[Antipsychotic drugs and cardiovascular safety: need for monitoring the QT interval].
Torsades de pointes (TdP), a form of ventricular arrhythmia that can 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 an increased risk of TdP. Safe combinations of antipsychotic drugs have been recommended by the French drug agency (Agence française de sécurité sanitaire des produits de santé). Many other drugs, including psychotropic drugs such as tricyclic antidepressants, can 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. TdP is most often diagnosed only after observing QT prolongation. This underlines the need to monitor QT intervals attentively to prevent the risk of cardiac arrhythmia in patients treated with antipsychotic drugs.