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torsades de pointes

- Torsades de pointes (twisting of the points) is a characteristic form of ventricular tachycardia (VT) that displays gradual alteration in the amplitude & direction of electrical activity - it occurs in the setting of QT prolongation. Etiology: 1) congenital long QT syndromes 2) end-stage cardiomyopathy 3) bradycardia 4) 3rd degree AV block or AV dissociation 5) drug-induced prolongation of the QT interval (most common cause) 6) electrolyte disturbances a) hypokalemia b) hypomagnesemia 7) endocrine disorders a) hypothyroidism b) hypoparathyroidism c) pheochromocytoma d) hyperaldosteronism 8) intracranial disorders a) subarachnoid hemorrhage b) stroke c) encephalitis d) head trauma Epidemiology: - 70% of cases NOT associated with congenital long QT syndromes occur in women Clinical manifestations: 1) intermittent & recurrent 2) transient hemodynamic compromise a) lightheadness b) syncope or near-syncope 3) complete hemodynamic collapse may occur Special laboratory: - electrocardiogram: 1) prolongation of the QT interval prior to onset of torsades 2) initiation of torsades is triggered by long-short sequences: a) coupled premature ventricular complexes (PVCs) b) ventricular bigeminy 3) QRS complexes undergo gradual change in amplitude & axis Differential diagnosis: - monomorphic ventricular tachycardia - due to structural heart disease, old myocardial infarction - intravenous amiodarone, procainamide or lidocane for hemodynamically stable patient Management: 1) DC cardioversion if hemodynamically unstable 2) discontinue offending agents 3) MgSO4 1-2 g IV push followed by infusion of 2-20 mg/min 4) increase heart rate to eliminate long-short sequence: a) isoproterenol 2-10 ug/min - avoid in patients with: ischemia, severe coronary artery disease b) temporary pacing at 80-120/min 5) congenital long QT syndrome - beta-adrenergic receptor antagonists 6) some patients may respond to: a) lidocaine b) phenytoin c) bretylium 7) avoid pharmacologic agents that increase the QT interval - class Ia & III antiarrhythmic agents

Related

drug-induced prolongation of the QT interval long QT syndrome QT interval

General

polymorphic ventricular tachycardia

Figures/Diagrams

EKG: Torsades de pointes

References

  1. Stedman's Medical Dictionary 26th ed, Williams & Wilkins, Baltimore, 1995
  2. Manual of Medical Therapeutics, 28th ed, Ewald & McKenzie (eds), Little, Brown & Co, Boston, 1995, pg 149-150 & 175
  3. Medical Knowledge Self Assessment Program (MKSAP) 11, 16. American College of Physicians, Philadelphia 1998, 2012
  4. Mayo Internal Medicine Board Review, 1998-99, Prakash UBS (ed) Lippincott-Raven, Philadelphia, 1998, pg 80-81
  5. Prescriber's Letter 11(11): 2004 Drugs That Prolong the QT Interval and/or Induce Torsades de Pointes Detail-Document#: 201115 (subscription needed) http://www.prescribersletter.com
  6. Drew BJ, Ackerman MJ, Funk M et al Prevention of torsade de pointes in hospital settings: a scientific statement from the American Heart Association and the American College of Cardiology Foundation. Circulation. 2010 Mar 2;121(8):1047-60. PMID: 20142454