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(Circulation. 1997;96:581-584.)
© 1997 American Heart Association, Inc.

Articles

Prediction of Head-Up Tilt Test Result by Analysis of Early Heart Rate Variations

Ziad Mallat, MD; Eric Vicaut, MD, PhD; Adama Sangaré, MD; Jordanka Verschueren, MD; Guy Fontaine, MD, PhD; ; Robert Frank, MD

From the Centre de Rythmologie et de Stimulation Cardiaque (Z.M., A.S., J.V., G.F., R.F.), Hôpital Jean Rostand, Ivry-sur-Seine, and the Laboratory of Biophysics and INSERM (E.V.), Unité 141, Hôpital Fernand Widal, Paris, France.

Correspondence to Robert Frank, MD, Centre de Rythmologie et de Stimulation Cardiaque, Hôpital Jean Rostand, 39, rue Jean-le-Galleu, 94200 Ivry-sur-Seine, France.

	Abstract

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Background Head-up tilt testing is a useful test for investigating vasovagal syncope. The determination of early, accurate, predictive criteria for a negative result would permit a reduction in the duration of the tilt test.

Methods and Results Patients with no drug use and no illnesses other than recurrent unexplained syncope were recruited. In an initial study (110 consecutive patients), we aimed to determine a predictive criterion based on heart rate variations during the first minutes of upright tilting that could distinguish between patients with positive and negative tilt tests (patients with an early continual decrease in heart rate or blood pressure were excluded). Then we tested the predictive value of the established criterion in a second independent sample of patients with unexplained syncope (109 consecutive patients). An early sustained increase in heart rate 18 bpm during the first 6 minutes of upright tilting at a 60° angle allowed us to predict negative tilt tests with 100% specificity, 100% positive predictive value, and 88.6% sensitivity. This criterion was validated in the second, prospective arm of the study (96.4% specificity, 98.4% positive predictive value, and 87.3% sensitivity), even with subsequent use of isoproterenol in low doses.

Conclusions In patients with no drug use and no illnesses other than recurrent unexplained syncope, a simple clinical criterion identifies patients who will not develop syncope during a prolonged upright tilt.

Key Words: isoproterenol • syncope • tests • heart rate

	Introduction

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Recurrent syncope is a common medical problem.¹ Head-up tilt testing with or without isoproterenol infusion has been shown to be a useful diagnostic test in patients referred for recurrent unexplained syncope.^{2 3 4 5 6} The wide use of this diagnostic technique has also been favored by the development of accurate noninvasive methods for continuous monitoring of blood pressure.⁷

The decrease in venous return on the assumption of an upright posture during passive head-up tilt testing stimulates a reflex increase in sympathetic activity. The enhanced strength of myocardial contraction in relatively underfilled cardiac chambers^{8 9} is thought to be responsible in some predisposed subjects for the abnormal stimulation of cardiac mechanoreceptors and the activation of vagal afferent fibers firing toward the vasomotor centers.^{10 11 12 13} This would initiate a reflex withdrawal of sympathetic tone with enhanced parasympathetic activity, resulting in severe peripheral vasodilation and bradycardia leading to syncope, ie, the Bezold-Jarisch reflex.^{14 15 16}

Analyses of markers for autonomic nerve activity have shown increased sympathetic tone with diminished or preserved parasympathetic activity during head-up tilt testing before the onset of syncope.^{17 18 19 20} On the basis of these observations, we hypothesized that in patients with no illnesses other than recurrent unexplained syncope, the early response of the autonomic nervous system to the assumption of an upright posture would distinguish between patients with positive and negative tests. Such a discrimination using an early marker would permit drastic reduction of the duration of the tilt test in these patients, making its use more convenient. Therefore, we analyzed the early heart rate response to head-up tilt testing in patients referred for recurrent unexplained syncope and evaluated its ability to predict the tilt test result.

	Methods

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Patient Selection
Patients referred for recurrent unexplained syncope were included according to the following criteria: no history of cardiovascular disease, no history of any disease that might affect the autonomic nervous system, no drug use, normal neurological evaluation, and physical ability to perform a head-up tilt test.

Study Design
This work was divided into two parts, as described below.

Study 1
One hundred eighty-nine consecutive patients referred for recurrent unexplained syncope were screened, of whom 110 patients were determined to be eligible for the study. To find the threshold value of early heart rate increase that could be an optimal criterion for prediction of the tilt test result,²¹ we plotted the percentages of positive and negative tilt tests against the corresponding levels of increase in heart rate classified in successive 2-bpm intervals. The optimal threshold value of early heart rate increase was determined on the basis of its positive predictive value for a negative tilt test.

Study 2
After the best predictive criterion had been established, we prospectively tested its predictive value in a second, independent sample of consecutive patients referred for recurrent unexplained syncope (135 patients screened, of whom 109 were determined to be eligible for the study). In addition, in these patients, we investigated the ability of the established criterion to predict the result of a head-up tilt test after an infusion of isoproterenol.

Tilt Protocol
Study 1
After 30 minutes of rest in the supine position, each patient was submitted to passive head-up tilt testing at a 60° angle for 45 minutes (Westminster protocol). Heart rate and blood pressure were continuously monitored by the use of digital plethysmography (Finapress, Ohmeda), and recordings were obtained on a low-speed graduated paper. A positive tilt test was defined as a drop in systolic blood pressure >60% from baseline values or an absolute value of <80 mm Hg with or without bradycardia (defined as a drop of >30% from baseline value or to <40 bpm), associated with symptoms of imminent syncope (eg, lightheadedness or dizziness).²² Syncope was classified according to Sutton²³ in three forms: mixed (type 1), cardioinhibitory (types 2A and 2B), and vasodepressor (type 3).

Study 2
Patients were first subjected to the same head-up tilt test protocol described in study 1 and, if negative, to an isoproterenol tilt test. A methodology was chosen that could provide adequate sensitivity and specificity.²⁴ While the patient was in the supine position, isoproterenol was infused through an antecubital intravenous catheter at a rate of 1 µg/min and increased by 0.5 µg/min (maximal infusion rate, 3 µg/min) until a 30% increase in heart rate at rest was reached. The isoproterenol infusion was conducted over a 5-minute period with the patient in the supine position and was maintained during 10 minutes of upright tilting at a 60° angle.

Definitions for Criterion
The extent of the early increase in heart rate was defined as the highest heart rate during the first 6 minutes of tilting minus the baseline heart rate. The baseline heart rate value was defined as the mean heart rate value during the last 10 minutes of rest. The highest heart rate value during the first 6 minutes of tilting was defined as the mean value of the highest rate sustained for 30 seconds. All data were analyzed by two independent physicians who were unaware of the results of the tilt test and who had to measure the extent of the early increase in heart rate according to the defined criteria. Patients with an unstable heart rate during the last 10 minutes of rest preceding the tilt test (ie, continuous variation of >8 bpm between minimal and maximal heart rates) were excluded from analysis because of the inability to obtain an accurate measurement of the early increase in heart rate in these patients. Because the first aim of the study was to allow the prediction of a tilt test result early during the tilt, we excluded all patients with a continuous decrease in heart rate or blood pressure during the early upright tilt, since these patients could easily be considered at high risk for tilt-induced syncope (ie, there was no need for a predictive criterion in these patients).

Statistical Analysis
All results are given as mean±SD. Comparisons between means were made by use of two-sided Student's t test for quantitative variables or ² test for qualitative variables at a 5% significance level.

	Results

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Study 1
One hundred eighty-nine consecutive patients were screened, of whom 110 patients were determined to be eligible for the study (62 women and 48 men; mean age, 50.6±17.6 years). Reasons for exclusions were as follows: presence of cardiovascular disease in 33 patients, drug use in 39, diabetes mellitus in 4, and early termination of the tilt test because of physical disability in 3.

Of the 110 patients included in the study, 9 (8.2%) were subsequently excluded because of an inability to obtain stable measurements of heart rate. Three other patients (2.7%) had constant decreases in blood pressure and heart rate from the beginning of the tilt test and were excluded from the study (these patients later experienced syncope, 2 with type 2A and 1 with type 2B). Thus, 98 patients (57 women, 41 men) ranging in age from 21 to 85 years (mean, 50.5±17.3 years) were suitable for analysis in this study.

Seventy patients (71.4%) had a negative tilt test, whereas 28 patients (28.6%) experienced vasovagal syncope. Sex and age did not differ significantly between patients with negative or positive tilt tests. Mean time to tilt-induced syncope was 20.1±10.7 minutes and was not correlated to age, sex, or type of syncope. Fifteen patients (53.6%) experienced a mixed reaction, 10 (35.7%) had a cardioinhibitory response (9 with type 2A and 1 with type 2B), and 3 (10.7%) had a vasodepressor response.

Time to early maximal increase in heart rate was 2.0±1.3 minutes in patients with a negative tilt test and 2.8±1.7 minutes in patients with a positive tilt test result (P<.05).

Patients with a negative tilt test had a mean early increase in heart rate (as defined above) of 12.3±5.2 bpm, whereas patients with a positive tilt test result had a mean early increase of 27.9±6.7 bpm (P<.001). As shown in Fig 1, statistical distributions of the early increase in heart rate in patients with negative or positive tilt tests were completely different. As observed by both independent physicians who analyzed heart rate variations, all patients with a positive tilt test increased their heart rate by >18 bpm during the first 6 minutes of head-up tilt testing (Fig 2). Consequently, an early increase in heart rate (as defined above) 18 bpm (found in 62 patients) had 100% specificity and 100% positive predictive value for a negative head-up tilt test, with 88.6% sensitivity. Age was not significantly correlated to the early increase in heart rate. However, considering the patients with an early increase in heart rate at the threshold limit of 18 bpm (ie, between 18 and 22 bpm), those with a negative tilt test result were younger (mean age, 35.0±13.0 years) than those with a positive tilt test result (mean age, 70.2±3.7 years).

View larger version (32K): [in this window] [in a new window]   Figure 1. Statistical distribution (according to observer 1) of the early increase in heart rate, classified in successive 2-bpm intervals, in patients with negative (TILT-) and positive (TILT+) tilt tests (classification by observer 2 differed in only three patients). All patients with positive tilt tests had an early increase in heart rate of >18 bpm.

View larger version (18K): [in this window] [in a new window]   Figure 2. Percentages of negative and positive tilt tests plotted against the early increase in heart rate according to the two observers. For both observers, all patients with positive tilt tests had an early increase in heart rate of >18 bpm.

Study 2
One hundred thirty-five consecutive patients were screened, of whom 109 (65 women and 44 men; mean age, 50.8±18.5 years) were determined to be eligible for the study. Reasons for exclusions were as follows: presence of cardiovascular diseases in 12 patients and drug use in 14. Of the 109 patients included in the study, 2 were later excluded because of a physical inability to perform a tilt test and 3 because of an inability to obtain stable measurements of heart rate and blood pressure. Five other patients had constant decreases in heart rate and blood pressure during the first 6 minutes of upright tilting and were then excluded from analysis (these patients later experienced syncope, 3 type 2A and 2 type 2B). Thus, 99 patients (56 women and 43 men) ranging in age from 15 to 83 years (mean, 49.1±18.7 years) were included in the analysis.

Sixty-three patients (64%) had an early increase in heart rate (as defined above) 18 bpm, and 36 (36%) were above this value. Seventy-one patients (72%) had a negative head-up tilt result, whereas 28 (28%) had tilt-induced syncope (14 had a mixed vasovagal response, 12 had a cardioinhibitory response [11 type 2A and 1 type 2B], and 2 had a vasodepressor response). All but 1 of the 63 patients with an increase in heart rate 18 bpm had negative tilt tests. Consequently, this criterion had 96.4% specificity and 98.4% positive predictive value for a negative Westminster tilt test, with 87.3% sensitivity. Thirty (48%) of the 63 patients with a negative tilt result and an increase in heart rate 18 bpm were subjected to an isoproterenol tilt test with an infusion rate of 2.25±0.61 µg/min; the other patients did not give their consent for the isoproterenol infusion for individual reasons. All 30 patients still had negative tilt test results after the isoproterenol tilt test (100% positive predictive value for a negative isoproterenol tilt test). However, 3 (50%) of 6 patients with an increase in heart rate >18 bpm and a negative Westminster tilt test developed tilt-induced syncope when subjected to an isoproterenol tilt test (mean infusion rate, 2.67±0.41 µg/min).

	Discussion

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Previous animal and human studies²⁰ emphasized the important role of the autonomic nervous system as both a trigger and an effector in the pathogenesis of the vasovagal response. Even though an increase (or an absence of decrease) in vagal input after upright tilting has been reported in some patients with tilt-induced syncope, a switch toward an increased sympathetic-to-parasympathetic response ratio occurred in response to head-up tilt testing in these patients, as demonstrated by observations based on time- and frequency-domain analyses of heart rate variability.^{18 19 25 26 27} Several studies^{18 19 25} reported a trend toward a greater increase in mean heart rate in patients with a positive tilt test than in patients with a negative tilt test, even though continuous monitoring and precise determinations of the highest sustained heart rate during early upright tilting were not performed. Indeed, in our patients with recurrent unexplained syncope and no additional disease, head-up tilt was positive in those who showed a major early increase in heart rate. Conversely, we showed that an early sustained increase in heart rate 18 bpm during the first 6 minutes of upright tilting was highly predictive of a negative tilt result even with subsequent infusion of isoproterenol in low doses.

The aim of the present study was to allow the accurate prediction of a negative head-up tilt test result by analyzing early changes in heart rate and blood pressure. Therefore, patients with continuous decreases in heart rate or blood pressure during the early upright tilt, who are at high risk of developing an abnormal tilt test and need no further predictive criteria, were excluded from analysis. Note that all these patients ultimately developed syncope during the tilt test. In addition, close inspection of their data revealed interesting observations. Analyzing our two consecutive populations of patients, we noted that type 2B syncope occurred in 3 of the 8 consecutive patients with an early sustained decrease in heart rate and blood pressure (excluded from analysis), whereas it occurred in only 2 of the 56 consecutive patients who developed syncope in the studied population. These findings further underscore the usefulness of this classification and suggest that the pathogenic pathways involved in the genesis of one form of vasovagal syncope might not apply to its other forms.

Study Limitations
It should be stressed that the present results were obtained in patients referred for recurrent unexplained syncope with no cardiovascular or neurological diseases and no drug use. In addition, to accurately measure the early increase in heart rate, eligible patients should have a relatively stable heart rate in the supine position before the tilt test, as was the case for the vast majority of our patients. Therefore, these results should not be extrapolated to patients with other characteristics. Because the percentage of patients explored for syncope who satisfied our inclusion criteria was 50%, the procedure proposed here can be applied in only 50% of protocols. In addition, because the present study was performed in a single center, it is possible that the demographic characteristics and patient history in the sample we studied differ from those of other institutions and consequently that the proportion of patients eligible for the present procedure could differ from that reported here.

Potential Implications of the Study
A current basic approach to the clinical diagnosis of vasovagal syncope is the passive tilt at a 60° angle for 45 minutes.²¹ However, the long duration of the test, justified by a mean time to syncope of 26 minutes, could hamper its wide use in the large population of patients referred for recurrent unexplained syncope. In this study, we showed that the absence of a major increase in heart rate during the first 6 minutes of a Westminster tilt test was sufficient to predict a negative result even with subsequent use of isoproterenol. This could apply to as much as 60% of the population of patients referred for recurrent unexplained syncope who fulfill the inclusion criteria of our study. Therefore, in patients with a slight increase in heart rate (18 bpm), the duration of the Westminster tilt test could be drastically reduced from 45 minutes to a minimum of 6 minutes of upright tilting with a very low risk of overlooking positive test results. Patients with a major increase in heart rate (>18 bpm) and a negative Westminster tilt test would need further exploration with isoproterenol infusion, because three of six patients with these characteristics had tilt-induced syncope after a low-dose isoproterenol tilt test in our study.

However, because the present study involved a single center with a relatively small number of patients, we think our results should be confirmed by a multicenter study based on the simple criterion proposed herein before a 6-minute test is substituted for standard protocols in selected patients.

Conclusions
In patients with no illnesses other than recurrent unexplained syncope, a simple clinical criterion allows the selection of patients who will not develop syncope during a prolonged upright tilt test. If these results are confirmed by a multicenter study, the use of this criterion might drastically reduce the duration of the test.

	Acknowledgments

 
Dr Mallat was supported by an award from Assistance Publique, Hôpitaux de Paris. We are indebted to Patricia Briant for her valuable aid and technical assistance.

Received October 24, 1996; revision received January 30, 1997; accepted February 3, 1997.

	References

Top Abstract Introduction Methods Results Discussion References

 
1. Kapoor WN, Karpf M, Wieand S, Peterson JR, Levey GS. A prospective evaluation and follow-up of patients with syncope. N Engl J Med. 1983;309:197-204.[Abstract]

2. Kenny RA, Ingram A, Bayliss J, Sutton R. Head-up tilt: a useful test for investigating unexplained syncope. Lancet. 1986;1:1352-1354.[Medline] [Order article via Infotrieve]

3. Abi-Samra F, Maloney JD, Fouad-Tarazi FM, Castle LW. The usefulness of head-up tilt testing and hemodynamic investigations in the workup of syncope of unknown origin. Pacing Clin Electrophysiol. 1988;11:1202-1214.[Medline] [Order article via Infotrieve]

4. Almquist A, Goldenberg IF, Milstein S, Chen MY, Chen X, Hansen R, Gornick C, Benditt DG. Provocation of bradycardia and hypotension by isoproterenol and upright posture in patients with unexplained syncope. N Engl J Med. 1989;320:346-351.[Abstract]

5. Waxman MB, Yao L, Cameron DA, Wald RW, Roseman J. Isoproterenol induction of vasodepressor-type reaction in vasodepressor-prone persons. Am J Cardiol. 1989;63:58-65.[Medline] [Order article via Infotrieve]

6. Fitzpatrick AP, Sutton R. Tilting towards a diagnosis in recurrent unexplained syncope. Lancet. 1989;1:658-660.[Medline] [Order article via Infotrieve]

7. Imholz BP, Settels JJ, Van der Meiracker AH, Wesseling KH, Wieling W. Noninvasive continuous finger blood pressure measurement during orthostatic stress compared to intra-arterial pressure. Cardiovasc Res. 1990;24:214-221.[Abstract/Free Full Text]

8. Oberg B, Thorén P. Increased activity in left ventricular receptors during haemorrhage or occlusion of the caval veins in the cat. Acta Physiol Scand. 1972;85:164-172.[Medline] [Order article via Infotrieve]

9. Shalev Y, Gal R, Tchou PJ, Anderson AJ, Avitall B, Akhtar M, Jazayeri MR. Echocardiographic demonstration of decreased left ventricular dimensions and vigorous myocardial contraction during syncope induced by head-up tilt. J Am Coll Cardiol. 1991;18:746-751.[Abstract]

10. Thorén P. Role of cardiac vagal C fibers in cardiovascular control. Rev Physiol Biochem Pharmacol. 1979;86:1-94.[Medline] [Order article via Infotrieve]

11. Gupta BN, Thames MD. Behavior of left ventricular mechanoreceptors with myelinated and nonmyelinated afferent vagal fibers in cats. Circ Res. 1983;52:291-301.[Abstract/Free Full Text]

12. Abboud FM. Ventricular syncope: is the heart a sensory organ? N Engl J Med. 1989;320:390-392.[Medline] [Order article via Infotrieve]

13. Waxman MB, Cameron DA, Wald RW. Role of ventricular vagal afferents in the vasovagal reaction. J Am Coll Cardiol. 1993;21:1138-1141.[Medline] [Order article via Infotrieve]

14. Wallin BG, Sundolf G. Sympathetic outflow to muscles during vasovagal syncope. J Auton Nerv Syst. 1982;6:287-291.[Medline] [Order article via Infotrieve]

15. Victor RG, Thorén P, Morgan DA, Mark AL. Differential control of adrenal and renal sympathetic nerve activity during hemorrhagic hypotension in rats. Circ Res. 1989;64:686-694.[Abstract/Free Full Text]

16. Mark AL. The Bezold-Jarisch reflex revisited: clinical implications of inhibitory reflexes originating in the heart. J Am Coll Cardiol. 1983;1:90-102.[Abstract]

17. Nelson SD, Stanley M, Love CJ, Coyne KS, Schaal SF. The autonomic and hemodynamic effects of oral theophylline in patients with vasodepressor syncope. Arch Intern Med. 1991;151:2425-2429.[Abstract/Free Full Text]

18. Morillo CA, Klein GJ, Jones DL, Yee R. Time and frequency domain analyses of heart rate variability during orthostatic stress in patients with neurally mediated syncope. Am J Cardiol. 1994;74:1258-1262.[Medline] [Order article via Infotrieve]

19. Lippman N, Stein KM, Lerman BB. Failure to decrease parasympathetic tone during upright tilt predicts a positive tilt-table test. Am J Cardiol. 1995;75:591-595.[Medline] [Order article via Infotrieve]

20. Abboud FM. Neurocardiogenic syncope. N Engl J Med. 1993;328:1117-1120.[Free Full Text]

21. Fitzpatrick A, Theodorakis G, Vardas P, Sutton R. Methodology of head-up tilt testing in patients with unexplained syncope. J Am Coll Cardiol. 1991;17:125-130.[Abstract]

22. Raviele A, Alboni P. Sincope: un aggiornamento sulla fisiopatologia, diagnosi e terapia. G Ital Cardiol. 1994;24:1227-1260.[Medline] [Order article via Infotrieve]

23. Sutton R. Vasovagal syncope: clinical presentation, classification and management. In: Aubert AE, Ector H, Stroobandt R, eds. Cardiac Pacing and Electrophysiology: A Bridge to the 21^stCentury. Dordrecht, Netherlands: Kluwer Academic Publishers; 1994:15-22.

24. Natale A, Akhtar M, Jazayeri M, Dhala A, Blanck Z, Deshpande S, Krebs A, Sra JS. Provocation of hypotension during head-up tilt testing in subjects with no history of syncope or presyncope. Circulation. 1995;92:54-58.[Abstract/Free Full Text]

25. Lipsitz LA, Mietus J, Moody GB, Goldberger AL. Spectral characteristics of heart rate variability before and during postural tilt: relations to aging and risk of syncope. Circulation. 1990;81:1803-1810.[Abstract/Free Full Text]

26. Theodorakis GN, Kremastinos DT, Avrambos GT, Stefanakis GS, Karavolis GK, Toutouzas PK. Heart rate variability in patients with vasovagal syndrome. Pacing Clin Electrophysiol. 1992;15:2221-2225.[Medline] [Order article via Infotrieve]

27. Pruvot E, Vesin JM, Schlaepfer J, Fromer M, Kappenberger L. Autonomic imbalance assessed by heart rate variability analysis in vasovagal syncope. Pacing Clin Electrophysiol. 1994;17:2201-2206.[Medline] [Order article via Infotrieve]

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This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Mallat, Z. Articles by Frank, R. Search for Related Content PubMed PubMed Citation Articles by Mallat, Z. Articles by Frank, R. Pubmed/NCBI databases Medline Plus Health Information Fainting