The purpose of this study is to evaluate the efficacy and safety of a wearable device in detecting previously undiagnosed atrial fibrillation through non-invasive long-term monitoring using a wearable single-lead ECG patch (MEMO Patch M, MEMO Patch2) in 100 patients with Embolic Stroke of Undetermined Source (ESUS) who require atrial fibrillation screening. Participants who meet all inclusion and exclusion criteria and provide written informed consent will wear the MEMO Patch M and undergo in-hospital telemetry monitoring using MEMO Cue for a minimum of 12 hours and up to 8 days. During hospitalization, 24-hour Holter monitoring will also be conducted. Before discharge, the investigator will review these results to determine whether implantable loop recorder (ILR) implantation is necessary. At the time of discharge, participants will wear MEMO Patch2 for up to 14 days for the first ECG monitoring period. One month after discharge, the investigator will review the results of the first monitoring and initiate the second ECG monitoring with MEMO Patch2. Three months after discharge, the results of the second ECG monitoring will be reviewed, and participation in the clinical trial will be completed.

This clinical study is designed as a prospective, single-center, investigator-initiated exploratory clinical trial.

1. Screening Participants will be assigned a screening number in the order in which informed consent is obtained. Through interviews and review of previous medical records, demographic information, medical history, surgical/procedural history, prior medications, and other required assessment items will be collected. Eligibility for study participation will be determined by reviewing the inclusion and exclusion criteria.
2. Visit 1 (In-Hospital Telemetry Monitoring) Eligible participants will be fitted with the investigational medical device, MEMO Patch M, and will undergo in-hospital telemetry monitoring using MEMO Cue for a minimum of 12 hours and up to 8 days. A 24-hour Holter monitor will also be applied after admission. Prior to discharge, participants will review the MEMO Patch M (in-hospital telemetry) results to determine whether ILR implantation is required.
3. Discharge (First ECG Monitoring) At discharge, participants who were not detected with atrial fibrillation using the Holter ECG or MEMO Patch M will receive an Implantable Loop Recorder (ILR). Participants in whom atrial fibrillation is detected will not receive ILR implantation. Regardless of ILR implantation, all participants will wear MEMO Patch2 and undergo additional ECG monitoring for up to 14 days after discharge. After the scheduled monitoring period ends, MEMO Patch2 will be returned using the Huinno courier service.
4. Visit 2 (Review of First ECG Monitoring Results - 1-Month Visit) At the 1-month outpatient visit, participants will review the results of the first ECG monitoring. They will then undergo a second monitoring period by wearing MEMO Patch2 for up to 14 days. After completing the scheduled monitoring period, MEMO Patch2 will be returned using the Huinno courier service.
5. Visit 3 (Review of Second ECG Monitoring Results - 3-Month Visit) At the 3-month outpatient visit, participants will review the results of the second ECG monitoring. After this visit, participation in the clinical study will be completed.

Inclusion Criteria:

Participants may take part in this clinical study only if they meet all of the following criteria:

1. Adults aged 19 years or older who voluntarily provide written informed consent to participate in the study
2. Patients diagnosed with ESUS (Embolic Stroke of Undetermined Source)
3. Patients who require in-hospital or out-of-hospital electrocardiographic (ECG) monitoring

Exclusion Criteria:

Participants who meet any of the following criteria cannot be enrolled in this clinical study:

1. Individuals already diagnosed with atrial fibrillation or atrial flutter
2. Individuals with a clearly identified cause of stroke
3. Individuals known to have allergic reactions to adhesives or hydrogels
4. Individuals who, in the investigator's judgment, have cognitive vulnerability that makes it difficult to understand the study information and voluntarily decide on participation
5. Any other individuals whom the principal investigator considers to be at potential risk by participating in the study or otherwise unsuitable for participation