Sotalol is an antiarrhythmic medication with proven effects for the suppression and prevention of supraventricular and ventricular arrhythmias. Due to its potential proarrhythmic effect, its introduction should be cautious, and several guidelines recommend starting the medication in hospital settings. However, patients at low risk for a proarrhythmic effect start the medication in outpatient units, despite the lack of clinical studies in the literature that demonstrate the safety of introducing the medication outside the hospital environment.

This research project aims to assess the safety introduction of sotalol in an outpatient unit basis. Our hypothesis is that outpatient introduction of sotalol is safe for low-risk patients and an electrocardiographic analysis after 2 hours of the first dose of medication is a predictor of electrocardiographic changes found after 72 hours.

In this research, serial electrocardiographic analysis with measurements of the QT corrected intervals and its dispersion, as well as clinical and laboratory parameters will be performed in 110 patients.

Participants will be prospectively recruited with sequential electrocardiographic assessments .Their indication and dose will be prescribed at the discretion of the attending physician. The following data to be analyzed are: age, ethnicity, anthropometric data (height, weight and BMI), clinical indication for sotalol, prescribed dose, comorbidities, other concomitant drugs, biochemical analysis (urea, creatinine, estimated creatinine clearance as also sodium, potassium and magnesium serum levels), echocardiogram and Holter monitoring when indicated.

Participants must have a standard 12-lead electrocardiogram (25mm/s) available at the start of treatment, 2 hours after the first dose of medication, and after 3 days, to calculate the corrected QT interval (QTc) and to analyze the dispersion of this interval. The patient will remain in the hospital until the second electrocardiogram is performed.

The QT interval will be measured manually, from the beginning of the QRS to the end of the T wave, by the tangent method, in DII, V5 or V2, in this order of preference. The QTc interval dispersion will be calculated manually, considering the difference between the longest and the shortest QT interval measured in the conventional 12 leads ECG.

All measurements will be made by the same arrhythmologist and later confirmed by a second arrhythmologist. Any divergent measures will be resolved by consensus. If there is no agreement, a third arrhythmologist will analyse the data.

The clinical evolution of the patients (minimum period of 30 days) after the beginning of the medication will be evaluated via face-to-face consultation or by telephone contact. At that moment, the patient's medications, adherence to sotalol use and the occurrence of adverse events will be checked again.

Inclusion Criteria:

• Indication of sotalol for the treatment of any supraventricular or ventricular arrhythmias
• Age ≥ 18 years
• Provide written informed consent

Exclusion Criteria:

• Complete bundle branch block
• Bradycardia with a frequency less than or equal to 55 bpm
• Ventricular pacing determined by artificial pacemaker
• Corrected QT interval greater than or equal to 460ms
• Heart failure with reduced ejection fraction, less than 40%
• Lactation period
• Dose required greater than 160 mg/day
• Estimated creatinine clearance less than 60mL/min
• Hypokalemia and hypomagnesemia documented in a patient at risk of spoliation of these components.
• Concomitant use of other drugs with proarrhythmic potential related to increased corrected QT interval (eg, tricyclic antidepressants, macrolide antibiotics, electrolyte-depleting diuretics, etc.).
• Others formal contraindications to the use of sotalol (e.g.: asthma)