The following are key points to remember from this review about the current and future use of insertable cardiac monitors (ICMs):

1. ICMs are small, subcutaneously implanted devices offering continuous ambulatory electrocardiogram (ECG) monitoring with a lifespan of up to 3 years.
2. In addition to their use in the diagnosis of patients with palpitations and syncope, ICMs are being increasingly used in the evaluation of patients with cryptogenic stroke.
3. Cryptogenic stroke is a symptomatic cerebral infarct for which no probable cause is identified following an adequate diagnostic evaluation, albeit there is no uniformly agreed upon set of essential diagnostic criteria.
4. Atrial fibrillation (AF) is the cause of one in four ischemic strokes. Cryptogenic strokes are estimated to account for another 20-30% of all ischemic strokes.
5. ICM has been shown to be a method of detecting subclinical AF. The sensitivity, specificity, and positive and negative predictive values using an AF duration analysis are all in the mid to high 90%.
6. Device studies have shown that even brief episodes of subclinical AF (as little as 5 minutes) are associated with more than twice the risk of ischemic stroke; however, a causal relationship between subclinical AF and the risk of stroke has not been established.
7. The 2017 International Society for Holter and Noninvasive Electrocardiology/Heart Rhythm Society (ISHNE/HRS) Expert Consensus Statement on Ambulatory ECG and External Cardiac Monitoring/Telemetry provides a Class I indication for “prolonged monitoring” for patients with cryptogenic stroke. However, there is lack of consensus regarding the optimal timing, duration, and method of cardiac monitoring for occult AF in stroke patients.
8. The authors of the review suggest that patients with cryptogenic stroke undergo a 2- to 4-week ambulatory ECG monitoring. If no AF is identified, the CHA₂DS₂-VASc score is ≥2, and the patient is a potential candidate for anticoagulation, the authors recommend ICM implantation.
9. In the CRYSTAL AF study, the median time to detect AF in patients with ICM was 84 days. At 24 months after cryptogenic stroke, one of every five patients monitored with ICM had a diagnosis of AF.
10. Randomized prospective trials of anticoagulation in patients with recent stroke and detectable subclinical AF on ICM are needed.

Keywords: Anticoagulants, Arrhythmias, Cardiac, Atrial Fibrillation, Brain Ischemia, Cerebral Infarction, Electrocardiography, Electrocardiography, Ambulatory, Monitoring, Ambulatory, Secondary Prevention, Stroke, Syncope, Vascular Diseases

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