Torsades de pointes (TdP), a form of ventricular arrhythmia that con cause ventricular fibrillation and sudden death, may occur during prolongation of the QT interval.QT prolongation has recently been reported with antipsychotic drugs. Physicians should be able to obtain a corrected measurement of the QT interval.QT is measured from the beginning of the QRS complex to the end of the T wave (Qtm). This value must then be corrected to take heartbeat into account. The most common formula in current use is Bazett's.In practice, a QTc interval value greater than 500 ms indicates on increased risk of TdP.Safe combinations of antipsychotic drugs have been recommended by the French drug agency (Agence francaise de securite sanitaire des produits de sante).Many other drugs, including psychotropic drugs such as tricyclic antidepressants, con prolong the QT interval. Combinations of these medications with one another with antipsychotic medications, or with other concomitant factors, such as hypokalemia, also increase the risk.