Ventricular Tachyarrhythmias

Clinical Snapshot

Ventricular tachycardia (VT) is generally defined as 3 or more consecutive ventricular complexes at a rate over 100 beats per minute on the ECG; ventricular fibrillation (VF) is a rapid, disorganized rhythm with no recognizable QRS complexes that is almost always fatal without immediate defibrillation.^[1]

VT ranges from a clinically silent, incidental finding to a life-threatening emergency, and management hinges on 3 questions answered in sequence: is the patient pulseless or hemodynamically unstable (an immediate defibrillation/cardioversion emergency, never a medication-first problem); is the QRS morphology monomorphic or polymorphic (polymorphic VT with QT prolongation — torsades de pointes — needs fundamentally different pharmacotherapy from monomorphic VT, and treating it with a standard antiarrhythmic can make it worse); and is there underlying structural heart disease (the strongest predictor of recurrence and of the need for an implantable cardioverter defibrillator). This chapter covers all 3 scenarios, chronic secondary prevention, and drug-induced QT prolongation, since medications are the most common cause of acquired torsades de pointes risk.

Recognize the Condition

Symptom spectrum

Presentation ranges from entirely asymptomatic (most often nonsustained VT found incidentally on a monitor or Holter) to palpitations, dyspnea, chest discomfort, presyncope, or syncope, to cardiac arrest. Symptom severity does not reliably predict prognosis — even marked symptoms from brief nonsustained VT in a structurally normal heart can be prognostically benign, while asymptomatic nonsustained VT in a patient with left ventricular dysfunction can signal a real risk of future sustained VT or VF.^[1]

The 3 ventricular tachyarrhythmia categories

Monomorphic VT

Every QRS complex in the run has the same shape, implying a single abnormal focus or a fixed re-entrant circuit, usually around a scar. Most often associated with prior MI or other structural heart disease. Sustained monomorphic VT (30 seconds or more, hemodynamic compromise, or requiring intervention) needs urgent treatment; a working cutoff of over 15 seconds is used for management decisions.

Polymorphic VT, including torsades de pointes

QRS morphology varies beat to beat, usually in short repetitive salvos of 3-20 beats. When associated with a prolonged QT interval and a characteristic long-short initiating beat sequence, this is torsades de pointes — a distinct entity from monomorphic VT that requires magnesium and QT-prolonging-drug withdrawal rather than a standard antiarrhythmic (see Choose Initial Treatment). Polymorphic VT without QT prolongation instead suggests active myocardial ischemia and needs urgent evaluation for that cause.

Ventricular fibrillation

A rapid, disorganized rhythm with no recognizable QRS complexes. Almost always leads to cardiac arrest and is fatal without immediate defibrillation. Most patients who survive an out-of-hospital cardiac arrest with a shockable rhythm had VF as the underlying rhythm, even when the rhythm first documented by responders is asystole.

Any wide-complex tachycardia (QRS 0.12 seconds or more) in a patient over 50, or in a patient with known structural heart disease at any age, should be treated as VT until proven otherwise — most wide-complex tachycardias in any patient of any age are in fact VT, and defaulting to an assumption of supraventricular tachycardia with aberrancy is a common and dangerous error.^[1]

Risk Factors

General risk factors for VT/VF

Structural heart disease — coronary artery disease and prior myocardial infarction are the most common overall cause.
Cardiomyopathy (ischemic or nonischemic), reduced left ventricular ejection fraction.
Valvular or hypertensive heart disease.
Inherited arrhythmia syndromes — long QT syndrome, Brugada syndrome, catecholaminergic polymorphic VT, arrhythmogenic right ventricular cardiomyopathy.
Family history of sudden death or documented VT/VF, especially under age 65 — consider referral for genetic testing of known heritable disorders.
Electrolyte abnormalities — hypokalemia, hypocalcemia, hypomagnesemia.
Active myocardial ischemia.
Digitalis toxicity.
Cocaine or other stimulant use.
Exercise-induced ectopy, particularly when polymorphic — raises concern for catecholaminergic polymorphic VT or ischemia.

Risk factors for drug-induced torsades de pointes specifically

Because medications are the most common cause of acquired QT prolongation, a separate set of risk factors predicts torsades de pointes when a QT-prolonging drug is used — the more of these present, the more caution (or an alternative drug) is warranted.^[2]

Patient-related

Age over 65-67 years.
Female sex.
Bradycardia (heart rate under 45 beats/minute).
First 24 hours after cardiac arrest, syncope, or seizure.
First 7 days after an acute coronary syndrome.
First 7 days after cardioversion of atrial fibrillation to sinus rhythm.
First 7 days after stroke, subarachnoid hemorrhage, or head trauma.

Medical conditions

Congenital long QT syndrome.
Electrolyte disturbances — hypocalcemia, hypokalemia, hypomagnesemia.
Heart failure with left ventricular ejection fraction under 40%.
Hypertrophic cardiomyopathy.
Hypoglycemia, even without diabetes.
Hypothyroidism, anorexia nervosa, starvation.
Family history of sudden cardiac death.
Pheochromocytoma.
Sepsis.

Drug-related

Altered drug metabolism, e.g., renal or hepatic failure.
Loop diuretics, via the hypokalemia/hypomagnesemia they can cause.
Higher drug dosage.
Concomitant use of more than 1 QT-prolonging medication (see Drug Tables for the full list of QT-prolonging drug classes).

Red Flags & Refer

Any ventricular tachyarrhythmia with a pulse or hemodynamic problem is an immediate-action emergency — assess pulse and hemodynamic stability before anything else.

Pulseless VT or VF is a cardiac arrest — start CPR and defibrillate immediately; this is never a medication-first problem, and no drug is given before the first shock.
Hemodynamically unstable VT with a pulse (hypotension, altered level of consciousness, ongoing ischemic chest pain, or acute pulmonary edema) requires immediate synchronized cardioversion — do not delay for a trial of antiarrhythmic drug therapy.
Electrical storm — 3 or more separate episodes of sustained VT, VF, or appropriate ICD shocks within 24 hours — is a medical emergency requiring hospitalization and escalating therapy.
Torsades de pointes, even when self-terminating, is itself the red flag requiring immediate magnesium and identification/removal of the precipitating cause — it must never be treated with a standard Class Ia or Class III antiarrhythmic, which can worsen it (see Choose Initial Treatment).
A new wide-complex tachycardia in a patient over 50, or with known structural heart disease at any age, should be escalated and treated as VT until proven otherwise.
Syncope or a family history of sudden death under age 65, especially with a normal or near-normal heart on initial workup, warrants urgent electrophysiology referral and consideration of genetic testing for a heritable arrhythmia syndrome.

Assessment & Diagnosis

Differentiating monomorphic VT, polymorphic VT/torsades de pointes, and SVT with aberrancy

These 3 wide-complex rhythms are commonly confused on initial ECG review, and correct treatment differs for each — getting the differentiation right, or defaulting to treating an uncertain wide-complex tachycardia as VT, is a genuine patient-safety issue.^[1]

Feature	Monomorphic VT	Polymorphic VT / torsades de pointes	SVT with aberrancy
QRS morphology	Uniform, same shape every beat	Varies beat to beat; classic twisting appearance around the baseline in torsades	Uniform, same shape every beat (usually a fixed bundle-branch pattern)
Baseline QT interval	Usually normal	Prolonged, specifically in torsades de pointes	Normal
Underlying substrate	Scar-related re-entry or abnormal focus, usually with structural heart disease	A QT-prolonging drug, an electrolyte abnormality, or congenital long QT syndrome (torsades); active ischemia (polymorphic VT without QT prolongation)	An accessory pathway or AV-nodal re-entry with a pre-existing or rate-related bundle branch block
Typical trigger pattern	Not rate-dependent in a specific way	A characteristic long-short initiating sequence — a pause followed by a premature beat — in torsades	Abrupt onset/termination typical of re-entrant SVT
First-line treatment	Procainamide or amiodarone IV if stable; synchronized cardioversion if unstable	Magnesium sulfate IV, and stop the offending QT-prolonging drug — never a standard Class Ia/III antiarrhythmic	Vagal maneuvers, adenosine, or a rate-slowing agent — not an antiarrhythmic aimed at VT
Key safety point	Distinguishing from SVT with aberrancy matters because VT-directed therapy is needed; when uncertain, treat as VT	Distinguishing from monomorphic VT matters because standard antiarrhythmics (procainamide, sotalol, quinidine) prolong QT further and can worsen torsades	Giving a standard VT antiarrhythmic here is usually low-risk but ineffective; the real danger is misdiagnosing true VT as this

History

Syncope or severe presyncope.
Angina or heart failure symptoms.
History suggesting structural heart disease, especially prior MI or heart failure.
Symptom correlation with exercise or stress.
Recent ingestion of medications that might cause or contribute to arrhythmias — antiarrhythmics, or any QT-prolonging drug (see Drug Tables).
Family history of sudden death or documented VT/VF, especially under age 65 — consider referral for genetic testing of known heritable disorders.

Physical examination

Examine for signs of structural heart disease — cardiomyopathy, or valvular or hypertensive heart disease.

Laboratory testing

Check potassium, calcium, and magnesium in every patient presenting with a ventricular arrhythmia — electrolyte abnormalities are a common, correctable contributor.

12-lead ECG

Signs of prior MI or ongoing ischemia.
Repolarization abnormalities — short or prolonged QT interval, ECG signs of Brugada syndrome, early repolarization syndrome, T-wave inversions.
A 12-lead ECG documenting the tachycardia itself is very helpful when available; an ECG captured at tachycardia onset or offset is also very useful.

Echocardiogram

Assess left ventricular size and function and right ventricular size — the degree of LV dysfunction is the single most important prognostic factor and a key driver of ICD candidacy.

Additional testing

Holter or loop event recorder monitoring — assess the presence and morphology of ventricular ectopy and symptom-rhythm correlation.
Treadmill exercise testing — assess for exercise-induced VT and ECG or symptomatic evidence of myocardial ischemia.
When structural heart disease is absent: signal-averaged ECG, cardiac MRI (to assess structure and scar), and provocative drug testing (isoproterenol for suspected long QT syndrome, procainamide for suspected Brugada syndrome) under specialist direction.

Calculating and interpreting the QT interval

The QTc is the rate-corrected QT interval; the most commonly used correction is the Bazett formula, which divides the measured QT interval (in seconds) by the square root of the R-R interval (in seconds). Bazett's formula undercorrects at fast heart rates, so a QTc over 480 ms at a fast heart rate can still reflect normal repolarization.^[3]

Threshold	Interpretation
QTc 470 ms or more (men), or 480 ms or more (women)	Prolonged QTc, per the American Heart Association definition
QTc over 500 ms, or an increase of more than 60 ms from the patient's own baseline	Greatest concern for torsades de pointes risk

When further testing is not indicated

An asymptomatic patient with occasional, isolated premature ventricular complexes and no structural heart disease on a basic history and exam does not routinely need echocardiography, Holter monitoring, or electrophysiology referral — extensive investigation is reserved for sustained VT, symptomatic VT, or ventricular ectopy in the setting of known or suspected structural heart disease.

Treatment Targets

Restore a perfusing rhythm as quickly as possible in pulseless VT, VF, or cardiac arrest.
Terminate hemodynamically unstable VT immediately, without delay for drug therapy.
Correctly distinguish monomorphic from polymorphic VT/torsades de pointes, since the correct drug therapy for one can worsen the other.
Identify and correct reversible contributors — electrolyte abnormalities, active ischemia, and offending QT-prolonging drugs.
Prevent the potentially fatal recurrence of sustained VT or VF.
Establish appropriate chronic secondary prevention — ICD candidacy assessment, foundational beta-blocker therapy, adjunctive antiarrhythmic drug therapy, and catheter ablation where indicated.

Choose Initial Treatment

Direct treatment rule

Pulseless VT or VF (cardiac arrest)

1st line immediate defibrillation and high-quality CPR per the institution's ACLS protocol — this is never a medication-first problem.

For shock-refractory VF/pulseless VT persisting after the 3rd shock, give amiodarone 300 mg IV/IO bolus; a further 150 mg IV/IO bolus may be given if the arrhythmia persists or recurs.^[4]

Lidocaine 1-1.5 mg/kg IV/IO is a reasonable alternative to amiodarone, particularly if amiodarone is unavailable or contraindicated.^[5]

Per current AHA guidance, the benefit of procainamide, sotalol, or a beta-blocker for VF/pulseless VT that remains unresponsive to defibrillation is uncertain — these are not first-line choices in this specific shock-refractory arrest scenario, even though procainamide and sotalol both have established roles elsewhere in this chapter.^[4]

Hemodynamically unstable VT (with a pulse)

1st line immediate synchronized cardioversion for any VT causing hypotension, altered consciousness, ongoing ischemic chest pain, or acute heart failure — do not delay cardioversion to trial a drug first.

Hemodynamically stable monomorphic VT

1st line procainamide IV, indicated specifically for monomorphic VT, which slows or terminates the arrhythmia in most patients.

Amiodarone IV is a reasonable alternative, and is generally preferred over procainamide when left ventricular function is significantly reduced or heart failure is present.

Lidocaine IV is occasionally effective, in a minority of cases, and is a further alternative when procainamide and amiodarone are not options.

Move to synchronized cardioversion at any point if the patient becomes hemodynamically unstable, or electively if drug therapy is ineffective or not preferred.

Polymorphic VT / torsades de pointes

If the patient is pulseless, treat exactly as VF — immediate defibrillation and CPR; magnesium and cause-correction come after return of spontaneous circulation.

1st line, if a pulse is present magnesium sulfate 1-2 g IV, and simultaneously identify and stop any QT-prolonging drug and correct hypokalemia/hypomagnesemia.^[2]

Do not give a standard Class Ia or Class III antiarrhythmic — procainamide, sotalol, quinidine, or amiodarone — for torsades de pointes; these drugs further prolong the QT interval and can worsen the arrhythmia. This is the single most important distinction between managing monomorphic VT and managing torsades de pointes.

Pause-dependent or bradycardia-associated torsades — use isoproterenol or temporary overdrive pacing to increase the heart rate and shorten the QT interval while the underlying cause is corrected.

Chronic secondary prevention

1st line implantable cardioverter defibrillator for most patients with a history of cardiac arrest, VF, or sustained VT not due to a reversible cause — ICD therapy is superior to drug therapy alone for preventing sudden death in this population.^[1]

Foundational beta-blocker therapy for essentially all patients in whom drug therapy is used, whether or not an ICD is also present; for electrical storm specifically, propranolol has shown faster storm termination than metoprolol in a randomized trial.^[6]

Amiodarone or sotalol can be added to beta-blocker therapy to reduce the frequency of ICD shocks, but are adjuncts rather than substitutes for an ICD when ICD criteria are met.

Catheter ablation is preferred first-line therapy for patients with a structurally normal heart, and is a first-line alternative — not just a rescue option — alongside beta-blocker therapy for selected patients with ischemic cardiomyopathy and VT.^[7]^[8]

Non-Pharmacologic Treatment

Immediate CPR and defibrillation remain the primary, life-saving therapy for pulseless VT/VF — no medication replaces this.
Synchronized cardioversion — a synchronized biphasic shock is usually effective for hemodynamically unstable VT with a pulse.
Implantable cardioverter defibrillator (ICD) — effective at terminating VT/VF episodes and reduces mortality compared with antiarrhythmic drug therapy alone in patients who meet criteria, though it does not itself prevent arrhythmia recurrence.^[9]
Catheter ablation — first-line for structurally normal hearts, and an effective first-line alternative to escalating antiarrhythmic drug therapy for selected patients with ischemic cardiomyopathy and VT, generally comparable to amiodarone and superior to other drugs such as sotalol.^[7]
Stereotactic cardiac radioablation — a largely investigational, not widely available technique reserved as a last resort for VT refractory to other treatment options.
Temporary transvenous or transcutaneous overdrive pacing — for pause-dependent or bradycardia-associated torsades de pointes, while the underlying cause is corrected.
Correction of electrolyte abnormalities (potassium, calcium, magnesium) — a core, non-drug intervention in every ventricular arrhythmia presentation.
Identification and discontinuation of any offending QT-prolonging medication.
Genetic counselling and first-degree family member screening when a heritable arrhythmia syndrome (long QT syndrome, Brugada syndrome, catecholaminergic polymorphic VT) is suspected or confirmed.

Pharmacologic Treatment Options

Drug / intervention	Role	Dose / use	Important adverse effects	Teaching points
Amiodarone (IV) Preferred	Pulseless VT/VF (cardiac arrest) and hemodynamically stable monomorphic VT	Arrest: 300 mg IV/IO bolus, may repeat 150 mg IV/IO. Stable VT: 150 mg IV over 10 min, then a tapering infusion.	Hypotension (especially with rapid infusion), bradycardia, phlebitis	Give through a central line where possible; give IV rather than IO when both are available, since IO administration may blunt efficacy.
Lidocaine (IV, antiarrhythmic) Alternative	Alternative to amiodarone in pulseless VT/VF	1-1.5 mg/kg IV/IO bolus; may repeat 0.5-0.75 mg/kg to a total of 3 mg/kg	CNS toxicity (tremor, confusion, seizures) at high levels; hypotension is uncommon	Reasonable when amiodarone is unavailable or contraindicated; reduce the dose in hepatic impairment, heart failure, or shock.
Procainamide (IV) Preferred	Hemodynamically stable monomorphic VT	100 mg IV every 5 minutes (rate 50 mg/min or less) to 1 g total, then an infusion of 2-6 mg/minute	Hypotension, QRS/QT widening	Indicated for monomorphic VT specifically — do not use for torsades de pointes.
Magnesium sulfate (IV) Preferred	Torsades de pointes, first-line	1-2 g IV push if pulseless, or 1-2 g IV over 5-60 minutes with a pulse	Flushing, hypotension	Give regardless of the measured serum magnesium level; not effective for monomorphic VT.
Isoproterenol Special situation	Pause-dependent or bradycardia-associated torsades, bridge to pacing	IV infusion titrated to increase heart rate and shorten the QT interval	Tachyarrhythmia, hypotension or hypertension	A temporizing measure while arranging overdrive pacing and correcting the underlying cause.
Sotalol Alternative	Chronic secondary prevention, adjunct or alternative to amiodarone	80 mg PO twice daily initial, titrate every 2-3 days to 160-320 mg/day	Torsades de pointes — its own major proarrhythmic risk — plus bradycardia	Must be initiated in hospital with rhythm monitoring; never used for torsades de pointes itself.
Propranolol (IV) Preferred	IV beta-blockade for electrical storm	Per institutional IV protocol, titrated to rhythm and rate response	Bradycardia, hypotension, bronchospasm	Some evidence favors propranolol over metoprolol specifically for terminating electrical storm.
Metoprolol Preferred	Foundational chronic beta-blocker for secondary prevention	25-50 mg PO twice daily initial, titrated to 100-200 mg/day in divided doses	Bradycardia, fatigue, hypotension	Recommended for essentially all patients on drug therapy, with or without an ICD.
Mexiletine Special situation	Refractory electrical storm, add-on last resort	600-900 mg/day PO in divided doses	CNS effects (tremor, dizziness) are common	Add cautiously only when a beta-blocker plus amiodarone has failed; entirely empiric use.

Special Populations

Pregnancy

Manage a pulseless or hemodynamically unstable ventricular arrhythmia in pregnancy with the same urgency and the same defibrillation/cardioversion-first approach as in a non-pregnant patient — maternal resuscitation is the priority, and defibrillation is safe throughout pregnancy. Beta-blockers are the preferred chronic antiarrhythmic in pregnancy. Amiodarone crosses the placenta and can cause fetal or neonatal thyroid dysfunction, so it is reserved for pregnancy only when a life-threatening arrhythmia leaves no safer alternative — this reservation never delays its use during an actual cardiac arrest or hemodynamically unstable VT. An ICD, when indicated, is safe to implant during pregnancy and should not be withheld.

Breastfeeding

A single emergency antiarrhythmic dose given during resuscitation or acute stabilization is not a reason to withhold or delay breastfeeding once the mother has recovered, though interruption for several half-lives is reasonable after a large amiodarone dose given its very long half-life. Beta-blockers (metoprolol, propranolol) are compatible with breastfeeding. Sotalol is excreted into breast milk at higher concentrations than most beta-blockers — monitor the infant for bradycardia or poor feeding if sotalol is continued during breastfeeding.

Pediatrics

Ventricular tachyarrhythmias in children without structural heart disease more often reflect an inherited channelopathy (long QT syndrome, catecholaminergic polymorphic VT) than acquired coronary disease, and pediatric dosing for the antiarrhythmics in this chapter should be directed by pediatric cardiology/electrophysiology specialists rather than extrapolated from adult doses. Beta-blocker therapy and avoidance of QT-prolonging drugs remain foundational in pediatric long QT syndrome specifically.

Renal impairment

Sotalol is renally cleared and requires interval adjustment — every 24 hours for creatinine clearance 30-60 mL/min, every 36-48 hours for creatinine clearance 10-30 mL/min, and individualized dosing below that. Procainamide excretion is also delayed in renal impairment, requiring reduced frequency of administration and closer plasma-level monitoring. Magnesium sulfate should not exceed 20 g in any 48-hour period in significant renal impairment, with close serum magnesium monitoring.

Hepatic impairment

Lidocaine clearance depends on hepatic blood flow and is reduced in hepatic impairment and heart failure — reduce both the bolus and the infusion dose. Amiodarone can itself cause hepatotoxicity and requires baseline and periodic liver enzyme monitoring regardless of baseline hepatic status.

Older adults

Age over 65-67 is itself an independent risk factor for torsades de pointes — use extra caution with any QT-prolonging drug in this population. Start antiarrhythmics at the lower end of the dosing range and titrate more slowly, reflecting the higher likelihood of reduced hepatic, renal, or cardiac function and of interacting medications.

Monitoring & Follow-Up

Acute / in-hospital

Continuous ECG and blood pressure monitoring during any IV antiarrhythmic infusion; QRS width and PR interval before each procainamide dose; QTc after any magnesium/isoproterenol adjustment; serum potassium and magnesium, targeting potassium over 4.5 mEq/L and magnesium over 2 mg/dL in patients being treated for or at risk of torsades de pointes.

Chronic secondary prevention

ICD device interrogation per the device clinic schedule; amiodarone-specific monitoring (thyroid function, liver enzymes, chest imaging, ophthalmologic exam) if used chronically; sotalol QTc and renal function at initiation and with dose changes; resting heart rate and blood pressure on chronic beta-blocker therapy.

Assessing a patient who needs a QT-prolonging medication

Community and hospital pharmacists are often the first to catch a risky combination of QT-prolonging drugs. Before dispensing or recommending any QT-prolonging medication in a patient with 1 or more torsades de pointes risk factors: confirm the drug is genuinely necessary and cannot be swapped for a non-QT-prolonging alternative; ask about a personal or family history of ventricular arrhythmia, congenital long QT syndrome, syncope, or sudden death, and avoid QT-prolonging drugs altogether in confirmed congenital long QT syndrome; review the patient's other medications and conditions for additional risk factors or impaired drug metabolism; use the lowest effective dose; and counsel the patient to report palpitations, dizziness, or fainting, and to report any illness or new medication — especially a diuretic — that could cause hypokalemia.^[2]

Consult a current, regularly updated QT-drug reference, such as CredibleMeds, when uncertain whether a specific medication carries a meaningful QT-prolongation risk.^[10]

Using 2 or more QT-prolonging medications together does not automatically cause dangerous QT prolongation or arrhythmia, and necessary medications should not be withheld purely out of fear of QT prolongation once the patient has been properly risk-assessed.^[2]

Treatment Failure / Next Step

VT/VF recurs despite an ICD in place: assess for reversible triggers (recurrent ischemia, electrolyte disturbance, a new interacting or QT-prolonging medication), optimize beta-blocker and any adjunct antiarrhythmic therapy, and refer for catheter ablation.
Electrical storm resistant to a beta-blocker plus amiodarone: consider cautiously adding a Class I agent such as mexiletine, or quinidine (available only through the Health Canada Special Access Program), as an entirely empiric last resort, ensure adequate sedation, and pursue urgent ablation or mechanical circulatory support referral.
Torsades de pointes recurs despite magnesium: re-check and correct potassium and magnesium, confirm every QT-prolonging drug has actually been stopped, and add isoproterenol or temporary overdrive pacing, particularly if the pattern is pause-dependent or bradycardia-associated.
QTc continues to rise on a medication that is still judged necessary: reduce the dose, switch to a non-QT-prolonging alternative if one exists, or discontinue the drug — reassess the overall risk picture rather than continuing unchanged.
Suspected inappropriate ICD shocks: arrange device interrogation to distinguish a misclassified supraventricular arrhythmia from true recurrent VT, and adjust device programming or antiarrhythmic therapy accordingly.

Common Errors to Avoid

Treating torsades de pointes with a standard Class Ia or Class III antiarrhythmic (procainamide, sotalol, quinidine, amiodarone) — these further prolong the QT interval and can worsen torsades rather than treat it.
Reaching for procainamide, sotalol, or a beta-blocker as primary therapy for shock-refractory pulseless VF/VT — current AHA guidance considers their benefit uncertain in that specific scenario; amiodarone or lidocaine are the appropriate choices.^[4]
Giving amiodarone intraosseously when IV access is available — IV administration is preferred, since the IO route may blunt efficacy.^[4]
Forgetting to identify and stop the offending QT-prolonging drug(s) as part of torsades de pointes management — magnesium alone does not fix a persistent drug-induced trigger.
Missing hypokalemia or hypomagnesemia correction while treating torsades de pointes.
Withholding a genuinely necessary QT-prolonging medication purely out of fear, once the patient has been properly risk-assessed.
Assuming a wide-complex tachycardia in an older patient, or a patient with known structural heart disease, is supraventricular with aberrancy by default — treat as VT until proven otherwise.
Delaying synchronized cardioversion in unstable VT to try a drug first.
Relying on antiarrhythmic drug therapy alone for long-term secondary prevention in a patient with left ventricular dysfunction who meets ICD criteria — drug therapy is an adjunct to, not a substitute for, the ICD in this population.
Missing a genetic testing/electrophysiology referral for a young patient with unexplained VT/VF or a family history of sudden death.

Clinical Decision Algorithm

Pulseless VT or VF (cardiac arrest)

Cardiac arrest with pulseless VT or VF on the monitor

Start high-quality CPR; defibrillate immediately (unsynchronized shock)

Resume CPR; give epinephrine per ACLS protocol; defibrillate again every 2 minutes as indicated

Shock-refractory after the 3rd shock

Give amiodarone 300 mg IV/IO bolus (may repeat 150 mg IV/IO); lidocaine 1-1.5 mg/kg IV/IO is a reasonable alternative^[4]

Return of spontaneous circulation

Post-arrest care: 12-lead ECG, identify and treat the cause, consider continuing the effective antiarrhythmic as an infusion, arrange ICD/EP evaluation

Hemodynamically stable monomorphic VT

Sustained monomorphic VT confirmed, patient has a pulse

Hemodynamically unstable (hypotension, altered consciousness, ischemic chest pain, pulmonary edema)

Immediate synchronized cardioversion — do not trial a drug first

Hemodynamically stable

Procainamide IV (1st line), or amiodarone IV (preferred if reduced LV function or heart failure)

Arrhythmia terminates

Monitor; arrange ICD/EP evaluation for chronic secondary prevention

Persists, or patient becomes unstable

Proceed to synchronized cardioversion

Polymorphic VT / torsades de pointes

Polymorphic VT confirmed

Pulseless

Treat exactly as VF — immediate defibrillation and CPR

Pulse present

Magnesium sulfate 1-2 g IV; identify and stop any QT-prolonging drug; correct potassium/magnesium

Do not give a standard Class Ia/III antiarrhythmic (procainamide, sotalol, quinidine, amiodarone) — this can worsen torsades de pointes

Pause-dependent or bradycardia-associated

Isoproterenol or temporary overdrive pacing while the cause is corrected

Resolves with magnesium and cause correction

Monitor QTc; arrange EP/genetics referral if no clear acquired cause is found

Assessing a patient who needs a QT-prolonging medication

A patient needs a medication known to prolong the QT interval

Confirm the drug is genuinely necessary and cannot be swapped for a non-QT-prolonging alternative

Ask about personal/family history of ventricular arrhythmia, congenital long QT syndrome, syncope, or sudden death

Confirmed congenital long QT syndrome

Avoid QT-prolonging drugs; use a non-QT-prolonging alternative

No congenital long QT syndrome

Review other medications/conditions for additional torsades de pointes risk factors; correct hypokalemia/hypomagnesemia first

Use the lowest effective dose; consider baseline and follow-up ECG if the baseline QTc is already prolonged

Counsel the patient to report palpitations, dizziness, or fainting, and any new illness or medication that could cause hypokalemia

Drug Tables

How to use this table: Doses are adult doses and require patient-specific confirmation, including renal/hepatic adjustment. Select any drug name to open its complete Pharmasist Drug Database page.

Immediate therapy for pulseless VT/VF (cardiac arrest)

Given only after CPR and defibrillation have started — never before the first shock. Current AHA guidance considers procainamide, sotalol, and beta-blockers of uncertain benefit specifically for VF/pulseless VT unresponsive to defibrillation, so they are not used in this scenario even though they have established roles elsewhere in this chapter.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Amiodarone (IV)	Initial bolus: 300 mg IV/IO Repeat bolus if needed: 150 mg IV/IO	Hypotension (especially with rapid administration), bradycardia, phlebitis	Additive bradycardia/AV block with other AV-nodal-blocking drugs	Give IV rather than IO when both are available — IO administration may blunt efficacy. Likely the most effective agent for electrical storm.
Lidocaine (IV, antiarrhythmic)	Initial bolus: 1-1.5 mg/kg IV/IO Repeat bolus: 0.5-0.75 mg/kg IV/IO, to a total of 3 mg/kg	CNS toxicity (tremor, confusion, seizures) at high levels; hypotension is uncommon	Additive cardiac depression with amiodarone or other Class I antiarrhythmics	Reasonable alternative to amiodarone; effective in a minority of cases of sustained monomorphic VT specifically.

Hemodynamically stable monomorphic VT

Not for pulseless arrest, and not for polymorphic VT/torsades de pointes.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Procainamide (IV)	IV loading, direct injection: 100 mg every 5 minutes, rate 50 mg/min or less, to 1 g total IV loading, alternative method: 500-600 mg infused over 25-30 minutes IV maintenance infusion: 2-6 mg/minute Weight-based alternative loading: 10-15 mg/kg IV over 30-45 minutes	Hypotension (especially with rapid infusion), QRS/QT widening, lupus-like syndrome with prolonged oral use	Additive QT prolongation with other Class Ia/III agents or other QT-prolonging drugs	Indicated for monomorphic VT specifically; stop if the QRS widens more than 50%, blood pressure falls more than 15 mmHg, or a total of 1 g has been given.
Amiodarone (IV, stable VT)	Rapid loading infusion: 150 mg over 10 minutes Slow loading infusion: 360 mg over the next 6 hours Maintenance infusion: 540 mg over the next 18 hours	Hypotension, bradycardia, phlebitis	Additive bradycardia/AV block with other AV-nodal-blocking drugs	Preferred over procainamide when LV function is significantly reduced or heart failure is present.

Polymorphic VT / torsades de pointes

A distinct entity from monomorphic VT — standard Class Ia/III antiarrhythmics are not used here and can worsen the arrhythmia.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Magnesium sulfate (IV)	Pulseless (cardiac arrest): 1-2 g IV/IO push With a pulse: 1-2 g IV over 5-60 minutes, then 0.5-1 g/hour infusion if recurrent	Flushing, hypotension (especially with rapid non-arrest administration)	Additive CNS/neuromuscular depression with other depressants; caution with calcium channel blockers	Give regardless of the measured serum magnesium level; not effective for monomorphic VT.
Isoproterenol	IV infusion: Titrated to increase heart rate and shorten the QT interval	Tachyarrhythmia, hypotension or hypertension, angina in patients with coronary artery disease	Sotalol and other beta-blockers antagonize isoproterenol's effect	A temporizing measure for pause-dependent or bradycardia-associated torsades while arranging overdrive pacing and correcting the cause.

Chronic secondary prevention

Beta-blockers are foundational for essentially all patients on drug therapy; amiodarone, sotalol, and mexiletine are adjuncts, not substitutes for an ICD when ICD criteria are met.

Drug	Dosage	Adverse effects	Drug interactions	Comments
Metoprolol	Oral: 25-50 mg PO twice daily initial, titrated to 100-200 mg/day in divided doses	Bradycardia, hypotension, fatigue	Additive bradycardia with digoxin, calcium channel blockers, amiodarone	Especially useful for exercise-, stress-, or ischemia-induced VT.
Atenolol	Oral: 25 mg PO once daily initial, usual maintenance 50 mg once daily, maximum 100 mg once daily	Bradycardia, hypotension, fatigue	Additive bradycardia with digoxin, calcium channel blockers, amiodarone	Longer half-life allows once-daily dosing.
Bisoprolol	Oral: 2.5-5 mg PO once daily initial, titrated to a maximum of 10 mg once daily	Bradycardia, hypotension, fatigue	Additive bradycardia with digoxin, calcium channel blockers, amiodarone	Longer half-life allows once-daily dosing.
Propranolol (IV, electrical storm)	IV: Per institutional protocol, titrated to response	Bradycardia, hypotension, bronchospasm (non-selective)	Additive bradycardia with digoxin, calcium channel blockers, amiodarone	Some evidence favors propranolol over metoprolol specifically for terminating electrical storm.
Amiodarone (oral)	Loading dose: 800-1600 mg/day PO for 7-10 days Maintenance dose: 200-400 mg/day PO	Pulmonary, thyroid, hepatic, ophthalmologic, and dermatologic toxicity with long-term use	Reduce digoxin dose by 50%; reduces warfarin/quinidine/procainamide clearance; additive bradycardia with beta-blockers/calcium channel blockers	Likely the most effective antiarrhythmic for preventing recurrence, but requires extensive long-term monitoring; less effective than an ICD at preventing sudden death.
Sotalol	Initial: 80 mg PO twice daily Usual maintenance: 160-320 mg/day PO, divided twice daily Refractory, life-threatening arrhythmia: Up to 480-640 mg/day PO, only when benefit clearly outweighs proarrhythmic risk	Torsades de pointes — its own major proarrhythmic risk — plus bradycardia and fatigue	Additive QT prolongation with other QT-prolonging drugs; additive bradycardia with digoxin/calcium channel blockers/other beta-blockers	Must be initiated and dose-increased only in hospital with rhythm monitoring; never used for torsades de pointes itself.
Mexiletine	Oral: 600-900 mg/day, in divided doses	CNS effects (tremor, dizziness, nausea) are common and often dose-limiting	Phenytoin and rifampin may reduce mexiletine levels	Rarely used as monotherapy; added empirically, only as a last resort, to a beta-blocker plus amiodarone for refractory electrical storm.
Quinidine	Oral: 800-1600 mg/day, sulfate equivalent	GI intolerance (common), fever, thrombocytopenia (rare), torsades de pointes	Reduces digoxin clearance; inhibits CYP2D6 and P-glycoprotein, many interactions	Available in Canada only through the Health Canada Special Access Program; used only as an empiric last-resort addition for refractory electrical storm, cautiously combined with a beta-blocker plus amiodarone or with mexiletine.

QT-interval-prolonging drug classes

Medications are the most common cause of acquired QT prolongation. This is a reference list of drug classes commonly associated with QT prolongation, not a treatment table — consult a current, regularly updated QT-drug list (e.g., CredibleMeds) for a complete inventory.

Class	Examples
Antiarrhythmics	Amiodarone, disopyramide, flecainide, ibutilide, procainamide, quinidine, sotalol
Antibiotics (quinolone, macrolide)	Azithromycin, ciprofloxacin, clarithromycin, erythromycin
Antidepressants	Citalopram; tricyclic antidepressants such as amitriptyline carry a higher risk in older adults
Antiemetics	Domperidone, ondansetron
Antifungals (azole)	Fluconazole, itraconazole
Antihistamines	Diphenhydramine; hydroxyzine rarely at high doses with other risk factors present
Antipsychotics	Typical agents (e.g., haloperidol, thioridazine) and atypical agents (e.g., olanzapine, quetiapine, risperidone)
Chemotherapy agents	Oxaliplatin; small-molecule inhibitors including arsenic trioxide, CDK4/6 inhibitors, panobinostat, and tyrosine kinase inhibitors
General anesthetics	Propofol, sevoflurane
Opioid analgesic	Methadone

Evidence note: Drug inventory, dosing, adverse effects, and comments reflect real Canadian product-labelled dosing (Health Canada product monographs), cross-checked against current AHA/ACC/HRS guidance^[1] and current AHA resuscitation guidance^[4].

References

2017 AHA/ACC/HRS Guideline for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death — Circulation, American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society (Al-Khatib SM, Stevenson WG, Ackerman MJ, et al.). Circulation 2018;138(13):e272-e391
Prevention of torsade de pointes in hospital settings: a scientific statement from the American Heart Association and the American College of Cardiology Foundation — Journal of the American College of Cardiology (Drew BJ, Ackerman MJ, Funk M, et al.). J Am Coll Cardiol 2010;55(9):934-947
2022 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death — European Heart Journal, European Society of Cardiology (Zeppenfeld K, Tfelt-Hansen J, de Riva M, et al.). Eur Heart J 2022;43(40):3997-4126
2025 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care — Part 9: Adult Advanced Life Support — Circulation, American Heart Association. Circulation 2025
Amiodarone, lidocaine, or placebo in out-of-hospital cardiac arrest — New England Journal of Medicine, Resuscitation Outcomes Consortium Investigators (Kudenchuk PJ, Brown SP, Daya M, et al.). N Engl J Med 2016;374(18):1711-1722
Propranolol versus metoprolol for treatment of electrical storm in patients with implantable cardioverter-defibrillator — Journal of the American College of Cardiology (Chatzidou S, Kontogiannis C, Tsilimigras DI, et al.). J Am Coll Cardiol 2018;71(17):1897-1906
Catheter ablation or antiarrhythmic drugs for ventricular tachycardia — New England Journal of Medicine (Sapp JL, Tang ASL, Parkash R, et al.). N Engl J Med 2025;392(8):737-747
2020 Canadian Cardiovascular Society/Canadian Heart Rhythm Society Position Statement on the Management of Ventricular Tachycardia and Fibrillation in Patients With Structural Heart Disease — Canadian Journal of Cardiology (Deyell MW, AbdelWahab A, Angaran P, et al.). Can J Cardiol 2020;36(6):822-836
A comparison of antiarrhythmic-drug therapy with implantable defibrillators in patients resuscitated from near-fatal ventricular arrhythmias — New England Journal of Medicine, Antiarrhythmics versus Implantable Defibrillators (AVID) Investigators. N Engl J Med 1997;337(22):1576-1583
QTdrugs List — CredibleMeds, AZCERT (Woosley RL, Heise CW, Gallo T, et al.). CredibleMeds.org, AZCERT Inc.

Professional reference only. Apply clinical judgment and verify patient-specific decisions against current authoritative guidance and product information.