[The predictive value of very low frequency power for the efficacy of vitamin D treatment in children with postural orthostatic tachycardia syndrome].

Objective: To explore the predictive value of very low frequency (VLF) for the efficacy of vitamin D treatment in children with postural orthostatic tachycardia syndrome (POTS). Methods: A retrospective case-control study was conducted. A total of 65 POTS children from the Department of Pediatrics of the Second Hospital of Lanzhou University from November 2023 to May 2024 were selected as the research subjects, while 102 healthy children from the same period were selected as the control group. The 25 (OH) D levels between POTS children and healthy children were compared. The frequency of eight main symptoms, including palpitations, headache, cold sweat, blurred vision, chest tightness, dizziness, fainting, and digestive discomfort in the POTS group were analyzed, the symptom scores of the orthostatic intolerance were calculated, and the parameters related to short-range heart rate variability (HRV) during the upright test, head-up tilt test (HUTT) were collected. The correlation between 25 (OH) D levels and symptom scores of orthostatic intolerance symptoms and HRV parameters in children with POTS were analyzed by Pearson correlation analysis. The total symptom scores of children with POTS were compared for 3 months before treatment and 2 months after treatment with vitamin D 800 U/d. The difference in score before and after treatment was ≥2 as responsive group, and the score difference before and after treatment was <2 as non-responsive group. The demographic characteristics including age, gender, height, weight, body mass index, as well as HRV parameters such as the standard deviation of nn intervals (SDNN), the standard deviation of the average NN intervals (SDANN), the root mean square of successive differences (rMSSD), low-frequency (LF), high-frequency (HF), very-low-frequency (VLF) were compared between the responsive group and non-responsive group. Multivariate Logistic regression was analyzed to screen independent influencing factors of vitamin D treatment efficacy for POTS. The marker molecules related to the efficacy of vitamin D treatment in children with POTS were analyzed through receiver operating characteristic (ROC) curve. Results: A total of 167 children were included in this study. There were 65 children in the POTS group, 38 males and 27 females, with the age of (10.6±2.2) years. There were 102 healthy children in the control group, 53 males and 49 females, with the age of (11.2±1.8) years.There was no statistically significant difference in gender and age between the two groups (both P>0.05). The serum 25 (OH) D level in children in the POTS group was (37±18)nmol/L, lower than that in the control group (61±17)nmol/L (P<0.05).Pearson correlation analysis showed that serum 25(OH)D was positively correlated with VLF, SDNN and HF (r=0.43, 0.65, 0.36, respectively, all P<0.05). Among the POTS children, there were 48 cases in responsive group and 17 cases in non-responsive group. Univariate analysis revealed that responsive group exhibited significantly lower values in age, SDNN, SDANN, and VLF compared to the non-responsive group (all P<0.05). Multivariate Logistic regression analysis showed that age (OR=1.47, 95%CI 1.08-2.01), SDNN (OR=1.01, 95%CI 1.00-1.22) and VLF (OR=1.01, 95%CI 1.00-1.15) were independent influencing factors in the effect of vitamin D in POTS children (all P<0.05). ROC curve analysis showed that the area under the curve of VLF predicting response to vitamin D treatment for POTS was 0.72 (95%CI 0.58-0.85, P=0.008). When the cutoff value was 1 272 ms², the sensitivity and specificity were both 70%. Conclusion: VLF may help predict the efficacy of vitamin D treatment in children with POTS.