Atrial fibrillation drug-related

Digitoxin and related drugs are used as cardiac stimulants, causing a positive inotropic effect. Thus, they increase the strength and intensity of the contractions and so are used in the treatment of heart failure. Because they slow the electrical conduction between atria and ventricles, they can also be used in the treatment of atrial fibrillation, atrial tachycardia, and atrial flu ter. 

Drugs that block beta-1 receptors on the myocardium are one of the mainstays in arrhythmia treatment. Beta blockers are effective because they decrease the excitatory effects of the sympathetic nervous system and related catecholamines (norepinephrine and epinephrine) on the heart.5,28 This effect typically decreases cardiac automaticity and prolongs the effective refractory period, thus slowing heart rate.5 Beta blockers also slow down conduction through the myocardium, and are especially useful in controlling function of the atrioventricular node.21 Hence, these drugs are most effective in treating atrial tachycardias such as atrial fibrillation.23 Some ventricular arrhythmias may also respond to treatment with beta blockers. 

Qf 136 patients with atrial fibrillation treated with either amiodarone (n = 96) or propafenone (n = 40), 15 developed subsequent persistent atrial flutter, nine of those taking amiodarone and six of those taking propafenone (58). In all cases radiofrequency ablation was effective. It is not clear to what extent these cases of atrial flutter were due to the drugs, although the frequency of atrial flutter in previous studies with propafenone has been similar. Atrial enlargement was significantly related to the occurrence of persistent atrial flutter in these patients. 

The beneficial effects were related to these plasma concentrations, as were the time to the first bout of atrial fibrillation, the frequency of bouts of atrial fibrillation, and the time between episodes. However, when atrial fibrillation occurred there was no difference in the ventricular rate in the different groups. Adverse effects necessitated drug withdrawal in four patients one had heart failure and two had gastrointestinal symptoms. These effects were not dose-related, although there were too few occurrences for a definitive conclusion. The authors suggested that this stepwise approach, with increasing doses of propafenone and increasing doses of quinidine could be beneficial in the treatment of paroxysmal atrial fibrillation. 

Propafenone, l- 2-[2-hydroxy-3-(propylamino)propoxy]phenyl -3-phenylpropan-l-one, is a conunonly used sodium and potassium channel blocker for the treatment of ventricular tachycardia and atrial fibrillation [15]. Propafenone hydrochloride is a class IC antiarrhy tmic agent that shows structural similarity and activity related to p-adrenoly tic agents. The drug is efficacious in suppressing supraventricular and ventricular rhythm disorders [15] (Figure 14.12). 

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