Non-Dihydropyridine CCBs

Verapamil and diltiazem are non-dihydropyridine CCBs that block L-type calcium channels primarily in cardiac tissue — the SA and AV nodes. By reducing calcium entry into nodal cells, they slow automaticity and conduction velocity through the AV node, which lowers heart rate and controls supraventricular tachyarrhythmias (SVT, atrial fibrillation/flutter with rapid ventricular response). They also reduce myocardial contractility (negative inotropic effect) and provide moderate vasodilation, making them useful for rate control, angina, and hypertension. Verapamil has the strongest cardiac selectivity and greatest negative inotropic effect; diltiazem is intermediate, balancing cardiac and vascular effects. Key indications: rate control in atrial fibrillation/flutter, SVT termination when adenosine is ineffective or contraindicated (IV verapamil or diltiazem), chronic stable angina, and hypertension. They are contraindicated in heart failure with reduced ejection fraction because further depressing contractility worsens pump failure. They should not be combined with beta-blockers without careful monitoring because both suppress the SA and AV nodes, risking severe bradycardia or heart block.