Atrial Fibrillation

Atrial Fibrillation

Explain why digoxin is given in atrial fibrillation.
Answer:

Atrial fibrillation is a condition in which the heart rate is more than 350 beats per minute. The high number of impulses generated in the atria is transmitted to the ventricles resulting in an increase in ventricular rate.

At such high rates, the ventricles do not get the time to completely contract leading to ineffective ventricular contractions (ventricles contract but cannot pump blood properly). This may be fatal for the individual.

For this condition, we need to either convert the atrial fibrillation to sinus rhythm or at least control the ventricular rate (achieved with digitalis). The mechanism of action of digoxin is as follows:

• Digoxin has a vagomimetic action due to which it increases the effective refractory period (ERP) of 96 Mastering the BDS IInd Year (Last 25 Years Solved Questions) Pharmacology AV node. Thus, the number of impulses which are
  able to pass down the AV node to the ventricles is significantly reduced.
• The vagomimetic action of digoxin also reduces the refractory period of the atria leading to an increased frequency of atrial contractions. The increased number of impulses hitting the AV node makes the AV node refractory for the subsequent impulses. Thus, less number of impulses can be transmitted to the ventricles.
• The reduction in the number of impulses reaching the ventricles reduces the ventricular rate leading to more effective contractions i.e. ventricles can contract more strongly increasing the cardiac output.