Insertable Cardiac Monitors Detect Atrial Fibrillation in Stroke Patients

Insertable cardiac monitors correctly detected atrial fibrillation (AF) in more than 12% of cryptogenic stroke victims who took part in a recent observational study.

Researchers implanted such devices in 1,247 patients to determine how frequently they could identify AF via long-term, continuous cardiac monitoring. After a median follow-up of 182 days, the monitors had detected the condition in 147 (12.2%) of the patients.

The study was designed to complement the CRYSTAL AF study, a randomized clinical trial that found implantable devices greatly superior to conventional monitoring in the detection of AF.

A paper on the earlier study appeared last year in TheNew England Journal of Medicine. Results of the new study were unveiled ahead of a presentation at American Stroke Association's International Stroke Conference in Nashville.

“Unlike a randomized study, an observational study provides a practical way to study real-world clinical practice,” said study co-author Mark Richards, PhD, MD, director of Arrhythmia Services at ProMedica Physicians Cardiology in Toledo, Ohio.

“What's most exciting is that the detection of AF in real clinical practice exceeded that observed in the rigorously-controlled CRYSTAL AF study, allowing physicians to intervene even more with stroke preventive therapies. This suggests that AF may go undetected at an even greater rate and reinforces the benefits of long-term rhythm monitoring in cryptogenic stroke patients,” Richards said.

The new study did not compare the performance of the insertable cardiac monitors (ICMs) to any other detection technique, but the numbers from the earlier trial provide some context for the findings.

In that study, after 6 months of follow-up, AF had been detected in 8.9% of patients in the ICM group (19 patients) versus 1.4% of patients in the control group using conventional AF detection (3 patients) (hazard ratio [HR], 6.4; 95% CI, 1.9 to 21.7; P<0.001).

By 12 months, AF had been detected in 12.4% of patients in the ICM group (29 patients) versus 2.0% of patients in the control group (4 patients) (HR, 7.3; 95% CI, 2.6 to 20.8; P<0.001).

The authors of the original study noted that their results suggested that the detection of a single case of AF within a 6-month window would require, on average, that doctors implant devices in 14 patients. The detection of a single case within a 3-year window would require 4 devices.

This observation led many to assume that ICMs would therefore prove an impractically expensive method of detecting AF, but a new economic analysis reaches the opposite conclusion.

That study, which was also announced ahead of a presentation at the conference, finds that the detection rates associated with the CRYSTAL AF study translate into an incremental cost per quality-adjusted life year (QALY) that falls well within the “acceptable” range defined by the United Kingdom’s National Institute of Clinical Excellence.

“Detecting AF in cryptogenic stroke patients enables physicians to change their medical therapy so we can reduce their risk of having a second stroke,” said Klaus Witte, MD, in a news release. Witte is the lead clinician for cardiology at the University of Leeds and Leeds Teaching Hospitals. “These results show that continuous cardiac monitoring with an ICM is a cost-effective tool.”

The announcement did not specify the study’s conclusions about exact QALY cost implied by the controlled trial, but the institute’s current “acceptable” threshold is 20,000 pounds (about $30,700). The QALY cost implied by the observational study, moreover, would be lower because that study reported higher detection rates.

All 3 studies were sponsored by Medtronic, the Dublin-based company that makes the Reveal LINQ ICM System.