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When polymorphic ventricular tachycardia (VT) is encountered the 1st step is to examine the QTc interval before/after the VT to see if it's prolonged
Torsades de pointes (TDP) typically begins with a premature ventricular depolarization, followed by a compensatory pause, and then a sinus beat with a markedly prolonged QT interval, subsequently followed by a train of polymorphic VT
The risk of developing TDP correlates with the degree of prolongation of QTc interval
Risk = 1.052x, where X is a 10-ms increase in QTc interval
Tx algorithm: ECG reveals prolonged QTc, review drug hx, discontinue all QT prolonging drugs, suppress early after depolarization (EAD) w/magnesium bolus & infusion, maintain serum K levels >4.5meq/L, consider isoproterenol infusion + cardiac pacing
References
Congenital and Acquired Long QT Syndrome.Cardiology in Review. 12(4):222-34, 2004 Jul-Aug.