Endothelial function in young subjects with vaso-vagal syncope

Serum uric acid predicts therapeutic response to midodrine hydrochloride in children with vasovagal syncope: a pilot study

Serum uric acid (UA) level has been proven to be related to several cardiovascular and metabolic diseases. In the present study, we examined if baseline serum UA level could predict the therapeutic efficacy of midodrine hydrochloride on vasovagal syncope (VVS) in children. The pediatric VVS patients who received midodrine hydrochloride from November 2008 to October 2022 were enrolled. After a median treatment duration of 3 months, the therapeutic effect was evaluated. According to the patients' responses to midodrine hydrochloride, which was determined by the recurrence of syncope, they were divided into effective and ineffective groups. The baseline variables were explored using univariable and multivariate logistic analysis. The predictive efficacy was assessed by receiver operating characteristic curve (ROC), precision-recall curve (PR), Hosmer-Lemeshow test, calibration curve, and decision curve analysis (DCA). Totally, 53 participants were included in the study. Among the 51 patients who were successfully followed up, 29 (56.9%) responded to midodrine hydrochloride (effective group), and the other 22 (43.1%) failed to respond to midodrine hydrochloride (ineffective group). The participants in effective group had lower baseline serum UA level than those in ineffective group (276.5 ± 73 μmol/L vs. 332.7 ± 56 μmol/L, p = 0.004). Multivariable logistic analysis showed that serum UA was associated with the therapeutic response (odds ratio (OR): 0.985, 95% confidence interval (CI): 0.974-0.997, p = 0.01). ROC analysis indicated that using baseline serum UA < 299 μmol/L as a threshold value yielded a sensitivity of 77.3% and a specificity of 79.3% in predicting the treatment response to midodrine hydrochloride. The area under the PR curve was 0.833. Hosmer-Lemeshow test yielded a p value of 0.58, and calibration plot indicated that the model was well-fitted. DCA demonstrated that treatment decision depending on the baseline serum UA level resulted in a favorable net benefit.   Conclusion: This pilot study suggested that the baseline serum UA level could be taken as a predictor of therapeutic effect of midodrine hydrochloride on VVS in children. What is Known: • Empirical and unselected use of midodrine hydrochloride has an unfavorable therapeutic effect on VVS in children. Serum uric acid (UA) is closely linked to cardiovascular events. What is New: • A low baseline serum UA level successfully predicts the therapeutic effectiveness of midodrine hydrochloride on VVS in children.

Predicting therapeutic efficacy of oral rehydration salts in children with vasovagal syncope

Objective

This study was designed to develop an easy-to-perform and inexpensive measure to predict efficacy of the oral rehydration salts (ORS) in children with vasovagal syncope (VVS).

Materials and methods

Children diagnosed with VVS and treated with ORS for a median of 3 months at the Peking University First Hospital, China, were enrolled and followed up. Demographic data, clinical hemodynamic parameters, and variables related to red blood cells were collected at the baseline. On the basis of changes in symptom scores after treatment, participants were divided into effective or ineffective groups at the end of the follow-up. Logistic regression analysis was used to investigate parameters related to therapeutic efficacy of ORS and a predictive model of ORS effectiveness was created. The predictive efficiency was evaluated using the receiver operating characteristic curve. The accuracy/consistency was evaluated by the Hosmer-Lemeshow test and calibration curve. Internal validation was done using the bootstrap approach.

Results

Totally 97 pediatric participants were included in the study and 4 (4.1%) were lost during the follow-up. ORS therapy was effective in 46 children and ineffective in 47 children. Children in the effective group had higher baseline red blood cell count, hemoglobin, and hematocrit than those in the ineffective group (p < 0.01). Through logistic regression analysis, the baseline hematocrit and body mass index (BMI) were included in predictive model for the response to ORS treatment. The predictive efficacy of the model showed an area under the curve of 0.77 (p < 0.01). The predicted probability cut-off value of 0.5 was found to be optimal, with a resulting sensitivity of 67.4% and specificity of 80.9%. In the Hosmer-Lemeshow test, p-value was 0.75, and the calibration plot showed a good model fitness. Internal validation was performed using the bootstrap approach (n = 1,000), showing 95% confidence interval of 0.67-0.86.

Conclusion

Hemoglobin combined with BMI was useful for predicting the therapeutic efficacy of ORS in children with VVS.

Biomarkers and Hemodynamic Parameters in the Diagnosis and Treatment of Children with Postural Tachycardia Syndrome and Vasovagal Syncope

In children, vasovagal syncope and postural tachycardia syndrome constitute the major types of orthostatic intolerance. The clinical characteristics of postural tachycardia syndrome and vasovagal syncope are similar but their treatments differ. Therefore, their differential diagnosis is important to guide the correct treatment. Therapeutic methods vary in patients with the same diagnosis because of different pathomechanisms. Hence, in patients with vasovagal syncope or postural tachycardia syndrome, routine treatments have an unsatisfactory efficacy. However, biomarkers could increase the therapeutic efficacy significantly, allowing for an accurate and detailed assessment of patients and leading to improved therapeutic effects. In the present review, we aimed to summarize the current state of research into biomarkers for distinguishing the diagnosis of pediatric vasovagal syncope from that of postural tachycardia syndrome. We also discuss the biomarkers that predict treatment outcomes during personalized therapy for each subtype.

Acute hypotension attenuates brachial flow-mediated dilation in young healthy men

PURPOSE

This study aimed to test our hypothesis that acute hypotension attenuates brachial flow-mediated dilation (FMD) as an index of endothelial function in healthy humans.

METHODS

Twelve healthy men (21.8 ± 1.6 years, body mass index; 22.2 ± 1.6 kg/m²) participated in this study. Brachial FMD was measured in three trials: standardized FMD protocol (control trial), abrupt decrease in blood pressure (BP) via thigh cuff inflation-deflation (hypotension trial) and decrease in shear rate (SR) via a shortened forearm occlusion time (SR reduction trial). Brachial diameter and blood velocity were measured using Duplex ultrasound.

RESULTS

Mean arterial pressure during reactive hyperaemia showed a marked decrease in the hypotension trial (- 23.7 ± 6.0 mmHg), but not in the control and SR reduction trials. SR area under the curve was attenuated in the SR reduction trial (P < 0.001), but not in the control and hypotension trials (P = 0.316). Consequently, FMD was attenuated in the hypotension and SR reduction trials compared with that in the control trial (P = 0.003 and P = 0.043, respectively), and was attenuated to a greater extent in the hypotension trial compared with the SR reduction trial (P = 0.006; control, 6.9 ± 3.5%; hypotension, 3.5 ± 1.7%; SR reduction, 5.0 ± 2.2%). After adjusting FMD using SR, FMD remained attenuated in the hypotension trial (P = 0.014), but not in the SR reduction trial.

CONCLUSION

Our findings indicate that arterial pressure as well as sympathetic nervous system activation could be an important determinant of FMD. Blunted FMD of peripheral arteries may be a rational response to restore BP and/or prevent further reduction of BP following acute hypotension in healthy humans.

Reactive Vasodilation Predicts Mortality in Primary Systemic Light-Chain Amyloidosis

Supplemental Digital Content is available in the text.

Cardiac involvement and hypotension dominate the prognosis of light-chain amyloidosis (AL). Evidence suggests that there is also peripheral vascular involvement in AL but its prognostic significance is unknown.

Postsynaptic α1-Adrenergic Vasoconstriction Is Impaired in Young Patients With Vasovagal Syncope and Is Corrected by Nitric Oxide Synthase Inhibition

BACKGROUND

Syncope is a sudden transient loss of consciousness and postural tone with spontaneous recovery; the most common form is vasovagal syncope (VVS). During VVS, gravitational pooling excessively reduces central blood volume and cardiac output. In VVS, as in hemorrhage, impaired adrenergic vasoconstriction and venoconstriction result in hypotension. We hypothesized that impaired adrenergic responsiveness because of excess nitric oxide can be reversed by reducing nitric oxide.

METHODS AND RESULTS

We recorded cardiopulmonary dynamics in supine syncope patients and healthy volunteers (aged 15-27 years) challenged with a dose-response using the α1-agonist phenylephrine (PE), with and without the nitric oxide synthase inhibitor N(G)-monomethyl-L-arginine, monoacetate salt (L-NMMA). Systolic and diastolic pressures among control and VVS were the same, although they increased after L-NMMA and saline+PE (volume and pressor control for L-NMMA). Heart rate was significantly reduced by L-NMMA (P<0.05) for control and VVS compared with baseline, but there was no significant difference in heart rate between L-NMMA and saline+PE. Cardiac output and splanchnic blood flow were reduced by L-NMMA for control and VVS (P<0.05) compared with baseline, while total peripheral resistance increased (P<0.05). PE dose-response for splanchnic flow and resistance were blunted for VVS compared with control after saline+PE, but enhanced after L-NMMA (P<0.001). Postsynaptic α1-adrenergic vasoconstrictive impairment was greatest in the splanchnic vasculature, and splanchnic blood flow was unaffected by PE. Forearm and calf α1-adrenergic vasoconstriction were unimpaired in VVS and unaffected by L-NMMA.

CONCLUSIONS

Impaired postsynaptic α1-adrenergic vasoconstriction in young adults with VVS can be corrected by nitric oxide synthase inhibition, demonstrated with our use of L-NMMA.

Nitric oxide synthase inhibition restores orthostatic tolerance in young vasovagal syncope patients

OBJECTIVE

Syncope is sudden transient loss of consciousness and postural tone with spontaneous recovery; the most common form is vasovagal syncope (VVS). We previously demonstrated impaired post-synaptic adrenergic responsiveness in young VVS patients was reversed by blocking nitric oxide synthase (NOS). We hypothesised that nitric oxide may account for reduced orthostatic tolerance in young recurrent VVS patients.

METHODS

We recorded haemodynamics in supine VVS and healthy volunteers (aged 15-27 years), challenged with graded lower body negative pressure (LBNP) (-15, -30, -45 mm Hg each for 5 min, then -60 mm Hg for a maximum of 50 min) with and without NOS inhibitor N^G-monomethyl-L-arginine acetate (L-NMMA). Saline plus phenylephrine (Saline+PE) was used as volume and pressor control for L-NMMA.

RESULTS

Controls endured 25.9±4.0 min of LBNP during Saline+PE compared with 11.6±1.4 min for fainters (p<0.001). After L-NMMA, control subjects endured 24.8±3.2 min compared with 22.6±1.6 min for fainters. Mean arterial pressure decreased more in VVS patients during LBNP with Saline+PE (p<0.001) which was reversed by L-NMMA; cardiac output decreased similarly in controls and VVS patients and was unaffected by L-NMMA. Total peripheral resistance increased for controls but decreased for VVS during Saline+PE (p<0.001) but was similar following L-NMMA. Splanchnic vascular resistance increased during LBNP in controls, but decreased in VVS patients following Saline+PE which L-NMMA restored.

CONCLUSIONS

We conclude that arterial vasoconstriction is impaired in young VVS patients, which is corrected by NOS inhibition. The data suggest that both pre- and post-synaptic arterial vasoconstriction may be affected by nitric oxide.

Endothelial Function and Cardiovascular Autonomic Activity in Neurally Mediated Syncope

OBJECTIVES

The aim of this study was to investigate endothelial function and cardiovascular autonomic activity in patients with neurally mediated syncope (NMS).

METHODS

Patients with a typical history of NMS were divided according to the result of a head-up tilt (HUT) test. There were 25 patients each in the HUT-positive (HUT+), HUT-negative (HUT-) and control groups. Flow-mediated dilation (FMD) and 24-hour ambulatory electrocardiography (AECG) were performed before the HUT tests.

RESULTS

The HUT+ group had a significantly higher FMD than that of the HUT- group and the control group (8.8 ± 3.3 vs. 6.4 ± 2.9%, p = 0.006, and 8.8 ± 3.3 vs. 5.7 ± 2.2%, p = 0.001, respectively). On a 24-hour AECG, the parasympathetic indexes of time domain, such as rMSSD and the pNN50, were significantly higher in the HUT+ group than in the HUT- group (39.0 ± 9.6 vs. 31.6 ± 9.6 ms, p = 0.016, and 16.5 ± 8.1 vs. 10.2 ± 7.2%, p = 0.002, respectively) and the control group (39.0 ± 9.6 vs. 28.9 ± 9.6%, p = 0.001 and 16.5 ± 8.1 vs. 8.7 ± 6.7%, p = 0.001, respectively). High-frequency spectra (parasympathetic activity) of the frequency domain showed similar results.

CONCLUSIONS

Not only parasympathetic activity, but also endothelial function may affect the results of HUT tests in patients with NMS.

Endothelial dysfunction state in migraine headache and neutrally mediated syncope in children and young adults

Background:

Recent evidences have supported migraine headache and neurally mediated syncope as the especial types of endotheliopathies. To determine endothelial function in patients with migraine headache or those with neurally mediated syncope, the present study was conducted.

Materials and Methods:

This cross-sectional study was performed on 93 consecutive patients aged 5-20 years in four groups; neurally mediated syncope, migraine, both neurally mediated syncope and migraine, and control groups. All subjects were tested for basic biophysical and biochemical features including age, gender, body mass index, systolic, and diastolic blood pressures, intima-media thickness (IMT) and flow-mediated dilation (FMD), blood hemoglobin, fasting blood glucose, lipid profile, intercellular adhesion molecule (ICAM), vascular cell adhesion molecule (VCAM), and E-selectin.

Results:

The mean levels of VCAM and ICAM were significantly higher in all groups when compared to control group (P < 0.05). FMD was significantly higher in syncope, migraine, and syncope and migraine groups than in the control group (P < 0.05). Furthermore, mean IMT was significantly lower in migraine and also in syncope and migraine groups than in syncope group and control group (P < 0.05). Examining the association between IMT and other baseline parameters showed positive association of IMT with systolic and diastolic blood pressures.

Conclusion:

Endothelial dysfunction is seen in both migraine headache and neurally mediated syncope. Changes in endothelial functional indices are also dependent on the blood pressure.

Neurally mediated syncope: Is it really an endothelial dysfunction?

OBJECTIVE

Syncope is a common problem in children and adolescents. Neurally mediated syncope is the most frequent form of this disorder. Although several studies have evaluated the pathophysiology of neurally mediated syncope, it is still not completely understood.

METHODS

We performed a cross-sectional study that included 27 patients aged 5-20 years with unexplained syncope and 30 healthy subjects as a control group. All subjects in both groups were assessed for endothelial function by investigating the following physical and chemical factors: flow-mediated dilation (FMD), intima-media thickness (IMT), circulating vascular cell adhesion molecule (VCAM), intercellular adhesion molecule (ICAM)], and endothelial leucocyte adhesion molecule (E-selectin), as well as epinephrine and norepinephrine. The data were statistically analyzed utilizing the SPSS 20.Significant differences between the groups in terms of mean scores were assessed using an independent sample t-test.

RESULTS

Mean FMD was significantly higher in the syncope case group than in the control group (p=0.028). There was no significant difference in IMT between the two groups; however, mean levels of ICAM (p=0.02) and VCAM (p=0.008) were significantly higher in the case group than in the control group. The levels of E-selectin also increased in the case group, but not to a statistically significant extent. The mean levels of epinephrine (p=0.01) were significantly lower in the case group than in the control group, and the level of norepinephrine serum decreased slightly, but not significantly, in the syncope patients.

CONCLUSION

Our results showed that an endothelial dysfunction or augmented endothelial function might exist in patients with neurally mediated syncope.

Endothelial function in vasovagal syncope

Vasovagal syncope (VVS) is a common form of fainting. The pathophysiology of VVS is complex and involves changes in the autonomic and vascular tone, resulting in reflex bradycardia with marked hypotension. Paradoxical peripheral vasodilation caused by endothelial dysfunction may also play a key role in inappropriate hypotension during VVS. Endothelial hyperactivity due to up regulation of nitric oxide synthase leads to profound vasodilation, much stronger than vasodilation caused by adrenergic stimulation in response to orthostatic stress alone. Studies have reported significantly higher flow-mediated dilation and higher plasma nitric oxide concentration in people with vasovagal syndrome. Patients with VVS showed decreased vasoconstrictive agent endothelin-1 levels during orthostatic stress. Coagulation and fibrinolysis activity also play important roles in endothelial function in syncopal patients. The response of the endothelium to orthostatic stress is similar to the reaction to haemorrhagic stress and is likely to be a remnant from the evolutionary adaptation of primates.

An increased endothelial-independent vasodilation is the hallmark of the neurally mediated syncope

BACKGROUND

The neurally mediated syncope (NMS) is sustained by complex cardiac and vascular reflexes, acting on and amplified by central autonomic loops, resulting in bradycardia and hypotension.

HYPOTHESIS

Our aim was to assess whether the pathophysiology of NMS is also related to an abnormal peripheral vasoreactivity.

METHODS

We evaluated by ultrasound the flow-mediated vasodilation (FMD) and the nitrate-mediated dilation (NMD) in 17 patients with NMS, induced by drug-free tilt test in 6 subjects and by nitrate-potentiated tilt test in the other 11 cases; the syncope was classified as vasodepressive (VD) in 8 cases, cardioinhibitory (CI) in 7, and mixed in 2.

RESULTS

The FMD was not different from controls (10.2 ± 4.5 vs 11.4 ± 3.9, P = ns), with normal recovery times; the NMD was greater in fainting subjects than in controls (26.7 ± 7.3 vs 19.0 ± 3.6, P < 0.05), with higher values in VD than in CI syncope (31.1 ± 7.0 vs 23.1 ± 5.0, P = ns); compared to controls, subjects with NMS showed normal recovery times after FMD but longer recovery times after nitrate administration (13.0 ± 5.6 vs 6.3 ± 0.7 minutes, P < 0.05).

CONCLUSIONS

The evaluation of endothelial function supports evidence that NMS is characterized by a marked and sustained endothelial-independent vasodilation, in the presence of a normal FMD; vascular hyperreactivity in response to nitrate administration is particularly overt in vasodepressive syncope and can explain the high rate of responses to nitrate administration during tilt test.

Vasodilation in vasovagal syncope and the effect of water ingestion

Abnormal (increased, but also decreased) vasodilative responses have been observed in patients with vasovagal syncope (VVS). The objective was to assess reactive vasodilation in supine patients with VVS and its relation to severity of the syndrome. Reactive vasodilation was also assessed after a simple therapeutic intervention (water drinking). Thirty-four patients were studied, all with recurrent VVS and a recent positive head-up tilt test result. Seventeen matched healthy subjects served as controls. Venous occlusion plethysmography was used to assess forearm blood flow (FBF) and forearm vascular resistance resistance (1) at rest and (2) during reactive hyperemia. Clinical severity of the syndrome was related to the intensity and duration of the vasodilative reflex. The same plethysmographic measurements were repeated 60 minutes after drinking 500 ml of water. Before water drinking, no difference was observed between groups in baseline measurements. However, duration of hyperemia was longer in patients (p <0.05) and was related to the duration of the previous positive tilt test (r = -0.69, p <0.05) and total number of each patient's symptomatic vasovagal episodes (r = 0.49, p <0.05). After water ingestion, baseline FBF decreased in patients (p <0.05) and remained stable in controls. In patients, duration of hyperemia decreased to normal values. Hyperemic FBF remained similar between groups. In conclusion, increased reactive vasodilative reflexes were observed in patients with VVS. They seemed to be of significant pathophysiologic significance. Water drinking can normalize them for >or=60 minutes.