Dysrhythmias arise from abnormal impulse formation (automaticity, triggered activity) or abnormal conduction (reentry). Antiarrhythmic drugs change the flow of ions across cardiac cell membranes to slow conduction, suppress automaticity, or lengthen the refractory period. The Vaughan Williams classification is still the framework used in teaching.

Key principle: every antiarrhythmic can also cause dysrhythmias (proarrhythmia). Class IA and III drugs lengthen the QT interval and can trigger torsades de pointes; class IC drugs increase death in clients with structural heart disease.

Cardiac arrest dosing (adult): for VF/pulseless VT that persists after shocks, amiodarone 300 mg IV/IO, then 150 mg, or lidocaine 1–1.5 mg/kg, then 0.5–0.75 mg/kg. Defibrillation and CPR come first; drugs never replace a shock.

AF management combines stroke prevention (anticoagulation — see Anticoagulants), rate control (beta blocker or diltiazem/verapamil; digoxin as an add-on), and, in selected clients, rhythm control (antiarrhythmic drug, cardioversion, or ablation).

Boxed warning (oral amiodarone): potentially fatal pulmonary toxicity, hepatic injury, and worsened arrhythmia. It is labeled only for life-threatening recurrent ventricular arrhythmias (AF use is guideline-based but off-label), and it is started with close monitoring.

Other boxed warnings: flecainide — excess deaths after MI (CAST) and not for structural heart disease; sotalol and dofetilide — start in a facility with continuous ECG and creatinine clearance-based dosing (torsades risk); dronedarone — contraindicated in NYHA IV or recently decompensated HF and permanent AF.

• Structural heart disease or prior MI: avoid class IC drugs (flecainide, propafenone).
• Long QT (QTc > 500 ms), hypokalemia, hypomagnesemia: avoid starting QT-prolonging drugs; correct electrolytes first.
• HFrEF: avoid diltiazem, verapamil, dronedarone, flecainide, disopyramide.
• Second- or third-degree AV block or sick sinus syndrome without a pacemaker: avoid beta blockers, diltiazem/verapamil, digoxin, amiodarone.
• Pre-excited AF (Wolff–Parkinson–White): avoid AV nodal blockers (adenosine, diltiazem, verapamil, digoxin, IV beta blockers) and IV amiodarone — they can speed conduction down the accessory pathway and cause VF; procainamide or ibutilide is used, or synchronized cardioversion if unstable.
• Adenosine: avoid in irregular or polymorphic wide-complex tachycardia and second- or third-degree block; caution in asthma. Dipyridamole and carbamazepine increase its effect (lower dose); theophylline and caffeine reduce it.
• Asthma: nonselective beta blockers and sotalol can cause bronchospasm.
• Pregnancy: amiodarone can cause fetal thyroid disorders and bradycardia — generally avoided; choice of drug in pregnancy is specialist-directed. Beta blockers and adenosine are commonly used when needed.
• Amiodarone interactions (important and long-lasting):
  • Raises warfarin effect — INR rises; the warfarin dose is usually reduced (often by one-third to one-half) with close INR checks
  • Raises digoxin levels — the digoxin dose is usually reduced
  • Simvastatin — limit to 20 mg/day (myopathy risk)
  • Sofosbuvir-containing hepatitis C regimens — severe bradycardia
  • Other QT-prolonging drugs (macrolides, fluoroquinolones, ondansetron, antipsychotics, methadone) → torsades
• Grapefruit juice raises amiodarone and some calcium channel blocker levels.
• Diltiazem/verapamil + beta blocker → additive bradycardia and heart block.

1. Continuous ECG monitoring for IV antiarrhythmics and during initiation of sotalol, dofetilide, and ibutilide. Measure PR, QRS, and QTc before and after doses; report new heart block, QRS widening, or QTc > 500 ms or an increase > 60 ms.
2. Assess before each dose: apical pulse and BP; hold per parameters (e.g., heart rate below about 50–60/min or systolic BP below ordered limit) and notify.
3. Electrolytes: keep potassium 3.5–5.0 mEq/L (mmol/L) — many protocols aim for ≥ 4.0 — and magnesium 1.7–2.2 mg/dL (0.70–0.91 mmol/L) or higher per protocol.
4. Adenosine technique: large proximal vein (antecubital), rapid IV push over 1–2 seconds followed immediately by a 20 mL saline flush, elevate the arm; record the rhythm strip during the push; have emergency equipment ready. Use 3 mg via a central line, after heart transplant, or with dipyridamole or carbamazepine.
5. IV amiodarone: infusion pump; central line for concentrations above 2 mg/mL (phlebitis); non-PVC container or in-line filter per product for longer infusions; watch for hypotension and bradycardia.
6. Amiodarone baseline and follow-up: chest X-ray and pulmonary function tests, thyroid function (TSH) and liver tests at baseline and about every 6 months, eye examinations; report new cough or dyspnea.
7. Lidocaine infusion: neurologic checks (level of consciousness, speech, perioral numbness); lower dose in liver disease, HF, and older adults. Therapeutic level about 1.5–5 mcg/mL.
8. Procainamide: monitor BP, QRS, QTc, CBC; stop infusion for hypotension or QRS widening > 50%.
9. IV diltiazem: commonly 0.25 mg/kg over 2 minutes, then infusion; monitor BP and heart rate.
10. Sotalol and dofetilide: start in a facility with continuous ECG for at least 3 days; check creatinine clearance and QTc before each dose increase.

• Take the drug exactly as prescribed; do not skip, double, or stop without talking to the provider
• Check your pulse daily if taught; report a pulse below the set limit, fainting, palpitations, or dizziness
• Amiodarone: report new cough, shortness of breath, or fever; use sunscreen and protective clothing (photosensitivity, blue-gray skin); report vision changes, weight change, heat or cold intolerance (thyroid), yellow skin, or dark urine; keep laboratory and eye appointments; effects last for weeks to months after stopping
• Avoid grapefruit juice with amiodarone and some calcium channel blockers
• Tell every prescriber and pharmacist you take an antiarrhythmic — many common drugs (some antibiotics, antidepressants, antinausea drugs) prolong the QT interval
• Report diarrhea or vomiting (electrolyte loss increases dysrhythmia risk)
• Verapamil: increase fiber and fluids for constipation
• Beta blockers and diltiazem/verapamil: rise slowly; do not stop suddenly
• Wear medical identification; learn when to call emergency services (chest pain, fainting, severe palpitations)

• Torsades de pointes (drug-induced long QT): IV magnesium sulfate, stop QT-prolonging drugs, correct potassium; defibrillate if pulseless; overdrive pacing or isoproterenol for recurrent episodes.
• Class I (sodium channel blocker) toxicity with wide QRS (flecainide, procainamide, also tricyclic overdose): IV sodium bicarbonate.
• Lidocaine toxicity / local anesthetic systemic toxicity: stop the infusion, airway support, benzodiazepines for seizures, IV lipid emulsion for severe toxicity.
• Beta blocker overdose: bradycardia, hypotension, hypoglycemia → atropine, IV fluids, glucagon, high-dose insulin with dextrose, vasopressors, pacing.
• Calcium channel blocker overdose: hypotension, bradycardia, hyperglycemia → IV calcium, high-dose insulin with dextrose, vasopressors, lipid emulsion in refractory cases.
• Digoxin toxicity: digoxin immune Fab (see Heart Failure Drugs).
• Amiodarone: no antidote; pulmonary toxicity is treated by stopping the drug and giving corticosteroids; its long half-life means toxicity persists.
• Adenosine effects last only seconds; prolonged asystole is rare.

• Vaughan Williams: I = sodium, II = beta, III = potassium (long QT), IV = calcium
• Amiodarone → pulmonary fibrosis (most serious), thyroid, liver, photosensitivity, blue-gray skin, corneal deposits
• Amiodarone raises warfarin (INR) and digoxin levels
• Adenosine 6 mg rapid push + flush, then 12 mg; brief asystole is expected
• Atropine 1 mg, maximum 3 mg for symptomatic bradycardia
• Refractory VF/pVT: amiodarone 300 mg then 150 mg, or lidocaine
• Lidocaine toxicity = CNS (perioral numbness, confusion, seizures)
• Procainamide → lupus-like syndrome, blood dyscrasias
• Torsades → magnesium sulfate; report QTc > 500 ms
• Class IC drugs → not in structural heart disease or after MI
• Diltiazem/verapamil → avoid in HFrEF; verapamil → constipation
• All antiarrhythmics can be proarrhythmic — correct potassium and magnesium first