#drug-induced-arrhythmias #arrhythmia-management #pharmacology #QT-prolongation

Drug-Induced Arrhythmia

Definition

Drug-induced arrhythmia refers to any cardiac arrhythmia caused or exacerbated by a pharmacological agent. This encompasses a wide spectrum: bradyarrhythmias, supraventricular arrhythmias (AF/AFL, AT, AVNRT), and ventricular arrhythmias (monomorphic VT, Brugada syndrome unmasking, and torsades de pointes). Awareness that a patient's arrhythmia may be drug-induced is a critical clinical skill.

Key Concepts

Bradyarrhythmias

Drug-induced bradyarrhythmias arise from sinus node dysfunction or AV block; mechanisms include inhibited automaticity, slowed conduction, or prolonged nodal repolarization. (sources/drug-arrhythmia-aha-2020, rating: very high)
Key offenders: β-blockers (0.6–25%), non-DHP calcium channel blockers (diltiazem 4.2–16%, verapamil 0–11%), digoxin (0–7%), amiodarone (3–20%), ivabradine (3.7–15.7% via If channel inhibition), fingolimod (0.5–3.7% via S1P1 receptor modulation), acetylcholinesterase inhibitors (donepezil 0.6–48%). (sources/drug-arrhythmia-aha-2020)
Critical interaction — amiodarone + sofosbuvir-containing HCV regimens (Harvoni, Sovaldi): FDA black box warning for rare but potentially fatal bradycardia when amiodarone is co-administered with sofosbuvir (NS5B polymerase inhibitor). Mechanism not fully characterized but involves additive sinus nodal and AV nodal depression. No prospective management protocol exists; co-prescribing should be avoided. (sources/amiodarone-cvdrug-2020, rating: high)
~50% of patients experience persistent or recurrent bradycardia after drug discontinuation and may still require a permanent pacemaker. (sources/drug-arrhythmia-aha-2020)
Overdose management: glucagon (3–10 mg IV bolus then 3–5 mg/h) for β-blocker/CCB overdose; high-dose insulin (1 unit/kg + 0.5 units/kg/h) in refractory AV block. (sources/drug-arrhythmia-aha-2020)

Drug-Induced Atrial Fibrillation / Atrial Flutter

Drug-induced AF/AFL results from multiple mechanisms: catecholaminergic augmentation (stimulants, bronchodilators), shortened atrial effective refractory period (alcohol, bisphosphonates, adenosine), inflammatory cytokine release (bisphosphonates, anticancer agents), and thyrotoxicosis (amiodarone, some kinase inhibitors). (sources/drug-arrhythmia-aha-2020)
Particularly high-risk drug categories: anticancer agents (trastuzumab 1.2–19.9%, alkylating agents up to 15.5%), antipsychotics (clozapine OR 2.81), alcohol (pooled OR 1.51), dobutamine (0–18%), ibrutinib (BTK inhibitor). (sources/drug-arrhythmia-aha-2020)
Class IC agents (flecainide, propafenone) can slow atrial conduction, increase AFL cycle length, and produce 1:1 AV conduction with wide QRS — AV nodal blocking drugs must be co-prescribed in patients with AFL. (sources/drug-arrhythmia-aha-2020)
Management: discontinue offending agent; rate control if haemodynamically stable; TOE/anticoagulation before cardioversion if AF ≥48 h or unknown duration. (sources/drug-arrhythmia-aha-2020)

Drug-Induced Atrial Tachycardia

Multifocal AT is most commonly triggered by theophylline (serum level >20 μg/mL) and β-agonists; digoxin toxicity causes paroxysmal AT with AV block via intracellular Ca²⁺ overload + vagomimetic activity. (sources/drug-arrhythmia-aha-2020)
Risk factors for digoxin-induced AT: digoxin concentration >2 ng/mL, renal impairment, hypomagnesaemia, drug interactions (amiodarone, verapamil, quinidine). (sources/drug-arrhythmia-aha-2020)
Multifocal AT management includes magnesium supplementation and treatment of the underlying pulmonary/metabolic trigger; digoxin toxicity may require digoxin-immune Fab. (sources/drug-arrhythmia-aha-2020)

Drug-Induced AVNRT

AVNRT requires dual AV nodal pathway substrate; drugs trigger it by enhancing conduction or generating premature extrastimuli that dissociate fast/slow pathway refractory periods. (sources/drug-arrhythmia-aha-2020)
Common triggers: albuterol (nebulised, 0–21%), dobutamine (0–12%), caffeine, theophylline, methylphenidate. (sources/drug-arrhythmia-aha-2020)
Immediate treatment: vagal maneuvers + IV adenosine (first-line); IV diltiazem, verapamil, or β-blocker if adenosine fails; catheter ablation of slow pathway for recurrent cases. (sources/drug-arrhythmia-aha-2020)

Drug-Induced Monomorphic Ventricular Tachycardia

Mechanisms include sodium channel inhibition (reduced conduction velocity → reentry; Class IC agents), sodium channel activation (increased automaticity; aconite alkaloids), Ca²⁺ overload triggered activity (digoxin toxicity, theophylline), and coronary steal (adenosine, dipyridamole). (sources/drug-arrhythmia-aha-2020)
Critical CAST trial finding: Class IC antiarrhythmic agents (flecainide, encainide, propafenone) significantly increased mortality in patients with structural heart disease — they are contraindicated in prior MI or cardiomyopathy. (sources/drug-arrhythmia-aha-2020)
Narrow therapeutic windows: digoxin must be maintained <2 ng/mL; theophylline <20 μg/mL; both require heightened vigilance in renal impairment, hypomagnesaemia, or hypokalaemia. (sources/drug-arrhythmia-aha-2020)

Drug-Induced Brugada Syndrome

Drug-induced Brugada pattern develops in patients with previously normal ECGs; the underlying genetic substrate (SCN5A loss-of-function or other) is often present but silent. (sources/drug-arrhythmia-aha-2020)
Caused predominantly by sodium channel blockers — ajmaline, pilsicainide, flecainide, procainamide, propafenone; also TCAs, cocaine, propofol, lithium, oxcarbazepine; full list at brugadadrugs.org. (sources/drug-arrhythmia-aha-2020)
Drug-induced BrS SCD risk: ~0.08%/year — meaningfully lower than spontaneous BrS. Ambulatory ECG monitoring is required after drug discontinuation to exclude latent BrS. (sources/drug-arrhythmia-aha-2020)
Procainamide is contraindicated for managing drug-induced Brugada VT (potentiates sodium channel inhibition). (sources/drug-arrhythmia-aha-2020)
See entities/Brugada-Syndrome for full detail.

Torsades de Pointes (Drug-Induced)

The most clinically serious drug-induced arrhythmia; >200 drugs with TdP potential remain on the market; TdP can degenerate into VF and SCD. (sources/drug-arrhythmia-aha-2020)
Primary mechanism: IKr inhibition → action potential duration prolongation → early afterdepolarizations → TdP. Some drugs also augment late sodium current (INa-L): dofetilide, ibutilide, d-sotalol. (sources/drug-arrhythmia-aha-2020)
Repolarization reserve theory: Multiple redundant repolarization mechanisms exist; when one is perturbed (e.g., by a latent LQTS mutation), adding an IKr-inhibiting drug depletes repolarization reserve and unmasks QT prolongation/TdP. This explains why ~30% of drug-induced TdP patients carry latent LQTS variants. (sources/drug-arrhythmia-aha-2020)
Key risk factors: QTc >500 ms or increase ≥60 ms, female sex, age >65, bradycardia, hypokalaemia, hypomagnesaemia, hypocalcaemia, HFrEF, ≥2 concurrent QT-prolonging drugs, prior drug-induced TdP, renal/hepatic impairment. (sources/drug-arrhythmia-aha-2020)
Prevention: K⁺ >4.0 mEq/L, Mg²⁺ >2.0 mg/dL, avoid QT drug combinations, baseline ECG, adjust doses in organ dysfunction. (sources/drug-arrhythmia-aha-2020)
Management: discontinue causative drug; IV magnesium 1–2 g; overdrive pacing or isoproterenol for recurrent TdP with bradycardia; defibrillation for haemodynamically unstable TdP; oral mexiletine 200–450 mg/day for refractory cases. (sources/drug-arrhythmia-aha-2020)
See concepts/Torsades-de-Pointes for full detail.

Contradictions / Open Questions

Drug-induced TdP — latent LQTS prevalence discrepancy: The AHA 2020 statement reports ~30% of drug-induced QT prolongation patients carry pathogenic variants in 1 of 5 major LQTS genes. The arrhythmia genetics review (2025) cites only 10–15% as representing unmasked hidden LQTS. This ~2-fold discrepancy likely reflects different methodologies and gene panels — it has not been reconciled, and neither figure is sufficient to justify universal pre-prescription genetic screening. (sources/drug-arrhythmia-aha-2020, sources/arrhythmia-genetics-mgenetik-2025)
Drug-induced type 1 BrS — diagnostic weight: A drug-induced type 1 ECG alone is insufficient for a definitive Brugada syndrome diagnosis; however, many patients with drug-induced type 1 also have spontaneous type 1 on ambulatory monitoring. No consensus exists on how to weight drug-induced type 1 ECG within the Shanghai Diagnostic Score. (sources/drug-arrhythmia-aha-2020, sources/brs-jaccep-2022)
General genetic screening for TdP prevention — not recommended: Despite the high (~30%) prevalence of latent LQTS variants among drug-induced TdP patients, routine genetic testing before prescribing QT-prolonging drugs is not currently recommended. The cost-effectiveness, turnaround time, and clinical feasibility of such screening remain unresolved. (sources/drug-arrhythmia-aha-2020)

Connections

Related to concepts/Torsades-de-Pointes
Related to entities/Brugada-Syndrome
Related to entities/Long-QT-Syndrome
Related to entities/Atrial-Fibrillation
Related to concepts/Cardiac-Action-Potential
Related to concepts/Shanghai-Score-System
Related to entities/KCNH2
Related to entities/SCN5A