Nitrotest Versus Isotest for Vasovagal Syncope: Do They Explore Different Mechanisms?

  • J. Niño
  • C. A. Morillo
Conference paper


During the last decade, head-up tilt (HUT) has become the diagnostic method of choice for the evaluation of patients with recurrent vasovagal syncope [1–7]. However, there is still little consensus regarding the ideal HUT protocol. In an attempt to improve the sensitivity and specificity of the test, several approaches have been evaluated, such as varying the degree of inclination and the duration of orthostatic stress as well as the use of provoking agents [8–22]. The sensitivity and specificity of HUT are largely related to the protocol used, and range from 25% to 87%, and from 35% to 100%, respectively [9, 14, 15, 22–24]. The lack of a standard methodology that provides a test with a high sensitivity without sacrificing specificity is largely due to our poor understanding of the mechanisms that mediate neurocardiogenic responses. A wide variety of provoking agents that include sympathomimetics (isoproterenol) and nitrovasodilators (nitroglycerin and isosorbide dinitrate) have been proposed on the basis of the hypothesized mechanisms that trigger the vasovagal response. Orthostatic stress increases venous pooling, leading to a drop in right ventricular filling pressure that causes an increase in catecholamine levels associated with augmented ventricular inotropism. In the susceptible individual, a reduced preload, particularly in the left ventricular cavity, may reflexly activate vagal-C mechanoreceptors, which, associated with impaired baroreflex counter-regulatory mechanisms, precipitate the vasovagal response.


Heart Rate Variability Isosorbide Dinitrate Vasovagal Syncope Orthostatic Stress Unexplained Syncope 
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Copyright information

© Springer-Verlag Italia 2000

Authors and Affiliations

  • J. Niño
    • 1
  • C. A. Morillo
    • 2
  1. 1.Laboratory of Autonomic PhysiologyFundación Cardiovascular del Oriente Colombiano, Instituto del CorazónFloridablanca, SantanderColombia
  2. 2.Department of Cardiology and Cardiovascular SciencesFundación Cardiovascular del Oriente Colombiano, Instituto del CorazónFloridablanca, SantanderColombia

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