Systematic vs. opportunistic screening
Although “opportunistic screening in individuals aged 65 and older” is recommended by current European Society of Cardiology guidelines, systematic screening, such as that used in STROKESTOP, has a much weaker evidence base, observed Renate B. Schnabel, MD, PhD, University Heart & Vascular Center, Hamburg, Germany, as the invited discussant after the STROKESTOP presentation.
STROKESTOP “is one of the first studies, if not the first study,” to show a clinical benefit from screening for AF, Dr. Schnabel said.
Fewer-than-projected primary outcome events were seen during the trial, and event curves for screened and control participants didn’t start to separate until about 4 years into the study, she said. It therefore might take a long time for the screened elderly to realize the clinical benefits of screening.
Studies such as the recent SCREEN-AF and mSTOPS have amply shown that AF screening in the asymptomatic elderly can reveal previously unrecognized AF far more often than would be detected in routine practice, allowing them the opportunity to go on OAC. But the trials weren’t able to show whether the benefits of such management outweigh the risks or costs.
Indeed, on April 20, the U.S. Preventive Services Task Force (USPSTF) released a draft recommendation statement concluding that “the current evidence is insufficient to assess the balance of benefits and harms” associated with AF screening in asymptomatic people at least 50 years of age.
In STROKESTOP, however, benefit for the primary outcome reached significance in the prespecified ITT analysis and “appeared to be driven by the reduction in ischemic stroke incidence,” Dr. Schnabel said.
“The future guidelines have gained strong evidence to judge on systematic atrial fibrillation screening” as it was performed in the trial, she said. “How to implement atrial fibrillation screening, including systematic screening in health care systems across Europe and beyond, remains an open question.”
A randomized population
STROKESTOP considered all 75- and 76-year-olds living in Sweden’s Stockholm County (n = 23,888) and the Halland region (n = 4,880) and randomly assigned them to the ITT group or a control group, with stratification by sex, birth year, and geographic region. In both groups, 54.6% were female and the mean CHA2DS2VASc score was 3.5.
People assigned to the ITT cohort were invited to be screened and followed. Those who agreed to participate underwent a baseline ECG assessment to detect or rule out permanent AF. Guideline-based OAC and follow-up was offered to those found with the arrhythmia. Those in sinus rhythm with no history of AF used a handheld single-lead ECG recorder (Zenicor) for 30 seconds twice daily for 14 days.
Structured management, including OAC, was offered to anyone demonstrating sufficient AF, that is, at least one bout without p waves in one 30-second recording or at least two such episodes lasting 10-29 seconds during the 2-week screening period.
In the ITT analysis, the hazard ratio (HR) for the composite clinical primary endpoint was 0.96 (95% confidence interval, 0.920-0.999; P = .045), but in the as-treated analysis, the HR for ischemic stroke was 0.76 (95% CI, 0.68-0.87; P < .001).
“I believe that this will likely be generalizable to most countries’ elderly residents,” Dr. Svennberg said. “I think if we can find a significant difference in our elderly population in Sweden, most countries will be able to do so, or find even more significant results.”
That’s because “baseline detection of AF in Sweden is high,” she said, “so new detection is likely more difficult.” Also, in Sweden, “care can be sought without monetary concern, and prescriptions are provided at low costs to the patients.” Therefore, patients newly identified with AF, whether in studies or not, “would likely be started on therapy.”
It will be important to know whether the screening strategy is cost-effective, Dr. Schnabel said, because “the overall effect, with a hazard ratio of 0.96, is not too big, and costs incurred by systematic screening are comparatively high.”
STROKESTOP “now provides sound information for cost-effectiveness analyses, which to date have largely relied on assumptions.”
STROKESTOP was partially supported by Carl Bennet AB, Boehringer-Ingelheim, Bayer, Bristol-Meyers Squibb, and Pfizer. Dr. Svennberg disclosed receiving fees for lectures or consulting from Bayer, Bristol-Meyers Squibb, Pfizer, Boehringer-Ingelheim, Merck Sharp & Dohme, and Sanofi; and institutional grants from Roche Diagnostics and Carl Bennett Ltd.
A version of this article first appeared on Medscape.com.