直立倾斜试验诊断血管迷走性晕厥的价值

目的研究直立倾斜试验（ＨＵＴ）诊断血管迷走性晕厥的价值。方法６７例原因不明的晕厥患者、２０例正常对照组行ＨＵＴ时,并采用特异性及敏感性较高的静滴异丙肾上腺素重复试验。观察心率、收缩压、舒张压变化。结果４３例阳性患者中,血管抑制性晕厥３１例（３１／６７）,混合性晕厥１２例。患者组,基础早搏时与阳性时的心率、收缩压、舒张压之间有高度显著性差异（Ｐ＜０００１）。静滴异丙肾上腺素敏感性６４％,特异性８５％。结论静滴异丙肾上腺素重复倾斜试验对诊断血管迷走性晕厥具有重要价值。     

A randomized and controlled pilot trial of beta-blockers for the treatment of recurrent syncope in patients with a positive or negative response to head-up tilt test

The aim of this study was to assess the efficacy of lipophilic beta-blockers in preventing recurrent neurocardiogenic syncope and the value of head-up tilt test (HUT) in predicting response to therapy. The efficacy of beta-blockers in recurrent syncope is controversial. The value of HUT in predicting efficacy of therapy has not been investigated. Fifty-six patients (44+/-18 years, 36 women) with recurrent syncope (> 1 event in the last 6 months) of suspected neurocardiogenic origin were included in the study. Independent of the response to HUT, patients were randomized to receive metoprolol or propanolol at the maximal tolerated dose (28 patients, group A, 86+/-23 vs 98+/-29 mg/d) or no pharmacological therapy (28 patients, group B). The primary endpoint was the first recurrence of syncope. During the 1-year of follow-up, 20 patients of group A and 8 of group B had no recurrence. In group A, of 20 patients without recurrences 12 had a positive and 8 a negative HUT result while of 8 patients with recurrences 5 had a positive and 3 a negative response to HUT. In the group B, of 20 patients with recurrences 10 had a positive and 10 a negative HUT result while of 8 patients without recurrences 4 had a positive and 4 a negative response to HUT. In a multivariate Cox-regression analysis, medical therapy was the only independent factor for predicting recurrence of syncope (P = 0.004); HUT had no influence in this regard (P = 0.773). In conclusion, lipophilic beta-blockers appear efficacious in preventing recurrent syncope of suspected neurocardiogenic origin. The efficacy of therapy seems to be not predicted by HUT.     

Haemodynamic response to peripheral venous congestion in patients with unexplained recurrent syncope

In patients with recurrent unexplained syncope, exaggerated peripheral venous pooling and impaired circulatory adjustment is thought to contribute to the outcome of a head-up tilt (HUT) test. The present study investigated the role of leg volume changes during venous congestion in the haemodynamic response of patients with recurrent unexplained syncope and the ability to predict the outcome of a HUT test. Changes in calf volume (strain gauge plethysmography), heart rate and arterial blood pressure were recorded in 60 patients with history of unexplained syncope (without postural tachycardia symptom) during venous congestion provoked by pneumatic thigh cuffs while supine at rest and during the initial 10 min of a 45 min 70 degrees HUT test. Twenty-seven patients [age (mean+/-S.D.), 39+/-16 years] exhibited symptoms [HUT(+)] and 33 patients (45+/-14 years) were asymptomatic [HUT(-)]. During venous congestion, mean+/-S.E.M. calf volume increased in both groups [HUT(-), 4.5+/-0.2; HUT(+), 4.8+/-0.4 ml x 100 ml(-1), not significant), but significantly less during head-upright tilt [HUT(-), 3.3+/-0.2, P <0.01; HUT(+), 2.6+/-0.3 ml x 100 ml(-1), P <0.001] without differences between the groups. During venous congestion, arterial pressure increased significantly in asymptomatic HUT(-) patients, but not in the HUT(+) patients. Calf volume changes did not correlate with a symptomatic outcome to a 70 degrees HUT. The lack of exaggerated venous pooling during venous congestion and the inability of calf volume changes to predict a positive HUT suggest that excessive venous pooling does not contribute to the outcome of HUT. Attenuated changes in arterial pressure during venous congestion while supine suggest impaired adjustment of peripheral resistance to leg venous occlusion.     

Predictors of Positive Head-Up Tilt Test in Patients with Suspected Neurocardiogenic Syncope or Presyncope

OH, J.H., et al .: Predictors of Positive Head-Up Tilt Test in Patients with Suspected Neurocardiogenic Syncope or Presyncope. Neurocardiogenic syncope is the most common cause of syncope in patients who present in outpatient clinics. Head-up tilt test (HUT) has been widely used to diagnose neurocardiogenic syncope. However, the HUT does not always produce a positive response in patients with suspected neurocardiogenic syncope. The aim of the present study was to assess the clinical history and characteristics of patients with suspected neurocardiogenic syncope or presyncope who undertook HUT, and to identify prognostic factors of a positive HUT response. During the first phase of HUT, patients were tilted to a 70-degree angle for 30 minutes. If the first phase produced a negative response, the second phase was subsequently performed involving intravenous isoproterenol administration. Of 711 patients, 423 (59.5%) patients showed a positive HUT response. In contrast to previous studies, this study showed that the vasodepressive type (76.6%) was the most common pattern of positive response, and that the rate of positive response during the first phase was low (7.1%). By multivariate analysis, the occurrence of junctional rhythm was found to be a predictor of an impending positive response in HUT   (P < 0.001)   . The shorter time interval between the last episode and HUT was also a predictor of positive response   (P = 0.0015)   . Younger age   (P = 0.0003)   and a history of physical injury during a syncopal episode   (P = 0.019)   were found to be associated with a positive response in the first phase of HUT. (PACE 2003; 26[Pt. I]:593–598)     

Intravenous nitrates for pharmacological stimulation during head-up tilt testing in patients with suspected vasovagal syncope and healthy controls

Nitrates may be used for pharmacological stimulation during tilt testing for the diagnosis of vasovagal syncope. In this study we assessed the diagnostic value of intravenous nitrates during tilt testing in patients with a typical history of vasovagal syncope. Twenty patients and 23 controls were tilted at 700 for a maximum duration of 30 minutes. After a 10-minute baseline supine phase, the test started with a continuous nitrate infusion at 1 microg/kg/min and increased every 5 minutes by 1 microg/kg/min, to a maximum of 6 microg/kg/min at the end of the test. The test was ended if the subjects developed a positive response (syncope or presyncope). Nineteen patients (95%) and 17 (74%) of the controls had a positive response. At test end sensitivity was 95%, but specificity was 26% and accuracy was 58%. Receiver operator characteristics (ROC) analysis revealed a maximum accuracy of 79% at 18 minutes, with a sensitivity of 80% and a specificity of 78%. Intravenous nitrates during tilt testing in patients with typical clinical criteria of vasovagal syncope is highly effective in provoking vasovagal syncope. Based on the ROC analysis, a maximum accuracy of 79% was attained at 18 minutes (at a dose of 4 microg/kg/min), suggesting a good diagnostic performance when tilt duration is limited to this point. A positive result requiring more than 18 minutes of stimulated tilting should be interpreted with caution, due to the accompanying considerable decrease of specificity.     

Impairment of Coronary Microvascular Function in Patients with Neurally Mediated Syncope

CHEN, J.-W., et al .: Impairment of Coronary Microvascular Function in Patients with Neurally Mediated Syncope. Recent evidence suggests that myocardial ischemia may occur in patients with neurally mediated syncope and normal coronary angiograms. This study was conducted to evaluate if coronary microvascular function is impaired in such patients. Coronary hemodynamic studies and head-up tilt table tests (HUTs) were performed on 30 consecutive patients with normal coronary angiograms and recurrent syncope. Another ten subjects with atypical chest pain and no evidence of myocardial ischemia or syncope served as a control. Great cardiac vein flow (GCVF) and coronary sinus flow (CSF) were measured by the thermodilution method at baseline and after dipyridamole infusion (0.56 mg/kg IV for 4 minutes). Coronary flow reserve (CFR), derived from CSF and GCVF, was significantly lower in the 15 patients with positive HUT than in the other 15 patients with negative HUT (   1.75 ± 0.48   vs   2.64 ± 0.8   ,   P < 0.01   and   2.29 ± 0.45   vs   3.07 ± 0.63   ,   P < 0.01   , respectively). Ischemic-like ECG was noted during treadmill exercise test in 40% of the former and in 7% of the latter group   (P = 0.01)   . There was no significant difference in CFR between patients with negative HUT and control subjects. Coronary microvascular function was impaired in syncopal patients with positive HUT and relatively preserved in those with negative HUT, suggesting the possible linkage between coronary microvascular dysfunction and the development of neurally mediated syncope. (PACE 2003; 26[Pt. I]:605–612)     

Short head-up tilt test potentiated with oral nitroglycerine: comparison with a conventional test using isoproterenol

Conventional tilt test protocols are time consuming and there is no consensus regarding the optimal duration of the test and the provocative drug to be used. This study evaluated the diagnostic power of a short nitroglycerine test against a conventional isoproterenol protocol. A cohort of 128 patients with unexplained syncope was studied. A group of 64 consecutive patients were tilted with a short nitroglycerine test consisting of a passive phase of 15 minutes and if this proved negative, 400 microg of sublingual nitroglycerin spray for a further 15 minutes. The control group consisted of 64 patients tilted with a conventional isoproterenol protocol with a passive phase of 30 minutes and a drug-challenge phase of 20 minutes. In the nitroglycerine protocol 39 (60.9%) patients showed a positive response versus 27(42.2%) in the isoproterenol group (P = 0.034). The duration of the protocol was 23.2 +/- 7.2 minutes in the nitroglycerine group versus 41.1 +/- 15.5 minutes with isoproterenol (P = 0.001). The time until syncope was 18.87 +/- 6.1 versus 29 +/- 18, respectively (P = 0.002). For evaluating unexplained syncope the short tilt test protocol with nitroglycerine is less time consuming, easier to perform, and has a higher rate of positive response than a conventional isoproterenol protocol.     

An association between anxiety and neurocardiogenic syncope during head-up tilt table testing

To study the association between anxiety and neurocardiogenic syncope as determined by head-up tilt table testing (HUT) in men and women with presyncope or syncope, patients with unexplained syncope or presyncope undergoing HUT were asked to complete the Burns Anxiety Inventory (BAI), a validated inventory of 33 questions with responses graded from 0 to 3. HUT consisted of a 30-minute tilt to 60 degrees, which if negative, was repeated with an isoproterenol infusion. A positive HUT was defined as symptomatic hypotension and/or bradycardia. Of the 66 patients who completed the BAI and underwent HUT, 33 were men and 33 were women. The mean age was 57 +/- 18 years (17-91 years). Patients with a positive HUT had a higher BAI score than those with a negative HUT (22 +/- 12 vs 14 +/- 13, P = 0.017). This association was stronger in women with a BAI score of 24 +/- 11 in those with a positive HUT versus 13 +/- 8 in those with a negative HUT (P = 0.005). In contrast, the mean BAI score for men with a positive HUT was 19 +/- 13, as compared to 15 +/- 16 for a negative HUT (P = 0.5). In conclusion, the present study demonstrates a statistical association between anxiety (as determined by BAI) and HUT result. Gender-based analysis revealed a more statistically significant relationship between anxiety and HUT outcome for women as compared to men.     

Head-Up Tilt Test in Patients with High Pretest Likelihood of Neurally Mediated Syncope: An Approximation to the "Real Sensitivity" of this Testing

This study was designed to examine the "true sensitivity" of a specific head-up tilt (HUT) testing protocol using clinical findings. The HUT protocol used 45 minutes at 60 degrees for the baseline portion and intermittent boluses of 2, 4, and 6 micrograms of isoproterenol in the second phase. Eighty-eight patients (40 men and 48 women; mean age of 33.8 +/- 16 years) with recurrent syncope and high pretest likelihood of neurally mediated syncope were included. The following were considerated as high pretest likelihood criteria: (1) at least two syncopal episodes; (2) no structural heart disease and normal baseline ECG; (3) age < 65 years; (4) a typical history of neurally mediated syncope, triggering factors plus premonitory signs; and (5) short duration of symptoms and fast recovery without neurological sequelae. Fifty-four patients (61%) had a positive tilt test (34/88 baseline [39%] and 20/50 with isoproterenol [40%]). The shorter time interval between the last syncopal episode and baseline HUT test was the only predictor for a positive response (P < 0.003). Conversely, this time interval was not predictor of positive responses during isoproterenol-tilt testing. In conclusion: (1) we claim a "sensitivity" for this combined protocol of 61%; and (2) our results indicate that patients with syncope of unknown origin must be tilted nearest as possible to the last syncope to increase the positive responses of HUT test.     

Clonidine for treatment of postoperative pain: a dose-finding study.

The aim of this double-blind randomized study was to evaluate the optimal intravenous dose of clonidine administrated during the peri-operative period, after lumbar hemilaminectomy for herniated disk repair. The "optimal intravenous dose" was defined as that providing minimal analgesic request, stable haemodynamic profile and a minimal sedation score during 12h after extubation. Eighty adult patients, ASA physical status I-II, undergoing lumbar hemilaminectomy for herniated disk (L(4)-L(5), L(5)-S(1)) were included in the study. All the patients were randomly assigned to one of four study groups (A, B, C, D), 20 patients each. The same standardized general anaesthesia was performed for each group. Thirty minutes before the end of surgery, group A, B and C patients received three different loading doses of intravenous clonidine (5 microg/kg, 3 microg/kg, 2 microg/kg respectively), followed by the same infusion of intravenous clonidine (0.3 microg/kg per hour). Group D patients received a bolus dose and a continuous infusion of NaCl 0.9%. In the recovery unit, postoperative pain was treated by a patient-controlled analgesia device, containing morphine. Pain relief was evaluated by the total morphine requirement during the postoperative period. Systolic blood pressure (SBP), heart rate and sedation were also noted during the first 12h postoperatively. Intravenous clonidine decreased morphine requirements in a dose-dependent manner. Group A, B, C and D patients requested 5 +/- 2, 11 +/- 3, 19 +/- 4 and 29 +/- 8 doses of morphine respectively. Clonidine also affected SBP in a dose-related manner. Group A, B and C patients had an SBP decrease respectively of 26 +/- 3%, 7 +/- 4% and 2 +/- 2% compared with basic values while, at the same time, in group D patients no SBP variation was registered. In conclusion, this study demonstrates that, when sedation and analgesic effect of clonidine is required, 3 microg/kg bolus dose followed by a continuous infusion of 0.3 microg/kg per hour has to be considered the optimal intravenous dose. The higher dose of intravenous clonidine (5 microg/kg) produced better analgesia but the degree of hypotension and sedation was more severe and longer lasting; it required ephedrine administration and careful monitoring of the patient. On the other hand, the bolus of intravenous clonidine 2 microg/kg (group C) was less effective in terms of pain relief but with similar side-effects to the 3 microg/kg dosage (group B).     

Changes in the transthoracic impedance signal predict the outcome of a 70 degrees head-up tilt test

We determined whether early changes in central haemodynamics, as determined by transthoracic impedance, induced by a 70 degrees head-up tilt (HUT) test could predict syncope. Heart rate, arterial blood pressure and central haemodynamics [pre-ejection period and rapid left ventricular ejection time ( T (1)), slow ejection time ( T (2)) and d Z /d t (max) (where Z is thoracic impedance), assessed by the transthoracic impedance technique], were recorded during supine rest and during a 45 min 70 degrees HUT test in 68 patients (40+/-2 years) with a history of unexplained recurrent syncope. We found that 38 patients (42+/-3 years) had a symptomatic outcome to 70 degrees HUT (fainters) and 30 (39+/-2 years) had a negative outcome (non-fainters). When measured between 5 and 10 min of 70 degrees HUT, T (2) had increased significantly only in the fainters, and a change in T (2) of >40 ms from baseline predicted a positive outcome with a sensitivity of 68% and a specificity of 70%. During supine rest prior to 70 degrees HUT, the fainters exhibited a shorter T (2) than non-fainters (183+/-10 compared with 233+/-14 ms; P <0.01), and a T (2) of <199 ms predicted a positive outcome to 70 degrees HUT with a sensitivity of 68% and a specificity of 63%. Incorporation of the changes that occurred from rest to 70 degrees HUT in other haemodynamic variables (heart rate >11 beats/min, systolic pressure <2 mmHg, diastolic pressure <7 mmHg and pulse pressure <-3 mmHg) increased the specificity to 97% and the positive predictive value to 93%. Thus transthoracic impedance could detect differences in central haemodynamics between fainters and non-fainters during supine rest and during the initial period of 70 degrees HUT with a consistent sensitivity and specificity when combined with peripheral haemodynamic variables.     

Myocardial contractility and cardiac filling measured by impedance cardiography in patients with nitroglycerine-induced vasovagal syncope

OBJECTIVE: Increased myocardial contractility and inadequate cardiac filling leading to activation of the Bezold-Jarisch reflex were proposed as possible triggering mechanisms of vasovagal syncope (VVS). In the present study noninvasive hemodynamic measurements were performed in order to examine the role of myocardial contractility and cardiac filling in pathogenesis of VVS. METHODS: Hemodynamic parameters were measured during head-up tilt test (HUT) by impedance cardiography in 46 patients with unexplained syncope. Myocardial contractility was measured as index of contractility (IC), acceleration index (ACI), and ejection fraction (EF). Afterload was measured as systemic vascular resistance index (SVRI) and preload was expressed as end-diastolic index (EDI). Serial measurements were done 1 minute before HUT, during HUT at 1-minute intervals, and 1 minute after completion of HUT. RESULTS: HUT was positive in 30 patients (10 men, 20 women, mean age 36 +/- 16 years) and negative in 16 patients (8 men, 8 women, mean age 31 +/- 14 years). No significant differences were observed between HUT(+) and HUT(-) groups in hemodynamic parameters at supine rest and during HUT until the development of syncope. SVRI was lower in HUT(+) than in HUT(-) group at syncope (122.7 + 66.3 vs 185.6 + 51.4 dyn sec cm(-5)/m2, P = 0.002) and after syncope (117.0 + 61.1 vs 198.0 + 95.7 dyn sec cm(-5)/m2, P = 0.007). ACI, IC, EF, and EDI did not differ between groups at syncope. After syncope EF was higher in HUT(+) group compared to HUT(-) group (59.2 + 6.1 vs 52.7 + 9.4%, P = 0.02). CONCLUSION: The role of increased myocardial contractility and decreased cardiac filling is not confirmed in the present study.     

Monitored anesthesia care with a combination of ketamine and dexmedetomidine during cardiac catheterization

No specific regimen has been universally accepted as ideal for sedation during cardiac catheterization in infants and children. We evaluated a combination of ketamine and dexmedetomidine for sedation during cardiac catheterization in children with congenital heart disease. The study design included a retrospective analysis of data sheets and hospital records. The protocol for sedation was standardized and data collected prospectively for an ongoing quality assurance project. Heart rate, blood pressure, and oxygen saturation were recorded every 1 minute for the first 5 minutes and then at 5-minute intervals. The efficacy of sedation was judged by the need for supplemental ketamine doses. The study cohort included 16 infants and children undergoing either diagnostic or therapeutic cardiac catheterization. Sedation was initiated with a bolus dose of ketamine (2 mg/kg) and dexmedetomidine (1 microg/kg) administered over 3 minutes followed by a continuous infusion of dexmedetomidine (2 microg/kg per hour for the initial 30 minutes followed by 1 microg/kg per hour for the duration of the case). Supplemental analgesia/sedation was provided by ketamine (1 mg/kg) as needed. The baseline heart rate was 103 +/- 21 beats/minute. After the bolus dose of ketamine and dexmedetomidine, the heart rate increased by 7 +/- 5 beats/minute. The greatest increase was 15 beats/minute. The low heart rate after the bolus dose of ketamine/dexmedetomidine or during the subsequent dexmedetomidine infusion was 91 +/- 20 beats/minute (P < 0.001 compared with baseline) and the high heart rate was 110 +/- 25 beats/minute (P < 0.01 compared with baseline). In two patients, the dexmedetomidine infusion was decreased from 2 to 1 microg/kg per hour at 12 to 15 minutes instead of 30 minutes as a result of a decreased heart rate. No clinically significant changes in blood pressure or respiratory rate were noted. Two patients developed upper airway obstruction, which responded to repositioning of the airway. No apnea was noted. During the procedure, the PaCO2 varied from 37.5 to 48 mm Hg and was > or =45 mm Hg in seven patients. No patient responded to local infiltration of the groin and placement of the arterial and venous cannulae. Three patients required a supplemental dose of ketamine (1 mg/kg) during the procedure. In two of these patients, this was required before changing the cannulae. Our preliminary data suggest that a combination of ketamine and dexmedetomidine provides effective sedation for cardiac catheterization in infants and children without significant effects on cardiovascular or ventilatory function.     

Enhanced plasma catecholamine and cAMP response during the head-up tilt test in patients with vasovagal syncope

AIMS: Vasovagal syncope appears related to transient changes in sympathetic neural outflow. Several studies have documented sympathetic inhibition at the time of syncope. However, data on the activity of the sympathetic nervous system a short time before the onset of syncope are controversial. The aim of the study was to examine sympathoadrenal activity by measuring levels of plasma catecholamines and plasma cAMP in patients with vasovagal syncope induced in the head-up tilt test (HUT). METHODS AND RESULTS: Sixty-one syncopal patients (age 35 +/- 15 years) underwent the passive HUT (60 degrees, 45 minutes). Blood samples for measurement of noradrenaline (NA), adrenaline (A) and dopamine (D) were obtained prior to tilt (0 minutes), at 5 minutes of tilt and at syncope or at the end of the HUT (45 minutes). Two samples were obtained for measurement of cAMP: at 0 minutes and at the end of the test. Plasma levels of NA, A and D were measured using high-performance liquid chromatography; plasma cAMP was measured using a radioimmunoassay technique. Thirty-three patients (15 men, age 35 +/- 16 years) developed vasovagal syncope during the test (HUT-positive); twenty-eight patients (15 men, age 34 +/- 14 years) completed the test without syncope (HUT-negative). No significant differences in NA, A and D were observed between the two groups at baseline or at 5 minutes of tilt. At the time of syncope, catecholamine levels in HUT-positive patients were higher than baseline levels (NA 428 vs. 209 pg/ml, A 90 vs. 55 pg/ml, D 297 vs. 142 pg/ml) and higher than in HUT-negative patients (NA 428 vs. 263 pg/ml, A 98 vs. 67 pg/ml, D 297 vs. 195 pg/ml). cAMP levels increased at syncope and were higher than in non-syncopal patients at the end of the HUT (607 +/- 460 vs. 328 +/- 297 nmol/ml). CONCLUSION: Vasovagal syncope induced by tilt testing is associated with increased levels of noradrenaline, adrenaline, dopamine and cAMP. These results suggest that sympathoadrenal activation antecedes development of vasovagal syncope and may play a role in its pathophysiology.     

Frequency-domain analysis of heart rate variability during positive and negative head-up tilt test: importance of age

The study of autonomic behavior during a head-up tilt test (HUT) has been deemed important to understand the loss of consciousness mechanism. Though HRV in patients with HUT(+) and HUT(-) has been compared, few trials emphasized the importance of age. HRV in frequency domain was analyzed based on 5-minute samples in the supine position, and between 5 and 10 minutes during early tilt test (R1) in 102 patients with one or more episodes of syncope (mean age 44.3 +/- 20.8, range 15-85 years, 55 women). Two subgroups were selected afterwards: (1) young patients between 15 and 35 years of age (41 patients) and (2) elderly patients aged 60 or more (36 patients). The following parameters were taken into account: the sum of low (LF) and high frequency (HF) (LF and HF in absolute values and in normalized units), the LF/HF ratio (L/H ratio), and the percentage of change between baseline and R1 values. The HRV behavior in young and elderly patients with positive and negative HUT was established. We then analyzed the correlation between HRV and age and HUT outcome. A multiple regression analysis encompassing age, HUT outcome, gender, and number of syncope episodes was performed. In young patients, the LF and HF areas and the L/H ratio changed significantly between baseline and R1. The L/H ratio increases from baseline to R1. Conversely, these differences were not significant in the elderly. No differences between HUT(+) and HUT(-) within the same age group were observed. Age related significantly to practically all HRV parameters analyzed, whereas the tilt test outcome correlates poorly with HF normalized units and LF normalized units during R1, and the L/H ratio changes between baseline and R1. By means of a multivariate analysis, only age shows a significant correlation with the HRV values. Despite an all age triggering of vasovagal syncope during HUT, the young and elderly patients' autonomic behavior differs. The young considerably increase their sympathovagal balance during HUT, whereas the elderly have a mitigated autonomic response. No significant differences were observed during the first minutes of the test between those with a HUT(+) and those with a HUT(-) within the same age group. Age, and not the HUT response, is the major determinant of the autonomic behavior during early HUT.     

Holter Monitoring vs Tilt Testing in the Investigation of Suspected Vasovagal Syncope

The aim of this study was to compare the diagnostic yield of 48-hour Holter monitoring with head-up tilt (HUT) test in patients presenting with blackouts suggestive of vasovagal syncope. One hundred and eighteen consecutive patients, 68 women, aged (mean [SD])   50 ± 20  years   (range 16–88 years), underwent 48-hour Holter monitoring and 60° HUT test within 3 months. Endpoints were symptom-ECG correlation during Holter monitoring and positive HUT test. Syncope occurred in 3 (3%) patients during Holter monitoring, the rhythm being sinus tachycardia in all. Presyncope was reported in 22 (19%), the rhythm being sinus tachycardia in 6, persistent atrial fibrillation in 2, and normal sinus rhythm in the remainder. Asymptomatic arrhythmias were recorded in 103 (87%) patients. Positive HUT tests occurred in 39 (33%), the pattern being mixed (VASIS type 1) in 14 (36%), cardioinhibitory (VASIS type 2) in 3 (8%), and vasodepressor (VASIS type 3) in 22 (56%). Change in patient management occurred in 3 (3%) patients following Holter monitoring and 39 (33%) patients following HUT test. Holter monitoring produces a low yield of clinically useful information in the investigation of suspected vasovagal syncope. An HUT test should be considered the primary investigation of choice in such patients. (PACE 2003; 26[Pt. I]:1523–1527)     

Assessment of orthostatic fluid shifts with strain gauge plethysmography

We evaluated the use of strain gauge plethysmography (SGP) for the assessment of orthostatic fluid shifts during head up tilt (HUT). Subjects wore a parachute harness fixed to the tilt table to avoid muscle tension in the lower limbs during HUT. 22 Healthy subjects (9 women) were tilted for 5 minutes. Calf volume changes as measured by SGP, surface EMG, heart rate and blood pressure were measured continuously. Ten subjects underwent a second tilt test during which circulation in one leg was occluded with a pressure cuff at 250 mmHg. During HUT with occlusion, calf volume increased in the non-occluded leg by 1.9+/-0.3% (mean +/- SEM) and 0.2+/-0.2% in the occluded leg (p<0.001). During HUT without occlusion a significant correlation (r = 0.9) was found between measurements of the left and right leg with a mean difference of 0.03+/-0.1%. HUT did not cause significant changes of surface EMG. An unexpected gender effect was found: calf volume increased significantly more in men than in women. Men were significantly taller, but the hemodynamic response to HUT did not differ between both sexes. The gender effect on orthostatic increases of calf volume remained significant after adjustment for heart-to-calf distance. SGP during HUT with a parachute harness is a new, promising method to assess orthostatic fluid shifts. The gender differences in orthostatic pooling in the calf may be explained by a higher calf compliance in men together with a greater hydrostatic pressure due to a greater height in men.     

Sensitivity and Specificity of the Tilt Table Test in Young Patients with Unexplained Syncope

The usefulness of the head-up tilt testing (HUT) has heen previously addressed in diagnosing vasovagal neuroregulatory syncope in the teenage population. However, data concerning sensitivity and specificity is deficient due to the lack of control groups. We compared the response to HUT in young patients referred because of syncope or near syncope (n = 44, mean age 16 ± 3 years SD) to healthy young volunteers with a normal physical examination and no previous history of syncope (n = 18, mean age 16 ± 2 years) and io determine the sensitivity and specificity of HUT. The graded tilt protocol was performed at 15°, 30°, and 45° (each for 2 min), and then 60° for 20 minutes. Cuff blood pressure was measured every minute and lead IIECG was continuously monitored. Results; 25 of the 44 patients (57%) developed a vasovagaJ response or became symptomatic after 13.8 ± 5.7 minutes of HUT. Three of the 18 volunteers (17%) had a vasovagal response and became symptomatic after 9 ± 3 minutes of HUT. There was no statistical difference among the four groups (with and without tilt induced vasovagal response) in terms of age and baseline hemodynamic data. The sensitivity of 20 minutes HUT was 57% and its specificity was 83%. The presyncopal hemodynamic response in patients with history of syncope that was characterized by a significant decrease in systolic blood pressure and lack of increase of diastolic blood pressure as compared with baseline and with other groups. Gonclusions: 20 minutes at 60° HUT has a high specificity for the diagnosis of vasovagal syncope. Its limited sensitivity is counterbalanced by the advantage of limiting the incidence of false-positive results in patients without the vasovagal syndrome.     

Is Absolute Hypovolemia a Risk Factor for Vasovagal Response to Head-Up Tilt?

To test the hypothesis that hypovolemia is associated with an increased incidence of vasovagal syncope during head-up tilt (HUT) 45 patients with history of syncope or presyncope were studied. Blood volume (radio-iodinated serum albumin) was determined, then subjects underwent a graded HUT (from 15°–60° HUT) with cuff blood pressure and ECG monitoring. All patients were kept on their own medications during evaluation. Thirty patients (12 male, 18 female, mean age 50 ± 19 [SD] years) had hypovolemia, defined as blood volume < 90% of lab normal for corresponding sex, while 15 patients (7 male, 8 female, mean age 52 ± 21 years) were normovolemic with blood volume ranging from 91%-110% of sex-matched normal subjects. The normovolemic patients served as controls. During HUT, a vasovagal response was elicited in 5 of the 30 hypovolemics and in 4 of the 15 normovoiemic (16.7% and 26.7%, respectively, P = NS). In those who developed vasovagal response, the changes of heart rate and blood pressure during HUT were not significantly different between hypovolemics and normovolemics, neither at the endpoint (vasovagal response) nor immediately before the development of the vasovagal response. In patienis with nonvasovagal events, four types of hemodynamic responses to tilt were observed; normal blood pressure response associated with normal heart rate increase, normal blood pressure response in association with accentuated increase in heart rate, orthostatic hypotension with normal acceleration of heart rate, and orthostatic hypotension with accelerated increase in heart rate. The percent distribution of these responses were 44%, 20%. 0%, and 36% in the 25 nonvasovagal hypovoiemics versus 73%, 0%, 18%, and 9% in the 11 nonvasovagal normovolemics. The results demonstrate that supine total blood volume does not predict the occurrence of vasovagal response to HUT. However, accentuated orthostatic tachycardia was more prevalent in hypovolemics as compared to normovolemics with nonvasovagal response to tilt.     

A prospective evaluation of the continuous infusion of cis-atracurium for neuromuscular blockade in the pediatric intensive care unit patient: efficacy and dosage requirements.

PURPOSE: To prospectively evaluate the efficacy and dosage requirements of cis-atracurium administered by continuous infusion for neuromuscular blockade in a pediatric intensive care unit population. METHODS: Neuromuscular function was monitored by a train-of-four (TOF) over the ulnar or peroneal nerve. cis-Atracurium was administered as a bolus dose (0.2 mg/kg) followed by a continuous infusion starting at 3 microg/kg/min. The infusion was increased or decreased by 1 mIcrog/kg/min to maintain one twitch of the TOF. All patients also received a benzodiazepine infusion. Results: The study population included 15 children ranging in age from 10 months to 11 years and in weight from 4-28 kg. The duration of the infusion varied from 18-224 hours for a total of 1088 hours in the 15 patients. The cis-atracurium infusion requirements varied from 2.1 to 3.8 microg/kg/min (3.1 +/- 0.6) on day 1, to 1.4 to 6.4 microg/kg/min (3.4 +/- 1.4) on day 2, to 2.9 to 8.1 microg/kg/min (4. 5 +/- 1.6) on day 3. Overall, the infusion requirements varied from 1.4-22.7 microg/kg/min. The highest infusion requirements (22.7 and 10.2 microg/kg/min) were noted in patients who received cis-atracurium for prolonged periods of time (150 and 224 hours, respectively). The lowest infusion requirement occurred with the use of hypothermia to treat increased intracranial pressure. Conclusions: cis-Atracurium can be used by continuous infusion to provide neuromuscular blockade in the pediatric intensive care unit patient. Because of the variability in infusion requirements, monitoring of neuromuscular function is suggested.