WASHINGTON – Continuous cardiac monitoring via Medtronic’s insertable REVEAL XT device resulted in detection of atrial fibrillation in 30% of cryptogenic stroke patients at 36 months of follow-up in the CRYSTAL AF trial.

In stark contrast, the AF detection rate was a mere 3% in the control group randomized to standard monitoring with serial ECGs and Holter monitoring, Dr. Rod S. Passman reported at the annual meeting of the American College of Cardiology.

Seventy-seven percent of first episodes of AF detected through 36 months were asymptomatic.

"These data support the use of long-term continuous cardiac monitoring in patients with cryptogenic stroke," concluded Dr. Passman, medical director of the program for atrial fibrillation at the Bluhm Cardiovascular Institute at Northwestern University, Chicago.

Thirty percent of all strokes are cryptogenic; that is, of unknown mechanism despite a thorough workup. The rationale underlying the CRYSTAL AF (Cryptogenic Stroke and Underlying Atrial Fibrillation) study was that many of these strokes are actually due to AF, which has gone undetected by conventional methods. The detection of AF in a patient with a history of ischemic stroke warrants initiation of long-term oral anticoagulation therapy, the cardiologist noted.

The CRYSTAL AF study randomized 441 cryptogenic stroke patients to the REVEAL XT insertable cardiac monitor (ICM) or conventional monitoring for possible AF. The 6- and 12-month outcomes were presented earlier this year at the International Stroke Conference. The AF detection rates were significantly higher in the ICM group at both time points. At ACC 14, Dr. Passman presented the updated 36-month outcomes.

The median time from randomization to AF detection was 8.4 months in the ICM recipients. That’s well beyond the time frame during which external monitoring can realistically be used, he noted.

Fully 95% of patients with AF detected via ICM had at least 1 day with an episode duration greater than 6 minutes. Among patients with AF detected by ICM within the first 12 months, about half had one or more episodes of 12 hours duration or longer.

The detection of five cases of AF through 36 months in the control group required considerable use of resources, including 202 ECGs and 52 Holter monitoring sessions.

When AF was discovered in patients in either arm of the study, physicians took action. In 90% of cases, patients were switched from antiplatelet therapy to an oral anticoagulant, even though that measure wasn’t addressed in the study protocol.

Dr. Passman said that in order to avoid using an ICM in all patients with cryptogenic stroke, investigators are now trying to develop a prediction rule that can identify those at highest risk of having AF. So far, age and left atrial size as determined using transesophageal echocardiography are among the better predictors.

Session cochair Dr. Yochai Birnbaum expressed reservations regarding whole-hog adoption of the ICM approach to AF detection.

"We are getting to a situation here like with ultrasensitive troponin assays," the cardiologist observed. "We now have very sensitive tools, and we tend to look at AF as an all or none cause of stroke. But the question for me is: Is 10 minutes of atrial fibrillation that is detected occasionally – not every day – really a risk for stroke? What I’m missing here in CRYSTAL AF is a control group of patients without a history of stroke who had a REVEAL XT monitor for 3 years, asking the question, ‘How often do you detect short runs of AF?’ "

"If we are saying 30% of cryptogenic stroke patients will eventually have evidence of atrial fibrillation, then it might be cheaper to treat all of the people from the beginning with an oral anticoagulant," added Dr. Birnbaum, professor of medicine at Baylor College of Medicine, Houston.

Dr. Passman conceded that the burden of AF needed to have a stroke remains unknown, as does the extent of AF in an age-matched, disease-matched population without cryptogenic stroke.

"But we do know that we have good therapies to prevent stroke in patients who have AF, and that patients with cryptogenic stroke are a high-risk population. Whether their AF is causal or not is something we can debate, but certainly finding AF is important," he countered.

The leadless Reveal XT ICM is implanted in a simple 15- to 30-minute outpatient procedure done under local anesthesia. The MRI-compatible device can be followed remotely and includes an automatic AF detection algorithm.

The CRYSTAL AF study was funded by Medtronic. Dr. Passman reported receiving research funds from and serving as a consultant to as well as on the speakers bureau for the company. In addition, he is on speakers bureaus for Pfizer, Bristol-Myers Squibb, Janssen, and Boehringer Ingelheim.

bjancin@frontlinemedcom.com

Insertable monitor reveals AF in 30% of cryptogenic stroke patients