More than half a century ago, Holter ECG monitors transformed cardiology by allowing clinicians to study heart rhythm continuously over an extended period. Invented by physics researcher Jeff Holter, early iterations of these ambulatory monitors were marvels of their time, enabling overnight recording—a much-needed capability for spotting more insidious silent arrhythmias and other cardiac events.1
In the years since, ambulatory ECG monitoring has evolved rapidly, thanks to the sustaining innovation and resulting uptake of these early devices. Recorders have gone from a single channel to twelve, with media storage and device footprints getting progressively smaller as data analytics grow more powerful.2 By now, so-called "Holters" have become a household name, certainly among cardiologists, but also among many patients.
One outstanding question is how ambulatory Holter monitoring devices fit into today's watershed moment of digital health. Internet- and cloud-based monitors have ushered in a new era of mobile ECG, creating more capabilities and data—and potentially more confusion—in a quickly expanding field of ambulatory devices.
With familiar choices such as Holters and event recorders joining a wave of remote patient monitoring technologies like smartwatches, patches, and other ECG-capable leadless sensors, it's important to differentiate between the offerings and contextualize their capabilities so that cardiologists can better meet their patients' needs. Here's what clinicians should know in this fast-evolving landscape of ambulatory ECG.
Holter Monitoring
With the ability to monitor heart rate, ectopic beats, and other identifications for up to 48 hours continuously, or even longer in some cases, Holter monitors can be ideal for detecting events such as presyncope, syncope, or palpitations that take place approximately every day.3 These devices are the more well-known choice for ambulatory monitoring, having been around for decades. That time in the market also lends itself to more clinical evidence, which has helped to shape the technology's status as a standard of care.
Holters may not be ideal for patients who require longer-term monitoring, such as those whose arrhythmias occur less frequently than a Holter's standard two-day reporting window. Additionally, although Holter designs have improved since their mid-century predecessors, patients may find even modern lead placements disruptive, which has been found to impact adherence.4,5
Even so, Holters are still preferred in many instances, such as for locating the source of arrhythmia. Traditionally, clinicians use a 3-lead ECG to assess for ectopic atrial arrhythmia, and 12-lead devices for documenting ventricular tachycardia for ablation.
Event Recording
Event recorders offer continuous monitoring for up to 30 days (or three years for implantable devices), but they don't record that time continuously. Instead of storing a full-disclosure record, these devices help to conserve the amount of space available by recording events of concern that are either automatically flagged by the system itself or self-reported by the patient via a button once symptoms occur. Some devices operate on a looping structure, where eventful loops can override uneventful ones.
Recommended use cases tend to skew toward patients at lower risk and those whose arrhythmias might be too infrequent to reliably detect on a Holter. However, some devices, such as external loop recorders, may not be ideal for patients whose events occur less than once a month.4
Wearables and Mobile Monitors
Technological innovations have helped to establish a new frontier in mobile cardiac telemetry, with patches and other wearable sensors being validated in the clinic and accepted by patients as one possibility in the world of cardiac monitoring. Many mobile ECG monitors use internet connectivity to report cardiac events as they happen, allowing clinicians to evolve care plans (such as prescribing anticoagulants) based on real-time rhythm changes. In many cases, patients use remote monitoring devices for weeks at a time, or longer for everyday wearables such as smartwatches.
Use cases most suited to mobile monitoring include high-risk patients in need of real-time monitoring, such as survivors of cryptogenic stroke or patients who have just initiated antiarrhythmic therapy.4 In contrast, consumer wearables such as the Apple Watch are largely approved for informational purposes, not diagnosis.4 The monitoring of sporadic events is an additional use case for patches or watches.
However, these devices require infrastructural and personnel support, which is not always feasible, or fundable, for that matter. That's why, across devices, AI-supported interpretations can help to make data more actionable and boost clinicians' confidence in using them for select candidates.
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A Changing Universe for ECG
Although the landscape for remote cardiac monitoring is evolving toward slimmer device profiles and leadless systems, Holter monitors are still part of the cardiologist's modern toolkit. Anthony Pearson, MD, of the Skeptical Cardiologist blog and contributor to GE Healthcare Insights, has written about the benefits of having a diverse set of ambulatory monitors for patients without a known Afib diagnosis, for example.6
Some limitations to remote devices also emphasize the continued utility of Holter monitors, however. For example, in a 2020 Journal of the American College of Cardiology review, the author suggests that insurance reimbursement and privacy issues could hold back the broader uptake of mobile monitoring devices.7
Mobile-Supported—but Not Mobile-Only—Heart Monitoring
The wave of new ECG-capable technologies has created an interesting dynamic for practitioners. On one hand, there are more options than ever for prescribers to recommend for patients with suspected arrhythmias, particularly for those who may be more resistant to wearing a multi-lead device for hours at a time.
On the other hand, this influx of new technologies can make it more difficult to determine the appropriate care pathway based on clinical indications, payer realities, personal preferences, and data processing. Fortunately, the cardiology industry has become well-attuned to these concerns, with ongoing dialogue appearing in academic journals, associations, and trade media.4,7,8
As authors Pothineni and Deo wrote in Circulation in 2020, "As we await results of outcome trials regarding the management of subclinical AF, it is important for healthcare systems to prepare for the surge in AF that will be detected through reliable and widely available continuous cardiac rhythm monitors."9
Until the landscape evolves so that wireless capabilities become more of a reality across clinical evidence, policy, and practical use, nevertheless, Holters very much still have a place to stay in the cardiac continuum. However, they are just one option of many in a new era of ambulatory monitoring, and that kind of choice can make all of the difference to the patients who need it most.
References:
- Mar BD. The History of Clinical Holter Monitoring. Annals of Noninvasive Electrocardiology. 2005;10(2):226-230. https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1542-474X.2005.10202.x
- Kennedy HL. The Evolution of Ambulatory ECG Monitoring. Progress in Cardiovascular Diseases. 2013;56(2):127-132. https://doi.org/10.1016/j.pcad.2013.08.005
- Grond M, Jauss M, Hamann G, et al. Improved Detection of Silent Atrial Fibrillation Using 72-Hour Holter ECG in Patients With Ischemic Stroke. Stroke. 2013;44(12):3357-3364. https://www.ahajournals.org/doi/10.1161/STROKEAHA.113.001884.
- Sanders D, Ungar L, Eskander MA, Seto AH. Ambulatory ECG monitoring in the age of smartphones. Cleveland Clinic Journal of Medicine. 2019;86(7):483-493. https://doi.org/10.3949/ccjm.86a.18123.
- Lee SP, Ha G, Wright DE, et al. Highly flexible, wearable, and disposable cardiac biosensors for remote and ambulatory monitoring. npj Digital Medicine. 2018;1(1). https://doi.org/10.1038/s41746-017-0009-x.
- Pearson A. Which Ambulatory ECG Monitor for Which Patient? Medpagetoday.com. https://www.medpagetoday.com/opinion/skeptical-cardiologist/82296. Accessed September 19, 2022.
- Wearable Devices for Ambulatory Cardiac Monitoring: JACC State-of-the-Art Review. Journal of the American College of Cardiology. https://www.jacc.org/doi/10.1016/j.jacc.2020.01.046. Accessed September 19, 2022.
- Patrick K. How Will the Roadmap for Diagnostic Cardiology Devices Develop? DAIC. https://www.dicardiology.com/article/how-will-roadmap-diagnostic-cardiology-devices-develop. Accessed September 19, 2022.
- Pothineni NVK, Deo R. Screening for Atrial Fibrillation: Closing the "LOOP." Circulation. 2020;141(19):1523-1526. https://doi.org/10.1161/CIRCULATIONAHA.120.046298.
