Rapid Review·Cardiovascular
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Arrhythmias: Ventricular & Arrest
T1Must knowTorsades de Pointes
Focus on
Polymorphic VT on top of a long QT — the QRS twists around the baseline. Give IV magnesium even if the level is normal, stop the QT-prolonging drug, replete potassium, and pace or give isoproterenol if it is bradycardia-dependent; defibrillate if unstable. Know the drug list.
Key takeaways
What it is and what causes it
Torsades de pointes
a polymorphic ventricular tachycardia whose QRS complexes twist around the isoelectric line in cyclic, sinusoidal bursts.The danger
it can degenerate into ventricular fibrillation.The substrate is a long QT
congenital (Romano-Ward, Jervell and Lange-Nielsen: Long QT Syndrome) or acquired.Acquired causes
hypocalcemia, hypokalemia, hypomagnesemia, and QT-prolonging drugs.| Class | Drugs |
|---|---|
| Antiarrhythmics | Class Ia (quinidine, procainamide, disopyramide); class III (sotalol, dofetilide, ibutilide) |
| Antibiotics | Macrolides (erythromycin, azithromycin); fluoroquinolones (ciprofloxacin, levofloxacin) |
| Psychiatric | Haloperidol; tricyclic antidepressants |
| Others | Ondansetron; fluconazole; protease inhibitors (ritonavir, nelfinavir); methadone; thiazides; chloroquine |
Before a QT-prolonging drug
check the electrocardiogram (ECG) before intravenous haloperidol or another QT-prolonging drug.- Withhold the drug if the corrected QT is already prolonged (over 450 ms).
Diagnosis
Electrocardiogram
polymorphic ventricular tachycardia (VT) with complexes that twist around the baseline in bursts, as in the Torsades de pointes ECG.Torsades vs ventricular fibrillation
torsades still has an isoelectric line; ventricular fibrillation has none.Management
Stable
intravenous magnesium first line, to stabilize the myocardium and prevent recurrence.Unstable
defibrillation.Congenital long QT
prophylactic propranolol; a beta blocker limits the exertional heart rate and shortens the QT, and a pacemaker is added in some.Prevention
avoid electrolyte disturbances, vigorous exercise, and potassium-channel-blocking drugs.A patient on azithromycin and ondansetron develops palpitations; the ECG shows a polymorphic wide-complex tachycardia twisting around the baseline, and she is still stable. What is the rhythm and the first-line drug?
Torsades de pointes from QT-prolonging drugs. Give intravenous magnesium; stop the drugs and correct potassium, magnesium and calcium. Defibrillate if she becomes unstable.
How it's tested
A woman on haloperidol and levofloxacin with a potassium of 3.0 has recurrent syncope; the monitor shows a polymorphic VT that twists around the baseline; BP is 100/60: torsades de pointes — IV magnesium, replete potassium, stop both drugs.
Same rhythm, pulseless: defibrillate.
Torsades that keeps recurring after magnesium, with a sinus rate of 45: overdrive pacing or isoproterenol to shorten the QT.
Which antiarrhythmic must not be given for torsades: amiodarone (and procainamide, sotalol) — they prolong the QT.
What to check before giving IV haloperidol to an agitated patient: a baseline ECG; withhold if QTc > 450–500 ms.
Go deeper
Guidelines: 2017 AHA/ACC/HRS Ventricular Arrhythmias and Sudden Cardiac Death Guideline
Related Step 2 pages: Long QT Syndrome, Ventricular Tachycardia, Antiarrhythmic Drugs, Cardiac Arrest & ACLS
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