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False Positive Responses to Head-up Tilt Testing in Patients With Paroxysmal Lone Atrial Fibrillation.

A.Sideris, K.Tsilias, N.Stamelos, G.Filippatos, D.Kardara, M.Efremidis, D. Athanasias, L.Anthopoulos, F.Kardaras.

1st and 2nd Departments of Cardiology
Evangelismos Hospital
Athens, Greece.

Abstract
Introduction
Purpose
Patients and Methods
Results
Discussion
Conclusions
References

Abstract
The autonomic nervous system has profound influences on atrial electrophysiology and is extremely important in the pathogenesis of atrial fibrillation. In normal atria, the vagal influences predominate. Orthostatic stress represents a means of stimulating vasovagal reactions. However, data are lacking on tilt responses in patients with paroxysmal lone atrial fibrillation (LAF). We performed head-up tilt test (HUT) (60° , 45min) in 20 patients (15 males-5 females) with LAF, aged 26-47 years, while on sinus rhythm. No patient had previous history of presyncope or syncope. Thirty age and sex-matched normal individuals(N) were also studied as a control group. The following positive responses to HUT were observed:
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*p< 0.05 versus N. No patient developed atrial fibrillation during HUT.
Conclusion: A significant number of false positive results during HUT, may be expected in patients with LAF. Autonomic reflexes probably play a major role in causing positive results in these patients although their role in the genesis of LAF calls for further investigation.

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Introduction:

The autonomic nervous system has profound influences on atrial electrophysiology and is extremely important in the pathogenesis of atrial fibrillation. Especially in young adults, who generally have normal hearts, the clinical pattern of vagally-mediated paroxysmal atrial fibrillation is preferentially observed (1). Upright tilt and the subsequent blood pooling in lower extremities result in decreased venous return, a more forceful cardiac contraction and, finally, trough the activation of mechanoreceptors, to vasovagal syncope (2).

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Purpose:

Of our study was to investigate, by means of the head up tilt test (HUT), the susceptibility of lone paroxysmal atrial fibrillation (PAF) patients, in activating the vasovagal syncope mechanism.

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Patients and Methods:

We performed HUT testing in 20 patients, with paroxysmal atrial fibrillation, aged 26-47 years. All patients had no clinical, electrocardiographic or echocardiographic evidence of organic heart disease while their laboratory evaluation revealed no significant abnormal values. No patients had previous history of syncope or presyncope. Patients were held in 60 degrees, for 45 minutes, according to the existing reccomendations (3), while no chemical agents were used to complement the test. As control group, 30 age and sex matched normal individuals were used. The positive responses to head up tilt test were used for comparison. Fisher’s exact test was used for statistical analysis. Always p<0.05 was considered as statistically significant.

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Results:

The following positive responses to head up tilt were observed:

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*p< 0.05 versus N. N=normal subjects. PAF= paroxysmal lone atrial fibrillation group
No patient developed atrial fibrillation during head up tilt.

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Discussion:

Autonomic imbalances precede episodes of paroxysmal atrial fibrillation. Increased sympathetic drive has been observed, preceding the onset of PAF, in patients with organic heart disease, while vagally induced PAF is the rule in patients without structural heart disease (4). In some patients the two mechanisms operate during different hours of the day (4). In normal hearts, vagal influences are predominant and the vagally mediated paroxysmal atrial fibrillation is characteristically observed in the young (5).
Our paroxysmal atrial fibrillation patients, were all <50 years old (26-47) and therefore candidates for a vagal mechanism as the likely pathophysiologic explanation for their arrhythmia. We investigated the neural response in head up tilt during sinus rhythm, in patients with paroxysmal atrial fibrillation without syncope. Our findings (30% of the results were positive) suggest a trend toward a vasovagal activation during HUT, among young patients with paroxysmal lone atrial fibrillation. Brignole et al performed HUT in patients with PAF (6). HUT, in sinus rhythm was positive in 37% of patients who had had a history of syncope with PAF, while only 12% of PAF patients without a history of syncope had such a response. The older age and the presence of structural heart disease in Brignole’s group could account for the discrepancy between his and our results. Our study may offer a better insight to lone paroxysmal atrial fibrillation pathophysiology, as it presents another expression of the vagal hyperreactivity, that is observed in such patients.
Furthermore, the positive result in our study must be interpreted as false positive, given that no clinical history of syncope existed. The head up tilt test value, in the diagnostic approach, of young syncopal patients, with paroxysmal atrial fibrillation, becomes questionable thus limiting its value as a diagnostic tool in this specific case. However the follow up of our patients will prove whether the positive tilt test is actually a predictor of future syncopal episodes in paroxysmal lone atrial fibrillation.

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Conclusions:

A significant number of false positive results during head up tilt, may be expected in patients with lone atrial fibrillation. Autonomic reflexes probably play a major role in causing positive results in these patients although their role in the genesis of lone atrial fibrillation calls for further investigation.

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References

1. Coumel P. Paroxysmal atrial fibrillation: a dsirder of autonomic tone? Eur heart J 1994;15 suppl A:9-16.
2. Braunwald E (ed.) Heart disease: a textbook of cardiovascular medicine. 5th Edition. WB Saunders Company, Philadelphia 1997, pp 870.
3. Fitzpatrick AP, Theodorakis G, Vardas P, Sutton R. Methodology of head-up tilt in patients with unexplained syncope. J Am Coll Cardiol 1991;17:125.
4. Fioranelli M, Piccoli M, Mileto GM, Sgreccia F, Azzolini P, Risa MP, Francanelli RL, Venturini E, Puglisi A. Analysis of heart rate variability five minutes before the onset of paroxysmal atrial fibrillation. Pacing Clin Electrophysiol 1999;22:743-749.
5. Coumel P. Autonomic influences in atrial tachyarrhythmias. J Cardiovasc Electrophysiol 1996;7(10):999-1007.
6. Brignole M, Gianfranchi L, Menozzi C, Raviele A, Oddone D, Colli G, Bottoni N. Role of autonomic reflexes in syncope associated with paroxysmal atrial fibrillation. J Am Coll Cardiol 1993;22(4):1123-1129.

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Update
Dic/04/1999