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ECG Basics: Torsades de Pointes

Dawn's picture
Sat, 07/13/2013 - 12:30 -- Dawn

Torsades de pointes, or polymorphic ventricular tachycardia, is a ventricular tachycardia precipitated by and associated with long QT Syndrome.  Long QT Syndrome can be congenital or acquired.  Torsades is life-threatening, and can be made worse by many drugs, including some of the drugs used to treat VT.  The rate is usually 150 - 250 / min. and the appearance is of a wide-complex tachycardia with QRS morphology changes.  In some leads, it will appear as if it is "twisting" around the isoelectric line, giving it the French name, Torsades de pointes, a ballet term meaning twisting of the points.  For a thorough discussion of Torsades, check this LINK.

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ekgpress@mac.com's picture
     
     Although often considered as equivalent — Torsades de Pointes and PMVT (PolyMorphic VT ) actually have a number of distinguishing features. The encompassing term is PMVT — which is defined as an irregular WCT (Wide-Complex Tachycardia) rhythm with constantly varying QRS morphology.
  • Torsades de Pointes — is defined as polymorphic VT that occurs in association with a prolonged QT interval on baseline ECG. If the QT is not prolonged — then technically the rhythm is not "Torsades". 
This definition serves to highlight a number of important clinical points:
  • Much of the time the clinician will not know IF the baseline QT is prolonged or not. There may not be a readily available 12-lead tracing close to the bedside of a coding patient. Even if there is — assessment of QT interval duration is often quite challenging when the baseline is erratic and the underlying supraventricular rhythm is tachycardic. I've had many a tracing for which even when I DID have a "baseline tracing" — I had no idea if the baseline QT was prolonged or not ....
  • Clinically — it "does" and it "does not" make a difference if the rhythm is truly Torsades. I say this because practically speaking — initial management is the same. IF the patient is unstable — SHOCK! You can't synchronize PMVT (or Torsades) — so this is unsynchronized shock that is needed.
  • IF the patient goes in-and-out of the irregular WCT rhythm — Magnesium Sulfate is indicated regardless of whether the rhythm is PMVT or Torsades. One starts with 1-2 gm IV Mg++ — and repeats this up to doses of 4-8 gm IV every few minutes as needed. IV Mg++ infusion may be needed to prevent recurrence. Adverse effects from IV Mg++ are generally minimal — and many patients will respond to this medication regardless of whether or not serum Mg++ levels are normal or low.
  • That said — it is well to keep in mind that clinical response to IV Mg++ tends to be less good IF the patient has PMVT (ie, no QT prolongation). Ischemia (and on occasion underlying Brugada syndrome) tend more often to be the underlying etiology of PMVT — vs Drug effect / Lyte abnormality (low K+/low Mg++) or other cause of QT prolongation seen as the etiology of Torsades.
  • IV Amiodarone and/or Beta-Blockers are more likely to effectively treat PMVT if IV Mg++ does not work when the rhythm is PMVT (ie, no prolonged QT ).
BOTTOM LINE: The therapeutic approach is essentially the same regardless of whether baseline QT is prolonged or not — BUT — the etiology of the rhythm as well as the likely response to treatment may be different.
  • For those interested - Please CLICK HERE to download a 6-page summary PDF on PMVT/Torsades from my ACLS-2013-Arrhythmia book. 

Ken Grauer, MD  www.kg-ekgpress.com   [email protected] 

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