Definition:Â prolonged QTc interval, calculated by Bazett’s formula: QTc = QT : sqr (previous RR interval). normal <440 ms (460 ms in women and children).
Congenital causes:Â
Jervell and Lange-Nielsen syndrome, Romano-Ward syndrome, idiopathic
Acquired causes:Â
metabolic – hypokalemia, hypomagnesemia, hypocalcacemia; drugs – quinidine, procaine, amiodarone, sotalol, erythromycin, terfenadine, haloperidol, TCA, risperidone, methadone, droperidol, organophosphates, or myocardial ischaemia, HIV, hypothermia
Diagnosis:
pQTS measured via Bazett’s formula, Torsades de pointes, T-wave alternans, syncope, family history
Treatment:
1. acute:Â haemodynamically unstable patient: DC 2 J/kg, MgSO4 (0.2 mmol/kg), lignocaine (1 mg/kg over 2 min), isoprenaline infusion (0.05-1 mcg/kg/min), overdrive pacing
2. chronic: β-Blocker, pacemaker, ICD, sympathectomy
References:
[1] American Heart Journal, 1957, 54, 59 – 68: Jervell et all: Congenital deaf-mutism, functional heart disease with prolongation of the Q-Y interval and sudden death
[2] Circulation, 2000, 102, 782 – 784: Splawski et all: Spectrum of mutations in long QT syndrome genes: KVLQT1, HERG, SCN5A, KCNE1, and KCNE2
[3] JAMA, 2003, 23, 2041 – 2044: Moss: Long QT Syndrome
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