Drug-induced QT Prolongation

T/F: all QT prolongation will lead to TdP if the patient has it long enough

false

what is the life-threatening polymorphic ventricular tachycardia called

Torsade de Pointe (TdP)

T/F: normal QT needs to be corrected for heart rate which gives it the name QTc

true

what is a normal QTc in men

< 470 ms

what is a normal QTc in women

< 480 ms

what portion of the ECG is elongated in QTc prolongation?

prolongs/extends the refractory period (plateau phase)

If the QT interval elongates too far, what can it cause?

TdP :(

What values for QTc demonstrate QTc prolongation?

a QTc >= 500 ms OR QTc of >= 60 ms from baseline

what are some common medication classes that cause QT interval prolongation?

Antiarrhythmics (amiodarone, sotalol, dofetilide), Antibiotics (fluoroquinolones, macrolides), Antipsychotics (class I worse than class II), Antidepressants (citalopram, TCAs), Antiemetics (ondansetron), and Antifungals (-azole antifungals)

non-modifiable risk factors that can lead to QT prolongation and TdP:

> 65 years old, female, genetic predisposition, and cardiac disease

modifiable risk factors that can lead to QT prolongation and TdP:

diuretic treatment, electrolyte abnormalities, > 1 QT-prolonging agent, organ function

T/F: You should avoid QTc interval prolonging drugs in patients with pretreatment intervals > 450 msec

True

Step 1 for treating drug-induced TdP

discontinue the offending agents that can potentially cause prolonged QT

Step 2 for treating drug-induced TdP

if the patient has no pulse give them a magnesium push; if the patient has a pulse give a magnesium infusion; Pay attention to other electrolytes too as K and Ca may need to be repleted

Step 3 for treating drug-induced TdP

transcutaneous pacing (similar to DCCV - provides shock to try and get back to sinus rhythm)

Step 4 for treating drug-induced TdP

Isoproterenol infusion (guideline recommended) if too expensive/not available - give epinephrine or atropine

if at any point in treating torsade de pointes the patient becomes hemodynamically unstable what is required to be done

Cardioversion or defibrillation

MOA of isoproterenol

stimulates beta-1 & 2 receptors resulting in increased HR and contractility, along with some vasodilation of peripheral vasculature

ADRs for isoproterenol

angina, chest pain

onset of isoproterenol

immediate

how is isoproterenol adminsitered

continuous infusion

monitoring for isoproterenol

HR, BP, and ECG