Antipsychotics are associated with cardiovascular risk, but the relationship between their anticholinergic properties and cardiac function is not clear. We hypothesize that antipsychotics with a high muscarinic affinity (HMA) may reduce parasympathetic modulation, which should be observable by means of heart rate variability (HRV) measurement. We also assume that anticholinergics, which are commonly used in patients with schizophrenia to treat drug-induced parkinsonism, interact with antipsychotics, and this may also affect HRV. Fifty-five patients with schizophrenia were recruited into this study. Twenty-eight subjects used antipsychotics with an HMA and 27 subjects used antipsychotics with a low muscarinic affinity (LMA). Heart rate variability values between the patients on antipsychotics with HMA and those on antipsychotics with LMA were compared. Correlation and regression analysis were then performed to clarify the relationship between HMA, LMA, and HRV. The influence of anticholinergics was also assessed by correlation analysis. The HMA group showed significantly reduced low-frequency (LF) power, high-frequency (HF) power, total power (TP), and normalized LF (LF%) than the LMA group. Regression analysis supported the hypothesis that muscarinic affinity was related to LF (β =-0.447; P < 0.001), HF (β =-0.390; P = 0.002), and TP (β =-0.399; P = 0.001). The interaction between LMA and anticholinergic use also influenced LF% (β = 0.326; P = 0.006). In the LMA group, the use of anticholinergics was positively correlated with LF% and LF/HF. In the HMA group, after exclusion of the patients using anticholinergics, the equivalent dose of antipsychotics showed a negative correlation with HF. Our results suggest that the muscarinic affinity of antipsychotics affects both sympathetic and parasympathetic modulation and that anticholinergics interact with antipsychotics to influence HRV.
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