Extended monitoring of heart rhythm detects paroxysmal atrial fibrillation in patients who previously had a cryptogenic stroke or transient ischemic attack (TIA) at significantly higher rates than conventional methods do, according to two randomized studies published June 26 in the New England Journal of Medicine.

Revealing occult atrial fibrillation is crucial because stroke survivors whose atrial fibrillation is unrecognized typically receive antiplatelet therapy for secondary prevention, which is inferior to the anticoagulation treatment given for clinically apparent atrial fibrillation, said both groups of researchers.

ECG Monitoring Was Superior to Holter Monitoring
In one study, investigators used noninvasive ambulatory ECG monitoring to track heart rhythm for 30 days in 572 patients (mean age, 72) soon after they had an ischemic stroke or TIA. Comprehensive evaluations, typically including the conventional 24-hour session of Holter monitoring, failed to identify any atrial fibrillation or other cause of the event, so it was classified as cryptogenic, said David J. Gladstone, MD, PhD, stroke neurologist at the University of Toronto and coleader of the University of Toronto Stroke Program, and his associates.

At 16 stroke centers across Canada, the patients were randomly assigned during a three-year period to either prolonged ECG monitoring (287 patients) or to one additional round of 24-hour Holter monitoring (285 control subjects) for the detection of occult atrial fibrillation. The extended ECG monitoring was superior to Holter monitoring; it detected at least one episode of atrial fibrillation in 16.1% of patients, compared with 3.2% in the control group. The extended monitoring also was superior at detecting continuous atrial fibrillation lasting from 2.5 minutes to many hours. This outcome was found in 9.9% of the intervention group and 2.5% of the control group, the investigators reported.

The prolonged monitoring “nearly doubled the proportion of patients who subsequently received anticoagulant therapy for secondary prevention of stroke—a finding we interpret as a clinically meaningful change in treatment that has the potential to avert recurrent strokes,” said Dr. Gladstone.

“We think that the common practice of relying on 24 to 48 hours of monitoring for atrial fibrillation after a stroke or TIA of undetermined cause is insufficient and consider it an initial screen rather than a final test, especially given our finding that the yield of clinical follow-up alone as a means of detecting atrial fibrillation was negligible,” he added.

ICM Was Superior to Conventional Follow-Up
In the other study, conventional follow-up was compared with heart rhythm monitoring using an insertable cardiac monitor (ICM) in 441 patients (mean age, 61.5) who recently had an ischemic stroke or TIA classified as cryptogenic. The ICM automatically detected and recorded atrial fibrillation, irrespective of heart rate or symptoms. Patients in the control group “underwent assessment at scheduled and unscheduled visits, with ECG monitoring performed at the discretion of the site investigator,” said Tommaso Sanna, MD, a researcher at the Catholic University of the Sacred Heart in Rome, and his associates.

At six months, atrial fibrillation was detected in 8.9% of the 221 participants randomly assigned to the study intervention, compared with 1.4% of the 220 control subjects. At 12 months, the atrial fibrillation detection rates were 12.4% and 2.0%, respectively. This difference in detection was consistent across all subgroups of patients, regardless of age, sex, race or ethnicity, type of index event, presence or absence of patent foramen ovale, and CHADS score, said Dr. Sanna.

The use of oral anticoagulants for secondary prevention more than doubled among patients who received an ICM. The researchers calculated that 14 ICM devices would need to be implanted to detect one episode of atrial fibrillation during six months of monitoring, 10 devices to detect an episode of atrial fibrillation during 12 months of follow-up, and four devices to detect an episode of atrial fibrillation during 36 months of follow-up.

The findings of both studies indicate that in current practice, a substantial number of patients who have been diagnosed with cryptogenic stroke or TIA have occult atrial fibrillation that goes undiagnosed and untreated.

Should the Standard of Care Change?
The results of these two studies indicate that “prolonged monitoring of heart rhythm should now become part of the standard care of patients with cryptogenic stroke,” said Hooman Kamel, MD, Assistant Professor of Neuroscience at the Weill Cornell Brain and Mind Research Institute at Weill Cornell Medical College in New York City.

“Most patients with cryptogenic stroke or TIA should undergo at least several weeks of rhythm monitoring. Relatively inexpensive external loop recorders, such as those used in the [Gladstone] trial, will probably be cost-effective; the value of more expensive implantable loop recorders is less clear,” he noted.

—Mary Ann Moon

Prolonged Monitoring May Be the Best Way to Detect Atrial Fibrillation After Cryptogenic Stroke