Comparison of Sensitivity and Specificity of Tilt Protocols with and without Isoproterenol in Children with Unexplained Syncope

Head-up tilt testing with or without isoproterenol is extensively used in the evaluation of patients with unexplained syncope. However, sensitivity and specificity of tilt protocols with and without isoproterenol have not been clarified in children, due to lack of age matched control subjects. This study was designed to assess and to compare the sensitivity and specificity of tilting alone and tilting in conjunction with isoproterenol. Thirty children with unexplained syncope (group I) and 15 age-matched control subjects (control group I) underwent successive 60° head-up tilts for 10 minutes during infusions of 0.02, 0.04, and 0.06 μg/kg/min of isoproterenol, after a baseline tilt to 60° for 25 minutes. Also, 35 children (group II) with unexplained syncope and 15 healthy control subjects (control group II) were evaluated by head-up tilt to 60° for 45 minutes without an infusion of isoproterenol. In response to tilt protocol with graded isoproterenol, 23 (76.6%) of the patients in group I and 2 of the 25 (13.3%) control subjects developed syncope. Accordingly, the sensitivity of tilt testing with isoproterenol was 76.6%, and its specificity was 86.7%. Tilt testing without isoproterenol was positive in 17 (48.5%) of the patients in group II but in only 1 of the 15 (6.6%) control subjects. Thus, sensitivity and specificity of tilt testing without isoproterenol were 48.5% and 93.4%, respectively. The mean heart rate and systolic blood pressure decreased significantly (P < 0.001) in all tilt positive patients during syncope. In conclusion, the head-up tilt test is a valuable diagnostic test in the evaluation of children with unexplained syncope, and isoproterenol is likely to increase the sensitivity of the test without decreasing its specificity.     

Safety and Tolerability of an Aggressive Tilt Table Test Protocol in the Evaluation of Patients with Suspected Neurocardiogenic Syncope

Safety and tolerability of a one-step tilt table test with high dose (5 μg/min) isoproterenol (ISO) without intermediate stages were evaluated in a symptomatic population of 300 patients referred for clinical syncope, near syncope, or dizziness. ISO has been used as a provocative test but remains controversial. A population of 118 male and 182 female patients with a mean age of 45 (range 5–90) years underwent 300 tests. Heart rate and blood pressure were monitored continuously. A positive test was one in which clinical symptoms were reproduced or hemodynamic criteria met. Patients were initially supine for 5 minutes followed by head upright tilt (HUT) to an angle of 80± for 10 minutes. Negative tests were repeated with an infusion of ISO at a rate of 5 μg/min, HUT was positive in 133 (44.3%) of 300 tests. With a 10-minute HUT alone, only 17 (5.7%) of 300 of tests were positive. Of the initial negative tests, 273 of 283 were tested with ISO. With ISO, 116(42.5%) of 273 were positive. ISO in high dose (5 μg/min) was used in 264 of 273 patients, while low dose (1.0–2.5 μg/min) was used in 9 of 273 under special circumstances. High dose ISO was tolerated in 164 (62.1 %) of 264 patients, reduced in 87 (33%) of 264, and discontinued in 11 (4.2 %) of 264. Reasons for reduction included tachycardia (40 patients), nausea (31 patients), chest pain (2 patients), arrhythmia (5 patients), or other (9 patients). Adverse effects resolved within 1 minute of dose reduction. This one-step high dose ISO protocol reproduced neurocardiogenic syncope in symptomatic patients who tested negative without ISO and was safe, tolerated, and expeditious.     

Tilt Training: A Treatment for Malignant and Recurrent Neurocardiogenic Syncope

The treatment of neurocardiogenic syncope is insufficient in many cases. We hypothesized that the repeated exposure of the cardiovascular system to orthostatic stress could have a therapeutic effect on the regulation of cardiovascular reflex mechanisms. We have started a program of tilt training for heavily symptomatic patients. After hospital admission, patients were tilted daily (60-degree inclination), until syncope, or until a maximum of 45–90 minutes. The patients were instructed to continue a program of daily tilt training at home: two 30-minute sessions of upright standing against a vertical wall. No medication was prescribed. A total of 260 tilt table sessions were performed in 42 patients. The first tilt test was positive after 21 ± 13 minutes. The syncope was cardioinhibitory in 14 cases, vasodepressor in 19, mixed in 9. At the time of hospital discharge, 41 patients could support 45 minutes of head-up tilting. After a mean follow-up time of 15.1 (SD 7.8) months, 36 patients remained completely free of syncope. Syncope still occurred in one patient and presyncope in four patients. One patient died from an extensive myocardial infarction. The abnormal autonomic reflex activity of neurocardiogenic syncope can be remedied by a program of continued tilt training without the administration of drugs. This new treatment has proven to be effective for the vasodepressor and the cardioinhibitory type of syncope.     

Responses of Normal Subjects During 80° Head Upright Tilt Table Testing Witb and Witbout Low Dose Isoproterenol Infusion

Head upright tilt table testing has emerged as a standard technique for the evaluation of patients with recurrent unexplained syncope. To determine the specificity of head upright tilt table testing with and without a low dose isoproterenol infusion, the following study wns undertaken. A total of 34 normal volunteers (21 men, 13 women, mean age 32.9 ± 1.7 years) with no history of syncope, presyncope, or vertigo underwent head upright tilt table testing for 45 minutes. A positive test was defined as the production of syncope or presyncope associated with hypotension and bradycardia. If the test wns negative the patient was lowered to the supine position and a low dose isoproterenol infusion started (sufficient to raise the heart rate 20–25% above baseline) and the patient retilted for 20 minutes. Three subjects (8.8%; 95% CI 2, 26; P = 0.23) developed syncope during the test, two during the baseline tilt, and one during isoproterenol infusion. Interestingly, one of these subjects later bad a clinical syncopal episode. We conclude that head up tilt table testing at 80° with or without low level isoproterenol infusion provides an adequate specificity.     

Reproducibility of Head Upright Tilt Table Test Results in Patients with Syncope

Head upright tilt table testing is a promising technique for the evaluation and management of vasovagal (neuroregulatory) syncope. In order to determine the day-to-day reproducibility of results using this technique we performed head upright tilt table testing (with or without graded isoproterenol infusion) in 21 patients (12 males, 9 females, mean age 34 ± 19.1 years). During the first tilt study a total of 14 patients experienced syncope (six during baseline tilt, mean tilt time 15.8 ± 7 minutes, eight following tilt with graded isoproterenol infusion, mean tilt time 17.7 ± 9 minutes) while seven were negative. During the second tilt study (performed 3–7 days following the first study) the results of the first study were duplicated in 19 patients (90%) (six during baseline tilt, mean time 17.5 ± 8 minutes, eight following graded isoproterenol infusion, mean time 15.9 ± 7 minutes), however the level of provocation required to provoke syncope differed from that needed in the initial test in five patients (24%). We conclude that the results of head upright tilt table testing with graded isoproterenol infusions can be duplicated in 90% of patients, although some day-to-day variability exists in the degree of provocation necessary to elicit a positive response.     

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.     

Tilt Training: A New Treatment for Recurrent Neurocardiogenic Syncope and Severe Orthostatic Intolerance

Medical treatment of neurocardiogenic syncope is insufficient in many cases. We have observed a therapeutic effect of repeated head-up till testing. Therefore, we have started a program of tilt training for heavily symptomatic patients. After hospital admission, they were tilted daily (60° inclination) until syncope, or until a duration of 45–90 minutes (90 sessions in 13 patients). The mean tilt tolerance, at the first diagnostic head-up tilt table test, was 22.3 minutes (st. dev. 10.9). Before hospital discharge, 12/13 patients could sustain the full duration of tilt table testing without any symptom. In one patient syncope persisted. The patients were instructed to continue a program of daily tilt training at home, by standing against a wall for 30 minutes, one or two times per day. This resulted in a complete disappearance of syncope in all 13 patients.
Orthostatic intolerance and the excessive autonomic reflex activity of neurocardiogenic syncope can be remedied by a program of continued tilt training, without the administration of drugs.     

Vasovagal Syncope: Diagnostic Role of Head-Up Tilt Test in Patients with Positive Ocular Compression Test

We investigated the relative merits of the ocular compression test and the head-up tilt test to aid differentiation of syncope and seizures in young patients. Sixteen patients (10 males and 6 females) with a mean age of 14 ± 4.7 (SD) years (range 7–22 years) underwent graded head-up till (15°, 30°, and 45° for 2 minutes each, then 60° for 20 minutes) following positive ocular compression testing defined as precipitation of asystole for at least 3 seconds (mean 5 seconds ± 2 seconds, range 3–12 seconds). Each patient presented with recurrent unexplained loss of consciousness (mean number of episodes 30 ± 45, mean duration of illness 52 ± 40 months), and seven patients were receiving anticonvulsant medications, three of these had normal EEGs. Eleven patients (69%) developed vasovagal syncope during head-up tilt, reproducing their clinical episodes (systolic blood pressure decreased from 105 ± 10 mmHg to 84 ± 13 mmHg, diastolic blood pressure from 75 ± 9 to 22 ± 25 mmHg, and heart rate from 89 ± 13 beats/mm to 37 ± 20 beats/min). Asystole occurred in two patients during vasovagal syncope lasting 11 seconds in one and 16 seconds in the other, and, it was associated with myoclonic movements in both (convulsive syncope). Based on these findings, and given the perceived potential hazards of the ocular compression test, the head-up tilt test may be a safer procedure that adds useful information to the diagnostic evaluation of these patients.     

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.     

The Use of Head-Upright Tilt Table Testing in the Evaluation and Management of Syncope in Children and Adolescents

Recurrent syncope in an otherwise healthy child or adolescent is a common anxiety provoking disorder. Vasovagally mediated hypotension and bradycardia are believed common, yet difficult to diagnose, causes of syncope in this age group. Upright tilt table testing has been suggested as a potential method to test for vasovagal episodes. This study evaluated the utility of this technique in the evaluation and management of recurrent syncope in children and adolescents. Thirty patients with recurrent unexplained syncope were evaluated by use of an upright tilt table test for 30 minutes, with or without an infusion of isoproterenol (1 to 3 micrograms/min given intravenously), in an attempt to produce hypotension, bradycardia, or both. There were 15 males and 15 females, mean age 14 +/- 6 years. Each of the tilt positive patients received therapy with either fluorohydrocortisone, beta blockers, or transdermal scopolamine. Syncope occurred in six patients (20%) during the base line tilt and in 15 patients (50%) during isoproterenol infusion (total positives 70%). All initially positive patients were rendered tilt negative by therapy. Over a mean follow-up period of 20 months, no further episodes have occurred. We conclude that tilt table testing is a useful and effective test in the evaluation of unexplained syncope in childhood.     

Low Dose Disopyramide Often Fails to Prevent Neurogenic Syncope During Head-Up Tilt Testing

Low dose disopyramide has been used to prevent neurally-mediated syncope during head-up tilt testing but a correlation between blood levels and efficacy has not been described. We measured disopyramide levels in 15 patients with recurrent syncope and positive 70° head-up tilt tests who underwent one or more repeat tests on the drug. There were 9 males and 6 females, age range 15–78 years. Fourteen of the 15 patients had structurally normal hearts. The daily disopyramide dose was 645 ± 165 mg (mean ± SD). Patients developed syncope during 9 tests and had no syncope during 12 tests. The mean disopyramide level in patients with positive tests was significantly lower than the level in patients with negative tests (2.4 ± 0.15 μ/mL vs 3.2 ± 0.22 μ/mL, P = 0.018). Six patients were tested twice on different disopyramide doses. Five of these six patients had syncope during head-up tilt testing on the lower dose and negative tests on the higher dose (disopyramide levels 2.2 μ 0.17 μ/mL vs 3.2 μ0.17 fi/mL, P = 0.004). Thus, disopyramide is effective in preventing neurogenic syncope during head-up tilt testing, but higher blood levels are often necessary for efficacy. In a given patient, failure to respond to low dose disopyramide does not preclude success on higher doses.     

Plasma Catecholamines and Cyclic AMP Response During Head-Up Tilt Test in Patients with Neurocardiogenic (Vasodepressor) Syncope

To examine hemodynamic, plasma Catecholamines, and cyclic AMP changes during tilt in patients with neurocardiogenic (vasodepressor) syncope, six patients underwent 80± head-up tilt test for 10 minutes with isoproterenol infusion (1–3 μg/min). Venous blood was sampled in the supine position, at 3 minutes of tilt, and at the onset of vasodepressor reaction during tilt. AH patients had previous tilt studies in which vasodepressor syncope had been induced reproducibly (mean 3.3 episodes in each patient). Syncope was induced at 6.1 ± 0.4 minutes of tilt with an infusion of isoproterenol (mean 1.7 ± 0.3 fig/min). Although arterial pressure and heart rate did not change significantly between in the supine position and at 3 minutes of tilt, plasma norepinephrine increased significantly at 3 minutes of tilt (0.44 ± 0.10 ng/mL; P < 0.05) and at the onset of vasodepressor reaction (0.49 ± 0.12 ng/mL; P < 0.01) compared to the supine position with isoproterenol (0.34 ±0.10 ng/mL). Also, cyclic AMP (cAMP) increased significantly at 3 minutes of tilt (25.3 ± 2.0 pmol/mL; P < 0.005) and at the onset of vasodepressor reaction (29.6 ±1.7 pmol/mL; P < 0.005) compared to the supine position with isoproterenol (20.4 ±1.9 pmol/mL). After administration of selective beta₁-blocker, metoprolol (40 mg/day), plasma norepinephrine, and cAMP during tilt did not change significantly compared to baseline tilt. However, metoprolol prevented the syncope in 3 of 6 patients. After administration of beta₁-, beta₂- blocker, propranolol (30 mg/day), cAMP at 3 minutes of tilt decreased significantly compared to the baseline tilt (16.9 ±1.4 pmol/mL vs 25.3 ± 2.0 pmol/mL; P < 0.05) and propranolol prevented the syncope in all six patients. We concluded that the increase of cAMP may play an important role for the induction of vasodepressor reaction in patients with neurocardiogenic (vasodepressor) syncope. The concentration ofcAMP showed more sensitive response to vasodepressor reaction than that of norepinephrine.     

Dual Chamber Pacing for Neurally Mediated Syncope with a Prominent Cardioinhibitory Component

The role of cardiac pacing for treatment of recurrent neurally mediated syncope (NMS) remains controversial. We hypothesized that dual chamber pacing in NMS patients with a prominent cardioinhibitory component may be beneficial. Twelve patients (mean age = 37.8 ± 17 years, range 15–78 years, 7 men and 5 women) with a mean of 4 ± 2.2 episodes of syncope underwent tilt table evaluation. Patients were passively tilted to 70° head-up position for 20 minutes and then returned to the supine position. Isoproterenol was then infused at 1–2 μg/min to increase heart rate by ≥ 25% and tilt was repeated. Patients lost consciousness after 16 ± 6 minutes of tilt; nine patients had syncope in the baseline state and three during isoproterenol infusion. All patients had at least 5 seconds of asystole with a mean of 9.5 ± 4 seconds (range 5–20 s). A dual chamber permanent pacemaker with a special feature allowing heart rate acceleration in response to bradycardia was implanted in all patients. During a mean follow-up of 18.6 ± 4.2 months, 11 (92%) of these patients were free of syncope and had negative tilt table test. One (8%) patient had two episodes of syncope. We conclude that dual chamber pacing may be beneficial in patients with NMS with a prominent cardioinhibitory component.     

Upright Tilt Test: Correlation Between Results and Patient Clinical Features

The aim of our study was to analyze how the clinical history and the main clinical characteristics of patients suffering from loss of consciousness may influence the results of the upright tilt test. A series of 745 patients (333 males, 412 females; mean age 44 ± 18 years) with recurrent episodes of syncope or presyncope underwent complete clinical and noninvasive laboratory examination, including vagal maneuvers and upright tilt test (60° for 45 min). Cardiological and neurological findings were normal in every case. Upright tilt test was positive in 462 patients (62%). Patients with presyncope showed a lower positivity compared to patients with syncope (70.2% vs 42.9%, P < 0.001). Younger patients (< 25 years) displayed highest upright tilt test positivity (68.5%), while familial occurrence of syncope or presyncope, results of vagal maneuvers, and different gender did not correlate with the results of the test. The time interval between the last syncopal episode and the day of upright tilt test negatively influenced the proportion of positive tests (> 30 days = 45.1 % vs < 30 days = 77.2%; P < 0.001). Patients with more than three syncopal episodes in the 2 months preceding the test showed a higher upright tilt test positivity (83.9% vs 64.5%, P < 0.001). In conclusion, upright tilt test seems to be more sensitive in young patients with syncopal episodes during symptomatic periods. These findings suggest both an individual and temporal variability in autonomic nervous system activity, the implication of which are relevant to the indications for testing as well as the analysis of results.     

Asystolic Cardiac Arrest During Head-Up Tilt Test: Incidence and Therapeutic Implications

Occasionally, the cardioinhibitory response may be profond during tilt induced syncope. Whether this response is associated with more severe symptoms or predicts a poor response to pharmacotherapy remains controversial. The aim of this study was to characterize patients with vasovagally mediated asystole occurring during head-up tilt test and to evaluate the respective interests of sequential pacing and β-blockers to treat them. We performed 60° tilt testing in 179 consecutive patients with unexplained syncope (91 women and 88 men, age 36.6 ± 20.1 years). Asystole was defined as a ventricular pause > 5 seconds. All patients with tilt induced asystole received therapy with either β-blockers or sequential pacing, the efficacy of which was evaluated with serial tilt tests. Of 77 patients with positive tilt test, 10 developed syncope related to asystole (mean duration 11.9 ± 4.9 s), 2 with spontaneous recovery, and 8 with seizures needing a brief cardiopulmonary resuscitation. When compared with patients without asystole, asystolic patients had more severe symptoms (seizures: 6/10 vs 9/67, P = 0.05, injury: 9/10 vs 27/67, P = 0.0048). In the first six patients in whom cardiac pacing was considered, syncope or presyncope still occurred despite atrioventricular pacing at 45 beats/min. Five of these 6 patients, as well as the remaining 4 asystolic patients, were tilted with β-biockers: 3 patients became tilt-negative; 3 were significantly improved; and 3 did not respond. During follow-up (mean 22.7 ± 11.7 months) with every patient taking β-blockers and seven having a permanent pacemaker, no syncopal recurrence was observed. Tilt-induced asystole that may require resuscitative maneuvers occurs especially in patients with a history of seizures or injury. Therapy with β-blockers is often effective to prevent induction of syncope as well as recurrences.     

Syncope: The Diagnostic Value of Head-Up Tilt Testing

To determine the usefulness of prolonged head-up tilt in the diagnosis of neurally mediated syncope, 201 patients with history of syncope of unknown cause and 102 age and gender matched control subjects underwent a 40 minute 60 degree head-up tilt test. Head-up tilt elicited syncope (i.e., was positive) in 74 of the 201 patients (37%) with a history of unexplained syncope and in only 6 of the 102 controls (6%). The specificity of the test was 100% in patients 60 years of age and older. Symptoms during tilt-induced syncope were identified by the patients as similar to those they had suffered during their spontaneous episodes. All 80 subjects who had tilt-induced syncope recovered without sequelae. The positive predictive value of a positive response to head-up tilt was 93% and the negative predictive value was 43%. The results indicate that the prolonged head-up tilt test is a very specific procedure of high diagnostic value in patients with a history of unexplained syncope. It is particularly useful in the elderly age groups who have a high incidence of syncope.     

Comparison of a Shortened Isosorbide Dinitrate-Potentiated Head-Up Tilt Testing with the Conventional Protocol: Tolerance and Diagnostic Accuracy

Background: The head-up tilt test (HUT) is widely used to investigate unexplained syncope; however, in clinical practice, it is long and sometimes not well tolerated. Objectives: To compare the sensitivity, specificity, accuracy, and patients' tolerance of a conventional and shortened HUT. Methods: Patients with a history of vasovagal syndrome (VVS) were randomized to a conventional HUT (group I) consisting of 20-minute passive tilt followed by 25 minutes after administration of sublingual isosorbide dinitrate (ISDN), or a shortened HUT (group II) where ISDN was given immediately after tilt and observed for 25 minutes. The control group consisted of age- and gender-matched subjects without VVS symptoms. A specific questionnaire to evaluate tolerance was applied. Results: Sixty patients (29 ± 10 years, 82% female) were included. In group I, 22/30 patients had a positive HUT compared to 21/30 in group II (73% vs 70%, P = 0.77). There was also no difference in the accuracy between the two protocols (63% vs 73%, P = 0.24). The time to positivity was shorter in group II (13.2 minutes vs 30 minutes, P < 0.001). Within the control group (n = 60), the frequency of false-positives was 47% and 23% for the conventional and shortened HUT, respectively (P = 0.058). After conventional HUT, 65.2% subjects reported that the test was too long compared to 25% subjects after the shortened HUT (P = 0.002). Conclusion: In this study, the HUT without passive phase was not inferior to the conventional HUT regarding sensitivity, specificity, and accuracy. Furthermore, the shortened ISDN-potentiated protocol allowed faster diagnosis and was better tolerated. (PACE 2012; 35:1005-1011).     

Cerebral Syncope: Loss of Consciousness Associated with Cerebral Vasoconstriction in the Absence of Systemic Hypotension

Transcranial Doppler (TCD) ultrasonography done during headupright tilt induced neurocardiogenic syncope has demonstrated that cerebral Vasoconstriction occurs concomitant with (or precedes) loss of consciousness. This article demonstrates evidence that cerebral blood flow changes alone (vasoconstriction), in the absence of systemic hypotension, may result in syncope. Five patients (4 men, 1 woman; mean age 41 ± 17 years) with recurrent unexplained syncope were evaluated by use of an upright tilt table test for 45 minutes with or without an infusion of low dose isoproterenol. TCDoppler ultrasonography was used to assess middle cerebral artery systolic velocity (Vs); diastolic velocity (Vd); mean velocity (Vm); and pulsatility index (PI = Vs = Vd/Vmean). Syncope occurred in five patients during the baseline tilt and in one patient during isoproterenol infusion. During tilt induced syncope, at an average mean arterial pressure of 89 ± 16 mmHg, TCD sonography showed a 2%± 10% increase in systolic velocity; a 51%± 27% decrease in diastolic velocity; and a 131 %± 87% increase in pulsatility index. One patient underwent continuous electroencephalographic recording during tilt, which demonstrated diffuse slow wave activity (indicating cerebral hypoxia) at the time of syncope concomitant with the aforementioned TCD changes in the absence of systemic hypotension. These fndings reflect an increase in cerebrovascular resistance secondary to arteriolar vasoconstriction distal to the insonation point of the middle cerebral artery, that occurred concomitant with loss of consciousness and in the absence of systemic hypotension. We conclude that in some individuals abnormal baroreceptor responses triggered during orthostatic stress may result in a derangement of cerebral autoregulation leading to cerebral vasoconstriction with resultant cerebral hypoxia in the absence of systemic hypotension.     

The Postural Orthostatic Tachycardia Syndrome: A Neurocardiogenic Variant Identified During Head-Up Tilt Table Testing

Head upright tilt table testing has emerged as an accepted modality for identifying an Individual's predisposition to episodes of autonomically mediated hypotension and bradycardia that are sufficiently profound so that transient loss of consciousness ensues (neurocardiogenic syncope). However it has also become apparent that less dramatic falls in blood pressure, while not sufficient to cause full syncope, may produce symptoms such as near syncope, vertigo, dizziness, and TIA-like episodes. We have identified a subgroup of individuals with a mild form ofautonomic dysfunction with symptoms of postural tachycardia and lightheadedness, disabling fatigue, exercise intolerance, dizziness, and near syncope. During baseline tilt table testing these patients demonstrated a heart rate increase of ± 30 beats/min (or a maximum heart rate of 120 beats/min) within the first 10 minutes upright (unassociated with profound hypotension), which reproduced their symptom complex. In addition these patients exhibit an exaggerated response to isoproterenol infusions. Similar observations have been made by others who have dubbed this entity the Postural Orthostatic Tachycardia Syndrome (POTS). We conclude that POTS represents a mild (and potentially treatable) form of autonomic dysfunction that can be readily diagnosed during head upright tilt table testing.     

Polymorphic Ventricular Tachycardia Induced During Tilt Table Testing in a Patient with Syncope and Probable Dysfunction of the Sinus Node

We present a case of life-threatening arrhythmia occurring during tilt table testing in a 44-year-old man with syncope. Polymorphic ventricular tachycardia occurred while the patient was tilted up under the intravenous infusion of isoproterenol (2 μg/min). No ischemia, QTc prolongation, or electrolyte abnormality preceded this event. The arrhythmia was not induced by programmed ventricular stimulation or exercise testing. Based on electrophysiological and clinical data, the diagnosis of sick sinus syndrome was entertained.