Glyceryl trinitrate-induced blood pressure variability decrease during head-up tilt test predicts vasovagal response

Area of Science:

• Cardiovascular Physiology
• Autonomic Nervous System Function
• Pharmacology

Background:

• Head-up tilt testing is used to diagnose syncope.
• Glyceryl trinitrate (GTN) can provoke syncope by affecting blood pressure variability (BPV).
• Nitric oxide (NO) influences BPV independently of blood pressure (BP).

Purpose of the Study:

• To investigate if exogenous nitric oxide (NO) from GTN decreases BPV during the presyncope period.
• To determine if a decrease in BPV predicts syncope during a head-up tilt test.

Main Methods:

• Analysis of 29 tilt tests with GTN-induced syncope and 30 negative tests.
• Application of a recursive autoregressive model to assess BPV after GTN administration.
• Calculation of spectral power in respiratory and nonrespiratory frequency bands for BPV analysis.

Main Results:

• Nonrespiratory frequency BPV (systolic and diastolic) decreased by 30% after GTN in the syncope group.
• A decrease in nonrespiratory frequency diastolic BPV 20 seconds post-GTN predicted syncope (AUC 0.811).
• This predictive decrease showed 77% sensitivity and 70% specificity.

Conclusions:

• GTN application attenuates nonrespiratory frequency BPV during the presyncope phase, independent of BP changes.
• A significant reduction in nonrespiratory frequency diastolic BPV early after GTN administration is a predictor of cardioinhibitory syncope.