The primary objective of this observational study is to evaluate whether magnetocardiography (MCG) findings more accurately predict clinical outcomes in patients with acquired Long QT syndrome compared to ECG. The secondary objective is to assess differences in QT interval length between MCG and ECG. The primary safety objective is to characterize the safety profile of the CardiAQ MCG device.

Inclusion Criteria

1. Age ≥ 18 years on the date of consent
2. Ability for participant to comply with study requirements
3. Written informed consent
4. Confirmed diagnosis of atrial fibrillation and receiving dofetilide for rhythm control in the inpatient setting.

Exclusion Criteria

1. Pregnant or breastfeeding
2. Active thoracic metal implants (including pacemaker, insertable cardiac monitor, or internal defibrillators).
3. External electrical pads or devices (e.g. Pacer pads, ECG electrodes, heart rate patch), that must remain on patient's chest during MCG scan
4. Inability to lie down in a supine/inclined position and stay still on the examination bed
5. Clinical conditions that in the opinion of the Investigator would compromise the safety of the patient or ability to complete the protocol

Study candidates may be identified and recruited in one of the following ways:

• In-patient service at the study institution.
• From the Principal Investigator or Co-Investigator clinical practices
• Referral from other hospitals
• Cardiology Specialty Clinics