Thyroid Storm: Role of Amiodarone in Thyroxicosis Atrial Fibrillation

What is Amiodarone?

Plot of membrane potential versus time. The initial resting phase (region 4) is negative and constant flowed by sharp rise (0) to a peak (1).  The plateau phase (2) is slightly below the peak. The plateau phase is followed by a fairly rapid return (3) back to the resting potential (4).

Class 3 Anti Arrhytmic

Amiodarone may be an acronym for its IUPAC name (2-butyl-1-benzofuran-3-yl)-[4-[2-(diethylamino)ethoxy]-3,5-diiodophenyl]methanone, where ar is a placeholder for phenyl.

diiodoC25H29I2NO3   – 2 iodine (rich iodine)

Amiodarone structure.svg

figure: amiodarone structure

figure: thyroxine structure

structurally similar

Amiodarone is rich iodine drug. Money Money Money.

High Iodine lead to Wolff–Chaikoff effect

  • is a reduction in thyroid hormone levels caused by ingestion of a large amount of iodine
  • autoregulatory phenomenon that inhibits organification in the thyroid gland, the formation of thyroid hormones inside the thyroid follicle, and the release of thyroid hormones into the bloodstream.
  • an effective means of rejecting a large quantity of ingested iodide, and therefore preventing the thyroid from synthesizing large quantities of thyroid hormone.

Related image

 

figure: looks iodides inhibition on several steps

 

Amiodarone may cause thyroid dysfunction in patients with preexisting thyroid disease and destructive thyroiditis in patients with normal thyroid glands.

An antithyroid drug given simultaneously blocks iodine organification and prevents iodide-induced exacerbation of thyrotoxicosis. Hence, the thyrotoxicosis-induced effect of amiodarone should not preclude its use in thyrotoxic atrial fibrillation,[provided that it is given in conjunction with antithyroid agents.

But Amiodarone will convert AF to SR. Precaution to AF with unknown duration or >48 H -thrombus formation)

Amiodarone don’t look so bad. As long use with conjunction of anti thyroid drug right? So can Amiodarone be use?

Rate control: The first step in the management of atrial fibrillation, despite the cause, is to control the ventricular response.

Rate control

Rate control

Rate control

Shirley Ooi said it too.

IMG_6503[2335].jpgpage 310 2nd edition

 

So which agent should be use?

 

Heart failure or non heart failure?

Non heart failure

  • Beta Blocker
    • propranolol has the advantage of reducing the peripheral conversion of T4 to T3; however, this effect is of minor therapeutic value, and other cardioselective agents with longer half-lives are equally effective.
  • Calcium Channel Blocker
    • diltiazem or verapamil, can be useful for long-term control of ventricular rate in patients in whom beta-adrenergic blockade is contraindicated.
    • used cautiously, as these may cause severe hypotension and a further reduction in systemic vascular resistance that is already low in patients with thyrotoxicosis.

 

Heart failure

Image result for digoxin mechanism of action atrial fibrillation

 

Hyperthyroid atrial fibrillation is typically resistant to digoxin that is caused in part by an increase in the renal clearance and apparent volume of its distribution as well as increased sympathetic and reduced vagal tone. A larger-than-usual dose of digoxin is required, which increases the risk of its toxicity. Despite these limitations, digoxin should still be considered in patients with heart failure and concomitant thyrotoxic atrial fibrillation.

 

ref:

https://www.medscape.com/viewarticle/495668_3

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