From:  The objective imperative: advancing chronic orofacial pain research with the brain-heart axis

 Integrating the BHA to link psychosocial factors and biological function.

VariableImpact on HRVImpact on QTcRequirement for research
AgeDecrease with age (vagal decline)Gradual baseline lengtheningAge-matched controls.
TricyclicsReduces HRV (anticholinergic)Typically lengthens QTc Medication history screening.
CVDMarked reduction in HRVRisk of arrhythmia/long QTPre-existing condition screening.
CircadianPeaks during sleep (vagal)Fluctuates based on cycleStandardized time for ECG

BHA: brain-heart axis; QTc: corrected QT interval; HRV: heart rate variability; QTc: corrected QT interval; ECG: electrocardiogram.