The purpose of this study is to better understand the following aims:

1. Aim 1: To evaluate the rate of recurrent Atrial Fibrillation (AF)/Atrial Flutter (AFL) in hematopoietic stem call transplant (HCST) patients with incident AF/AFL identified during the initial 30 days of the transplant
2. Aim 2: To evaluate incident episodes of 1) stroke/TIA; 2) other thromboembolic events (not stroke/TIA); 3) Heart failure events; 4) Ischemic heart events
3. Aim 3: To evaluate overall implantation safety in this population

We propose a registry study in hematopoietic stem cell transplant (HSCT) patients with incident atrial fibrillation/atrial flutter (AF/AFL) during the initial 30 days of transplant who will be implanted with the Medtronic Reveal Linq Implantable Cardiac Monitor (ICM) within 90 days of HSCT. We will evaluate the rate of recurrent AF/AFL as well as incident episodes of major cardiovascular events and the safety of ICM implantation in this population.

Inclusion Criteria:

1. Age ≥18
2. CHADS-VASc ≥ 2
3. Recovery of platelets to >50,000 within 90 days of incident atrial fibrillation (AF) diagnosis
4. Discharge from the incident stem cell transplant (SCT) hospitalization
5. Normal sinus rhythm at the time of consent

Exclusion Criteria:

1. Prior history of atrial fibrillation (AF) or atrial flutter
2. CHADS-VASc <2
3. Platelets <50,000 after 90 days post transplantation
4. Continued SCT hospitalization at 90 days
5. Inability to receive anticoagulation
6. AF or other arrhythmia at the time of consent
7. Current use of a class IC or III antiarrhythmic medication
8. Inability to provide informed consent/significant cognitive impairment
9. Expected survival less than one year.

Adult patients with the diagnosis that requires them to undergo HSCT who develop incident AF/AFL in the first 30 days of transplant.