The tilt table test is useful for the diagnosis of vasovagal syncope and should not be abolished

The tilt table test (TTT) has been used continuously as a complementary test for the diagnosis of transient loss of consciousness (TLOC) or syncope, since its introduction in 1986 by Kenny et al1 Its use is still recommended for the diagnosis of TLOC by both the American College of Cardiology/American Heart Association/Heart Rhythm Society (ACC/AHA/HRS) and the European Society of Cardiology (ESC) guidelines.2, 3 The most common form of TLOC is syncope due to autonomic system dysfunction so-called vasovagal syncope (VVS), which affects young persons, mostly females,4 and accounts for a lifetime prevalence of between 1% to 3% for emergency room visits and ≥30% for hospital admissions.5 Although a comprehensive history and physical examination including an electrocardiogram (ECG) is a good diagnostic tool, it is not always confirmatory and a TTT is often necessary, since the cause of syncope is multifactorial with the most common types listed in Table 1.2, 3 In a recent editorial, Kulkarni et al.6 state that a comprehensive history and physical examination is all that is necessary for the diagnosis of VVS and that a TTT is not essential and should be abolished. We believe that this recommendation is not valid and that the TTT is still a very useful test for the evaluation and diagnostic confirmation of VVS, despite some limitations.7 With the assumption of upright posture, the blood volume is redistributed downwards due to gravity, and within 2 to 3 min, approximately 500-800 mL of blood or about 10% total blood volume and 25% of thoracic blood volume is rapidly displaced in the splanchnic and pelvic organs and lower extremities,8 which is further decreased with the prolongation of standing due to transcapillary diffusion of blood.8 The displacement of blood volume leads to decrease in blood pressure (BP), hypoperfusion of the brain, and the loss of consciousness. In healthy persons, the compensatory reflexes are quite effective and usually prevent the fainting spells. The blood volume redistribution leads to unloading of the carotid and cardiopulmonary baroreceptors leading to increase in noradrenaline secretion causing peripheral vasoconstriction and increase in peripheral vascular resistance (PVR) and heart rate (HR), which in combination with contraction of lower extremity muscles restores these hemodynamic changes with return of consciousness.9 The use of TTT provides the means to reproduce the orthostatic pathophysiology in a controlled monitoring setting and also to evaluate other syncopal syndromes such orthostatic intolerance (OI), orthostatic hypotension (OH), and the postural tachycardia syndrome (PTS), all subsets of the autonomic sympathetic dysfunction.9 We agree with Kulkarni et al.10 that the history and physical examination remains an indispensable component in the evaluation of VVS. However, the addition of TTT provides additional value in the ability to assess the hemodynamic responses to orthostatic stress apart from the action of large skeletal muscles and to provide the needed support of body weight. In addition, the TTT allows for the hemodynamic assessment for longer periods of time.9, 11 A comprehensive history and physical examination remains the cornerstone for the diagnosis of patients presenting with VVS but its diagnostic value is limited due to other types of TLOC.2, 3 The examining physician should ascertain whether the syncopal episode occurred from the standing position after either prolonged or short standing (more frequent) or from the sitting position (less often). Also, whether was precipitated by prodromal emotional symptoms such as fear and somatic symptoms such as pain, micturition, gastrointestinal stimulation (swallowing, defecation), cough or sneeze, or the sight of blood. Also, whether there was a quick and complete recovery and whether the patient had any memory loss during the fall, and whether such falls have happened in the past, or whether such falls have been witnessed by other people. In addition, whether the patient is taking any drugs that might cause the fainting spells such as diuretics or vasodilators, and whether the fainting spells occurred after the administration of such drugs. Some clinicians use the Calgary score (Table 2) developed by Sheldon et al10 and has been used by other investigators.12 This test consists of seven diagnostic questions about the medical history, triggers, circumstances, and signs and symptoms of TLOC. All questions are answered as yes or no, and if a question is answered as yes, points are added or subtracted, and the points are added at the end to obtain a total score (range − 14 to + 6). A score of ≥−2 is diagnostic of VVS. However, other studies have found this score to be not very reliable with low specificity of 32%, but high sensitivity of 92% for younger patients and 79% for older patients ≥50 years of age.12 The physical examination in patients with TLOC usually consists of cardiac auscultation to disclose any murmurs due to aortic valve stenosis or cardiac arrhythmias that could cause cardiac syncope.13, 14 In addition, the BP and HR should be measured immediately upon active standing and 3 min later. In patients with TLOC with orthostatic hypotension, the systolic BP (SBP) and diastolic BP (DBP) will decrease by ≥20 mmHg and ≥10 mmHg, respectively, with an increase in HR,15, 16 whereas in patients with VVS, the decrease in BP is usually associated with inappropriate decrease in HR.17 In addition, an ECG should be taken to diagnose possible causes of cardiogenic syncope such as sinus node dysfunction (sick sinus syndrome), bradyarrhythmia, tachyarrhythmia (supraventricular, ventricular), or high-grade atrioventricular block.14 The distinction between VVS and other causes of TLOC is essential, because the prognosis and treatment are different. In such cases, the use of TTT is useful in the evaluation and treatment of the different forms of TLOC.9 Although the measurement of BP in the supine and upright position is indispensable for the assessment of VVS, the addition of TTT provides the additional ability to assess the hemodynamic effects of passive head-up tilt and also allows for prolonged hemodynamic monitoring of BP changes,9 which are different from those of active standing. In healthy subjects, active standing causes greater transient reductions of BP and PVR and greater increases in HR and cardiac output during the first 30 sec, than those produced by the passive head-up tilt with the TTT.18 The greatest decrease in mean BP with active standing is about 39 ± 10 mmHg compared to 16 ± 7 mmHg with TTT, occurs within the first 10 sec, and is associated with a HR increase of 35 ± 8 b/min vs 12 ± 7 b/min with the TTT. Regarding the angle of tilting, the most optimal is 70° with a range of 60 to 80°. During the TTT, BP and HR are measured continuously with the arm at heart level and a 3 lead ECG. In patients with VVS, the BP and the HR decrease within the first 1-3 min upon tilting and remain low till the patient is returned in the supine position.19 They may also be followed with symptoms of dizziness, weakness, or fainting, if the mean BP falls below 50 mmHg. In such cases, the patient should be, immediately, returned to the horizontal position. If symptoms do not occur soon after tilting, the tilted position can be prolonged up to 45 or 60 min. Such patients have also impaired response to the valsalva maneuver.19 The TTT can also identify some OH variants such as initial OH defined as an immediate transient BP decrease of >40/>20 mmHg with symptoms of cerebral hypoperfusion occurring within 5-15 s upon assuming the upright posture.20 Patients with this condition usually do not have symptoms upon head-up tilt. Another variant of OH is a delay in BP fall of > 3 min upon head-up tilt.21 The TTT is also useful for the diagnosis of chronic orthostatic intolerance (COI) and POTS. These patients may complain of dizziness, weakness, warmth, dyspnea, nausea, or headache with or not hemodynamic abnormalities. The POTS is characterized by an increase in HR ≥ 30 or ≥ 40 b/min depending on age.9 In addition, the TTT can be diagnostic in patients with cardiac syncope by identifying cardiac arrhythmias (bradycardia, tachycardia), serious atrioventricular block, or sinus arrests.14 If the TTT is not diagnostic, ancillary measures can be used with the administration of either isoproterenol intravenously at 1-5 μg/min or nitroglycerin sublingually at 0.3 mg. A positive response is usually higher with nitroglycerin than with isoproterenol, 58.4% vs 35.9%, and also, the tolerance is higher with nitroglycerin vs isoproterenol 0.7% vs 3.2%.22 Similar findings have also been reported by other investigators.23 Based on the contribution of TTT in patients with VVS or unexplained syncope, the TTT is recommended by the ACC/ AHA, ESC and the American Autonomic Society, and the European Federation of Neurological Sciences.2, 3, 21, 24 Based on the studies presented, the TTT is an invaluable component of the clinical evaluation of the autonomic nervous system dysfunction and in particular for the evaluation of disorders of orthostatic intolerance. However, a detailed history and physical examination is still very valuable for the initial evaluation of patients with TLOC. The author declares no conflict of interest and that no funds were received for the preparation of the manuscript.