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I am thinking why electrical cardioversion is contraindicated in atrial fibrillation with digitalis toxicity/poisoning.

Cardiac digitalis is also called digoxin and cardiac glycoside. It is antiarrhythmic agent against supraventricular arrhythmias. It is contraindicated in Atrial Fibrillation with digitalis toxicity. The Pubmed's article about the topic is a stub without describing its Pharmacology.

Digitalis toxicity is a complication of digitalis therapy, here used for atrial fibrillation. This may be due to kidney failure when the medication accumulates in the body. Its treatment is activated charcoal and gastric lavage. However, assume that these methods do not help in treatment or that we in acute digitalis toxicity.

I think the reason why we cannot recently do electrical cardioversion in digitalis poisoning is the high probability of repolarizing incidences so the likelihood to stimulate heart at the right moment is very small. This is because digitalis poisoning is associated with cardiac disturbances: ventricular tachycardia, ventricular fibrillation, SA block and AV block. Without knowing more precisely about the complication, I think the electrical cardioversion has high risk of failure.

Why is electrical cardioversion contraindicated in Digitalis Poisoning of AF treatment?

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The mechanism of action of digitalis-like preparations based on inhibition of myocardial NA+/K+-ATPase as well as of cardiac conducting tissue. The inhibition of latter (conducting) is 2.5 greater than those of former (myocardial). This is why the main feature of digitalis intoxication are arrhythmias due to ectopic electric impulses and spontaneous depolarization (there is overloading of conducting system by Calcium as well as excess amounts of Noradrenaline released from sympathetic endings).

These metabolic changes in a case of digitalis intoxication could lead to irreversible ventricular arrhythmias after cardioversion - there are sporadic reports about this phenomenon. Based on these reports, it was thought that the use of digitalis during electrical cardioversion would provoke ventricular arrhythmias in patient even with clinically desirable concentration of digitalis.

In a study in patients with therapeutic nontoxic digitalis levels determined that these patients may safely undergo electrical cardioversion without reducing or withholding the dose of digitalis. Thus, the cardioversion is not contraindicated in a patient without signs of digitalis toxicity.

Although, the exact mechanism of the ventricular arrhythmias after cardioversion is not well understood, it is clear that mentioned above changes in electrolytes concentrations with electrical stimulation lead to premature beats overtaking restored sinoatrial pace. The rate of ventricular arrhythmias is in direct correlation with the level of the energy used for the cardioversion (this is why there is "pre-cardioversion" with low-energy pulses). Until these metabolic changes are not corrected, the resulting ventricular arrhythmias can be irreversible. This is why, digitalis intoxication is relative contraindication to electric cardioversion of atrial fibrillation/flatter.

Excerpt from the article mentioned:

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  • $\begingroup$ Excellent sentence The rate of ventricular arrhythmias is in direct correlation with the level of the energy used for the cardioversion (this is why there is "pre-cardioversion" with low-energy pulses). I would like to get more understanding about the nature and characteristics of this energy. What is the energy form? Ellipsoid pulses? Which other energy pulses are provided along the main energy signal? Any more studies about this? $\endgroup$ – Léo Léopold Hertz 준영 Jun 2 '15 at 20:15
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    $\begingroup$ @Masi It is clear that the more energy was used for cardioversion, the more its influence on the conducting system and myocardium. Since, the metabolic changes did not allow "actual" ventricular cardioversion, the higher-enegly impulses would have greater arrhythmic effect. $\endgroup$ – Ilan Jun 2 '15 at 20:20

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