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