Anxiety causes an increase in adrenaline, then adrenaline stimulates the parasympathetic nervous system, which stimulates the vagus nerve and induces the palpitations. This is why they are so common in people that suffer anxitey and panic attacks.


Hope this helps.

Well, that's a fair estimation but we need to make clarification.

Epinephrine (adrenaline) stimulates the sympathetic nervous system and generally prepares the body for action. The parasympathetic nervous system demonstrates an opposing action and generally maintains functions by the body at rest. The vagus nerve is part of the parasympathetic nervous system which mainly uses the neurotransmitter acetylcholine, not adrenaline.

Adrenaline does not cause palpitations to occur, nor does it stimulate the parasympathetic nervous system. The reason that you experience palpitations is due to a generally and often chronic stimulation of the central nervous system as a consequence of significant anxiety, producing a variable dysregulation. Among the features of such dysregulation is the random stimulation of the heart by the vagus nerve, either at the level of the proper nerve or below that region as the pneumogastric nerve which innervates the GI tract.

Evoked potentials by way of the neurotransmitter acetylcholine ascend the nerve until the reach all of the terminal points which the vagus nerve innervates, one of which is the heart. This signal is merely superimposed over the normal electroconductive architecture occurring within the heart at the time. Depending upon the precise moment the signal reaches the heart during the cardiac cycle, you can experience the event in the form of a palpitation. In other words, if the cardiac cycle is undergoing ventricular depolarization when the vagus nerve signal arrives, you might sense it as a powerful thud due to the significant pumping action by the ventricles. If the vagus nerve signal arrives at the point of atrial depolarization, you might experience a light fluttering sensation or hollow sensation in your chest, associated with the more subtle action by the atria. If the vagus nerve signal arrives during ventricular repolarization, then you might experience the result as the absence of a heart beat because this phase of the cardiac cycle is when the heart is instantaneously and momentarily at rest as it begins another round of the cardiac cycle.

The impact by the vagus nerve is fairly equal, but it is the particular entry during the cardiac cycle which changes its characterization. If stress or anxiety is elevated or undulating, or GI distress is significant, then stimulation by the vagus nerve can occur at variable frequency, from several per minute to hundreds in some cases.

To sum, adrenaline is associated with the sympathetic nervous system architecture and its actions are associated with an increase in functions of the heart, lungs, etc. The parasympathetic nervous system primarily uses acetylcholine to act in a reverse manner, slowing things down to normal. Palpitations occur as a consequence of inappropriate stimulation of the vagus nerve as part of overall influences by anxiety or stress on the nervous system in general.  

Best regards and Good Health