Arrhythmia Pharmacology Essentials

Start With Stability, Rhythm, and Substrate

Before selecting an antiarrhythmic, assess heart rate, blood pressure, symptoms, 12-lead electrocardiogram (ECG), corrected QT (QTc) interval, potassium, magnesium, kidney function, interacting medications, structural heart disease, prior myocardial infarction (MI) or coronary artery disease (CAD), and left ventricular ejection fraction (LVEF). The same drug that is appropriate in a structurally normal heart can be dangerous after MI or in heart failure with reduced ejection fraction (HFrEF) (Parker & Coons, 2026).

Vaughan Williams Framework

Class	Primary action	Representative drugs	High-yield concern
IA	Na+ block + repolarization prolongation	Quinidine, procainamide, disopyramide	QT prolongation; proarrhythmia
IB	Weak Na+ block	Lidocaine, mexiletine	Primarily ventricular arrhythmias
IC	Strong Na+ block	Flecainide, propafenone	Avoid with prior MI/CAD/structural disease
II	Beta blockade	Metoprolol, esmolol, propranolol	Bradycardia, hypotension, AV block
III	K+ channel/repolarization effects	Amiodarone, dofetilide, dronedarone, sotalol (also has nonselective beta-blocking activity)	QT prolongation; agent-specific organ toxicity
IV	Nondihydropyridine Ca2+ channel block	Diltiazem, verapamil	AV-node slowing; avoid in HFrEF
Other	AV-node or nodal effects outside Vaughan Williams	Adenosine, digoxin	Very drug-specific use and toxicity

Atrial Fibrillation: Rate Control

For long-term ventricular rate control with normal left ventricular function, a beta blocker or nondihydropyridine calcium channel blocker (CCB) is generally preferred. Digoxin controls resting rate but is less effective during activity. In HFrEF, diltiazem and verapamil should be avoided because of negative inotropy; beta blockers and selected digoxin use are more appropriate pharmacologic options (Parker & Coons, 2026).

Atrial Fibrillation: Rhythm Control

Rhythm-control drug selection depends on structural heart disease and ventricular function. Flecainide and propafenone should not be used in patients with prior MI or known CAD because of increased proarrhythmic mortality risk, and they are also inappropriate in HFrEF. Amiodarone, dofetilide, or other substrate-appropriate therapies may be considered when rhythm control is selected. Contemporary evidence also supports considering early rhythm control in appropriately selected patients with AF diagnosed within the previous 12 months because this strategy can improve cardiovascular outcomes compared with rate control alone (Parker & Coons, 2026).

Dronedarone is not simply a less-toxic substitute for amiodarone. Rhythm-maintenance therapy should not be continued once AF has been accepted as permanent, and heart-failure status matters when selecting antiarrhythmics because several agents, including dronedarone, can exacerbate HF. Ventricular function and recent decompensation should therefore be considered before selection (Parker & Coons, 2026; Ng & Yeung, 2026).

Dofetilide and Sotalol: Renal and QT Safety

Dofetilide and sotalol require kidney-function-based dosing and monitored initiation because excessive exposure can prolong QT and cause torsades de pointes. The 2026 chapter specifies inpatient initiation with continuous ECG monitoring. Correct hypokalemia and hypomagnesemia and review other QT-prolonging drugs before use (Parker & Coons, 2026).

Amiodarone: Effective but Toxicity-Limited

Amiodarone has broad antiarrhythmic activity but substantial long-term toxicity and interaction burden. Monitoring commonly includes ECG and heart rate, thyroid and liver function, pulmonary symptoms with targeted imaging when clinically indicated, ocular symptoms, and major drug interactions. New unexplained cough or dyspnea, thyroid dysfunction, hepatic injury, bradycardia, or visual symptoms should prompt reassessment. Amiodarone can increase exposure to warfarin, digoxin, and several statins, and its long half-life means adverse effects and interactions can persist after discontinuation (Parker & Coons, 2026).

Adenosine and Paroxysmal Supraventricular Tachycardia

Adenosine transiently blocks AV-node conduction and is used for selected regular narrow-complex supraventricular tachycardias after appropriate rhythm assessment. Its extremely short duration makes chest pressure, flushing, dyspnea, and transient AV block brief but dramatic. It is not a treatment for atrial fibrillation itself (Parker & Coons, 2026).

Digoxin Across HF and Arrhythmia Care

Digoxin slows AV-node conduction through vagal and direct nodal effects and can support rate control in selected AF patients, particularly when HFrEF limits CCB use. It is less effective during exertion and is primarily renally cleared. Older age, low lean body mass, kidney dysfunction, hypokalemia, hypomagnesemia, and interacting drugs increase toxicity risk (Parker & Coons, 2026; Ng & Yeung, 2026).

Do not miss digoxin toxicity: nausea, vomiting, anorexia, new visual disturbance such as yellow-green halos, unexplained bradycardia or AV block, and ventricular arrhythmias should prompt urgent reassessment of digoxin exposure, kidney function, electrolytes, interacting drugs, and a properly timed serum concentration. Interpret the concentration together with the clinical picture rather than in isolation (Parker & Coons, 2026).

Stroke Prevention Is a Separate AF Treatment Track

Rate or rhythm control does not prevent atrial-fibrillation-related thromboembolism. Assess stroke risk separately with the CHA₂DS₂-VASc framework: heart failure, hypertension, age ≥75 years (2 points), diabetes, prior stroke/transient ischemic attack/thromboembolism (2 points), vascular disease, age 65–74 years, and sex category. In the 2026 Pharmacotherapy chapter, oral anticoagulation is recommended at scores ≥2 in men or ≥3 in women and may be considered at intermediate scores using shared decision-making. Direct oral anticoagulants are generally preferred over warfarin for eligible patients; mechanical heart valves and moderate-to-severe mitral stenosis remain important exceptions. Kidney function affects agent selection and dosing, so anticoagulation should be reassessed as renal function changes (Parker & Coons, 2026).

Proarrhythmia and Electrolyte Safety

• Review QT-prolonging medications before adding another QT-active drug.
• Correct hypokalemia and hypomagnesemia when clinically possible.
• Use kidney-function-based dosing for renally cleared antiarrhythmics.
• Avoid flecainide and propafenone in prior MI/CAD or significant structural heart disease.
• Avoid diltiazem and verapamil in HFrEF.
• Do not treat asymptomatic PVCs simply to suppress the ECG finding; unnecessary class I suppression after MI can increase mortality.

High-Yield Distinctions

• Rate control, rhythm control, and stroke prevention are separate AF goals.
• CHA₂DS₂-VASc structures AF stroke-risk assessment; successful rate or rhythm control does not remove the need to reassess anticoagulation.
• Digoxin toxicity should be suspected with GI symptoms, yellow-green visual changes, AV block/bradycardia, or ventricular arrhythmias, especially with kidney dysfunction or electrolyte depletion.
• Structural heart disease and ejection fraction change antiarrhythmic selection.
• Dofetilide and sotalol require monitored initiation because of torsades risk.
• Flecainide and propafenone are inappropriate in prior MI/CAD and HFrEF.
• Diltiazem and verapamil are useful AV-node blockers but should generally be avoided in HFrEF.
• Amiodarone is effective but carries substantial multiorgan toxicity and interactions.
• Digoxin is renally cleared and is less effective for rate control during exertion.
• Electrolytes, QTc, renal function, and drug interactions are part of antiarrhythmic prescribing—not optional add-ons.

Related YourDNP Resources

• Arrhythmias
• Heart Failure
• Cardiac Pathophysiology Foundations

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References

Ng, T. M. H., & Yeung, S. L. (2026). Heart failure. In M. A. Chisholm-Burns, P. M. Malone, J. M. Kolesar, K. C. Lee, P. B. Bookstaver, & K. R. Matthias (Eds.), Pharmacotherapy principles & practice (7th ed., pp. 184–238). McGraw Hill.

Parker, R. B., & Coons, J. C. (2026). Arrhythmias. In M. A. Chisholm-Burns, P. M. Malone, J. M. Kolesar, K. C. Lee, P. B. Bookstaver, & K. R. Matthias (Eds.), Pharmacotherapy principles & practice (7th ed., pp. 327–386). McGraw Hill.