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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