Cryptogenic strokes—those without a clear underlying etiology—pose a significant clinical challenge since their diagnosis and treatment is uncertain. Results from the CRYSTAL-AF (Cryptogenic Stroke and Underlying Atrial Fibrillation) study, which were presented at the International Stroke Conference in February, 2014, showed that almost one-third of patients with cryptogenic stroke may have occult atrial fibrillation (AF) as detected by an implantable cardiac monitor.
Using a prospective multicenter design, investigators enrolled 441 patients (mean age, 61.5 years; 63% men) with cryptogenic stroke and randomized patients to either an implantable cardiac monitor (Medtronic) or conventional monitoring (ie, ECGs, Holter monitors). The device (Reveal XT ICM), which is MRI compatible, was implanted within 15 to 30 minutes in the outpatient setting using local anesthesia. Patients were followed and the rate of AF assessed for 6, 12, and 36 months. Only 3% (n=5) of patients in the standard monitoring arm had AF diagnosed at 3 years, whereas 30% of patients with the device were diagnosed with AF. Using data recorded by the implantable monitor, it was discovered that 95% of AF patients in that group had at least 1 day with an episode lasting longer than 6 minutes. In contrast, to detect the 5 cases found in the control group required the use of 202 ECGs and 52 Holter monitoring sessions over 3 years, suggesting that this monitor may also be a highly cost effective and informative approach.
The transient and often asymptomatic nature of AF makes it an elusive diagnosis, which is not always easily captured. Based on these results, it seems reasonable that patients with cryptogenic stroke and a high pretest probability of AF may benefit from undergoing invasive long term cardiac monitoring. The study authors are currently working to devise clinical prediction scores that may help to stratify patients and select those who are most likely to benefit from receiving the implantable monitor. Thus far, age and left atrial size are emerging as reliable predictors. Although the monitor may provide a cost effective alternative to ECG and Holter monitoring, a large residual treatment gap still exists, with approximately 70% of cryptogenic strokes lacking a clear etiology.
Although additional data is necessary before the device can be routinely adopted into practice, it does confirm that long term monitoring is necessary in these patients.
Bernstein RA, Lindborg K. Cryptogenic stroke and underlying atrial fibrillation (CRYSTAL AF) LB11. Presented at: International Stroke Conference 2014; Feb. 12-14, 2014; San Diego.