QT Prolongation
Considerations
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Potential for hemodynamic collapse secondary to rapid polymorphic VT & VF
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Avoid triggers of Torsades de Pointes: sympathetic stimulation, medications, electrolyte disturbances (↓K, ↓Mg, ↓Ca)
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Congenital long QT: may have pacemaker/AICD, perioperative β-blockade; avoid sympathomimetics
Goals
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Avoid triggers of Torsades:
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SNS stimulation (pain, nausea, emotional stress, loud noise)
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Bradycardia, tachycardia, hypertension, hypoxemia, hypercapnia
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Electrolyte disturbances: ↓K, ↓Mg, ↓Ca
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QT prolonging medications: antiemetics, antipsychotics, amiodarone, methadone
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Congenital long QT: avoid beta-agonists, ketamine
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Continue beta blockade for congenital long QT; ensure optimal AICD function if applicable
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Preparations for treating Torsades: defibrillator & pads in OR, MgSO4, resuscitation drugs
Various Definitions for Prolonged QTc
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QTc > 470 ms (males) to > 480 ms (females) (Anesthesiolgy, 2005)
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>460 ms (Stoelting Co-existing 6th Ed)
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>460 regardless of age (Cote 4th Ed)
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>470 ms (males) & >480 ms (females) (AHA/ACC Consensus statement 2011)
Treatment of Torsades
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Defibrillation & CPR as per ACLS
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Magnesium 2g IV over 2 min (30 mg/kg), q15min x 3; pediatrics 25-50mg/kg bolus
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Overdrive pacing to 90-110 with transvenous pacemaker
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Isoproterenol to ↑ HR 90-100
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↑ K to 4.5
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Stop QT prolonging medications: antipsychotics, antiemetics antibiotics, antifungals, antidysrhythmics, antidepressants, antihistamines, antineoplastics