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Limitations of studies on vasovagal syncope

      The report written by Ermis et al
      • Ermis C
      • Samniah N
      • Sakaguchi S
      • Lurie K.G
      • Pham S
      • Lu F
      • Benditt D.G
      Comparison of catecholamine response during tilt-table-induced vasovagal syncope in patients <35 to those >65 years of age.
      on the catecholamine response during tilt–table-induced vasovagal syncope illustrates 2 kinds of difficulties of the vasovagal syncope studies. The first is the lack of a true control group.
      • Brignole M
      • Alboni P
      • Benditt D
      • Bergfeldt L
      • Blanc J.J
      • Bloch Thomsen P.E
      • van Dijk J.G
      • Fitzpatrick A
      • Hohnloser S
      • Janousek J
      • et al.
      Task Force on Syncope, European Society of Cardiology
      Guidelines on management (diagnosis and treatment) of syncope.
      The second is the tilt-test limitations (the only one diagnostic tool available)
      • Brignole M
      • Alboni P
      • Benditt D
      • Bergfeldt L
      • Blanc J.J
      • Bloch Thomsen P.E
      • van Dijk J.G
      • Fitzpatrick A
      • Hohnloser S
      • Janousek J
      • et al.
      Task Force on Syncope, European Society of Cardiology
      Guidelines on management (diagnosis and treatment) of syncope.
      that include the timing of the blood withdrawals during the test. The control group of the study of Ermis et al
      • Ermis C
      • Samniah N
      • Sakaguchi S
      • Lurie K.G
      • Pham S
      • Lu F
      • Benditt D.G
      Comparison of catecholamine response during tilt-table-induced vasovagal syncope in patients <35 to those >65 years of age.
      is a group of patients with an iterative syncope history but a negative outcome to the tilt test. Medical history is the deciding factor of the diagnosis of vasovagal syncope. A typical history makes the diagnosis, and no further evaluations are needed excepted a clinical examination, an electrocardiogram, and supine and standing blood pressure measurements.
      • Brignole M
      • Alboni P
      • Benditt D
      • Bergfeldt L
      • Blanc J.J
      • Bloch Thomsen P.E
      • van Dijk J.G
      • Fitzpatrick A
      • Hohnloser S
      • Janousek J
      • et al.
      Task Force on Syncope, European Society of Cardiology
      Guidelines on management (diagnosis and treatment) of syncope.
      Study of vasovagal syncope should include patients with no doubt about the diagnosis. A positive outcome to a tilt test coming with a typical history allows the clinician to confirm the diagnosis and permits inclusion of the patient in a study. The group with a negative outcome to a tilt test, but a typical history of syncope, is certainly not a control group. It is hard to conceive a true control group for comparison with patients with vasovagal symptoms.
      • Brignole M
      • Alboni P
      • Benditt D
      • Bergfeldt L
      • Blanc J.J
      • Bloch Thomsen P.E
      • van Dijk J.G
      • Fitzpatrick A
      • Hohnloser S
      • Janousek J
      • et al.
      Task Force on Syncope, European Society of Cardiology
      Guidelines on management (diagnosis and treatment) of syncope.
      A clinical examination, and even further investigations performed between episodes, cannot make the difference between a group of normal subjects and the patients.
      • Brignole M
      • Alboni P
      • Benditt D
      • Bergfeldt L
      • Blanc J.J
      • Bloch Thomsen P.E
      • van Dijk J.G
      • Fitzpatrick A
      • Hohnloser S
      • Janousek J
      • et al.
      Task Force on Syncope, European Society of Cardiology
      Guidelines on management (diagnosis and treatment) of syncope.
      The incidence of unexplained syncope is so large (one in 6) that anybody may experience vasovagal symptoms at least once in a whole life.
      • Shen W.K
      • Gersh B.J
      Fainting: approach to management.
      It is why regular designs for clinical investigations (controlled studies) are probably not appropriate to study vasovagal syncope. However, it is difficult to draw a clear conclusion from uncontrolled studies.
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      References

        • Ermis C
        • Samniah N
        • Sakaguchi S
        • Lurie K.G
        • Pham S
        • Lu F
        • Benditt D.G
        Comparison of catecholamine response during tilt-table-induced vasovagal syncope in patients <35 to those >65 years of age.
        Am J Cardiol. 2004; 93: 225-227
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        • Alboni P
        • Benditt D
        • Bergfeldt L
        • Blanc J.J
        • Bloch Thomsen P.E
        • van Dijk J.G
        • Fitzpatrick A
        • Hohnloser S
        • Janousek J
        • et al.
        • Task Force on Syncope, European Society of Cardiology
        Guidelines on management (diagnosis and treatment) of syncope.
        Eur Heart J. 2001; 22: 1256-1306
        • Shen W.K
        • Gersh B.J
        Fainting: approach to management.
        in: Low P.A Clinical Autonomic Disorders. Lippincott-Raven, Philadelphia1997: 649-679