💊 Calcium Channel Blockers (Non-Dihydropyridine)

Non-dihydropyridine calcium channel blockers (non-DHP CCBs) are a class of cardiovascular medications that primarily act on the heart, reducing heart rate and contractility. They are used for arrhythmias, angina, and hypertension.

Non-DHP CCBs (verapamil and diltiazem) block L-type voltage-gated calcium channels in both cardiac muscle and vascular smooth muscle, but with a greater affinity for cardiac channels. This reduces calcium influx into myocardial cells and the sinoatrial (SA) and atrioventricular (AV) nodes, leading to decreased heart rate, reduced myocardial contractility, and slowed AV nodal conduction. They also cause some vasodilation.

Non-DHP CCBs are primarily used for rate control in supraventricular tachyarrhythmias like atrial fibrillation and flutter. They are also effective in the management of stable angina, reducing myocardial oxygen demand. They can be used for hypertension, particularly when there is a co-existing indication for rate control or angina.

Absolute contraindications include severe left ventricular dysfunction or decompensated heart failure due to their negative inotropic effects. They are also contraindicated in severe bradycardia, second or third-degree heart block without a pacemaker, and Wolff-Parkinson-White syndrome with atrial fibrillation. Avoid in significant hypotension.

Common side effects include bradycardia, heart block, and constipation (especially with verapamil). Hypotension and dizziness can occur due to vasodilation. They can worsen heart failure symptoms due to their negative inotropic effect. Peripheral oedema is less common than with DHP-CCBs.

Heart rate and blood pressure should be monitored regularly to assess efficacy and detect adverse effects like bradycardia or hypotension. An ECG may be required to assess for heart block or other conduction abnormalities, especially when initiating treatment or titrating the dose. Patients should be advised to report symptoms of dizziness or worsening heart failure.

Always check for a history of heart failure, severe bradycardia, or heart block. Counsel patients about potential side effects like dizziness, constipation, and the importance of reporting slow heart rate or shortness of breath. Be aware of significant interactions with beta blockers (risk of severe bradycardia and heart block) and grapefruit juice.

High-yield topics include their primary action on the heart (rate and contractility), their use for rate control in arrhythmias, and their contraindication in heart failure. Remember the key side effects like bradycardia and constipation. The interaction with beta blockers is a critical point to remember.

SBAs often test their primary use for rate control in atrial fibrillation and the contraindication in heart failure. Questions may present a patient with bradycardia or heart block after starting a non-DHP CCB. The distinction between DHP and non-DHP CCBs regarding their primary site of action and side effect profile is a common theme.