Insertable External Cardiac Monitors Better than ECG for Post-Stroke Atrial Fibrillation Detection

July 7, 2014
Andrew Smith

A pair of randomized controlled studies have both found that continuous monitoring of patients after cryptogenic strokes can detect several times as many cases of atrial fibrillation as conventional monitoring.

A pair of randomized controlled studies have both found that continuous monitoring of patients after cryptogenic strokes can detect several times as many cases of atrial fibrillation (AF) as conventional monitoring.

An accompanying editorial in The New England Journal of Medicine, which recently published papers on both studies, argued that the findings justify new standards of care. “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,” wrote Hooman Kamel, MD, of Weill Cornell Medical College in New York City.

“Therefore, most patients with cryptogenic stroke or transient ischemic attack should undergo at least several weeks of rhythm monitoring… Furthermore, the detection of subclinical atrial fibrillation in these patients should generally prompt a switch from antiplatelet to anticoagulant therapy,” wrote Kamel.

In the first study, Canadian researchers randomly assigned 572 older patients who had recently suffered a stroke or transient ischemic attack (TIA) to either a 30-day event-triggered recorder (intervention group) or a conventional 24-hour monitor (control group).

AF lasting at least 30 seconds was detected in 45 of 280 intervention-group patients (16.1%), but only 9 of 277 control-group patients (3.2%) (absolute difference, 12.9 percentage points; 95% confidence interval [CI], 8.0 to 17.6; P<0.001; number needed to screen, 8).

AF lasting at least 2.5 minutes was detected in 28 of 284 patients (9.9%) in the intervention group, compared to 7 of 277 (2.5%) in the control group (absolute difference, 7.4 percentage points; 95% CI, 3.4 to 11.3; P<0.001).

By 90 days, oral anticoagulant therapy had been prescribed for more patients in the intervention group than in the control group (52 of 280 patients [18.6%] vs. 31 of 279 [11.1%]; absolute difference, 7.5 percentage points; 95% CI, 1.6 to 13.3; P=0.01).

Researchers in the second study randomized 441 stroke patients between conventional follow-up and insertable cardiac monitors (ICMs).

By 6 months, AF had been detected in 8.9% of patients in the ICM group (19 patients) versus 1.4% of patients in the control group (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 majority of first episodes (79%) in the insertable monitor group were asymptomatic compared with 50% in the control group. More than twice as many patients in the monitor group were taking oral anticoagulants at the end of both six months (10.1% of monitor group vs. 4.6% of control group) and one year (14.7% of the monitor group vs. 6.0% of the control group).

Such numbers probably do not justify the cost of implantable monitors. Indeed, the study authors conclude that 14 patients would need to receive a monitor for every additional case of AF detected at six months.

The external loop monitors used in the other study, however, may well make economic sense according to both the NEJM editorial and the study authors.