antiarrhythmic drug

The heartbeat is set by tiny electrical currents flowing through cardiac cells. When those currents misfire, the rhythm goes too fast, too slow, or chaotic. Antiarrhythmic drugs are a class that reshapes these electrical signals to suppress an abnormal rhythm or keep a normal one steady.

They are traditionally grouped by which current they target, a scheme called the Vaughan Williams classification: sodium-channel blockers, beta-blockers, potassium-channel blockers, and calcium-channel blockers. Each alters the timing or excitability of heart cells in a slightly different way.

Their goal in rhythm disorders is either to convert an abnormal rhythm back to normal or to keep it from returning, distinct from drugs that simply slow a racing rate without fixing the rhythm. Choosing one depends on the specific arrhythmia and on the health of the underlying heart.

These are among the trickiest cardiac drugs, because by changing the heart's electricity they can paradoxically trigger new, sometimes dangerous rhythms — an effect called proarrhythmia. That is why many are started cautiously, sometimes in hospital, with close ECG monitoring.