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Acquired long QT for ECT29-year-old woman, 55 kg, for her first ECT in a remote psychiatric unit

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Know this first

  • Torsades risk rises when QTc exceeds 500 ms with bradycardia.
  • Acquired long QT: remove the QT drugs, correct potassium and magnesium; no beta-blocker.
  • Pulseless polymorphic VT needs an immediate unsynchronised shock.
  • Magnesium for torsades; overdrive pacing or isoprenaline if pause-dependent.

The patient

29-year-old woman, 55 kg, for her first ECT in a remote psychiatric unit. Severe depression on haloperidol and citalopram; eating poorly; fainted last week; climbs two flights unaided. ECG: QTc 520 ms. K+ 2.9 mmol/L, Mg 0.6 mmol/L. Vitals: BP 104/66, HR 58, SpO2 98%, RR 14.

The examiner asks

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  1. Consider

    What are your concerns?

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    • A 29-year-old with drug-induced long QT and low potassium, starting ECT in a remote unit. Patient
    • QTc 520 with a rate of 58 puts her at high torsades risk. Disease
    • Last week's faint may have been torsades; I take it seriously.
    • ECT gives a vagal phase with bradycardia, then a surge of hypertension and tachycardia. Surgery
    • Remote unit: full monitoring, a defibrillator and help must be there.

  2. Prepare

    Will you proceed today?

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    • Urgency: elective first ECT, so it can wait a day for correction. Stem trigger
    • Active cardiac condition? Yes: QTc 520 with a recent faint, possibly torsades. Disease
    • Risk score: no RCRI items, so RCRI 0.
    • Functional capacity: two flights unaided, over 4 METs.
    • Decision: not today; correct her K and Mg, psychiatry reviews her QT drugs, repeat ECG first.
    • Give potassium by pump, 20–40 mEq IV over 30 minutes, with ECG monitoring.
    • Magnesium sulfate by infusion, 1–2 g over 15 minutes.

  3. Plan

    How do you anaesthetise her when ready?

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    • Pads on, magnesium and isoprenaline in the unit before we start. (Disease)
    • Glycopyrrolate 0.1–0.2 mg IV to blunt the vagal slowing.
    • Methohexital 1–1.5 mg/kg and suxamethonium 0.75–1.5 mg/kg.
    • No beta-blocker for the ECT surge; slowing her heart lengthens QT.
    • Dexamethasone 4–10 mg for nausea, not ondansetron or droperidol, which lengthen QT.

  4. Crisis

    After the stimulus, she develops polymorphic VT with a twisting axis and no pulse. What do you do?

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    • Adult arrest, shockable: pulseless polymorphic VT after the stimulus, in a woman with QTc 520. (Crisis)
    • Pads are on: unsynchronised shock now, at the maker's dose or maximum if unknown; then CPR.
    • Polymorphic VT can't be synchronised, so it must be unsynchronised.
    • Her torsades branch: magnesium sulfate 1–2 g IV over 5 minutes.
    • Initial shocks have failed: adrenaline 1 mg, then every 3–5 minutes.
    • Her reversible causes: potassium 2.9 and magnesium 0.6, so potassium 20–40 mEq over 3–10 minutes.
    • No amiodarone; if it recurs after pauses, overdrive pacing, or isoprenaline 2 mcg/min until pacing is ready.

Fatal mistakes

  • Amiodarone for torsades.
  • A synchronised shock for pulseless polymorphic VT.
  • No defibrillator in the ECT unit.
  • Proceeding with potassium at 2.9.

Checked against: AHA guidelines: adult advanced life support (2025) · Miller 10e · Barash 9e · Stoelting 8e

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