QTc prolongation from psychiatric medications

What QTc prolongation is

The QT interval on the ECG measures the time from ventricular depolarization (start of QRS) to completion of ventricular repolarization (end of T wave). It shortens with faster heart rates, so it is typically corrected for rate as QTc using Bazett's or Fridericia's formula.

QTc prolongation reflects delayed repolarization, most often from blockade of the potassium channel encoded by hERG (KCNH2). Drugs that block hERG delay the outward potassium current that ends the cardiac action potential, prolonging the QT interval.

Clinical thresholds:

• Normal QTc: below 440 ms in men, below 460 ms in women
• Borderline: 440 to 500 ms
• Prolonged: above 500 ms (clinically meaningful risk of torsades)
• Increase of more than 60 ms from baseline is also considered concerning even if absolute QTc remains below 500 ms

The clinical consequence of concern is torsades de pointes, a polymorphic ventricular tachycardia that can degenerate to ventricular fibrillation and cause sudden cardiac death. Torsades is rare but potentially fatal. The absolute risk in any individual patient on a QT-prolonging drug is low.

Psychiatric drugs and QT

Highest QT risk (usually contraindicated with other QT drugs, or requires careful monitoring):

• Thioridazine (Mellaril): withdrawn in many markets, restricted use elsewhere. Black box warning.
• Mesoridazine: withdrawn.
• Pimozide: restricted use, requires baseline ECG.
• Haloperidol IV at high doses: substantial QT prolongation, particularly with rapid escalation for delirium or agitation.
• Ziprasidone (Geodon): real but modest QT effect. Requires food for absorption (which some argue partly explains dropout).
• IV droperidol: FDA black box warning for QT.

Moderate QT risk:

• Citalopram (Celexa): FDA dose limit of 40 mg/day (20 mg in age above 60 or in poor CYP2C19 metabolizers) after 2011 safety communication.
• Escitalopram (Lexapro): less than citalopram, generally considered safer at standard doses.
• Tricyclic antidepressants: substantial QT effects, particularly at overdose. Amitriptyline, nortriptyline, imipramine, desipramine, doxepin all prolong QT.
• Chlorpromazine and other low-potency first-generation antipsychotics.
• Quetiapine: mild-moderate at standard doses; more concerning at high doses.
• Iloperidone (Fanapt): dose-related QT effect.
• Trazodone: mild-moderate.

Low or minimal QT risk:

• Sertraline: minimal.
• Fluoxetine: minimal at standard doses.
• Aripiprazole, brexpiprazole, cariprazine: minimal.
• Bupropion, mirtazapine: minimal.
• Vortioxetine, vilazodone: minimal.
• Lurasidone: minimal (unlike ziprasidone).
• Olanzapine, risperidone, paliperidone: mild.
• Clozapine: mild-moderate but concerning for other cardiac reasons (myocarditis, cardiomyopathy).

Non-psychiatric drugs that commonly combine with psychiatric drugs and add QT risk:

• Methadone: substantial QT effect, dose-dependent. Baseline ECG standard.
• Ondansetron and other 5-HT3 antagonists: dose-dependent.
• Fluoroquinolones (ciprofloxacin, levofloxacin, moxifloxacin).
• Azole antifungals (fluconazole).
• Macrolide antibiotics (azithromycin, erythromycin, clarithromycin).
• Antiemetics (droperidol, promethazine).
• Antiarrhythmics (amiodarone, sotalol, quinidine).

The full list at CredibleMeds.org (Arizona CERT) is the standard reference for QT-affecting drugs.

Risk factors that amplify QT risk

Individual drug risk is modified substantially by patient and situation factors:

• Hypokalemia: potassium below 3.5 mEq/L significantly increases torsades risk. Diuretics, GI losses, and eating disorders are common contributors.
• Hypomagnesemia: often coexists with hypokalemia. Magnesium below 1.5 mg/dL is concerning.
• Bradycardia: slower rate prolongs QT and increases arrhythmia risk.
• Female sex: baseline longer QTc, higher torsades risk with drugs.
• Congenital long QT syndrome: high absolute risk with any QT drug.
• Preexisting heart disease: structural heart disease, prior MI, heart failure.
• Advanced age: older adults have higher baseline QT and more comorbidity.
• Hepatic or renal impairment: reduced clearance of QT drugs.
• Overdose: TCAs and antipsychotics can cause severe QT and lethal arrhythmias at overdose doses.

Monitoring recommendations

Baseline ECG for patients starting:

• IV haloperidol at high doses (delirium protocols)
• Ziprasidone
• Citalopram at doses above 20 mg or in older adults
• TCAs at doses above 100 to 150 mg/day
• Any QT-prolonging drug in a patient with cardiac history, other QT drugs, or electrolyte disturbance
• Methadone

Follow-up ECG at 1 to 2 weeks after starting or after dose increases for the drugs above. Repeat if any electrolyte disturbance, new QT drug added, or symptoms develop.

Electrolyte monitoring in patients on QT drugs with any risk factor for electrolyte loss (diuretics, GI symptoms, eating disorders).

When QTc exceeds 500 ms: consider dose reduction, switching to a lower-QT drug, and correcting any electrolyte or contributing factor. Cardiology involvement often appropriate.

Common questions

Which antidepressant has the highest QT risk? Among modern antidepressants, citalopram carries the largest labeled QT concern (FDA 40 mg maximum). Tricyclics have substantial QT effects, particularly at overdose. Escitalopram, sertraline, fluoxetine, bupropion, mirtazapine, vortioxetine, and vilazodone are all lower risk. See the citalopram vs escitalopram comparison.

Should I get an ECG before starting an antidepressant? For low-risk drugs (sertraline, escitalopram, fluoxetine, bupropion, mirtazapine, vortioxetine) in patients with no cardiac history and no other QT drugs, routine baseline ECG is not required. For citalopram at doses above 20 mg in older adults, for TCAs, for patients with cardiac history or multiple QT drugs, yes.

Can I combine two QT-prolonging drugs? Sometimes, with monitoring. Combinations are common in real practice (methadone plus an SSRI, ondansetron plus quetiapine, ciprofloxacin plus haloperidol). ECG monitoring and electrolyte checks are appropriate. The absolute risk is low but not zero. Alternatives should be considered when possible.

Is aripiprazole safe from a QT standpoint? Yes, one of the safest antipsychotics for QT. Along with brexpiprazole, cariprazine, lurasidone, and lumateperone, aripiprazole has minimal QT effect at therapeutic doses.

What does torsades de pointes look like? Polymorphic ventricular tachycardia with characteristic "twisting" QRS morphology on ECG. Can be self-limited (patient may report brief palpitations, dizziness, or syncope) or degenerate to ventricular fibrillation and cardiac arrest. Any patient on QT drugs with syncope or unexplained palpitations warrants ECG evaluation.

How is torsades treated? IV magnesium sulfate 2 g bolus is first-line even if magnesium level is normal. Correction of any hypokalemia or bradycardia. Discontinuation of the offending drug. Overdrive pacing or isoproterenol for recurrent episodes. This is a cardiology and emergency medicine event.

Does quetiapine cause QT problems? Mild to moderate. At standard doses in patients without other risk factors, clinically significant QT effect is uncommon. At high doses (600 to 800 mg/day) or in combination with other QT drugs or in overdose, QT prolongation and rare torsades have been reported.

Sources

• FDA Drug Safety Communication: revised recommendations for Celexa (citalopram hydrobromide) related to a potential risk of abnormal heart rhythms with high doses. August 24, 2011.
• Beach SR, Celano CM, Sugrue AM, et al. QT prolongation, torsades de pointes, and psychotropic medications: a 5-year update. Psychosomatics. 2018;59(2):105-122.
• Wenzel-Seifert K, Wittmann M, Haen E. QTc prolongation by psychotropic drugs and the risk of Torsade de Pointes. Dtsch Arztebl Int. 2011;108(41):687-693.
• CredibleMeds.org, Arizona Center for Education and Research on Therapeutics. QTdrugs list, updated continuously.
• Ray WA, Chung CP, Murray KT, Hall K, Stein CM. Atypical antipsychotic drugs and the risk of sudden cardiac death. N Engl J Med. 2009;360(3):225-235.