QT - prolonged and short intervals

Prolonged QTc >440 msec

QT measured from beginning of QRS complex to end of T wave.

QT varies w/ HR, correct with Bazett formula: QTc = QT/√RR

Etiologies:

• • Hypokalemia, hypocalcemia, hypomagnesemia

  • Drugs:

    • Antiarrhythmics: Class IA and III

      • Class IA: Quinidine, procainamide, disopyramide

      • Class III: Bretylium, amiodarone, sotalol, ibitulide

    • Antimicrobials: Macrolides (Clarithromycin, erythromycin), FQ (gatifloxacin, levofloxacin), pentamidine, voriconazole, atovoquone, choroquine, amantadine, foscarnet.

    • Psychatric drugs: chlorpromazine, thioridazine, TCA, haloperidol

    • Other drugs: Cisapride, antiemetics (droperidol, 5-HT3 antagonists), methadone, alfuzosin

  • Autonomic dysfunction: Stroke, ICH, SAH, head trauma, CEA, neck dissection

  • Pericarditis, myocarditis, MI, LVH,

  • Hypothermia

  • Hypothyroidism

  • Sinus bradyarrhytmias, 3rd deg. HB

  • Idopathic, congenital (K/Na channelopathies, may be assoc w/ deafness)

Telemonitoring is required.

Short QT <300 msec: digitalis, hypercalcemia