Psychotropic drugs are among medications connected with prolongation of the QT interval and greater occurrence of sudden cardiac death [1–7]. The QT interval is the sequence of the ECG from the beginning of the QRS complex to the end of the T wave and represents the temporal equivalent of ventricular depolarization and repolarization. Its value corrected for heart rate is referred as corrected QT interval (QTc). There is no consensus about the upper physiological limit for QTc . European Medicines Agency quotes different possible upper values (450 ms, 480 ms, and 500 ms) and calls for caution when change from baseline exceeds 30–60 ms . Significant QT prolongation ("long QT syndrome", LQTS), inherited or acquired, is associated with the increased susceptibility to ventricular tachyarrhythmia "torsade de pointes" (TdP) that either resolve spontaneously or deteriorate into ventricular fibrillation and sudden death. In comparison to men, women are at higher risk for developing TdP because the feminine gender is associated with a longer baseline QT interval, perhaps due to differences in circulating sex hormones [10–13]. For females, QTc interval values more than 450 ms are commonly used as borderline and those over 470 ms as prolonged [14–16].
Congenital forms of LQT syndrome are due to autosomal recessive (Jervell and Lange-Nielsen syndrome) or autosomal dominant (Romano-Ward syndrome) mutations of several genes encoding for cardiac ion channels with consequent disturbances in electrical activity of the heart [17–22]. LQTS mutation carriers are present in one of 1000 to 3000 individuals .
Acquired long QT syndrome occurs when one or more risk factors, such as drugs that block certain cardiac ion channels, provoke a prolonged QT interval. Common causes of acquired LQTS are several classes of drugs, e.g. Class I and III antiarrhythmics, macrolides antibiotics, antihistamines, antipsychotics and antidepressants . International Registry for Drug-Induced Arrhythmias by the University of Arizona  put some antipsychotics among the drugs with the most prominent arrhythmogenic activity (haloperidol, chlorpromazine, pimozide and thioridazine); less capable to induce arrhythmias are clozapine, lithium, quetiapine, risperidone, venlafaxine and ziprasidone. Antidepressants (amitriptyline, clomipramine, citalopram, fluoxetine, paroxetine and sertraline) are at lower risk if they are not combined with other risk factors known to prolong the QT interval (e.g. concomitant therapy with QTc prolonging drugs or inhibitors of cytochrome 450 enzymes, bradycardia, presence of congenital LQTS, and electrolyte imbalance like hypokalaemia and hypocalcaemia). Some studies pointed out the greater possibility for cardiac arrhythmias when antipsychotic drugs are combined with antidepressants .
Because concomitant use of antipsychotics and antidepressants are not infrequent in our clinical practice we decided to explore are there any differences in the length of QTc between patients on monotherapy with an antipsychotic or an antidepressant and patients treated with combination of these drugs (an antipsychotic plus an antidepressant).