Situation: A 72-year-old woman with chronic obstructive pulmonary disease (COPD) is admitted to the intensive care unit (ICU) with an exacerbation and started on noninvasive ventilation (NIV) by face mask. Her ordered oxygen saturation target is 88–92%. On day 2 she is receiving intravenous azithromycin, nebulized salbutamol (albuterol), and a corticosteroid. Results: potassium 3.2 mEq/L (normal 3.5–5.0 mEq/L), magnesium 1.3 mg/dL (laboratory normal 1.7–2.2 mg/dL), corrected QT interval 0.54 s. The monitor now shows runs of polymorphic ventricular tachycardia twisting around the baseline, each lasting 5–10 seconds; between runs she is awake with a pulse and a blood pressure of 108/64 mmHg. The physician has ordered each of the actions below. Which should the nurse carry out FIRST?

Runs of polymorphic ventricular tachycardia with a long QT interval are torsades de pointes, and intravenous magnesium sulfate is the immediate treatment that suppresses them. Correcting potassium and stopping QT-prolonging drugs are also needed, but they act more slowly or only prevent later episodes. She has a pulse and adequate blood pressure between runs, so electrical therapy is not the first step.

Clinical situation The monitor tracing shows polymorphic ventricular tachycardia that appears to twist around the isoelectric baseline, occurring in brief runs while the patient remains awake with a pulse and a stable blood pressure. The corrected QT interval is prolonged at 0.54 s, and both potassium and magnesium are low. This combination identifies the rhythm as torsades de pointes (TdP), a pause-dependent polymorphic VT driven by delayed ventricular repolarization ^[1][2].

Why magnesium comes first In acquired long QT with TdP, intravenous magnesium sulfate is the immediate pharmacologic intervention that suppresses the arrhythmia, even when the serum magnesium level is not markedly low ^[1][4]. Magnesium does not shorten the QT interval itself; rather, it stabilizes the myocardial membrane and reduces early afterdepolarizations that trigger the twisting runs ^[2]. Because the patient has a pulse and adequate perfusion between runs, the priority is pharmacologic termination of the electrical instability, not electrical cardioversion.

Role of the other ordered actions Potassium replacement is essential because hypokalemia prolongs repolarization and increases the risk of recurrent TdP, but potassium infusion acts more slowly than magnesium and is best used as an adjunct to correct the underlying substrate ^[1][4]. Holding azithromycin removes a QT-prolonging drug that blocks the rapid delayed rectifier potassium current (I_Kr), which is important for preventing further episodes, but it does not stop the runs that are already occurring ^[2]. Synchronized cardioversion is reserved for polymorphic VT with hemodynamic compromise; between runs this patient is awake with a blood pressure of 108/64 mmHg, so immediate electrical therapy is not indicated ^[1].

Why the rhythm is torsades de pointes TdP is a specific form of polymorphic VT that occurs in the setting of QT prolongation and often presents in self-limiting bursts, causing dizziness or syncope but sometimes degenerating into ventricular fibrillation ^[1]. The ECG hallmark is QRS complexes that appear to twist around the baseline, and the rhythm is typically pause-dependent, meaning it follows a long R-R interval ^[2]. Acquired QT prolongation in this patient is multifactorial: azithromycin blocks I_Kr, hypokalemia and hypomagnesemia further delay repolarization, and female sex is a recognized risk factor. ^[2]

Intervention	Mechanism	Timing in TdP management
IV magnesium sulfate	Suppresses early afterdepolarizations; membrane stabilization	First-line immediate treatment [1][4]
Potassium replacement	Corrects hypokalemia that prolongs repolarization	Adjunct; slower onset, prevents recurrence [1][4]
Hold azithromycin	Removes IKr-blocking drug that prolongs QT	Preventive; does not stop active runs [2]
Synchronized cardioversion	Electrical termination of unstable tachyarrhythmia	Only if hemodynamically unstable [1]

Watch out! Do not confuse synchronized cardioversion with defibrillation. Synchronized cardioversion delivers a shock timed to the QRS complex and is used for unstable tachyarrhythmias with a pulse; unsynchronized defibrillation is for pulseless VT or ventricular fibrillation. In TdP with a pulse, magnesium is given before electrical therapy ^[1].

Key point! The nurse should give IV magnesium sulfate first because it is the only intervention that immediately suppresses the active torsades de pointes runs while the patient remains hemodynamically stable. Potassium, drug withdrawal, and electrical therapy address the underlying cause or prevent recurrence but are not the priority for terminating the current arrhythmia ^[1][4].