What’s the best approach adjuvant therapy to defibrillation?
A 55-year-old male with a history of atrial fibrillation and sick sinus syndrome, for which he has a pacemaker and takes amiodarone, self-presents to an emergency department triage with weakness and palpitations.
Feeling nauseous, he took several leftover ondansetron pills and extra amiodarone without improvement. He loses consciousness just as telemetry leads are placed; their output is shown below. He is pulseless. Which of the following is the best adjuvant therapy to defibrillation?
- Amiodarone
- Epinephrine
- Lidocaine
- Magnesium
- Magnet placement on chest
Correct answer: D. Magnesium
The rhythm shown is a polymorphic ventricular tachycardia (PVT). This can be further categorized as torsades-de-pointes (TdP) if associated with a prolonged QT or as PVT with normal QT.
TdP, by association with a long QT interval, has a differential that includes all things that prolong the QT interval, such as congenital long QT and medications, the latter of which is probably what happened to this man. He had a long QT secondary to taking extra ondansetron and amiodarone, which led to an R-on-T phenomenon with his pacemaker, causing TdP. The best adjuvant therapy for TdP is high doses of magnesium, which shortens the QT interval.
Of note, causes of polymorphic ventricular tachycardia with normal QT include acute coronary syndrome, Brugada syndrome, electrolyte abnormalities and other causes.
Incorrect answer choices:
Both amiodarone (class III, Choice A) and lidocaine (class Ib, Choice C) are reasonable agents for typical ventricular tachycardia and not unreasonable to try in polymorphic ventricular tachycardia. However, the QT-prolonging medications suggest a long QT association with the tachycardia, favoring TdP, for which magnesium is best. Additionally, delivering more amiodarone would likely further prolong the QT interval. Lidocaine, in contrast, has been shown to decrease the QT interval that can occur with intubation but would still not be as effective as an adjuvant therapy.
Epinephrine (Choice B) is part of the pulseless ACLS algorithm, however, TdP is a specific rhythm that is best suited for specific therapy with magnesium.
Placing a magnet on the chest (Choice E) will increase the risk of R-on-T because it sends the pacemaker into VVO, pacing the ventricle, sensing the ventricle, but not responding to sensed QRS complexes. So the pacemaker will blindly pace at whatever rate was previously set. This will neither solve the PVT problem nor fix any underlying problem.
