In a cohort of patients electively treated for atrial arrhythmia with IV sotalol (initiation or dose escalation), this study will describe patient characteristics, short-term safety and efficacy, electrocardiographic monitoring, and PK and PD parameters (in a subset) associated with IV dosing approach.

Antiarrhythmic drug therapy plays a vital role in the achievement of rhythm control in patients with atrial arrhythmias. Class III antiarrhythmic drugs are frequently used in these patients. However, these drugs are associated with a nontrivial risk of QT interval prolongation and associated risk of life-threatening ventricular arrhythmias. In this setting, initiation and dose titration of these drugs is often performed on an inpatient basis for the first five oral doses, typically requiring hospitalization for two days or longer.

The availability of sotalol in intravenous (IV) form, recently approved for initiation or dose increase among patients with atrial arrhythmias, affords an opportunity to shorten hospitalization for these patients. This approach was approved based on translational science research that used computer-based simulation modeling to predict sotalol concentrations. There remain knowledge gaps regarding the use of IV sotalol in these patients, specifically around real-world outcomes, as well as pharmacodynamic and pharmacokinetic profiles in patients. The purpose of this registry is to collect data among patients and centers using IV sotalol loading for initiation or dose titration in the treatment of atrial arrhythmias, in order to fill the above knowledge gaps.

Inclusion Criteria:

1. Adults age 18 years and older
2. Eligible for the use of elective intravenous sotalol loading to treat atrial arrhythmias, per the treating clinician
3. IV sotalol infusion started for the treatment of atrial arrhythmias, in the setting of initiation or dose titration of chronic sotalol therapy
4. Elective hospital admission primarily for loading with intravenous sotalol with/without cardioversion, with no other planned therapy or procedures

Exclusion Criteria:

1. Study materials not available in the subject's preferred language.

2. Patients undergoing treatment for active concomitant ventricular arrhythmias

3. Standard exclusions for elective sotalol use (at the time of initiation):

   • Heart rate < 40 bpm or 2nd/3rd degree AV block without pacemaker
   • QTc ≥ 450 in absence of bundle branch block (≥ 500 in the presence of a bundle branch block)
   • Severe left ventricular hypertrophy (thickness >1.5 cm)

4. Patients who were previously intolerant to antiarrhythmic class III therapy

5. Patients missing key data elements in their electronic health record (for retrospective subjects only).

This registry study will enroll adult patients 18 years and older electively treated for atrial arrhythmia with standard of care IV sotalol (initiation or dose escalation). During their elective hospitalization the patient is not planned to receive any other intervention. The registry allows retrospective and prospective enrollment. Patients will be excluded if they are undergoing treatment for active concomitant ventricular arrhythmias, intolerant to class III antiarrhythmic therapy, not meeting standard criteria to receive elective IV sotalol, or if key data elements not available (retrospective enrolled patients only). Approximately 150 patients will be enrolled and for about 20 patients PK/PD data will be collected.