what is Torsade de Pointes ?
Ventricular tachycardia can be classified in a variety of ways. Monomorphic VT and polymorphic VT is one such classification based on VT morphology.Polymorphic VT generally conveys a meaning of origin from multiple focus .But in reality bulk of the polymorphic VT originate from a single focus .
PVT (Polymorphic ventricular tachycardia ) may or may not be associated with prolonged QT interval . when the PVT is associated with prolonged QT interval , the VT is called torsade de pointes .when the PVT is associated with normal QT interval , the VT is a regular from of PVT . Torsade de pointes should be differentiated from regular PVT because the treatment of torsade de points is different from that of regular PVT .
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Although the tachycardia of torsades de pointes and regular polymorphic VT look identical m treatment of these two arrhythmias are different because one is associated with prolonged QTc , whereas the other is not . in patients with torsade de pointes with acquired prolongation of the QT interval , the long QT interval is reversible and the cause should be identified and eliminated . this is in contrast to congenital long QT syndrome where prolongation of the QT may ot be reversible . nevertheless in both congenital and acquired long QT syndrome , any identifiable cause of QT prolongation shold be corrected .
The presence of prolonged QTc differentiates torsades de pointes from regular PVT . The QT interval is measured during normal sinus rhythm before or immediately on termination of the tachycardia. the QT interval should be corrected for heart rate because the QT interval measures longer with slower heart rates and shorter with faster heart rates . The QT interval corrected for heart rate is the QTc. The QTc is prolonged when it measures >0.44 seconds in men and >0,46second in women and in children . Prolonged QTc should always be recognized because it predispose to torsade de pointes even fatal .
Characteristics that distinguish torsade de pointes from other forms of VT include 1) Prolonged QT interval , 2) initiation with a short-long-short seqyesce and 3) typical “twisting of the points” appearance of the VT .
Torsade-de-pointes: a polymorphic ventricular tachycardia associated with the long-QT syndromes characterized by phasic variations in the polarity of the QRS complexes around the baseline. Ventricular rate is often >200bpm and ventricular fibrillation is a consequence.
- Presence of AV dissociation (independent atrial activity) vs. retrograde atrial capture
- Presence of fusion QRS complexes (Dressler beats) which occur when supraventricular beats (usually sinus) get into the ventricles during the ectopic activation sequence.
Differential Diagnosis: just as for single premature funny-looking beats, not all wide QRS tachycardias are ventricular in origin (i.e., they may be supraventricular tachycardias with bundle branch block or WPW preexcitation)!