Class III antiarrhythmics: blocks K channels, causing delayed repolarization; prolongs QTc interval

• Amiodarone

• Pro: Has both alpha and beta blocking properties and affects Na, K, and Ca channels. Very easy to use. Can be used in patients with structural heart disease. Comes in both oral and IV formulation. Very long half life so good in patients who miss doses

• Cons:  Many side effects, including thyroid, liver, and lungs. Will be in the system for a very long time

• Dosing: 150 mg IVPB, followed by IV infusion 1 mg/min x 6 hrs, then 0.5 mg/min x 18 hrs. May complete 6-10 g load with PO amiodarone once arrhythmia suppressed

• Considerations: If arrhythmia does not terminate within 10 min after end of 150mg IV infusion, you can repeat this bolus a second time

• Monitoring: Obtain a baseline chest X-ray, pulmonary function tests (including diffusion capacity), TSH, and LFTs when amiodarone therapy is initiated. Repeat history, physical exam, and chest X-ray every 3 to 6 months

• Dofetilide 

• Pro: Safe to use in patients with heart failure

• Cons: High risk of torsades, with higher risks if medication is not adjusted for renal function. Therefore, patients need to be admitted to the hospital during the first 3 days of initiation to monitor the QTc.

• Dosing: Dependent on renal function. With normal renal function, initial dosing is 500 mcg twice daily (maximum dose: 500 mcg twice daily).

• Considerations:

  • QTc interval should be measured 2 to 3 hours after the first 5-6 doses

  • For any QTc prolongation >15% or >500ms, dose adjustments must be made

  • If there is too much prolongation, this may preclude the patient from getting this medication. 

• Monitoring: Must get EKG, BMP, Mg, and Phos every 3-6 months after administration to monitor QTc, Cr, and electrolytes.

• Ibutilide

• Dosing: IV infusion 0.01 mg/kg over 10 min (weight < 60 kg) or 1 mg/kg over 10 min (weight ≥ 60 kg)

• Considerations:

  • Acute chemical cardioversion only, not indicated for chronic maintenance therapy

  • Discontinue as soon as arrhythmia terminates or marked QTc prolongation occurs

  • Do not use in patients with hemodynamic instability

  • Give pre-and post-infusion IV magnesium to reduce TdP risk (suppresses early after-depolarizations)

• Monitoring:

  • Pre-infusion Mg level (goal ≥ 2 mmol/L)

  • Requires continuous ECG during infusion AND at least 4 hours post-infusion due to high risks of Torsades. Make sure patient does not have hypokalemia or hypomagnesemia as this increases torsades risk!

  • Have crash cart at bedside

• Sotalol: Beta-blocker that helps to slow heart rate and AV conduction, as well as prolong atrial and ventricular action potentials 

  • Cons: High risk of torsades. Patients need to be hospitalized during initiation of this drug due to potential QTc prolongation 

  • Dosing: Dosing is renal dependent. For patients with normal renal function, start with 80mg BID. If this dose does not prolong QTc >500 after 3 days, can increase up to 160mg BID

  • Considerations: 

  • Should NOT be used in patients with HFrEF (EF<40%) as they are most likely also taking an additional AV nodal blocker (i.e. a beta blocker) and this can cause brady or tachy arrhythmias. 

  • QTc interval should be measured 2 to 3 hours after the first 5-6 doses. For any QTc prolongation >15% or >500ms, dose adjustments must be made. If there is too much prolongation, this may preclude the patient from getting this medication. 

  • Monitoring: Must get EKG, BMP, Mg, and Phos every 3-6 months after administration to monitor QTc, Cr, and electrolytes.