It is a hormone activated response mechanism that results from an insufficient Mean Arterial Pressure, or from an irregular pulmonary tachycardia. This reflex mechanism is conduced through a second messenger system; ACTH production in the anterior pituitary is stopped, thereby diminshing blood levels of cortisol. Transient depolarization of (nor)epinephrine neurotransmitters in the adrenal medulla becomes repressed. The parasympathetic nervous system homeostatically maintains membrane potentials in the neuromuscular junctions of the pace-making cells. Most importantly EKG of the patient will now be stable; the QRS complex now innervates normal electrical signals. More information regarding dopamine's interaction in this response is not well documented.
