We obtain ECGs for a number of reasons in the ED, but in the pediatric ED, we often obtain them in the child who presents with a complaint related to syncope.  We have discussed syncope issues previously (Syncope, Hair-combing syncope, SVT, Heat Related Illness, and Prolonged QTc and Submersion Injuries).  Since syncope is commonly seen, let us make sure we know what to do when we see one of the potential items we are looking for on that 12-Lead ECG: Prolonged QTc.

QT Basics

• The QT segment:
  • Is the duration of the segment from the start of the Q wave to the END of the T wave.
  • It represents the period of ventricular depolarization and repolarization.
  • It is inversely proportional to the heart rate (shorter with faster heart rates).
• The QTc:
  • Represents the “corrected” value that would be seen with a heart rate of 60bpm.
  • If heart rate is between 60 and 100 bpm, you can use the actual QT measurement.
  • Allows for comparison and detection of risk for dysrhythmias.
  • Multiple formulas used to determine the QTc…
    • None are perfect and I’m not smart enough to recommend one over the other.
    • I generally use what the computer says– otherwise I ignore the computer reading.
• The QTc Values:
  • Normal for men = 350ms – 440ms
  • Normal for women and children = 350ms – 460ms
  • Risk for dysrhythmias is increased when >500ms

Prolonged QTc Causes

• Drugs
  • Too many to actually list here, but some commonly used Rx in Peds are:
    • Antimicrobials
      • Macrolides (Erythromycin, Clarithromycin, Azithromycin)
      • Fluoroquinolones (Levofloxacin, Gatifloxacin, Ciprofloxacin)
      • Antifungals -(Fluconazole, Itraconazole, Voriconazole)
      • Bactrim (another reason not to use bactrim)
    • Antipsychotics (Amitriptyline, Desipramine, Imipramine, Sertraline)
    • Sedatives (Chloral hydrate)
    • ONDANSETRON (I know we have discussed it’s value, but nothing is perfect)
• Electrolyte Issues
  • Hypokalemia
  • Hypocalcemia
  • Hypomagnesemia
• Congenital Long QT Syndrome
  • Rare, but real problem.
• Others
  • Hypothermia
  • Cardiac ischemia
  • Increased ICP

Why We Care

• Prolonged QTc can precipitate Torsade de Pointes.
• Your evaluation of the syncope patient will include this as a possible etiology of poor cerebral perfusion.
• Many times you will find a “bordeline” QTc prolongation (460 – 500 ms) and you will need to deal with that issue.
  • One study showed that 1/3 of pediatric patients with borderline QTc had normalization on follow-up.
  • Be careful not to get the families too crazy about the borderline QTc… but do ensure follow-up.

What to Do

• If ventricular ectopy is present (or Torsade de Pointes) – treat with Magnesium 25-50mg/kg.
• If noted on ECG, but stable, look for causes (check lytes and go over each drug they are on).
  • Always be mindful of the medications you prescribe!
  • Stop any potential offending agents!
• Ask family about any family history of sudden death or unexplained drowning.
• Ensure appropriate follow-up.

References