Drug-Induced Cardiac Disease- QT Prolongation and TdP

Question 1

QTc prolongation increases the risk for what?

Answer 1

TdP

Question 2

Does all QT prolongation lead to TdP?

Answer 2

NO

Question 3

Normal QTc values for men

Answer 3

<470ms

Question 4

Normal QTc values for women

Answer 4

<480ms

Question 5

How does TdP develop (in terms of the QT interval chart thing)

Answer 5

Increase in positive ions (K+, Ca 2+, Na+ abnormalities) leads to an extension of the plateau and depolarization phases

Question 6

Drug-induced QT prolongation criteria

Answer 6

QTc ≥500ms OR QTc of ≥60ms from the patient’s baseline

Question 7

TdP risk in terms of QTc prolongation

Answer 7

The risk increases 5-7% exponentially for every 10ms the QTc extends

Question 8

Medications that prolong the QT interval

Answer 8

Antiarrhythmics (Class III drugs- amiodarone, sotalol, dofetilide)
Antibiotics (fluoroquinolones, macrolides)
Antipsychotics (FGAs > SGAs)
Antidepressants (citalopram, TCAs)
Antiemetics (ondansetron)
Antifungals (-azoles)

Question 9

Why do Class III antiarrhythmics prolong the QT interval?

Answer 9

They’re potassium channel blockers, so they increase the amount of K+ in the body and prolong the QT interval

Question 10

ABX most likely to prolong QT interval

Answer 10

Levofloxacin, ciprofloxacin, erythromycin, azithromycin

Question 11

Citalopram’s QT prolongation risk

Answer 11

Dose-dependent, watch out in the elderly!

Question 12

How else can drug-induced QT prolongation occur?

Answer 12

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!

Question 13

Non-modifiable risk factors for QT prolongation

Answer 13

> 65 years old
Female
Genetic predisposition
Cardiac disease

Question 14

Modifiable risk factors for QT prolongation

Answer 14

Diuretic treatment
Electrolyte abnormalities
>1 QT-prolonging agent
Organ function

Question 15

Approach to drug-induced QT prolongation

Answer 15

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

Question 16

Goal in drug-induced TdP treatment

Answer 16

Speed the heart up to catch the next beat before arrhythmia and restore sinus rhythm

Question 17

Patho behind the goal of drug-induced TdP treatment

Answer 17

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

Question 18

Steps in treating drug-induced TdP

Answer 18

D/C offending agent(s)

Mg PUSH OR INFUSION!!!

Transcutaneous pacing

Isoproterenol infusion (or atropine or epinephrine)

Question 19

How to choose between Mg push or infusion

Answer 19

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

Question 20

When to switch from Mg IV infusion to push

Answer 20

If the patient loses their pulse

Question 21

What else should you monitor during TdP treatment?

Answer 21

Electrolytes (especially K and Ca because Mg is replacing them)- draw labs immediately!

Question 22

If at any point the patient becomes hemodynamically unstable, what should you do?

Answer 22

Cardioversion or defibrillation required, skip transcutaneous pacing and IV isoproterenol/atropine/epinephrine

CPR is started/about to start at this point too