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1-How does massaging of carotid artery at chassaignac tubercle( anterior tubercle of transverse process of C6 vertebra ) can relieve the symptoms of Supraventricular Tachycardia?
My attempt: I think by massaging carotid artery we are somehow stimulating the satellate ganglion present at level of c7. Or, I think, by massaging the carotid artery we are increasing BP, thereby affecting the baroreceptors and somehow this relieves the symptoms of supraventricular tachycardia.
2-Why can't the same massage be done at level of other cervical vertebrae?
$\begingroup$It's not the vertebra that is important, but the carotid artery, and where it is most likely influenced by massage. There are too many interfering structures at C1/2; I believe C3-5 is ~ normal. Some guidelines indicate midpoint between the angle of mandible and the superior border of thyroid cartilage (so about C4-5), others just below the angle of the mandible (C3). C6 seems to be well below the carotid sinus to me. If you can refocus your question (not where and why) and show some research, I'd be happy to answer your question.$\endgroup$
$\begingroup$@anongoodnurse Unfortunately I could not find any reason by doing research. All the websites I saw only state the fact but didn't explain and my textbook too.$\endgroup$
$\begingroup$OK, then I won't post an answer. Sorry I could not help you, but I really prefer to help those who post according to our guidelines when possible.. :($\endgroup$
The reason massaging the carotid artery can relieve symptoms of supraventricular tachycardia is because by massaging the artery, as you point our yourself, you artificially increase BP within the carotid artery, this activates a reflex (via the glossopharyngeal nerve) that lowers bloodpressure by reducing the heart rate via the vagus nerve, by increasing the refractory period of the AV-node, so the heart rate drops.
It should be noted though, that it can be a bit dangerous to play with these reflexes in some patients, especially because massaging the carotid arteries can lead to an embolism in older individuals with atherosclerosis, or in some patients, it can lead to asystole or ventricular fibrillation (i.e. cardiac arrest).
It's not really about which vertebra is at the level you are massaging, rather it's about being near the carotid sinus, which is where the baroreceptors are located, and that might vary between individuals and how you position the head etc.
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