AF Screening in Asymptomatic Older Individuals Shows Promise

March 04, 2021

A new randomized trial provides more evidence in support of screening for atrial fibrillation (AF) in asymptomatic older individuals.

The SCREEN-AF trial, conducted in persons aged 75 years or older who had hypertension but without known AF, showed that the use of a wearable continuous electrocardiography (ECG) monitor was well tolerated and increased AF detection tenfold compared to standard care.

The screening group wore the monitor continuously during two 2-week periods 3 months apart. AF was detected in 5.3% of those patients, compared with 0.5% of patients in the control group. Anticoagulation was initiated in 75% of for whom AF was detected in the screening group.

The study was published online in JAMA Cardiology on February 24.

Dr David Gladstone

Embolic strokes related to AF can be catastrophic, resulting in permanent disability, dementia, or death. One of the best ways to prevent stroke is by identifying and treating AF, lead author David J. Gladstone, MD, told Medscape Medical News.

"Too often we see patients whose atrial fibrillation is first detected only after they have suffered a stroke," he added. "What we really want is to be able to find and treat AF earlier, before it ever leads to a stroke, and our study findings suggest that 1 in 20 patients in primary care who are over age 75 with hypertension have undiagnosed AF that could be identified through screening."

Gladstone, who is associate professor at the University of Toronto and medical director of the regional stroke prevention clinic at Sunnybrook Health Sciences Center, Toronto, Canada, said that SCREEN-AF added "much-needed randomized evidence to a growing body of AF screening studies."

Previous trials have demonstrated that ambulatory ECG monitoring is effective in detecting AF in patients who have recently had an ischemic stroke, but data from randomized controlled trials have been lacking regarding AF screening among healthy, asymptomatic individuals, he noted.

"Most previous AF screening studies in asymptomatic individuals have either been observational studies lacking a control group or trials of single time-point ECG screens, pulse palpation, or brief intermittent screening using 30-second handheld ECG devices," Gladstone explained. "The SCREEN-AF study is one of the first randomized trials to investigate the use of a continuous ECG strategy for AF screening in asymptomatic individuals."

One other randomized trial, the mSTOPS study, used a similar design. In that trial, the rate of AF was 3.9% among those who underwent screening, compared to 0.9% in the control group, Gladstone reported.

"Our SCREEN-AF results are consistent with mSTOPS, and these two trials together provide strong randomized evidence that a continuous wearable ECG monitoring strategy for 2 to 4 weeks is feasible, detects a substantial prevalence of potentially actionable AF that otherwise would have gone undiagnosed, and provides opportunities for anticoagulant treatment for stroke prevention," he stated.

Clinical Endpoints Needed

Although the current findings have potential implications for future stroke prevention, the authors caution that more research is needed before this type of AF screening can be implemented widely.

"The study results support the need for ongoing research to determine the impact that screening will have on hard clinical outcomes like stroke, death, and bleeding rates," Gladstone said. "Widespread AF screening cannot be recommended until we have evidence that it is both clinically effective and cost-effective. We need to know if the benefits of screening will outweigh the risks and costs."

The SCREEN-AF trial enrolled 856 participants from 48 primary care practices. All of the participants were of older age and had hypertension ― the two leading risk factors for the development of AF. They were randomly assigned to undergo screening with the ECG adhesive patch (Zio XT, iRhythm Technologies) or standard care, consisting of routine clinical follow-up plus a pulse check and heart auscultation at baseline and at 6 months.

In the screening group, over a 28-day period, median wear time of the monitor was 27.4 days. In the primary analysis, AF was detected in 23 of 434 participants (5.3%) in the screening group, vs 2 of 422 (0.5%) in the control group (relative risk, 11.2; P = .001), giving a number needed to screen of 21.

Of those for whom AF was detected, the median total time spent in AF was 6.3 hours; the median duration of the longest AF episode was 5.7 hours. Anticoagulation was initiated in 15 of 20 patients (75.0%) in whom AF was detected. By 6 months, anticoagulant therapy had been prescribed for 4.1% of those in the screening group, vs 0.9% of the control group.

The monitor was well tolerated. Five participants (1.2%) developed adverse skin reactions that required premature discontinuation; 80% of the participants rated the ECG monitor as comfortable to wear during daytime and sleep.

The trial also evaluated a second method of AF screening, in which all participants in the screening group were given an automated home blood pressure machine with oscillometric AF screening capability to use twice daily during the monitoring periods. This method was found to generate a high level of false positive results and to be inferior for detecting paroxysmal AF compared with the ECG patch.

The researchers point out that all the participants in this study were older than 75 and had hypertension that gave them a CHADS2–VASc (congestive heart failure, hypertension, age ≥75 years, diabetes, stroke or transient ischemic attack, vascular disease, age 65–74 years, sex category) score of at least 2 points. The median CHADS2–VASc score was 4.

Among patients at this risk level, the presence of clinical AF is associated with an annual predicted stroke risk of approximately 7%. This risk can be reduced to about 2% with anticoagulant treatment, Gladstone estimated, but he said the relevance of AF detected by screening is uncertain.

He explained that the stroke risk associated with subclinical device-detected AF is less than it is for clinically diagnosed AF but is greater than that for persons who do not have AF. The minimum degree of AF that is clinically significant is currently a matter of debate.

"Generally speaking, the greater the AF burden, the greater the stroke risk, but the minimum threshold of subclinical AF to warrant initiation of anticoagulation is still uncertain. For now, clinical equipoise exists for anticoagulation of patients with subclinical AF of less than 24 hours' duration," he said.

One of the main concerns related to AF screening is that it may result in very low-risk individuals receiving unnecessary long-term anticoagulant therapy, which would increase their risk of bleeding complications.

"We don't want at-risk patients to be undertreated, but at the same time, we don't want patients being overtreated if they don't need anticoagulation," Gladstone commented.

"The key unanswered question is whether the early AF detection and treatment that results from screening will translate into a net clinical benefit for patients in terms of stroke risk reduction. To address that question will require much larger sample sizes and longer patient follow-up," he said. "To that end, we plan to contribute our study data to a future patient-level meta-analysis that will combine other similar trials of AF screening that are being conducted around the world."

In an accompanying editorial, Roopinder K. Sandhu, MD, and Christine Albert, MD, Smidt Heart Institute, Cedars-Sinai Hospital, Los Angeles, California, write: "Gladstone and colleagues provide an important contribution to the literature in terms of better defining a method, population, and setting for an approach to AF screening."

But they add: "The needle will only move forward once the results from studies evaluating clinical end points and cost-effectiveness are completed and more data are available regarding potential harms of screening. Ultimately, implementation will require a detailed assessment of health care systems' capacity to integrate AF screening into routine care."

The trial was funded by grants from the Canadian Stroke Prevention Intervention Network, the Canadian Institutes of Health Research, the German Center for Cardiovascular Research, and Boehringer Ingelheim and through in-kind support from Microlife Corp, ManthaMed, and iRhythm. Gladstone has disclosed no relevant financial relationships. Sandhu has received research grant support from a BMS/Pfizer quality improvement grant and from the University Foundation and Servier Alberta Innovation in Health Fund. Albert has received grant support from St Jude Medical, Abbott, and Roche Diagnostics.

JAMA Cardiol. Published online February 24, 2021. Abstract, Editorial

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