THE CONTEXT
Class IV drugs block slow calcium channels and are used for supraventricular tachycardia prevention and ventricular rate control in atrial fibrillation.
Mechanism and indications
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Slow calcium channels are important for impulse generation and conduction in atrial and nodal tissue; they are also present in ventricular muscle.
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Class IV drugs prevent supraventricular tachycardia (SVT) by blocking the atrioventricular (AV) node and provide rate control in atrial fibrillation (AF).
Contractility and precautions
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These drugs depress cardiac contractility and should be avoided in left ventricular systolic dysfunction.
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Verapamil is the most widely used drug in this class.
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Intravenous verapamil may cause profound bradycardia or hypotension and should not be used with β-blockers.
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Diltiazem has properties similar to verapamil.