to 30 days on the skin and does not induce dermatitis as seen in previous patch devices. Custom software is used to analyze the long-term ECG data. The field of wearable computing provides an exciting venue for the testing and development of other novel technologies may be currently underway that the authors are not aware of and therefore did not include in the present review article.
Summary We provided a comprehensive overview on currently available and emerging new methodologies in ambulatory ECG monitoring with a focus on the diagnosis of AF and follow-up of patients after catheter ablation for AF. There is no perfect solution for ECG monitoring in AF patients. All the current technologies present certain advantages and disadvantages. Clinicians need to choose the method that is the most appropriate for the patient and for the clinical scenario. To provide guidance in this process, flowcharts were presented to facilitate decision making (Figs 2 and 3). Please note that individual clinical cases may need further consideration. Also, in developing countries, many of the techniques may not be available, or too costly, and may not be reimbursed. In this article, we did not aim to accommodate such conditions. National guidelines may introduce these additional limits.
Statement of Conflict of Interest All authors declare that there are no conflicts of interest.
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