Calcium Channel Blockers and Antiarrhythmics

Mechanisms

Welcome to this video tutorial on calcium channel blockers, a class of cardiovascular drugs. Let’s start out by looking at how this type of drug works at the cellular level. When muscles are relaxed, potassium ions are in the muscle cell and calcium and sodium ions are outside the muscle cell. For muscle contraction to occur, the potassium ions leave the cell and sodium and calcium ions enter the cell. The cell membrane contains L-type calcium channels through which calcium ions enter into the cell. These channels are responsible for regulating the entry of calcium into muscle cells which stimulate vascular smooth muscle contraction. Because calcium stimulates vascular smooth muscle contraction, when there is more calcium in the cells, the vessels become narrower & BP increases. When there is less calcium in the cells, the blood vessels are more relaxed & wider, so BP decreases. Calcium channel blockers are a class of drugs that block calcium from entering into the cells of heart & blood vessel muscles. So, when a patient has high BP, angina, or heart arrhythmias, calcium channel blockers block calcium from entering the cell by binding to the L-type calcium channels.

Therefore, calcium channel blockers cause smooth muscle relaxation (vasodilation). They dilate coronary arteries & peripheral arterioles, but NOT veins. They decrease the contractility of heart (also known as a negative inotropic effect). They decrease the heart rate (negative chronotropic effect). They decrease the conduction velocity within the heart, especially at the AV (atrioventricular) node (known as a negative dromotropic effect).

Therefore, calcium channel blockers are used to treat angina (chest pain), hypertension, and tachyarrhythmia (rapid irregular heartbeat). Angina is the pain that occurs when the heart is not getting enough oxygen in relation to its workload. Calcium channel blockers treat ANGINA by dilating the arterial walls (which reduces pressure), decreasing the ventricular afterload (which is the resistance the ventricle has to overcome to eject blood from the ventricle chamber) & decreasing the oxygen demand of the heart muscle.

CCB’s treat HYPERTENSION by causing smooth muscle relaxation – when the systemic vascular resistance decreases – the arterial blood pressure is lowered. Remember, the systemic vascular resistance, is the resistance that has to be overcome to push blood through the circulatory system to create flow.

CCB’s treat TACHYARRHYTHMIA by decreasing the electrical firing rate of the pacemaker sites within the heart and decreasing the force needed by the heart to contract. Slower contraction results in lower oxygen demand on the heart muscle resulting in a better oxygen supply to the heart muscle.

There are 3 classes of calcium channel blockers – dihydropyridines, phenylalkylamine, and benzothiazepine (the last two are considered non-dihydropyridines).

Uses and Types

The dihydropyridine class is the most smooth muscle selective class of CCB’s. They decrease the systemic vascular resistance & arterial pressure. Therefore, they are primarily used to treat hypertension. However, the vasodilatation & hypotension effects can lead to reflex tachycardia (which results in an increased oxygen demand on the myocardium). Because vasodilation decreases the blood returning to the heart, the heart has to beat harder & faster to keep up the supply – too much vasodilation then causes the reflex tachycardia. Take note that the drugs in this class end in “-pine.” Nifedipine (Procardia), Nicardipine (Cardene), Felodipine (Plendil), Isradipine (DynaCirc), and Amlodipine (Norvasc). Remember, these drugs all cause a decrease in BP and increase in heart rate.

Side Effects and Risks

Side effects of dihydropyridine calcium channel blockers include excessively low BP, dizziness, headaches, reflex tachycardia, flushing, rashes, constipation / nausea, and peripheral edema.

The phenylalkylamine class of drugs are a non-dihydropyridine that decreases the oxygen demand on the heart & reverses coronary vasospasm (the sudden, intense constriction of a coronary artery that can occlude the vessel). They are used to treat angina & arrhythmias. They cause less vasodilation, so less tachycardia. They actually can cause excessive bradycardia, impaired electrical conduction, and depressed contractility as side effects, so patients that already have any of these issues should not take non-dihydropyridine CCBs. Also, they should not be given with beta-blockers, because beta-blockers also depress cardiac mechanical and electrical activity. The drug commonly used in this category is Verapamil. This drug treats arrhythmias, as well as angina by reducing the myocardial oxygen demand and reversing coronary vasospasm.

Benzothiazepines are another non-dihydropyridine CCB that has cardio-depressant & vasodilation effects. They decrease arterial pressure without as much reflex tachycardia caused by dihydropyridines. They can also cause bradycardia as a side effect. The specific drug in this class is Diltiazem, which is in between verapamil and dihydropyridines in its selectivity for vascular calcium channels. The side effects are similar to the phenylalkylamine class – excessive bradycardia, impaired electrical conduction, & depressed contractility.

There are some rare, but possible side effects of calcium channel blockers – arrhythmias, heart block, and heart failure. CCB can cause further worsening of heart failure as a result of their negative inotropic effect – because they reduce the ability of the heart to contract & pump blood.

Patient education is important with all medications. Teach the patient taking calcium channel blockers, the following:

• Take with a meal or glass of milk to protect stomach.
• Avoid grapefruit juice – it increases the concentration of medicine in the blood
• Avoid drinking alcohol – it can cause severe side effects & affect the way the medication works, and
• Do not stop taking calcium channel blockers suddenly – it may make angina worse.

Review Questions

Let’s go over a practice question to review. A patient has been prescribed Amlodipine for hypertension. The nurse should educate the patient about the effects of this CCB, which include.

1. 1. Bradycardia and depressed contractility
   2. Dizziness, headaches, and reflex tachycardia
   3. Impaired electrical conduction
   4. Coronary vasospasm

Here’s another one

Calcium channel blockers are used to treat.

• Angina, bradycardia, and chest pain
• Hypotension, dizziness, and arrhythmias
• Angina, hypertension, and tachyarrhythmia
• Coronary vasospasm, reflex tachycardia, and bradycardia

Thank you for watching this video tutorial on calcium channel blockers. Be sure to check out our other videos!