Head up tilt test (HUTT)

Brief Review

Head up tilt test (HUTT) or tilt table test is commonly done for the evaluation of neurocardiogenic syncope (e.g. vasovagal syncope). Various protocols are followed in different centres. One protocol is as follows: The subject is strapped to the tilt table after venous and arterial access is obtained. Radial arterial access is used for continuous blood pressure monitoring as non-invasive recordings are often inaccurate and difficult to make at the time of syncope. Infusion pump is also set up to give isoprenaline infusion if required. Resuscitation tray and personnel are at hand during the test. ECG, pulse oximetry and invasive blood pressure are monitored throughout and the hemodynamic response is also charted. Initial supine phase is for 30 minutes, which is followed by a tilt phase of 20 minutes at an angle of 70 degrees. If syncope does not occur during this period, the table is brought to the supine position for a period of 10 minutes. After that isoprenaline infusion is started at a rate of 1 microgram per minute. The drip is run for 10 minutes with the table tilted to 80 degrees. Still if syncope does not occur within 10 minutes, the table is brought back to the supine position for 10 minutes. The test is repeated at 3 and 5 micrograms per minute of isoprenaline with intervening 10 minutes of supine position, if needed. If there is no syncope, the test is considered negative. Syncope can occur at any of the above stages either with bradycardia, hypotension or both. The first one is called cardioinhibitory, the second one vasodepressor and the third mixed variety.
A change in the pattern of HUTT response with age has been described, with cardioinhibitory response becoming less common with advancing age [1]. This difference is thought to be due to the higher vagal activity in younger age promoting more of cardioinhibitory responses.
VASIS (Vasovagal Syncope International Study) had classified syncope into VASIS I (mixed), VASIS IIA & VASIS IIB  (cardioinhibitory) and VASIS III (vasodepressive) varieties based on the result of head up tilt test. Further modifications were suggested by Brignole M et al [2].
Prognostic significance of unduly prolonged asystole of thirty or more seconds during head up tilt test has been studied by Carvalho MS and associates [3]. In their study of 2247 patients, 149 had asystole, of which 11 had 30 or more seconds of asystole. The longest pause recorded in their study was 63 seconds. None of these patients had received a pacemaker in this retrospective study. Four patients had recurrence of syncope after a follow up period which ranged from 30 to 76 months. One had scalp laceration related to the syncope and no patient died in this study.
Nine different hemodynamic patterns in response head up tilt test in pediatric patients have been described by et al after assessment of 400 pediatric patients [4]. These responses include postural orthostatic tachycardia syndrome in addition to the usual head up tilt test responses.
References

  1. Noormand R et al. Age and the Head Up Tilt Test Outcome in Syncope Patients. Res Cardiovasc Med. 2015 Sep 15;4(4):e27871.
  2. Brignole M et al. New classification of haemodynamics of vasovagal syncope: beyond the VASIS classification. Analysis of the pre-syncopal phase of the tilt test without and with nitroglycerin challenge. Vasovagal Syncope International Study. Europace. 2000 Jan;2(1):66-76.
  3. Carvalho MS et al. Prognostic Value of a Very Prolonged Asystole during Head Up Tilt Test. Pacing Clin Electrophysiol. 2015 Aug;38(8):973-9.
  4.  Yozgat Y et al. Different haemodynamic patterns in head-up tilt test on 400 paediatric cases with unexplained syncope. Cardiol Young. 2015 Jun;25(5):911-7.