anti-arrhythmic drugs

(anti-arrhythmics)

Drugs used for treating disordered heart rhythms (see arrhythmia). Anti-arrhythmic drugs either slow the flow of electrical impulses to the heart muscle or inhibit the ability of heart muscles to respond to these impulses; they are classified as class I, II, III, or IV anti-arrhythmics, depending on their mode of action. Class I drugs affect the response of the heart muscle to the signal received and may be subdivided into classes Ia (e.g. disopyramide); Ib (e.g. lidocaine); and Ic (e.g. propafenone hydrochloride and flecainide acetate). Class II anti-arrhythmic drugs are beta blockers, which reduce the ability of the pacemaker to pass electrical signals to the heart muscle. Class III drugs include amiodarone. Class IV comprise some, but not all, calcium antagonists, which interfere with the conduction of nerve impulses in the atria. Other drugs used are cardiac glycosides (digitalis drugs, such as digoxin), which affect the way signals are transmitted in the heart, and adenosine.

Side effects:
many of these drugs can depress normal heart function and may produce dizziness on standing (postural hypotension) or breathlessness on exertion. Mild nausea and visual disturbances are quite common. Side effects specific to particular drugs are listed in their entries.

Precautions and interactions with other drugs:
the effects of anti-arrhythmic drugs tend to be additive, therefore specialist care is necessary if two or more are used. Most of the drugs that control arrhythmias can also provoke them in some circumstances. Low potassium concentrations can enhance this effect; it is important, therefore, that when people are taking diuretics with anti-arrhythmic drugs, a potassium-sparing diuretic is used either alone or in combination with a loop diuretic or a thiazide diuretic. Details of specific interactions are given at entries for individual drugs.

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