One cause is paradoxical embolism that may be treated with patent foramen ovale closure^[2][3].

One cause is atrial fibrillation which may be detected by prolonged event monitors^[4] or prolonged, implantable recorders such as the LINQ^[5][6], or even smartphones^[7].

The various methods of diagnosis have been compared by a systematic reviews which:

• recommends” sequentially combining cardiac monitoring methods”^[8]. An example of a phase 4 (second ambulatory period) consisted of mobile cardiac outpatient telemetry, external loop recording, and implantable loop recording is the http://www.tlcdiagnostics.com/healthcare-professionals/cardiac-monitoring/king-hearts
• “evidence for a potential impact of PCM on secondary stroke prevention”^[9]

Clinical practice guidelines address the diagnosis strategy:

• The 2019 AHA/ACC/HRS Focused Update of atrial fibrillation guidelines contain a new section, “7.12. Device Detection of AF and Atrial Flutter,” which states “In patients with cryptogenic stroke (ie, stroke of unknown cause) in whom external ambulatory monitoring is inconclusive, implantation of a cardiac monitor (loop recorder) is reasonable to optimize detection of silent AF”. However, the guidelines do not address alternative methods to detect atrial fibrillation^[10].
• 2016 Guidelines by the ESC state “In stroke patients, additional ECG monitoring by long-term noninvasive ECG monitors or implanted loop recorders should be considered to document silent atrial fibrillation.”^[11]

The benefit of anticoagulation based on long-term monitoring is uncertain^[12].

For cryptogenic stroke on unknown source, anticoagulation may not help over aspirin^[13].