MGR review R4. 장 원 석

Long QT Syndrome (LQTS) QT interval = beginning of the QRS to the end of the T wave duration of activation and recovery of the ventricular myocardium. Bazett formula: QT/ square root of RR > 440 msecs in men > 460 msecs in women

Long QT Syndrome (LQTS) Disease of the ion channels –Prolongation of the action potential –Early after depolarization* Increased sympathetic activity –Imbalance in sympathetic innervation of heart

Action Potential

AcquiredMetabolic HypoK, HypoMg, HypoCal, Anorexia, + Hypothyroidism HypoK, HypoMg, HypoCal, Anorexia, + HypothyroidismMedications Antiarrhythmics (sotalol, amiodarone, etc) Antiarrhythmics (sotalol, amiodarone, etc) Antibiotics (Macrolides, Fluoroquinolones) Antibiotics (Macrolides, Fluoroquinolones) Psychotropic (Haldol, TCAs, Thioridazine) Psychotropic (Haldol, TCAs, Thioridazine) SSRIs, Risperidone, Methadone, Droperidol, protease inhibitors SSRIs, Risperidone, Methadone, Droperidol, protease inhibitors

Aquired LQTs management Direct current shock non synchrnoized Direct current shock non synchrnoized Discontinuation of the offending agent Discontinuation of the offending agent Any offending agent should be withdrawn. Any offending agent should be withdrawn. Predisposing conditions such as hypokalemia, hypomagnesaemia, and bradycardia should be identified and corrected Predisposing conditions such as hypokalemia, hypomagnesaemia, and bradycardia should be identified and corrected Suppression of early after depolarizations Suppression of early after depolarizations Magnesium is the drug of choice Magnesium is the drug of choice Isoproterenol Isoproterenol This drug can be used in bradycardia-dependent torsade that usually This drug can be used in bradycardia-dependent torsade that usually associated with acquired long QT syndrome (pause-dependent). associated with acquired long QT syndrome (pause-dependent). Temporary transvenous pacing Temporary transvenous pacing

Management Primary Prevention –Beta blockers –Avoidance of strenuous activity/sports –Left cardiac sympathetic denervation Secondary Prevention –Beta blockers –ICD –Avoidance of QT prolonging agents

Congenital LQTS managementPharmacologic Beta blockers MexiletineNonpharmacologic Permanent dual chamber pacemaker Left cardiac sympathetic denervation (cardiothoracic sympathectomy) Implantable cardioverter-defibrillator