Diagnostic Value of Nitrate Stimulated Tilt Testing Without Preceding Passive Tilt in Patients with Suspected Vasovagal Syncope and a Healthy Control Group

BACKGROUND

The contribution of the passive tilt phase, in a combined nitrate stimulated tilt protocol may be low yielding. In order to develop a shortened, and thus easier to perform test, we investigated the optimal duration of a nitrate tilt protocol without a preceding passive phase.

METHODS

Thirty-eight consecutive patients (18F/20M; mean age 46 +/- 16) with clinically suspected vasovagal syncope and 31 control subjects (15F/16M; mean age 40 +/- 18) were tested. The subjects were tilted to 70 degrees for a maximum period of 30 minutes, and sublingual nitroglycerin 0.4 mg spray was administrated directly after attaining erect posture. Receiver operator characteristics (ROC) analysis was done to determine the optimal test duration.

RESULTS

In the patient group 31 (82%) and in controls 5 (16%) had a positive test. Sensitivity, specificity, and accuracy at test end were 82, 84, and 83%, respectively. ROC analysis revealed that a maximum accuracy of 83% was attained at 14 minutes, with a sensitivity and specificity of 79 and 87%, respectively.

CONCLUSION

Nitrate stimulated tilt testing, without a preceding passive tilt phase, and limited to a test duration of 15 minutes, provides an accurate, sensitive, and specific method to provoke vasovagal reactions in subjects with clinically suspected vasovagal syncope.

Single-stage adenosine tilt testing in patients with unexplained syncope

INTRODUCTION

We previously have shown that a 3-minute single-stage adenosine tilt test has a diagnostic yield comparable to a two-stage protocol consisting of a 30-minute drug-free tilt followed by a 15-minute isoproterenol tilt. In this study, we sought to further define the clinical utility of adenosine tilt testing in patients with unexplained syncope by prospectively evaluating test specificity and determining predictors of a positive test response.

METHODS AND RESULTS

The specificity of single-stage adenosine tilt testing was determined using 30 control subjects. To determine the diagnostic yield of this protocol, adenosine tilts were performed in 129 patients with unexplained syncope. The adenosine tilt test protocol had high specificity (100%) but a low overall diagnostic yield (18%). However, the yield was affected significantly by age. In patients </=40 years of age, the tilt test was positive in 15 (41%) of 37 patients, which was significantly greater than the yield in patients between the ages of 41 and 64 years (6/41 patients [15%], P = 0.012) and those >/=65 years of age (2/41 patients [5%], P < 0.0001).

CONCLUSION

These data support single-stage adenosine tilt testing in patients </=40 years of age because the diagnostic yield of the test is maximal in this group and the test can be completed in </=3 minutes. Conversely, the diagnostic yield of adenosine tilt testing in patients >40 years of age is low, suggesting that the clinical utility of this protocol is limited in these patients.

Cardiovascular responses to lower body negative pressure in the elderly: role of reduced leg compliance

BACKGROUND

It is warranted to test the hypothesis that the orthostatic tolerance does not diminish in the aging process per se in healthy individuals.

OBJECTIVE

The purpose of the present study was to examine the effects of aging on cardiovascular response and baroreflex sensitivity during lower body negative pressure (LBNP) with a special reference to leg compliance.

METHODS

Fifteen healthy old male subjects [mean age 68.2 +/- (SE) 0.8 years] and 22 young male subjects [mean age 21.4 +/- (SE) 0.3 years] underwent a 21-min bout of ramped LBNP (from 0 to -60 mm Hg, 10 mm Hg each for 3 min). Heart rate (HR), blood pressure, stroke volume (SV), forearm blood flow, and leg volume were measured throughout the experimental period. The arterial baroreflex sensitivity was calculated from spontaneous changes in beat-to-beat arterial pressure and HR during LBNP.

RESULTS

The leg compliance was lower, and the orthostatic tolerance index was higher in old than in young participants. The LBNP-associated increases in leg volume and HR and the decreases in SV were lower in old subjects, suggesting that the reduction of venous return was less in magnitude in old subjects during LBNP. The baseline value of baroreflex sensitivity evaluated by the sequence analysis was smaller, and no LBNP-related change was observed in old subjects, whereas a gradual LBNP-related reduction was observed in young subjects. The slope of regression between DeltaSV and change in forearm vascular resistance during LBNP was identical in both age groups.

CONCLUSIONS

We conclude that: (1) aging per se does not increase the intolerance to orthostatic stress induced by LBNP; (2) a low magnitude of venous return reduction during LBNP contributes to a higher tolerance in the old because of lower leg compliance, and (3) the sensitivity of baroreflex control of the HR is attenuated in the old; however, there is no deterioration of the sensitivity of the peripheral vasoconstriction during LBNP.

Does an early increase in heart rate during tilting predict the results of passive tilt testing?

Head-up tilt testing is a useful but time-consuming procedure. If we could accurately predict the tilt testing results; we would be able to substantially shorten the duration of tilt protocol. To clarify the hypothesis that an early increase in heart rate (HR) during tilting can predict the passive tilt results in our protocol (80-degree angle for 30 minutes), we studied 115 consecutive patients (72 men, 43 women, mean age 46 +/- 19 years) who were clinically diagnosed with neurally mediated syncope. Twenty-nine (25%) patients had a positive tilt test (P group), whereas 86 (75%) patients had a negative test (N group). The early HR increase was defined as the maximum HR during the first 5 minutes of tilting minus the resting HR before tilting. The early HR increase was significantly higher in the P group (23.8 +/- 9.5 beats/min) than in the N group (17.5 +/- 8.2 beats/min, P = 0.0008), but it was negatively correlated with the tilt duration to positive response (r = -0.52, P = 0.0032) and the patient age in the entire study population (r = 0.62, P < 0.0001). Results of multiple regression analysis indicated that age, tilt result, and tilt duration were independently associated with the early HR increase. As a result, an early HR increase > or = 18 beats/min, the best apparent cut-off point obtained in our study, was a sensitive (100%) marker for prediction of a positive response at < or = 15 minutes of tilting, but it showed a low specificity (61%). In conclusion, an early HR increase during 80-degree tilting may be only predictive for a positive result < or = 15 minutes because it depends on the tilt duration to a positive response and patient age.

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.

A "dysautonomic" head-up tilt test pattern in elderly patients with neurocardiogenic syncope

The characteristics of neurocardiogenic syncope (NCS) in elderly patients remain unclear. We compared the hemodynamic profiles of young and older patients with consecutive and positive head-up tilt tests (HUT). Continuous, noninvasive, and reliable monitoring of arterial pressure (AP) and heart rate (HR) was done throughout 46 consecutive positive HUTs of symptomatic patients. The population (12-82 years old) was divided into two groups: younger patients, Y (n = 25, < or = 65 years), and older patients, O (n = 21). Changes in AP and HR after the first minute of tilting, during the stable orthostatic phase and during syncope were compared. Except for systolic pressure, baseline hemodynamic parameters were similar in Y and O. No difference appeared in the mean time elapsed before syncope (19+/-9 vs 22+/-2 min). Asymptomatic hypotension was observed, only in O, 1 minute after tilting, followed by a progressive fall in the mean AP before syncope (0+/-0.9 vs -1+/-0.7 mmHg/min) without HR increase (0.7+/-1 vs 0+/-0.6 beats/min). This pressure slope was strongly related to age (r = 0.54, P < 0.001). Hemodynamic recording during HUT identifies a dysautonomic pattern in elderly patients with NCS and the abnormal AP/HR responses to orthostasis may be a feature specific to this population. Although the central mechanism of NCS is common to all ages, the age-related characteristics of the trigger event may indicate the need for specific management at different ages.

Poor reproducibility of false-positive tilt testing results in healthy volunteers

Positive responses to head-up tilt testing occur in healthy subjects. However, the reproducibility of "false-positive" tilt testing results has not been clarified. To study the reproducibility of "false-positive" responses, we prospectively performed 2 tilt tests separated by 1 to 10 (mean 3.2) weeks in 20 healthy males aged 23 to 40 years (mean 30 years). The baseline tilt test (80 degrees for 30 minutes) ended positive in 4 (20%) subjects on the initial test and 2 (10%) on the second test with only 1 (5%) who had consecutive positive responses. No additional positive responses were noted during the isoproterenol (0.01 microgram/kg/min)-tilt test for 10 minutes. We demonstrated that a false-positive response occurred in 5 (25%) of 20 young males who underwent 2 tilt tests, however, only 1 (5%) subject had consecutive positive responses. Poor reproducibility may be characteristic of false-positive responses in head-up tilt testing.

Responses of normal subjects during 80 degrees head upright tilt table testing with and without 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 was 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 was 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 had a clinical syncopal episode. We conclude that head up tilt table testing at 80 degrees with or with out low level isoproterenol infusion provides an adequate specificity.

Neural circulatory control in vasovagal syncope

The orthostatic volume displacement associated with the upright position necessitates effective neural cardiovascular modulation. Neural control of cardiac chronotropy and inotropy, and vasomotor tone aims at maintaining venous return, thus opposing gravitational pooling of blood in the lower part of the body. The present concept of the vasovagal response or "common faint" implicates the development of inappropriate cardiac slowing due to sudden augmentation of efferent vagal activity, and arteriolar dilatation by sudden reduction or cessation of sympathetic activity. The venous pooling associated with lasting orthostatic stress results in development of central hypovolemia. At a certain point during the ongoing reflex adaptation to the hypovolemia in progress, a depressor reflex is set in train. The depressor reflex input along this second "peripheral" afferent pathway is postulated to originate from various sites in the cardiovascular system but remains uncertain. The common faint in humans is of both vaso- and vagal origin; the pure vagal response is less common than its vasodepressor variant. There is strong evidence for an early loss of vasomotor tone in the majority of fainting subjects. Blocking the vagus nerve or cardiac pacing is not of much help in preventing vasovagal syncope; though atropine or pacing may prevent bradycardia in vasovagal fainting, they have never been proven to prevent hypotension. Baroreflex modulation of autonomic outflow remains present during the presyncopal stages until it becomes offset by an opposing depressor reflex with relative bradycardia and relaxation of arterial resistance vessels. The nature of the vasodilatation associated with the vasovagal response has still not been settled.

Donor reactions and injuries from whole blood donation

In this review of common and uncommon donor reactions and injuries, donation-associated deaths were found to be extremely rare and generally thought to be coincidental; the rate of coincidental deaths was less than what would be expected based on life insurance tables. Vasovagal reactions, hematomas/bruises, and history of irritation or allergic reaction to adhesive tape or skin preparations are observed daily in a busy blood collection center. Syncopal vasovagal reactions sometimes resemble shock, but unlike shock, they reverse themselves and do not cause death. Through good management, a blood donor organization can minimize the incidence of syncope. Accidental arterial venipuncture is very uncommon (1 in 100,000), and donors with arterial punctures do well if pressure is applied for an extended period of time. Rarely, a pseudoaneurysm results, and this requires surgery. AV fistulas and compartment syndromes can also occur, but these are extremely rare; most experienced blood center physicians have never observed a case. Neurologic needle injuries occur approximately once in every 6,300 donations. Although neurologic needle injury complaints are usually received within 10 days of blood donation, 10% of the injured donors may complain weeks to months later. Most donors with needle injuries recover within a month and many within a day or two, but approximately 30% will have a recovery period of greater than 1 month and an occasional case may exceed 6 months. Donors with neurologic needle injuries generally have a full recovery, even when the recovery period may be extended. Thrombophlebitis has a low incidence (1 in 50,000 to 1 in 100,000), and infection at the phlebotomy site is rare. Both are easily treated and have little impact on the donor's health.

Autonomic profile of subjects prone to fainting

Syncope is the most common form of fainting that may occur at least once during a life-time in up to one-third of the general population. In 50% of patients the cause remains unknown. In an attempt to identify subtle disturbances of the autonomic nervous system, we examined 70 subjects, aged from 14 to 39 years, who suffered from recurrent neurally mediated syncope. We performed a battery of non-invasive tests assessing cardiovagal, sympathetic cholinergic and sympathetic adrenergic function. We compared the results with a group of 30 healthy, non-fainting subjects matched for age and sex. Basal records were similar in both groups. Patients had preserved cardiovagal function. The multivariate cluster analysis allowed us to find a homogeneous group of cases (46%) that simultaneously presented: greater fall in systolic and diastolic blood pressure after standing, increased 15:30 ratio, exaggerated absolute heart rate rise in response to standing and subclinical reduced sudomotor function in the foot. The results suggest the existence of a subclinical autonomic profile, with subtle sympathetic postganglionic impairment, evident in lower limbs. These findings may contribute to proving the existence of different types of neurally mediated syncope, all different in their onset and mechanism but with a common final manifestation: syncopal loss of consciousness.

Head-up tilt testing with and without isoproterenol infusion in healthy subjects of different ages

Passive head-up tilt testing with or without infusion of isoproterenol is used in the investigation and management of patients with syncope. Twenty-five healthy asymptomatic volunteers prospectively grouped according to age (young [28 +/- 1.7 years]: n = 9; middle [51 +/- 3.3 years]: n = 11; elderly [81 +/- 2.4 years]: n = 5; mean +/- SE) were studied during: (1) supine carotid sinus massage; (2) 60 degrees head-up tilt alone; and (3) infusion of isoproterenol to raise the heart rate 20% above supine baseline, prior to 10-minute repeat tilt. Symptoms occurred in three subjects (12%) and only occurred with passive tilting alone. Two young subjects had syncope with sinus pauses greater than 10 seconds. One elderly subject developed atrial flutter. No subject had symptoms or hypotension during tilt plus isoproterenol or a pause greater than 3 seconds with carotid sinus massage. With passive tilt, mean heart rate increased by 16 +/- 6 beats/min and 18 +/- 7.8 beats/min in the young and middle aged subjects (P < 0.05), but only by 6 +/- 5 beats/min in the elderly (P = NS, supine vs 60 degrees in each group). With head-up tilt plus isoproterenol infusion, the mean heart rate elevation in response to tilt was 17 +/- 9 beats/min, 8 +/- 3 beats/min, and 12 +/- 4 beats/min for the young, middle, and elderly subjects, respectively (P < 0.05, supine vs 60 degrees in each group).(ABSTRACT TRUNCATED AT 250 WORDS)