Class II antidysrhythmic medications

Class II antidysrhythmic medications, also known as beta blockers, are a class of medications that help control dysrhythmias, or abnormal heart rhythms. Now, there are two types of beta blockers: nonselective beta blockers, like propranolol, and cardioselective beta blockers, like metoprolol.

Alright, beta1 and beta2 receptors are adrenergic receptors that bind with catecholamines like norepinephrine and epinephrine, which are neurohormones of the sympathetic nervous system, or SNS. Beta1 receptors are located in the heart and beta2 receptors are mostly in the lungs. You can remember this by thinking we have one heart and two lungs. In the heart, beta1 receptors stimulate cardiac activity, whereas in the lungs beta2 receptors cause smooth muscle and bronchial relaxation.

Nonselective beta blockers, like propranolol, block effects of both beta1 and beta2 receptors of the heart and lungs, while cardioselective beta blockers, like metoprolol, block only the beta1 receptors unless given at higher doses.

Now, by blocking adrenergic receptors, beta blockers decrease the effects of the SNS, and can be used to decrease dysrhythmias that are caused by an excessive amount of SNS stimulation.

For instance, the excessive catecholamine response after a myocardial infarction, or MI, makes the heart hyperirritable, which can lead to dysrhythmias. Beta blockers block the actions of catecholamines on the beta1 receptors, reducing the risk of post-MI ventricular dysrhythmias.

Specifically, beta blockers decrease the heart rate by delaying the conduction through the atrioventricular, or AV, node and decreasing automaticity of the sinoatrial, or SA, node. They also reduce myocardial contractility, which decreases the workload of the heart.

Now, even though antidysrhythmics are indicated to treat dysrhythmias, they tend to have prodysrhythmic properties, meaning they can make the dysrhythmia worse, or even cause new dysrhythmias.  Other effects include bradycardia and AV block due to its effect on cardiac conduction. They also reduce cardiac output, because of reduced cardiac contractility, which can lead to hypotension, postural hypotension, and dizziness. And, since propranolol is nonselective beta blocker, it can cause bronchoconstriction because of its effects on beta2 receptors.

Now, beta blockers shouldn’t be given to patients with AV block, bradycardia, or heart failure because they can worsen these conditions. Propranolol is also contraindicated in patients with asthma because it can cause bronchoconstriction through beta2 blockade.

Propranolol should also be avoided in patients who have diabetes mellitus, since it can suppress signs of hypoglycemia, like tachycardia and tremors, and it reduces glycogenolysis, or the breakdown of glycogen into glucose through beta2 blockade in the liver and skeletal muscles. Likewise, propranolol should not be used if the patient has a history of anaphylaxis, because adrenergic blockade will prevent the rescue drug, epinephrine, from working since it blocks these receptors. Propranolol can also exacerbate depression and should be avoided in patients with this condition.

Lastly, beta blockers should never be stopped abruptly, since withdrawal of their beta-blocking actions can result in rebound hypertension, angina, and even an MI. In fact, metoprolol has a Black Box warning regarding the need for a gradual reduction in dose and close monitoring if the medication is discontinued.

Now, when caring for your patient who’s prescribed a class II antidysrhythmic, begin by performing a baseline cardiovascular assessment including vital signs, assessment of orthostatic hypotension, ECG, and laboratory tests results such as renal and liver function tests. Also be sure to place your patient on continuous cardiac monitoring and keep emergency equipment nearby. Following administration, assess your patient for side effects, and evaluate the effectiveness of antidysrhythmic therapy.

Then, when educating your patient about their medications, focus your teaching on safe self-administration. Teach them about the importance of taking their medications exactly as prescribed and to never stop their medication abruptly, since this can cause reemergence of their dysrhythmia. Also, remind them that sustained release tablets cannot be crushed or chewed, as this can cause a precipitous drop in their heart rate or blood pressure. If they experience GI symptoms during therapy, let them know that they can take their medications with food. Ensure they know how to check their blood pressure and pulse before administration.

Then, advise them to avoid alcohol use during therapy because it can contribute to hypotension; instruct them to avoid caffeine since it can increase catecholamine effects; and encourage them to stop using tobacco because it contributes to vasoconstriction. If they need assistance quitting provide them with counseling and referrals for smoking cessation. Finally, review common side effects, ensure they understand when they should notify their health care provider, and remind them to keep all scheduled follow-up appointments.

Alright, as a quick recap . . . . Class II antidysrhythmic medications, also known as beta blockers, block the effects of the SNS to help control dysrhythmias. Beta blockers can be nonselective, like propranolol, which blocks the effects of both beta1 and beta2 receptors of the heart and lungs, or cardioselective, like metoprolol, which selectively blocks beta1 receptors. Common side effects include bradycardia and hypotension, and they can either worsen or cause new dysrhythmias. Nursing considerations for class II antidysrhythmic medications include establishing a baseline assessment, monitoring for side effects, evaluating the effectiveness of therapy, and providing teaching for safe self-administration.