What is the HUTT (Head-Up Tilt) test?

Head-Up Tilt Test (HUTT): Diagnostic Tool for Syncope Evaluation

The Head-Up Tilt Test (HUTT) is a diagnostic procedure that evaluates a patient's cardiovascular response to postural change by monitoring blood pressure and heart rate while the patient is tilted to an upright position on a specialized table, primarily used to diagnose neurally mediated syncope and orthostatic hypotension. 1

Test Methodology

• Standard Protocol:

  • Patient is secured to a motorized table in supine position
  • Table is tilted to 60-70 degrees angle
  • Monitoring of blood pressure and heart rate throughout the procedure
  • Duration: 20-45 minutes (varies by protocol) 1, 2

• Common Protocols:

  • Passive tilt: Unmedicated phase lasting 20-45 minutes
  • Drug-potentiated tilt:
    • Low-dose intravenous isoproterenol (incremental doses to increase HR by 20-25%)
    • Sublingual nitroglycerin (300-400 μg) after a passive phase 1
    • Fast protocol: 10-minute passive phase + 10-minute nitroglycerin phase 3

Clinical Indications

Class I Indications (Strongly Recommended) 1

• Unexplained single syncopal episodes in high-risk settings (risk of injury, occupational implications)
• Recurrent episodes without organic heart disease
• When demonstrating susceptibility to neurally-mediated syncope would benefit patient education

Class II Indications (Reasonable to Perform) 1

• When understanding hemodynamic patterns may alter treatment approach
• Differentiating syncope with jerking movements from epilepsy
• Evaluating patients with recurrent unexplained falls
• Assessing recurrent pre-syncope or dizziness

Not Indicated (Class III) 1

• Assessment of treatment efficacy
• Single episode without injury in low-risk setting
• Clear clinical vasovagal features when demonstration of neural susceptibility would not alter management

Diagnostic Patterns and Interpretation

• Positive Responses:

  • Cardioinhibitory: Predominant bradycardia/asystole
  • Vasodepressor: Predominant hypotension without significant bradycardia
  • Mixed: Both hypotension and bradycardia 1
  • Orthostatic Hypotension: Progressive BP fall during upright position
    • Classic OH: BP drop ≥20 mmHg systolic or ≥10 mmHg diastolic within 3 minutes
    • Delayed OH: Similar BP drop occurring beyond 3 minutes 2

• Autonomic Response Patterns:

  • "Hyper-sensitive" pattern: Initial normal adaptation followed by abrupt vasovagal reaction (common in young, healthy patients)
  • "Hypo-sensitive" pattern: Progressive BP/HR decline without stable adaptation (common in older patients with comorbidities) 1

Diagnostic Value

• Sensitivity: 26-80% (varies by protocol)
• Specificity: Approximately 90% 1
• Higher sensitivity in:
  • Younger patients (74.7% in <20 years vs. 31.2% in >60 years)
  • Females (77.9% vs. 52.6% in males with syncope)
  • Patients with actual syncope vs. pre-syncope 4

Safety Considerations

• Complications:

  • Very low complication rate
  • Asystolic pauses (up to 73 seconds) may occur but are considered an endpoint, not a complication
  • Rare ventricular arrhythmias with isoproterenol (in patients with ischemic heart disease)
  • Minor side effects: palpitations (isoproterenol), headache (nitroglycerin) 1

• Contraindications for isoproterenol protocols:

  • Ischemic heart disease
  • Uncontrolled hypertension
  • Left ventricular outflow tract obstruction
  • Significant aortic stenosis 2

Limitations

• Test Reproducibility:

  • Higher reproducibility for negative responses (85-94%)
  • Lower reproducibility for positive responses (31-92%) 1
  • Limited value in assessing treatment efficacy 1

• Clinical Correlation:

  • A negative test does not exclude reflex syncope
  • Correlation between tilt-induced and spontaneous syncope patterns is questionable 1
  • Not predictive of long-term outcomes with pacing therapy 1

Clinical Utility Beyond Vasovagal Syncope

• Orthostatic Hypotension Detection:

  • Particularly valuable for delayed OH (39% of OH cases manifest after 10 minutes) 2
  • Important prognostic implications (54% of delayed OH progresses to classic OH within 10 years) 2

• Differential Diagnosis:

  • Distinguishing syncope from epilepsy, especially with convulsive features
  • Identifying psychogenic pseudosyncope
  • Differentiating syncope from falls in elderly patients 1, 2

The HUTT remains a valuable diagnostic tool in syncope evaluation when properly indicated, though its limitations in reproducibility and predictive value should be considered when interpreting results and planning management strategies.