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. 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...