In the LOOP study of individuals at high risk for stroke, ILR screening resulted in a three-fold increase in AF detection and anticoagulation initiation, "but we saw no significant reduction in stroke or systemic arterial embolism," Dr. Jesper Svendsen of the University of Copenhagen said in reporting the results at the European Society of Cardiology Congress 2021. The study was simultaneously published in The Lancet.
Atrial fibrillation raises the risk of ischemic stroke and death and many patients with AF have no symptoms and therefore remain undiagnosed, Dr. Svendsen noted.
"We also know that many stroke patients have undiagnosed atrial fibrillation and we have very effective treatment for atrial fibrillation to reduce the risk of stroke with oral anticoagulation," he said.
The LOOP study tested whether continuous monitoring for unknown AF and initiation of oral anticoagulation if AF was detected could prevent stroke in patients at high risk.
The LOOP study was an investigator-initiated randomized clinical trial of 6,004 adults aged 70 and older (47% women) with at least one additional stroke risk factor (hypertension, diabetes, prior stroke or heart failure).
A total of 1,501 were randomly allocated to ILR monitoring using the Reveal LINQ cardiac monitor from Medtronic and 4,503 to usual care (control group). The median duration of monitoring in the ILR group was 3.3 years.
During a median follow-up of 64.5 months, AF was diagnosed in significantly more adults in the ILR group than in the control group (31.8% vs. 12.2%; P<0.0001).
Oral anticoagulation was started in 29.7% of adults in the ILR group compared to 13.1% in the control group (P<0.0001). In the ILR group, anticoagulation was recommended if AF episodes lasted six minutes or longer.
The primary outcome (stroke or systemic arterial embolism) occurred in 318 participants (315 stroke and three systemic arterial embolism), with no significant difference between groups: 67 (4.5%) individuals in the ILR group and 251 (5.6%) in the control group (HR, 0.80; 95% confidence interval, 0.61 to 1.05; P=0.11).
"Although AF was diagnosed in more than 30% of participants in the ILR group and 91% of these initiated oral anticoagulation, the overall risk reduction was only 20% and non-significant," Dr. Svendsen noted in his presentation.
"If we assume that the 20% risk reduction is the correct estimate, then the number needed to screen to avoid one stroke or systemic arterial embolism would be 62 individuals," Dr. Svendsen reported.
In general, the findings were consistent across subgroups. There was an interaction with systolic blood pressure, with a potentially beneficial effect from ILR screening in those with very high blood pressure, a finding "in line with previous studies showing that hypertension, and especially high systolic blood pressure, is a predominant risk factor for atrial fibrillation and stroke alike. However, it should be stressed that these findings should only be considered as hypothesis generating," the researchers write in their paper.
The rates of bleeding were "modest" (4.3% in the ILR group and 3.5% in the control group). There was no effect of ILR on mortality.
Writing in a linked comment, Dr. Ben Freedman of the University of Sydney and Dr. Nicole Lowres of Concord Hospital, also in Sydney, Australia, say, "Although the results would conventionally be considered as negative, we can learn a lot from this large trial by examining why it did not succeed."
"The most important explanation is that shorter atrial fibrillation episodes found by long-term ILRs might not have the same stroke risk as atrial fibrillation detected through single-timepoint or less intense monitoring," they suggest.
Dr. Isabelle Van Gelder of the University of Groningen, in the Netherlands, who served as discussant for the trial, that the "optimal method for AF screening is not known yet and the LOOP contributes enormously to the data."
Collectively, the data to date suggest that AF detected by intermittent ECG in "high risk patients may identify more accurately those who will benefit from anticoagulation because they have clinical AF. The LOOP study contributes to the evidence that short episodes of subclinical AF are not worth screening for," Dr. Van Gelder said.
"More studies on AF screening are needed," she concluded.
Funding for the study was provided in part by the Innovation Fund Denmark, The Research Foundation for the Capital Region of Denmark, The Danish Heart Foundation and an unrestricted grant from Medtronic. Dr. Svendsen is a member of Medtronic advisory boards and has received speaker honoraria and research grants from the company.
SOURCE: https://bit.ly/3t0qt3J and https://bit.ly/2YhVncF The Lancet, online August 29, 2021.
By Megan Brooks
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