Autonomic responses to orthostatic stress in head-up tilt testing: relationship to test-induced prolonged asystole

Development of a nomogram model to predict malignant vasovagal syncope in Chinese children

Objective

Vasovagal syncope (VVS) is the commonest form of syncope, and malignant VVS draws substantial attention due to its life-threatening cardiac asystolic risk. This study aimed to explore the predictive role of a wide panel of clinical indicators for malignant VVS in children, and further to develop a nomogram model.

Methods

This is a retrospective case-control study. VVS is diagnosed based on head-up tilt test (HUTT). STATA software (version 14.0) was used for statistical analysis, and effect sizes are expressed as odds ratio (OR) and 95% confidence interval (CI).

Results

Total 370 children with VVS were analyzed, and of them 16 children had malignant VVS. Sixteen malignant VVS and 64 non-malignant VVS were matched on age and sex by a 1:4 propensity scores matching method. Mean corpuscular hemoglobin (MCH) and standard deviation of average RR intervals milliseconds (SDANN) were significantly and independently associated with malignant VVS after adjusting for confounders, with OR reaching 1.437 (95% CI: 1.044 to 1.979; P = 0.026) and 1.035 (95% CI: 1.003 to 1.068; P = 0.029), respectively. Calibration and discrimination analyses revealed that the addition of MCH and SDANN can enhance model performance. Then, a nomogram to predict malignant VVS was developed using general characteristics and two above significant factors, and higher values in medical history, number of syncope, MCH and SDANN were associated with a greater risk of malignant VVS.

Conclusion

MCH and SDANN were two promising factors for the development of malignant VVS, and modeling of significant factors in a nomogram can provide strong reference to aid clinical decision-making.

Non-contact monitoring of heart rate variability using medical radar for the evaluation of dynamic changes in autonomic nervous activity during a head-up tilt test

Electrocardiography (ECG) is a mandatory standard for monitoring electrical activity of the heart in many clinical settings such as intensive care and emergency units. However, in situations wherein the skin is damaged, such as acute burn injuries, it is impossible to efficiently attach electrodes to the skin. In this study, we developed a non-contact cardiac monitoring system using a 24-GHz medical radar for directly measuring the beat-to-beat heart mechanical activity at a distance from a subject. The heart rate variability (HRV) was analysed using an autoregressive model (AR) from the measured beat-to-beat intervals during a head-up tilt test. To investigate the feasibility of the proposed system, we compared medical radar and ECG recording by using Lin's correlation coefficient and Bland-Altman analysis, which showed a negligible mean difference from the substantial agreement of Lin's correlation coefficient of 0.9 between the radar and ECG. The non-contact radar clearly monitored dynamic changes in HRV indices induced by the head-up tilt test. This type of non-contact HRV-sensing technique as an alternative approach has significant potential for advancing personal healthcare in both clinical and out-of-hospital settings.

Altered fractal behavior and heart rate variability in daily life in neurally mediated syncope

Autonomic imbalance is thought to play an important role in the pathogenesis of neurally mediated syncope (NMS). Heart rate variability (HRV) indices and fractal dimension derived from 24 h ambulatory electrocardiogram (AECG) reflects the cardiac autonomic activity and provides useful information for understanding the pathogenesis of NMS. In this study, we sought the cardiac autonomic activity and the status of fractal dimension in daily life in patients with NMS. The 24 h ambulatory ECG recordings were performed in 36 NMS patients (NMS group) and in 11 healthy volunteers (CTRL group). Six time domain and frequency domain HRV indices were calculated. The regression of log (power) on log (frequency) was also calculated and the slope of the regression line (beta) was analyzed in three different periods such as total 24 h, awake and sleep phases. The values of mean RR, SDNN and SDANN were not significantly different, but the values of S.D. index, rMSSD, pNN50 and all the frequency domain HRV indices were significantly higher in NMS group than in CTRL group. For 24-h period, there was no significant difference in the values of beta. For awake phase, the value of beta was significantly higher in NMS group than in CTRL group. For sleep phase, the value of beta was significantly lower in NMS group than in CTRL group. Augmented autonomic activity and the deterioration of fractal dimension in daily life might contribute to the pathogenesis of NMS.