QTc interval
Mean baseline QTc intervals were similar in the two groups: 422 ± 26 ms in group 1 and 414 ± 22 ms in group 2 (Indipendent T-test p > 0,5). One patient in the monotherapy group, who started clozapine treatment, was excluded from this analysis and from pre-post treatment comparisons because QTc in DII was not measurable with sufficient accuracy.
Three patients in the first group had QTc values that exceeded 450 ms at baseline while no patients in Group 2 exceeded this threshold before starting treatment.
The average QTc interval after treatment was 421 ± 20 ms in the monotherapy group (range 391–452) and 438 ± 30 and in the polytherapy group (range 379–488) (Indipendent T test, p < 0,05) (see figure 1).
Figure 1  Mean QTc (bars indicate standard deviations) values at baseline (T0) and after four days at full dosage (T1) of antipsychotic therapy, in the monotherapy (1) and politherapy (2) groups.   Compared with the baseline, mean QTc change after treatment was – 1 ± 30 ms in Group 1 and 24 ± 21 ms in Group 2 (repeated measures ANOVA p < 0,05).
After treatment only one patient in Group 1 reached the threshold for borderline values of QTc interval in comparison to seven patients in Group 2 (Fisher Exact Text p < 0,05).
Moreover, in Group 2 two patients had a QTc exceeding 480 ms.
The highest prolongations of QTc intervals (66 ms and 55 ms) were found in two patients taking risperidone, the first in association to clomipramine and the second in association to escitalopram. However in these two cases plasmatic dosages of antipsychotics were not higher than in other patients who reported a shorter QTc prolongation.