Cholinergics, Hyperthyroidism and Atrial Fibrillation
How bethanechol precipitates atrial fibrillation in hyperthyroidism?
Atrial fibrillation is due to a supraventricular ectopic foci usually in the pulmonary veins. Any ectopic site can produce a rhythm which can have a very high rate more than 250 per minute, because the ectopic site is not under autonomic nervous control. When an ectopic site takes over, SA node activity is overtaken. When you suppress SA node activity, ectopic sites may take easily. Hyperthyroidism promotes the formation of ectopic sites and their continuous activity. Bethanechol is a ACh agonist which will suppress the activity of SA node. So giving cholinergic muscarinic agonists in persons with hyperthyroidism will definitely precipitate formation of ectopic sites and AF.
Thyroid hormone....is an universal accelerator of all cellular functions. So formation of ion channels, activation and deactivation of ion channels are all accelerated. So thyroid hormone increases contractility, conductivity, rate of contraction, rate of relaxation of myocardial cells. (Ionotropic, chornotropic, bathmotropic, lusitrophic).
During hyperthyroid crisis, AF is very common. We give corticosteriod to treat. Steriod corrects all dysfunctions of hyperthyroid state instantly till its blood levels are adequate. Corticosteriods act as universal brake. They act as brakes to decrease all cellular functions and dysfunctions. So corticosteroids are life saving drugs. Remember: Thyroxine is accelerator. Steroids are brakes.
Atrial fibrillation is due to a supraventricular ectopic foci usually in the pulmonary veins. Any ectopic site can produce a rhythm which can have a very high rate more than 250 per minute, because the ectopic site is not under autonomic nervous control. When an ectopic site takes over, SA node activity is overtaken. When you suppress SA node activity, ectopic sites may take easily. Hyperthyroidism promotes the formation of ectopic sites and their continuous activity. Bethanechol is a ACh agonist which will suppress the activity of SA node. So giving cholinergic muscarinic agonists in persons with hyperthyroidism will definitely precipitate formation of ectopic sites and AF.
Remember: though AF is a type of supraventricular activity, during AF only atrial rate increases much. Ventricular rate does not increase much. There is different atrial and ventricular rates. This is the reason for development of thrombus inside atrium. In usual supraventricular tachycardia, atrial and ventricular rates are usually same and blood flow is smooth. So no thrombus is formed.
Thyroid hormone....is an universal accelerator of all cellular functions. So formation of ion channels, activation and deactivation of ion channels are all accelerated. So thyroid hormone increases contractility, conductivity, rate of contraction, rate of relaxation of myocardial cells. (Ionotropic, chornotropic, bathmotropic, lusitrophic).
During hyperthyroid crisis, AF is very common. We give corticosteriod to treat. Steriod corrects all dysfunctions of hyperthyroid state instantly till its blood levels are adequate. Corticosteriods act as universal brake. They act as brakes to decrease all cellular functions and dysfunctions. So corticosteroids are life saving drugs. Remember: Thyroxine is accelerator. Steroids are brakes.
Comments
Post a Comment