Medication-Induced Variations on Electrocardiographic Patterns: A Contrast between Atypical Antipsychotics

Introduction: Prolongation of the Q-Tc interval is commonly accepted as a surrogate marker for the ability of a drug to cause torsade de pointes (TdP). In the present study, safety of olanzapine vs. risperidone was compared among a cluster of schizophrenic patients, to see the frequency of the electrocardiographic alterations that can be induced by those atypical antipsychotics. Method: Two hundred and sixty-eight female schizophrenic inpatients entered in one of the two parallel groups, to participate in an open study for random assignment to olanzapine (n=148) or risperidone (n=120). Standard 12-lead surface ECG was taken from each one of them at baseline, before initiation of treatment, and then at the end of management, just before discharge. The parameters that had been assessed included: heart rate (HR), P-R interval, QRS interval, Q-T interval (corrected = Q-Tc), Ventricular Activation Time (VAT), ST segment, T wave, Axis of QRS and finally inter-ventricular conduction process. Results: 37.83% of the cases in the olanzapine group and 30% of them in the risperidone cluster showed some Q-Tc changes. 13.51% and 24.32% of the patients in the olanzapine group showed prolongation and shortening of the Q-Tc, respectively. But, the altered cases in the risperidone group showed only prolongation of Q-Tc. Comparison of means showed a significant increment in Q-Tc by risperidone (p = 0.02). Also, Comparison of proportions, showed significantly more cases with shortening of QT-c against cases with its prolongation in the olanzapine group (p =0.01). No significant alterations with respect to other variables were evident. Post-hoc power analysis demonstrated an acceptable power of 0.88 regarding this trial.