The investigators seek to conduct a prospective study to assess the recurrence of AF in patients with acute AF using a long-term ECG monitoring strategy with an insertable cardiac monitor (ICM), which is clinically indicated in this scenario as part of the standard of care. The investigators hypothesize that patients diagnosed with acute AF in the setting of cardiac surgery will have higher rates of AF recurrence than acute AF diagnosed in the setting of non-cardiac surgery or medical illness.

Inclusion Criteria:

1. Patient has an existing clinical indication for implantation of an insertable cardiac monitor (ICM) and will undergo ICM implantation as part of their standard medical care.

2. Patient is scheduled to receive or has received a Boston Scientific LUX-DX™ insertable cardiac monitor.

3. Episode of acute AF. Acute AF is defined as AF detected in an acute care setting or during an acute illness. Before enrollment, the following tests are minimally required as standard tests to establish the diagnosis of acute AF:

   • 12-lead ECG for AF detection
   • 24-h ECG or telemetry monitoring for AF detection and PAC analysis

4. Patient or legally authorized representative signs and dates the patient consent form.

5. Patient is ≥18 years old.

6. Patient is willing and able to comply with all study procedures and attend the required follow-up visits for the duration of the study.

Exclusion Criteria:

1. Patient has a known history of AF or atrial flutter prior to the index acute AF episode.
2. Patient has another indication for antiarrhythmic medications according to AHA/ACC/HRS guidelines, independent of the acute AF episode.
3. Patient has a permanent contraindication to oral anticoagulation (OAC) that, in the opinion of the treating physician, would preclude any future consideration of OAC for AF management.
4. Patient is currently enrolled in another clinical trial that will affect the objectives or endpoints of this study.
5. Patient's life expectancy is less than one year, as determined by the treating physician.
6. Patient is pregnant.
7. Patient has a current indication for implant with a cardiac implantable electronic device (CIED) such as a pacemaker or defibrillator, or an implantable hemodynamic monitoring system, as the study intervention would be redundant or potentially interfere with the clinical indication.
8. Patient is not fit, able, or willing to follow the required procedures of the Clinical Investigation Plan.

The selection of participants for this study will be equitable, and no specific populations will be excluded without a clear and compelling rationale related to the health of the participants or the purpose of the research. Limited English proficiency will not be an exclusion criterion.

In general, de-identified data may be shared with other researchers for scientific purposes, subject to IRB approval and any data sharing agreements. Any such sharing will not include information that could reasonably identify individual participants. No plans to publish participant family pedigrees are anticipated for this study.