QT Prolongation

QT prolongation can cause a serious arrhythmia called torsades de pointes (TdP). Here are 3 steps for preventing TdP:

1. assess the patient:

   • Ask about history. Previous TdP and congenital long QT are major risk factors for TdP.
     Other risk factors include bradycardia, structural heart disease, electrolyte abnormalities, female gender, and older age
   • Ask about symptoms. Symptoms of TdP include heart palpitations and fainting.
     If you’re concerned, enquire about these symptoms at every refill
2. assess the drug:

   • Check the treatment. Macrolides and quinolones can cause TdP in higher risk patients.
     Safer options include beta lactams, cephalosporins and tetracyclins. Other drugs to watch are methadone, es/citalopram, ondansetron and antipsychotics. See crediblemeds.org for a full list
   • Check the dose. The risk of TdP tends to increase as higher doses are used (e.g., domperidone ≥30 mg/day).
     Make sure the patient doesn’t have any factors that can cause a higher than expected serum concentrations, such as a drug-drug interaction or renal impairment
   • Check the ECG. An ECG is appropriate if the patient has multiple risk factors for TdP and is prescribed a drug that prolongs the QT interval.
     Order an ECG at baseline and after 5 half-lives when the drug has reached steady state
3. take action:

   • Make a decision. Patients are at higher risk for TdP if the drug prolongs their QTc interval to >450 for males and >460 for females, or if it prolongs their QT interval by >60 msec.
     If this happens, stop the drug if possible. If not, decrease the dose