Laura Elliott

Cerebral vasoconstriction during head-upright tilt-induced vasovagal syncope. A paradoxic and unexpected response.

BackgroundTo determine the effect of vasovagally mediated syncope on the cerebral circulation, transcranial Doppler sonography was used to assess changes in cerebral blood flow velocity during head-upright tilt-induced syncope. Methods and ResultsThirty patients (17 men and 13 women; mean age, 43 ± 22 years) with recurrent unexplained syncope were evaluated by use of an upright tilt-table test for 30 minutes, with or without an infusion of intravenous isoproterenol (1–4 μg/min), in an attempt to provoke bradycardia, hypotension, or both. Transcranial Doppler sonography was used to assess middle cerebral artery systolic velocity (Vs), diastolic velocity (Vd), ratio of systolic to diastolic velocities, pulsatility index (PI = Vs-Vd/Vmean), and resistance index (RI = Vs-Vd/Vs) before, during, and after tilt. Syncope occurred in six patients (20%) during the baseline tilt and 14 (46%) during isoproterenol infusion (total positives, 66%). In the tilt-positive patients, concomitant with the development of hypotension and bradycardia, transcranial Doppler sonography showed a 75 ± 17% decrease in diastolic velocity, unchanged systolic velocity, a 46 ± 17% decrease in mean velocity, a 295 ± 227% increase in pulsatility index, and a 73 ± 34% increase in resistance index. ConclusionsThese findings reflect increased cerebrovascular resistance secondary to arteriolar vasoconstriction distal to the insonation point of the middle cerebral artery. This is paradoxic because the expected response of the cerebral circulation to hypotension is vasodilation. We conclude that abnormal baroreceptor responses triggered during vasovagal syncope result in a derangement of cerebral autoregulation with paradoxic vasoconstriction in the face of increasing hypotension.

Utility of upright tilt-table testing in the evaluation and management of syncope of unknown origin

PURPOSE Vasovagally mediated hypotension and bradycardia are believed to be common, but difficult to diagnose, causes of syncope. Upright tilt-table testing has been proposed as a possible way to test for vasovagal episodes. This study investigated the clinical utility of this technique in the evaluation and management of patients with syncope of unknown origin. PATIENTS AND METHODS Twenty-five patients with recurrent unexplained syncope and six control subjects were evaluated by use of an upright tilt-table test for 30 minutes, with or without an infusion of isoproterenol (1 to 3 micrograms/minute given intravenously), in an attempt to provoke bradycardia, hypotension, or both. Of the 25 patients, there were 14 males and 11 females, with a mean age of 50 +/- 16 years. Six control patients with no history of syncope were also studied. All tilt-positive patients received therapy with either beta-blockers, disopyramide, transdermal scopolamine, or hydroflurocortisone, the efficacy of which was evaluated by another tilt-table test. RESULTS Syncope occurred in six patients (24%) during the baseline tilt and in nine patients (36%) during isoproterenol infusion (total positives, 60%). None of the controls had syncope during the test. All patients who had positive test results eventually became tilt-table-negative by therapy, and over a mean follow-up period of 16 +/- 2 months no further episodes have occurred. CONCLUSION From this study we conclude that upright tilt-table testing combined with isoproterenol infusion is clinically useful in the diagnosis of vasovagal syncope and the evaluation of pharmacologic therapy.

Differentiation of Convulsive Syncope and Epilepsy with Head-Up Tilt Testing

OBJECTIVE To evaluate the usefulness of head-upright tilt table testing in the differential diagnosis of convulsive syncope from epileptic seizures in patients with recurrent idiopathic seizure-like episodes. DESIGN Prospective, nonrandomized study. SETTING Electrophysiology laboratory of a university hospital. PATIENTS Fifteen patients (8 men and 7 women patients; mean age, 29 +/- 20 years) with recurrent unexplained seizure-like episodes, unresponsive to antiseizure medication. MEASUREMENTS Head-upright tilt table testing with or without isoproterenol infusion. Five patients who were initially tilt positive had a second tilt test with continuous electroencephalographic (EEG) recording. MAIN RESULTS Syncope associated with tonic-clonic seizure-like activity occurred in six patients (40%) during the baseline tilt and in four patients (27%) during isoproterenol infusion (total positive tests, 67%). The EEG showed diffuse brain wave slowing (not typical of epileptic seizures) in five of five patients during the convulsive episode. All patients who had positive test results eventually become tilt table negative after therapy, and over a mean follow-up period of 21 +/- 2 months, no further seizure-like episodes have occurred. CONCLUSION Upright tilt table testing combined with isoproterenol infusion may be useful to distinguish convulsive syncope from epileptic seizures.

Usefulness of fluoxetine hydrochloride for prevention of resistant upright tilt induced syncope

Recurrent vasovagally mediated episodes of hypotension and bradycardia are a common cause of recurrent syncope that can be identified by head‐upright tilt table testing. Although the use of beta blockers, transdermal scopolamine, disopyramide, and fludrocortisone may be helpful in preventing further episodes, some patients are intolerant of or respond poorly to each of these agents. Following anecdotal observations, we investigated the utility of fluoxetine (a serotonin re‐uptake antagonist) in preventing head‐upright tilt induced hypotension/bradycardia in patients unresponsive to or intolerant of standard therapy. Sixteen patients (7 men and 9 women, mean age 42 ± 21 years) with recurrent syncope and positive head‐upright tilt studies (refractory to normal therapy) were placed on fluoxetine and restudied 5–6 weeks afterward. Three patients were intolerant of the medication. Of the 13 patients who underwent repeat tilt studies, seven patients (53% of the patients retested or 44% of the total group) were rendered tilt table negative, and, over a mean follow‐up period of 19 ± 9 months, have remained asymptomatic. We conclude that fluoxetine may be an effective therapy in patients with recurrent vasovagally mediated syncope refractory to other forms of therapy.

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

GRUBB, B.P., et al.: 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 μg/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.

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.

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.

Tilt table testing in the evaluation and management of athletes with recurrent exercise-induced syncope.

Recurrent idiopathic exercise-related syncope in the young athlete is often a challenging and frustrating condition. Vasovagally mediated hypotension and bradycardia is believed to be a common, but difficult to prove, cause of this form of syncope. This study evaluated the usefulness of head-upright tilt table testing in the evaluation and management of young athletes with recurrent idiopathic exercise-related syncope. Twenty-four trained young athletes (12 male, 12 female mean age 18 +/- 3.4 yr) with recurrent unexplained exercise-related syncope were evaluated by use of an upright tilt table test for 30 min, with or without an infusion of isoproterenol (1-3 micrograms.min-1 given intravenously) in an effort to provoke bradycardia, hypotension, or both. Ten control patients with no history of syncope were also studied. Syncope occurred in 10 patients (41%) during the baseline tilt and in nine patients (37%) during the isoproterenol infusion (total positives 79%). Seventeen patients who had positive test results eventually became tilt table negative with pharmacotherapy, and over a mean follow-up period of 23 +/- 7 months, no further syncopal episodes have occurred. Two patients refused pharmacotherapy and have continued to experience syncope. We conclude that head-upright tilt table testing combined with isoproterenol infusion is useful in the diagnosis of vasovagal syncope in young athletes with recurrent exercise related syncope, and in the evaluation of prophylactic pharmacotherapy.

Recurrent Unexplained Syncope in the Elderly: The Use of Head-Upright Tilt Table Testing in Evaluation and Management

To investigate the usefulness of head‐upright tilt table testing for vasovagal episodes in the evaluation and management of elderly patients with recurrent idiopathic syncope.

Adaptive Rate Pacing Controlled by Right Ventricular Preejection Interval for Severe Refractory Orthostatic Hypotension

A 72‐year‐old African‐American man with frequent recurrent syncope was found to have severe refractory orihostatic hypotension with concomitant supine hypertension. Pharmacotherupy was successful in controlling his supine hypertension but was unable to resolve his severe orihostatic hypotension. Temporary fixed rate tachypacing was only minimally effective in preventing syncope during upright tilt, while variable rate pacing based on degree of blood pressure fall was far superior. Following these observations, an adaptive rate pacing system controlled by right ventricular preejection interval was implanted (Precept DR Model 1200). The system adequately sensed the patients fall in blood pressure when sitting or standing and augmented its rate accordingly, thus preventing syncope. While supine, the pacing rate fell to 60 ppm, thereby, avoiding an exacerbation of his concomitant supine hypertension. Over a 3‐nionth follow‐up period, he has had no further orthostatic or syncopal episodes. We conclude that adaptive rate pacing using right ventricular preejection interval may be an effective treatment for severe refractory orthostatic hypotension.