Long Qt

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Long QT
Disorder of myocardial repolarization characterized by a prolonged QT interval on the ECG, is associated with an increased risk oftorsades de pointes (TdP)
TORSADES DE POINTES is a form of polymorphic VT that occurs in the setting of acquired or congenital QT interval prolongation.
Is defined as a ventricular rhythm faster than100 beats per min with frequent variations of the QRS axis, morphology, or both. The peaks of the QRS complexes appear to "twist" around the isoelectric line of the recording; "twisting of the points."Typical features of TdP include an antecedent prolonged QT interval, particularly in the last sinus beat preceding the onset of the arrhythmia, a ventricular rate of 160 to 250 beats per minute,irregular RR intervals, and a cycling of the QRS axis through 180 degrees every five to 20 beats.
PATHOPHYSIOLOGY — the development of early after depolarizations and triggered activity resulting fromprolonged repolarization.
There is an inverse correlation between the heart rate and QT interval. Virtually all of the drugs that produce LQTS act by blocking the outward IKr current, which ismediated by the potassium channel encoded by the HERG gene
DRUG-INDUCED TdP — The major classes of drugs
* Antiarrhythmic drugs (eg. Sotalol, Quinidine, Dofetilide & Amiodarone (rarelyassociated with TdP))
* Certain nonsedating antihistamines (eg, terfenadine and astemizole)
* Macrolide antibiotics
* Certain psychotropic medications (eg. Haloperidol) 
*Certain gastric motility agents (eg, cisapride).
Risk factors — 
* High drug doses
* Rapid intravenous infusion
* More than one drug that prolong the QT
* Diuretic treatment* Marked QT prolongation (QTc >500 ms),
* Bradycardia Premature complexes leading to short-long-short cycles
* Electrolyte disturbances, hypokalemia and hypomagnesemia
*...