Vagal Tone, Vagotonia and Hypervagotonia - What these terms imply in Cardiac Electrophysiology

Here are some of my thoughts on it ! 

Vagal tone is a measure of the activity of the vagus nerve. vagotonia is a condition where the vagus nerve is excessively excitable!

while Hypervagotonia is relatively rarer , which results in sinus node dysfunction and can result in significant symptoms!! 

A common misunderstanding among most of us is of autonomics believing that the nerve structures are either sympathetic or parasympathetic! 

Hence the commonly used term vagal tone is generally refer to describe the level of activity in the para sympathetic system 

Where as in reality the vagus and all the other cardiac nerves carries /contain both sympathetic &parasympathetic components. 

Vagal effects 

1. Vagal activation simultaneously affects both the sinus and AV nodes. 

The resulting ECG can include 

sinus slowing / Sinus arrest &

varying degrees of AV node block. 

2. One of the most commonly seen hallmarks changes of vagally mediated bradycardia on surface ECG is the simultaneous occurrence of AV block along with sinus slowing. 

(Therefore, when sinus slowing and AV block occur together ,it is correctly assumed as reflex in origin and therefore benign) 

( paradoxically On the other hand, it is often assumed that AV block that occurs during sinus acceleration (like ETT ) be assumed to be pathologic until proven otherwise, and often leads to consideration of ppm) 

3. Severe SN dysfunction can sometimes result from excessive vagal tone without intrinsic sinus node disease . 

(Hypervagotonia as an example can be seen in hypersensitive carotid sinus syndrome and neurocardiogenic syncope!! (most of our EP colleagues bradycardia, can be confirmed by evaluating the sinus rate response to atropine infusion particularly in younger patients .) 

Increases in vagal tone also can occur during valsalva , endotracheal intubation and vomiting, and coughing) 

Sinus slowing in this scenario is paroxysmal and may be associated with evidence of AV conduction delay, secondary to effects of the enhanced vagal tone on both the sinus node and AVN . 

4. The best effects of vagus / and its effects are best seen in well conditioned / trained athletes Bradyarrhythmias are more common in athletes than in the general population because of an increase in resting vagal tone as a response to regular strenuous exercise. (These changes, in the very initial stages, have been linked to enhanced vagal tone. However, over Times these tough trainings May lead to intrinsic changes in the sinus node & the conduction system resulting in dilatation and hypertrophy of the heart !!!! (athlete's heart) 

Some of the ecg changes seen in the highly trained athletes may be 

A. Significant sinus Brady is very common in highly trained athletes !!!             

B . Respiratory sinus arrhythmia C. wandering pacemaker, 

C. junctional bradycardia, 

D. first-degree AV block

E. Wckb (second-degree AV block are also more common in this population) 

F. AF (Studies have suggested that AF occurs more frequently in athletes than in the general population ).

Cause ! may be a consequence of increased vagal tone hence bradycardia allowing dispersion of atrial repolriazation and resulting in a higher susceptibility to AF!!!