Long QT Syndrome

OVERVIEW

• normal QT = < 440ms (two large squares) – prolonged QT > 450ms
• produces prolonged ventricular repolarisation -> predisposes to malignant ventricular arrhythmias

CAUSES

• drugs: amiodarone, TCA’s, many antibiotics, fluconazole, erythromycin, metoclopramide, quinidine, haloperidol, droperidol, methadone, ondansetron, SSRI’s
• genetic: cardiac ion channel mutation (Na+, K+)
• myocardial disease: MI, RF, 3rd degree HB, cardiomyopathy
• electrolytes: low Ca2+, low K+, low Mg2+

ASSESSMENT

HISTORY

• syncope
• exercised induced syncope
• cardiac arrest
• FHx

EXAMINATION

• may be normal

INVESTIGATIONS

• ECG: QTc >440ms (11 small squares or T wave after half the R-R distance)
• ECHO: structural heart disease

MANAGEMENT

• beta-blockade
• avoidance of increased sympathetic tone
• cardiac pacing
• treat cause
• ICD