Clinical meaning
Calcium channel blockers (CCBs) inhibit L-type voltage-gated calcium channels but differ critically in tissue selectivity. Dihydropyridines (DHP: amlodipine, nifedipine, felodipine) are vascular-selective, primarily relaxing arteriolar smooth muscle with minimal cardiac effects — they reduce systemic vascular resistance and are first-line for hypertension and vasospastic angina. Non-dihydropyridines (non-DHP: verapamil, diltiazem) have greater cardiac selectivity, slowing SA node automaticity, AV node conduction, and reducing myocardial contractility — making them useful for rate control in atrial fibrillation/flutter and SVT, as well as angina. The NP must apply prescribing logic: never combine non-DHP CCBs with beta-blockers (additive negative chronotropic and inotropic effects risk severe bradycardia, heart block, or cardiogenic shock), avoid non-DHP CCBs in HFrEF (negative inotropy worsens pump failure), and counsel patients to avoid grapefruit juice (CYP3A4 inhibition increases CCB levels).
Diagnosis & workup
Diagnostics & workup: - 12-lead ECG before initiation (assess baseline PR interval, heart rate, rhythm — prolonged PR or existing AV block contraindicates non-DHP agents) - Echocardiogram to assess left ventricular ejection fraction (non-DHP CCBs contraindicated if LVEF <40%) - Baseline blood pressure and heart rate (orthostatic measurements in elderly) - Hepatic function panel (dose adjustment needed in hepatic impairment) - Serum digoxin level if concurrent use (verapamil and diltiazem increase digoxin levels by 50-75%) - Ambulatory blood pressure monitoring for resistant hypertension evaluation