What is the Tilt Test (Head-Up Tilt Test)?
The tilt test is a diagnostic procedure that tilts a patient upright (typically 60-80 degrees) for 20-45 minutes to provoke and reproduce neurally-mediated reflex syncope by inducing orthostatic stress, blood pooling, and decreased venous return to the heart. 1
Physiologic Basis
The test exploits the body's response to orthostatic stress. When tilted upright, approximately 700 mL of blood pools in the lower extremities, causing a 15-20% decrease in plasma volume within 10 minutes 1. This reduces venous return and cardiac filling pressure, decreasing stroke volume 1. In susceptible individuals, compensatory vasoconstriction fails, triggering an abnormal autonomic reflex that produces hypotension and/or bradycardia—the hallmark of vasovagal syncope 1.
Standard Testing Protocols
The two most commonly used protocols are low-dose intravenous isoproterenol (increasing heart rate by 20-25% over baseline, usually 3 µg/min) and sublingual nitroglycerin (300-400 mg after a 20-minute unmedicated phase), both achieving similar positive response rates (61-69%) with high specificity (92-94%). 1
Protocol Details:
- Tilt angle: 60-80 degrees 1
- Duration: 20-45 minutes passive phase 1
- Patient preparation: 4-hour fast required 1
- Pre-tilt stabilization: 20 minutes for isoproterenol protocol; 5 minutes for nitroglycerin protocol 1
- Support: Footboard support (not bicycle saddle, which reduces specificity) 1
Primary Clinical Indications
The main indication is to confirm reflex syncope in patients with unexplained syncope after initial evaluation has not established a diagnosis. 1
Class I Indications (Strongly Recommended):
- Unexplained single syncopal episode in high-risk settings (potential for physical injury, occupational implications like pilots) 1
- Recurrent syncope without organic heart disease 1
- Recurrent syncope with organic heart disease after cardiac causes excluded 1
- When demonstrating susceptibility to neurally-mediated syncope will affect treatment decisions 1
Class II Indications (Reasonable to Perform):
- Differentiating syncope with jerking movements from epilepsy 1
- Evaluating recurrent unexplained falls in elderly patients 1
- Distinguishing syncope from psychiatric disorders in patients with frequent transient loss of consciousness 1
- Understanding hemodynamic patterns to guide therapy 1
Class III (Not Indicated):
- Tilt testing has no value in assessing treatment efficacy 1
- Single episode without injury and not in high-risk setting 1
- Clear-cut clinical vasovagal features already diagnosed by history 1
Test Responses and Interpretation
The endpoint is induction of reflex hypotension/bradycardia or delayed orthostatic hypotension associated with syncope or pre-syncope. 1
Response Classifications:
- Cardioinhibitory: Asystole >3 seconds or AV block 2
- Vasodepressor: ≥50 mmHg drop in systolic blood pressure 2
- Mixed: Combination of both components 1
Critical Limitation:
A positive cardioinhibitory response predicts asystolic spontaneous syncope with high probability, but a vasodepressor, mixed, or even negative response does not exclude asystole during spontaneous syncope. 1 This is a crucial pitfall—the test response pattern does not reliably predict the actual hemodynamic pattern during real-world syncope 1.
Reproducibility Concerns
The reproducibility of an initial negative response (85-94%) is substantially higher than the reproducibility of an initial positive response (31-92%). 1, 2 Approximately 50% of patients with baseline positive tilt tests become negative when repeated with treatment or placebo 1, 2. This poor reproducibility of positive responses is why the test should never be used to assess treatment effectiveness 1.
Safety Profile
Tilt testing is safe with no reported deaths, though rare life-threatening ventricular arrhythmias with isoproterenol have occurred in patients with ischemic heart disease or sick sinus syndrome. 1
Common Side Effects:
- Palpitations with isoproterenol 1
- Headache with nitroglycerin 1
- Self-limited atrial fibrillation 1
- Prolonged asystole (up to 73 seconds reported, but this is an expected endpoint, not a complication) 1
Rapid return to supine position immediately upon syncope onset is usually sufficient; brief resuscitation maneuvers are rarely needed. 1
Special Populations
In older patients, omitting the passive phase and commencing directly with nitroglycerin may improve compliance while maintaining diagnostic accuracy. 1 The shortened GTN-potentiated protocol provides satisfactory positivity rates and 97% specificity in patients ≥65 years 3.