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 anti muscarinic drugs and qt inte  

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why do anti muscarinic drugs prolong qt interval and cause torsades???


(muscarinic effect on heart-decrease heart rate & conduction velocity). Anti muscarinic drugs block muscarinic receptors and make sympathetic effect predominant. Thus, these drugs increase heart rate i.e. tachycardia. This may lead to ventricular tachycardia where ventricles depolarize early and stay in excited stage for longer time. On EKG, this leads to prolonged QRS complex and thus prolonged QT interval. This gives rise to torsades. (Torsades = abnormal VT with prolonged QT).

Hope this helps.

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