At-Home, Wearable ECG Patch May Improve Early Detection of AF

Damian McNamara

July 24, 2018

Continuous cardiac monitoring using a home-based, wearable electrocardiogram (ECG) sensor patch may improve early detection of atrial fibrillation (AF) in high-risk patients, new research shows.

Results of a study that compared the effects of immediate vs delayed use of the self-applied, adhesive, continuous monitoring patch show that at 4 months, new AF was identified in 3.9% of the immediate group vs 0.9% of the delayed group.

"The key clinical finding from our study is that asymptomatic atrial fibrillation can be easily detected via person-generated data using a self-applied ECG patch," Steven R. Steinhubl, MD, director of digital medicine at the Scripps Translational Science Institute in La Jolla, California, and principal investigator of the mHealth Screening to Prevent Strokes (mSToPs) study, told Medscape Medical News.

The study was published online July 10 in JAMA.

Leading Cause of Stroke

AF is the most common sustained arrhythmia and can increase the risk for stroke fivefold, previous research shows ( Cerebrovasc Dis . 2010;29:43-9). Experts implicate AF as the cause of nearly one third of all ischemic strokes ( Stroke . 2014;45:2599-605).

In addition, about 1 in 5 people who experience an AF-related stroke remain unaware of their arrhythmia until they have a cerebrovascular event ( Stroke . 1995;26:1527-30).

American Heart Association guidelines for primary prevention of stroke recommend pulse palpitation or an ECG rhythm strip obtained during a routine medical visit to screen for AF ( Stroke . 2011;42:517-84).

However, on the basis of this recommendation, some AF episodes may be missed.

"For those people found to have atrial fibrillation, the amount of time they spend in AF is surprisingly little ― a median of 0.9% ― which has important implications for optimal screening methods," said Steinhubl, principal investigator for the randomized controlled trial.

The investigators relied on technology to detect AF and to conduct the study. They recruited 2659 participants using digital technologies, including smartphones and the Internet. Participants were members of a large national health plan, the Aetna Fully Insured Commercial and Medicare Advantage Program. They were recruited between November 2015 and October 2016.

A total 1364 people were randomly assigned to the immediate continuous monitoring group and another 1291 to the delayed group.

Each person received mailed instructions along with two ECG patches that were approved by the US Food and Drug Administration (iRhythmZio, iRhythm Technologies). They wore each device for up to 2 weeks at a time, 3 months apart. They returned the patches for interpretation using a postage-paid envelope.

After completion of the 4-month trial, the researchers conducted a related 1-year observational study. They combined 1738 people from the immediate- and delayed-monitoring groups of the randomized controlled trial and then compared them to 3476 individuals who acted as the control group. They were matched for age, sex, CHA2DS2-VASc scores, and relevant comorbidities.

The patches performed well; the mean wear time was 12 days, and 98% of the stored ECG data were available for analysis.

The absolute difference in AF event detection of 3.0% between the immediate- and delayed-monitoring groups in the randomized trial was the primary outcome and was part of an intent-to-treat analysis. When the investigators compared these groups on a per-protocol basis, the absolute difference was 4.5%, again in favor of the immediate-monitoring group (5.1% vs 0.6%).

A total of 190 new cases of AF emerged during the observational study: 109 in the actively monitored participants vs 81 of the control patients. This translated to a rate of 6.7 events per 100 person-years vs 2.6 events, respectively, and an absolute difference of 4.1%.

Three participants with AF that was diagnosed via path experienced continuous AF throughout the duration of monitoring. All others had limited AF events, with a mean of nearly 10 episodes per monitoring period. The median duration of an individual's longest AF event was 186 minutes (IQR, 30.1 - 606.0 min).

Table. Duration of Patients' Longest AF Episode

Time Proportion of Patients With AF
Less than 5 min 7%
5 min to 6 hr 55%
6 hr to 24 hr 25%
More than 24 hr 13%

Risk Factors, Clinical Consequences

Twelve of 69 patients who had AF while wearing a patch, including those who had received a clinical diagnosis of AF prior to participation, reported feeling some symptoms at the time. Most of these symptoms were mild. Only two people in this group sought medical attention because of their symptoms.

Some participants had potentially actionable arrhythmias other than AF. These included 24 people with nonsustained ventricular tachycardia with cardiomyopathy, 22 with prolonged or symptomatic supraventricular tachycardia, 25 with significant pause or high-degree atrioventricular block, and one person who had very frequent ectopy.

Each additional 10 years of age or a history of heart failure or chronic obstructive pulmonary disease was associated with an increase in incidence of new AF, whereas female sex was a protective factor.

In contrast, participants who had been diagnosed clinically with AF were more likely to have chronic renal failure and were less likely to experience sleep apnea compared with those diagnosed via the ECG patch.

In general, the initiation rate of anticoagulation therapy was higher in the active-monitoring group than in the control group (5.7 vs 3.7 per 100 person-years). The rate specific to AF was likewise higher (2.4 vs 1.3 per 100 person-years).

Initiation of antiarrhythmic medication, ablation or cardioversion procedures, pacemaker or defibrillator placements, and overall use of healthcare resources were higher in the active monitoring group as well. In contrast, active monitoring was not associated with more emergency department visits or hospitalizations.

The findings suggest that spot-checking for AF, whether through random pulse check or through a brief ECG in a clinical setting, would likely miss most individuals with undiagnosed AF, the researchers note.

They add that a strength of the study is that digital outreach and participant-centered monitoring with a wearable sensor "even in this population with a mean age of 74 years" permitted a siteless, nationwide study that included people who otherwise might not be able to participate in a clinical trial.

With regard to study limitations, the 2655 participants represent only 2.6% of the potentially 102,553 eligible individuals who were invited to participate. In addition, health plan membership is fluid over time. In this study, more than 10% of participants were no longer members of their original health plan at 12 months.

The investigators plan to continue following the mSToPs study cohort "to better clarify the clinical consequences of ECG screening." The trial includes a 3-year follow-up assessment, at which point the clinical outcomes will be reported.

In addition, using what they learned in mSToPs, the investigators plan to incorporate new information of genetic risk markers for AF and screen a more refined, higher-risk population "to demonstrate even greater efficacy in the real-world implementation of an AF screening strategy."

Unanswered Questions

"The mSToPS data suggest that immediate, continuous screening for two weeks may be equivalent to weekly or biweekly, 30-second rhythm monitoring over a 12-month period in a population of similar risk," Benjamin A. Steinberg, MD, MHS, Division of Cardiovascular Medicine, University of Utah Health Sciences Center, Salt Lake City, and Jonathan P. Piccini, MD, MHS, Duke Center for Atrial Fibrillation, Duke University Medical Center, Durham, North Carolina, write in an accompanying editorial.

The trial also provides strong support for the use of 2 weeks of continuous rhythm monitoring to screen for AF in at-risk populations, given the detection rate of up to 5% at 4 months, they add.

"This appears to detect a substantial proportion of patients who might be detected using more inconvenient, invasive, costly or longer monitoring approaches," they write.

However, the editorialists note that before the mSToPS findings can be incorporated into clinical practice, it must be determined whether earlier, more sensitive detection of AF improves clinical outcomes, and if so, whether it is cost-effective.

A second accompanying editorial focused on the study design.

"While the study scores quite high for its pragmatic approach, there are trade-offs related to these efficiencies," write Eric D. Peterson, MD, MPH, Duke Clinical Research Institute, Duke University Medical Center, Durham, North Carolina, and Robert A. Harrington, MD, Stanford University, California.

Instead of randomizing participants to a patch vs no-patch group, the immediate vs delayed design ensured that all patients received the new technology. They note that this protocol might have made the study more acceptable to participants and "perhaps the insurer as well."

However, such a design only allowed the effectiveness of the patch to be compared with a control group for 4 months, which was "insufficient to assess the subsequent clinical or health care use," add Peterson and Harrington.

They acknowledge that the researchers attempted to correct for this in the observational study with a matched control group at high risk for AF who did not receive the patch to compare outcomes with those who did.

"While innovative, their resultant observational comparison provides less definitive conclusions than would have come from a randomized clinical trial," they write.

"Despite these limitations, mSToPS represents a brave new world for clinical research: an innovative, highly commendable, contemporary pragmatic health care IT study that tested an important question and yielded significant clinical findings," the editorialists conclude.

The study was funded by a research grant from Janssen Pharmaceuticals to Scripps Translational Science Institute and by the NIH National Center for Advancing Translational Science and the Qualcomm Foundation. Dr Steinhubl reported receiving grants from these three sources. Dr Steinberg receives grants or personal fees from Janssen, Dr Piccini receives clinical research funding from Janssen, and Dr Harrington receives grants from Janssen. Dr Peterson had reported no relevant financial relationships.

JAMA. Published online July 10, 2018. Abstract, Editorial 1, Editorial 2

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