Impedance cardiography: a role in vasovagal syncope diagnosis?

Glyceryl trinitrate-induced blood pressure variability decrease during head-up tilt test predicts vasovagal response

PURPOSE

Glyceryl trinitrate (GTN) provoked cardioinhibitory syncope during the head-up tilt test is preceded by a period of disrupted blood pressure variability (BPV). Endogenous nitric oxide (NO) attenuates BPV independently of blood pressure (BP). We hypothesized that exogenous NO donor GTN might decrease BPV during the presyncope period. A decrease in BPV may predict the tilt outcome.

METHODS

We analyzed 29 tilt test recordings of subjects with GTN-induced cardioinhibitory syncope and 30 recordings of negative subjects. A recursive autoregressive model of BPV after GTN was performed; powers of the respiratory (0.15-0.45 Hz) and nonrespiratory frequency (0.01-0.15 Hz) bands were calculated for each of the 20 normalized time periods. The post-GTN relative changes in heart rate, BP, and BPV were calculated.

RESULTS

In the syncope group, spectral power of nonrespiratory frequency systolic and diastolic BPV progressively felt for 30% after GTN application and stabilized after 180 s. BP started to fall 240 s after the GTN application. Decrease in nonrespiratory frequency power of diastolic BPV 20 s after GTN administration predicted cardioinhibitory syncope (area under the curve 0.811; 77% sensitivity; 70% specificity; cutoff value > 7%).

CONCLUSION

GTN application during the tilt test attenuates systolic and diastolic nonrespiratory frequency BPV during the presyncope period, independent of BP. A decrease in nonrespiratory frequency diastolic BPV 20 s after GTN application predicts cardioinhibitory syncope with good sensitivity and moderate specificity.

Cardiovascular autonomic responses during head-up tilt test in newly diagnosed type 2 diabetes

BACKGROUND

Autonomic dysfunction is commonly observed in patients with long-standing type 2 diabetes. Previous studies have confirmed the value of both subjectively assessed symptoms and objective measurements of autonomic nervous system function in diagnosing cardiovascular autonomic neuropathy. However, the head-up tilt test (HUTT) has been rarely used to investigate cardiovascular autonomic responses in subjects with high risk of newly diagnosed type 2 diabetes (nT2D).

OBJECTIVE

To evaluate autonomic cardiovascular responses through passive orthostatic challenge along the diabetes continuum.

METHODS

The study population was stratified as normoglycemic (n = 16), prediabetes (n = 20), and nT2D (n = 20). The prevalence of orthostatic intolerance and autonomic cardiovascular responses was evaluated with the Task Force Monitor during a 30-min passive HUTT. Spectral indices of heart rate and blood pressure variability and baroreceptor effectiveness index (BEI) were calculated through the HUTT. BEI was obtained by the sequence method.

RESULTS

There were no differences in the prevalence of orthostatic intolerance or in the indices of heart rate and blood pressure variability among the three groups of study. The BEI was attenuated in the nT2D group in supine rest and throughout HUTT compared with normoglycemic and prediabetes groups. The multivariable linear regression analysis showed that BEI was associated with fasting glucose (β =  - 0.52, p  < 0.001) and HbA1c (β =  - 0.57, p  < 0.001) independently of cardiovascular risk factors.

CONCLUSION

Cardiovascular autonomic neuropathy, expressed as blunted BEI, is the only abnormal autonomic nervous test detected in nT2D, and it was independently associated with fasting glucose and HbA1c values.

Quantitative Complexity Theory Used in the Prediction of Head-Up Tilt Testing Outcome

Background

Head-up tilt testing (HUTT), a well-established tool in the diagnosis of vasovagal syncope, is time-consuming, and every provoked vasovagal reaction may result in consolidating the reflex mechanism. Therefore, identification of parameters that could shorten the duration of HUTT and prevent fainting is desirable. Quantitative complexity theory (QCT) may provide holistic information on the cardiovascular reaction in HUTT. The aim of the present article was to evaluate the prognostic value of complexity in comparison with traditional haemodynamic parameters (HR and BP) in predicting the HUTT outcome.

Methods

Eighty-one healthy volunteers (74 men; mean age: 37.8 years) were included in this retrospective analysis of data collected within the project realized in Department of Cardiology and Internal Diseases, Military Institute of Medicine between January 2012 and October 2014. The subjects underwent HUTT, with beat-to-beat haemodynamic monitoring with a Niccomo™. The chosen haemodynamic parameters (including BP, HR, stroke volume, cardiac output, systemic vascular resistance) have been used in complexity analysis.

Results

HUTT was positive in 54 (66.7%) study participants. The values of complexity were already higher in fainting subjects than those were in nonfainting ones 300 s before HUTT termination (HUTT_end), with a significant upward trend starting 150 s before (pre)syncope. An area under the curve (AUC) over 0.700 was observed for complexity from 120 s before HUTT_end, with a sensitivity of 63% and specificity of 78% at this time point. The prognostic value of complexity was superior to that of the HR and mean arterial pressure (MAP).

Conclusions

Complexity has been shown to be a sensitive marker of cardiovascular haemodynamic response to orthostatic stress and proved to be superior over HR and BP in predicting HUTT outcomes.

Are women really more affected by vasovagal syncope than men?

It is commonly reported that vasovagal syncope (VVS) is more frequent in women. Presently, this issue has never been investigated. The purpose of this review was to evaluate, through an extensive review of the literature, whether women are really more affected by VVS than men. The gender distribution was investigated in individuals with classical and nonclassical VVS. The database PubMed was searched using the terms 'syncope', 'vasovagal syncope', 'neurally mediated syncope' and 'tilt testing'. Twelve studies dealing with classical and 75 with nonclassical VVS were eligible. In the individuals with classical (N = 1861) and nonclassical VVS (N = 9696), a trend towards a greater percentage of women emerged (P = 0.14 and 0.07, respectively). In the total population with VVS (N = 11 557), the percentage of women was significantly higher than that of men (58 versus 42%, P = 0.03). Most of the individuals were young or middle-aged. In 84% of the studies, the percentage of women was greater than that of men. A separate analysis was carried out in older VVS patients (≥60 years) and only two studies were eligible to be evaluated. Considering that almost all the studies were carried out in the western nations, where the number of men and women is almost superimposable until the age of 65 years and a bias by gender has never been reported in the management of VVS, these data strongly suggest that young and middle-aged women are more affected by VVS than their male counterparts. At present, data are too scant to draw a definitive conclusion in older VVS patients.

The complexity of hemodynamic response to the tilt test with and without nitroglycerine provocation in patients with vasovagal syncope

The paper presents a comparison of vasovagal syndrome occurrence in a head up tilt table test between patients with a positive result of passive tilt test and those with a positive result after pharmacological provocation. The study group consisted of 80 patients: 57 patients who experienced syncope in the passive phase of the test (43 women (aged: 35.6 ± 16.2) and 14 men (aged: 41.7 ± 15.6) and 23 patients who experienced syncope after pharmacological provocation (17 women (age: 32.3 ± 12) and 6 men (age: 43 ± 15). The main investigation was based on the assessment of monitored signals complexity: heart rate, blood pressure and stroke volume. The analysis of complexity in chosen measurement phases was performed with Sample Entropy. The investigation showed that the reactions of autonomic nervous system during tilt test and before syncope are similar for positive result of passive tilt test and positive result of tilt test with provocation. The differences in supine position occurred only in analysis based on impedance measurement (SV: p = 0.01). Significant differences were denoted for all signals just before the syncope (RRI, sBP, dBP: p = 0,00001 and SV: p = 0.01). In analysis of signals complexity the significant differences occurred just before the syncope for Sample Entropy of blood pressure (SampEn (sBP): p = 0.0008, SampEn (dBP): p = 0,0001).

Cardiovascular and Cerebral Hemodynamics in Asymptomatic Healthy Subjects With/Without Abnormal Head-up Tilt Test Versus Recurrent Fainters

PURPOSE

The aim of this study was to compare hemodynamic and autonomic responses during head-up tilt test (HUTT) between healthy volunteers and patients with a history of fainting and confirmed vasovagal syncope. We hypothesize that the autonomic and hemodynamic physiologic responses remain intact during orthostatic stress in people without previous fainting and negative HUTT, but deteriorate similarly in patients with recurrent vasovagal syncope and in asymptomatic healthy subjects who develop a vasovagal response during HUTT.

METHODS

The study included 57 asymptomatic healthy volunteers (42% women, mean age 23.7 ± 3.6 years) categorized as negative HUTT (n = 41) and positive HUTT (n = 16). They were compared with 14 patients (50% women, mean age 24.2 ± 6.1 years) with previous spontaneous recurrent syncope and inducible vasovagal response during HUTT. Cerebral and cardiovascular hemodynamic variables were assessed noninvasively during the HUTT in each participant.

RESULTS

In all patients with recurrent syncope, tilt was positive after a mean delay of 15.6 ± 8.6 minutes and did not differ from the time to syncope observed after 19.6 ± 6.9 minutes in asymptomatic healthy subjects with a positive test. A significant decrease throughout the tilting was observed in the blood pressure, peripheral resistances, cerebral blood flow, and vascular efferent sympathetic regulation in both groups of subjects with a positive test.

CONCLUSIONS

This study shows that there are subjects, without a history of syncope, who have a positive HUTT with hemodynamic and autonomic responses alike to patients with confirmed vasovagal syncope, precluding them to be selected as controls in vasovagal syncope studies.

The diagnostic assessment of hand elevation test in carpal tunnel syndrome

Objective

The aim of this study is to establish the value of hand elevation test as a reproducible provocative test for the diagnosis of carpal tunnel syndrome (CTS).

Methods

We had a prospective study of 45 hands of 38 patients diagnosed with CTS between April 2005 and February 2009. The diagnosis of CTS was based on the American Academy of Neurology clinical diagnostic criteria. Experimental and control group patients underwent Tinel's test, Phalen's test, carpal compression test and hand elevation test as provocative tests for CTS.

Results

We used chi-square analysis to compare Tinel's test and Phalen's test, carpal compression test with hand elevation test. The sensitivity and specificity of the hand elevation test is 86.7% and 88.9% each. Tinel's test had 82.2% sensitivity and 88.9% specificity. Phalen's test had 84.4% sensitivity and 86.7% specificity. Carpal compression test had 84.4% sensitivity 82.2% specificity. Comparisons of sensitivity and specificity between hand elevation test and Tinel's test, Phalen's test, and carpal compression test had no statistically significant differences. To compare the diagnostic accuracies of four tests, the area under the non-parametric receiver operating character curve was applied.

Conclusion

The hand elevation test has higher sensitivity and specificity than Tinel's test, Phalen's test, and carpal compression test. Chi-square statistical analysis confirms the hand elevation test is not ineffective campared with Tinel's test, Phalen's test, and carpal compression test.

Impaired hemodynamic response to meal intake in insulin-resistant subjects: an impedance cardiography approach

BACKGROUND

In the postprandial state, insulin regulates metabolic and cardiovascular responses. In insulin resistance, the insulin action is impaired at both levels. However, postprandial hemodynamic responses are poorly characterized in this setting.

OBJECTIVE

We investigated fasting and postprandial cardiac and vascular hemodynamic responses in subjects with and without insulin resistance.

DESIGN

Sixty-six atherosclerosis-free, healthy volunteers were studied in a fasted state and ≤180 min after ingestion of a mixed meal. The insulin sensitivity index was determined by using a minimal model analysis; hemodynamic response was monitored by using continuous impedance cardiography that allowed a reliable beat-to-beat noninvasive evaluation of stroke volume, cardiac contractility, and several derived variables.

RESULTS

Subjects were divided into insulin-resistant (IR; n = 33) and insulin-sensitive (IS; n = 33) groups. After fasting, IR subjects had significantly higher values of systolic and diastolic blood pressures and the systemic vascular resistance index (SVRI) than did IS subjects. In the postprandial state, acute vasodilatation was comparable and synchronous (at 30 min) in IR and IS subjects (P = 0.209), but subsequent vascular tone recovery (30-180 min) was significantly impaired in IR subjects (P = 0.018), even after adjustment for age and sex (P = 0.031). Hemodynamic dysregulation was directly correlated with metabolic disturbances in the postprandial state. In basal and postprandial states, hemodynamic variables related to cardiac function were not significantly different in IR and IS subjects.

CONCLUSIONS

IR subjects had a worse fasting vascular performance than did IS subjects. In the postprandial phase, insulin resistance was associated with a shorter duration of vasodilatation in the absence of an altered cardiac performance. Peripheral hemodynamic alterations in fasting and postprandial states may have a negative effect on cardiovascular performance in IR patients.

Impaired cardiovascular response to standing in chronic fatigue syndrome

BACKGROUND

Impaired skeletal muscle metabolism is recognized in chronic fatigue syndrome (CFS). This study examined the relationship between skeletal and cardiac muscle function and symptoms on standing in CFS using magnetic resonance spectroscopy (MRS) and impedance cardiography.

MATERIALS AND METHODS

Phosphocreatine (PCr)/adenosine triphosphate (ATP) ratio by cardiac MRS, PCr/ADP and proton efflux by muscle MRS were performed in 12 CFS (Fukuda) and 8 controls. Head up tilt (HUT) and cardiac contractility (left ventricular work index, LVWI) (n = 64 CFS and matched controls) were found. Fatigue impact was accessed by Fatigue Impact Scale and orthostatic symptoms by Orthostatic Grading Scale (OGS).

RESULTS

Cardiac PCr/ATP correlated with measures of muscle bioenergetic function (half-time PCr recovery [kappa = -0.71, P = 0.005] and half-time ADP recovery [kappa = -0.60, P = 0.02]) suggesting that the muscle and cardiac bioenergetic function correlate in CFS. Four of 12 (33.3%) CFS patients had PCr/ATP values consistent with significant cardiac impairment. Those with impaired cardiac energy metabolism had significantly reduced maximal and initial proton efflux rates (P < 0.05). Cardiac PCr/ATP ratio correlated with myocardial contractility (LVWI) in response to standing (P = 0.03). On HUT, LVWI on standing was significantly higher in CFS (P = 0.05) with symptoms on standing (OGS) occurring in 61/64 (95%) (vs. 25/64 [39%] controls; P < 0.0001). OGS scores were significantly higher in those with abnormal LVWI responses to standing (P = 0.04), with the LVWI on standing correlating with OGS scores (r(2) = 0.1; P = 0.03). HUT was positive in 19 (32%).

CONCLUSIONS

Skeletal muscle and cardiac bioenergetic abnormalities associate in CFS. Cardiac bioenergetic metabolism associates with increase in cardiac contractility on standing. Haemodynamic assessment in CFS is well tolerated and safe with a high diagnostic yield comparable with unexplained syncope.