In modern medicine, the sign is elicited when pressure is applied to an artery proximal to an arteriovenous fistula and said to be positive if the following occurs: In an AV fistula, there is shunting of blood from the arteries directly into a vein, bypassing the capillary beds.
Because blood pressure is directly proportional to peripheral vascular resistance, in an AV fistula there is a fall in blood pressure and subsequent reflex tachycardia.
When the artery proximal to the fistula is compressed, blood is no longer shunted and the peripheral vascular resistance is increased suddenly.
[5] Bradycardia soon follows due to the activation of the baroreceptors in the left ventricle (the Bezold–Jarisch reflex[5]).
It helps differentiate the cause of chest pain between high-output cardiac failure (AV-shunting) and cardiac (organic) causes in ESRD patients on hemodialysis with an AV fistula.