Additional weeks of heart rhythm monitoring may help detect afib after cryptogenic stroke

Additional heart rhythm monitoring after cryptogenic stroke helped detect atrial fibrillation in 2 new studies published last week in the New England Journal of Medicine.

In the EMBRACE trial, patients 55 years of age and older without known atrial fibrillation who had had a cryptogenic ischemic stroke or transient ischemic attack (TIA) in the previous 6 months were randomly assigned to additional monitoring with noninvasive ambulatory electrocardiography (ECG). The intervention group was monitored via a 30-day event-triggered recorder, while the control group received a conventional 24-hour monitor. The study's primary outcome was newly detected atrial fibrillation of 30 seconds or longer in the 90 days after randomization, while secondary outcomes were atrial fibrillation of 2.5 minutes or longer and anticoagulation status at 90 days.

Of 280 patients in the intervention group, 45 (16.1%) had atrial fibrillation lasting 30 seconds or longer compared with 9 of 277 patients (3.2%) in the control group (absolute difference, 12.9 percentage points; P<0.001; number needed to screen, 8). Twenty-eight of 284 patients in the intervention group (9.9%) had atrial fibrillation of 2.5 minutes or longer compared with 7 of 277 (2.5%) in the control group (absolute difference, 7.4 percentage points; P<0.001). Fifty-two of 280 patients (18.6%) in the intervention group had been prescribed anticoagulant therapy by 90 days versus 31 of 279 patients (11.1%) in the control group (absolute difference, 7.5 percentage points; P=0.01).

The authors noted that the total burden of atrial fibrillation for each patient could not be determined and that the prevalence of atrial fibrillation in the intervention group is probably a conservative estimate. However, they concluded that noninvasive ECG monitoring on an outpatient basis for 30 days after cryptogenic stroke or TIA outperforms standard short-term ECG monitoring in detecting atrial fibrillation.

In the CRYSTAL AF trial, patients at least 40 years of age who had no evidence of atrial fibrillation on 24 hours or more of ECG monitoring after ischemic stroke were randomly assigned within 90 days of the index event to receive long-term monitoring with an insertable cardiac monitor (ICM) or conventional follow-up (defined as assessment at scheduled and unscheduled visits and ECG monitoring at the site investigator's discretion). The primary end point was time to first detection of atrial fibrillation lasting at least 30 seconds in a 6-month period, while time to first detection of atrial fibrillation lasting at least 30 seconds in a 12-month period was one of the secondary end points. The study was funded by Medtronic.

Two hundred twenty-one patients were assigned to the ICM group (of these, 208 received the device), and 221 patients were assigned to the control group. During the trial, 12 patients in the ICM group crossed over to the control group and 6 patients in the control group crossed over to the ICM group, while 12 patients and 13 patients in each group, respectively, exited the study. A total of 8.9% of patients in the ICM group had atrial fibrillation detected by 6 months, compared with 1.4% of patients in the control group (hazard ratio, 6.4; P<0.001). At 12 months, these percentages were 12.4% and 2.0%, respectively (hazard ratio, 7.3; P<0.001).

The authors noted that they could not be sure whether atrial fibrillation detected via monitoring had caused the index stroke and that ICMs may not have detected all episodes of atrial fibrillation, among other limitations. However, they concluded that ICMs detected atrial fibrillation more frequently after cryptogenic stroke than did conventional follow-up.

The author of an accompanying editorial noted that more information is needed on other sources of embolism and improved markers of stroke mechanisms, in addition to appropriate therapy for subclinical atrial fibrillation. However, he wrote that “the weight of current evidence suggests that subclinical atrial fibrillation is a modifiable risk factor for stroke recurrence, and its presence should be thoroughly ruled out in this high-risk population.”

Most patients with cryptogenic stroke or TIA should have rhythm monitoring for at least several weeks, he wrote, and those in whom subclinical atrial fibrillation is detected should usually be switched from antiplatelet therapy to anticoagulants.

“At the least, patients should be followed closely in order to detect progression to clinically apparent atrial fibrillation, in which case the evidence unambiguously supports anticoagulant therapy for the secondary prevention of stroke,” the editorialist concluded.