Drug-Induced Cardiac Disease- QT Prolongation and TdP Flashcards
QTc prolongation increases the risk for what?
TdP
Does all QT prolongation lead to TdP?
NO
Normal QTc values for men
<470ms
Normal QTc values for women
<480ms
How does TdP develop (in terms of the QT interval chart thing)
Increase in positive ions (K+, Ca 2+, Na+ abnormalities) leads to an extension of the plateau and depolarization phases
Drug-induced QT prolongation criteria
QTc ≥500ms OR QTc of ≥60ms from the patient’s baseline
TdP risk in terms of QTc prolongation
The risk increases 5-7% exponentially for every 10ms the QTc extends
Medications that prolong the QT interval
Antiarrhythmics (Class III drugs- amiodarone, sotalol, dofetilide)
Antibiotics (fluoroquinolones, macrolides)
Antipsychotics (FGAs > SGAs)
Antidepressants (citalopram, TCAs)
Antiemetics (ondansetron)
Antifungals (-azoles)
Why do Class III antiarrhythmics prolong the QT interval?
They’re potassium channel blockers, so they increase the amount of K+ in the body and prolong the QT interval
ABX most likely to prolong QT interval
Levofloxacin, ciprofloxacin, erythromycin, azithromycin
Citalopram’s QT prolongation risk
Dose-dependent, watch out in the elderly!
How else can drug-induced QT prolongation occur?
DDIs or altered organ function that may lead to impaired elimination or metabolism
Taking multiple medications that all prolong the QT interval- it’s an additive effect!
Non-modifiable risk factors for QT prolongation
> 65 years old
Female
Genetic predisposition
Cardiac disease
Modifiable risk factors for QT prolongation
Diuretic treatment
Electrolyte abnormalities
>1 QT-prolonging agent
Organ function
Approach to drug-induced QT prolongation
Avoid QTc interval prolonging drugs in patients with pretreatment intervals >450msec
Reduce dose or D/C prolonging agents if QTc increases >60msec from pretreatment value
D/C prolonging agent if QTc increases >500msec
Maintain K >4, Mg >2
Avoid concomitant administration of QTc prolonging drugs
Avoid use of QTc interval-prolonging drugs in patients with a history of drug-induced TdP
Goal in drug-induced TdP treatment
Speed the heart up to catch the next beat before arrhythmia and restore sinus rhythm
Patho behind the goal of drug-induced TdP treatment
QT prolongation is due to a long recovery time from a heartbeat, but when a beat comes in early when the heart is still recovering, that’s what causes the arrhythmia
Steps in treating drug-induced TdP
D/C offending agent(s)
Mg PUSH OR INFUSION!!!
Transcutaneous pacing
Isoproterenol infusion (or atropine or epinephrine)
How to choose between Mg push or infusion
Push: patient loses pulse, needs chest compressions or ALCS protocol will be initiated
IV: patient has a pulse, might be awake and talking to you. Administer over 10-15 minutes
When to switch from Mg IV infusion to push
If the patient loses their pulse
What else should you monitor during TdP treatment?
Electrolytes (especially K and Ca because Mg is replacing them)- draw labs immediately!
If at any point the patient becomes hemodynamically unstable, what should you do?
Cardioversion or defibrillation required, skip transcutaneous pacing and IV isoproterenol/atropine/epinephrine
CPR is started/about to start at this point too
