6.6 Antiarrhythmics

An arrhythmia is any deviation from the normal rate or pattern of a heartbeat, including heart rates that are too slow (bradycardia), too fast (tachycardia), or irregular. The terms dysrhythmia (disturbed heart rhythm) and arrhythmia (absence of heart rhythm) are traditionally used interchangeably in clinical practice despite their difference in meaning.

The ECG is used to identify and monitor an arrhythmia. See more information about ECGs in the “Basic Concepts of the Cardiovascular and Renal Systems” section and an overview of arrhythmias in the “Common Cardiovascular Disorders” section.

Anti-arrhythmic medications regulate heart rate and rhythm by manipulating the conduction of electrical signals to change the heart rate or to attempt to revert an arrhythmia to a normal sinus rhythm. All anti-arrhythmic medications have a risk of producing an arrhythmia. Some anti-arrhythmic medications are used during emergency situations such as cardiac arrest, whereas others are used long-term, such as those used to control atrial fibrillation. Monitoring electrolytes and the ECG patterns are very important assessments for the nurse administering these types of medications.

Class I – Sodium Channel Blockers

Class I anti-dysrhythmic medications slow conduction and prolong depolarization by decreasing sodium influx into cardiac cells. There are three subgroups of sodium channel blockers: Class IA, IB, and IC. Quinidine is an example of a Class IA antidysrhythmic. Lidocaine is an example of a Class IB medication that is also used as a local anesthetic. Flecainide is an example of a class IC antidysrhythmic.

Mechanism of Action: Quinidine slows conduction and prolongs depolarization by decreasing sodium influx into cardiac cells. The conduction rate and automaticity are decreased. This medication also has alpha-antagonistic properties that cause peripheral vasodilation.

Indications: This medication is typically used for life-threatening ventricular dysrhythmias such as ventricular tachycardia or for conversion of atrial fibrillation that has not responded to other therapy.

Nursing Considerations: Sodium channel blockers are contraindicated in clients who have a history of thrombocytopenia or myasthenia gravis. Use cautiously with clients who have a serious heart block rhythm and do not have an artificial pacemaker, such as a 2nd-degree heart block. Grapefruit and sour orange juice should be avoided by clients taking this medication.

Side Effects/Adverse Effects: Quinidine may prolong QT interval leading to ventricular arrhythmias, such as ventricular tachycardia or torsades de pointes. There is an increased risk for toxicity with clients who have heart failure and renal or hepatic dysfunction due to drug accumulation. This medication’s safety has not been thoroughly evaluated in children and geriatric clients.

Quinidine may induce thrombocytopenia. Routine lab work may be evaluated by a client‘s health care provider. Common side effects of this medication are nausea, vomiting, diarrhea, fever, chills, abnormal ECG/arrhythmias, and headache.

In many research trials, use of anti-arrhythmic therapy for nonlife-threatening arrhythmias actually resulted in increased risk of death compared to placebo.^[1]

Some antiarrhythmic medications may cause dizziness and may increase sensitivity to light.^[2]

Health Teaching & Health Promotion: Clients should be instructed regarding the significance of compliance with therapeutic drug regimen and take medications as prescribed, even if not symptomatic. Clients or family members may need instruction on how to take pulse rate and parameters regarding reporting to their health care provider.

Now let’s take a closer look at the medication grid for quinidine in Table 6.6a.^[3] Medication grids are intended to assist students to learn key points about each medication class. Basic information related to a common generic medication in this class is outlined, including administration considerations, therapeutic effects, and side effects/adverse effects. Prototype/generic medication listed in the medication grid is also linked directly to a free resource from the U.S. National Library of Medicine called DailyMed. Because information about medication is constantly changing, nurses should always consult evidence-based resources to review current recommendations before administering specific medication.

Table 6.6a Quinidine Medication Grid

Class II – Beta-Blockers

Class II medications are beta-blockers that are used to decrease conduction velocity, automaticity, and the refractory period of the cardiac conduction cycle. Read additional information about beta-blockers in the “Autonomic Nervous System” chapter.

Sotalol is a Beta-1 and Beta-2 blocker that also has Class III anti-arrhythmic properties. Recall that other types of beta-blockers, such as metoprolol, are also used to treat hypertension. See the “Antihypertensives” section later in this chapter for more information about the use of beta-blockers to treat hypertension.

Mechanism of Action: Sotalol is a nonselective beta-adrenergic blocker that prolongs the cardiac action potential.

Indications: Sotalol is given to clients for life-threatening arrhythmias, such as ventricular arrhythmias or supraventricular arrhythmias. It is only recommended for clients with severe arrhythmias.

Nursing Considerations: Titration of this medication is done by evaluating renal function and monitoring QTc on the ECG 2-4 hours after each medication upon initiation. Clients with decreased renal function require dosage adjustment. Sotalol is contraindicated for clients with decreased serum potassium, bradycardia, 2nd- or 3rd-degree heart block, heart failure, and conditions leading to bronchospasm.

Side Effects/Adverse Effects: Common side effects for sotalol are arrhythmias, chest pain, palpitations, fatigue, dizziness, hypotension, bradycardia, heart failure, cardiac ischemia, bronchospasm, thyroid abnormalities, and hypoglycemia.^[4]

Boxed Warning: This drug can cause arrhythmias. This medication lengthens a client‘s QTc interval. Initiation of this medication requires a client to be in a facility to determine baseline QT and intermittent QT interval checks. QT interval checks are done 2-4 hours after each dose. If the QT corrected interval is greater than 500 msec, the dosing must be changed.

Health Teaching & Health Promotion: Clients should be instructed regarding the significance of compliance with therapeutic drug regimen and take medications as prescribed, even if not symptomatic. Clients or family members may need instruction on how to take pulse rate and blood pressure. They should receive parameters regarding reporting to their health care provider. They should report any pulse rate less than 50 bpm and significant changes in blood pressure.

Clients should also be advised that these medications may cause dizziness and visual changes. Clients may also notice orthostatic blood pressure decrease with position changes and should be advised to change positions slowly. If the client notices irregular, fast heart rate or experiences any fainting episodes, they should notify their health care provider immediately.

Additionally, these medications may also mask the signs of hypoglycemia, so diabetic clients must use extra caution to monitor for low blood sugar. They may also increase cold sensitivity.^[5]

Now let’s take a closer look at the medication grid for sotalol in Table 6.6b.^[6]

Table 6.6b Sotalol Medication Grid

Class III – Potassium Channel Blockers

Class III medications prolong repolarization by blocking the potassium channels in cardiac cells that are responsible for repolarization. They are used for emergency treatment of ventricular dysrhythmias. Amiodarone is an example of an antidysrhythmic that has predominantly Class III properties.

Mechanism of Action: Class III medications prolong repolarization by blocking the potassium channels in cardiac cells that are responsible for repolarization. Amiodarone also antagonizes alpha- and beta-receptors.

Indications: Amiodarone is indicated only for the treatment of life-threatening recurrent ventricular arrhythmias when these have not responded to documented adequate doses of other available antiarrhythmics or when alternative agents could not be tolerated.

Nursing Considerations: Amiodarone can cause fetal injury when administered to a pregnant client. Use cautiously with the geriatric population who may have decreased hepatic, cardiac, or renal function. Read drug label information carefully due to several potential drug interactions.

Side Effects/Adverse Effects: Neurological impairments (such as fatigue, tremors, involuntary movements, poor coordination, and gait) and GI disturbances are common adverse effects. Vision changes/loss of vision and photosensitivity may also occur.

Boxed Warning: Amiodarone has several fatal toxicities such as pulmonary toxicity, exacerbation of arrhythmia, liver injury, and heart block. Clients who require initiation of this therapy should be hospitalized and monitored closely. Neurological impairments (such as fatigue, tremors, involuntary movements, poor coordination, and gait) and GI disturbances are common adverse effects. Vision changes/loss of vision and photosensitivity may also occur.

Health Teaching & Health Promotion: Clients should be advised to closely follow the recommended dosing regimen. If one dose of medication is missed, the client should follow the normal dosing schedule and resume with the next dose. If more than one dose of medication is missed, the client should call the health care provider for guidance. Clients should be compliant with all follow-up appointments and monitoring.

Clients should avoid drinking grapefruit and sour orange juice during medication therapy. Some clients may experience photosensitivity and protective measures should be taken.^[7]

Now let’s take a closer look at the medication grid for amiodarone in Table 6.6c.^[8]

Table 6.6c Amiodarone Medication Grid

Class IV – Calcium Channel Blockers

Class IV medications include the calcium channel blockers verapamil and diltiazem. These medications increase the refractory period of the AV node by slowing the influx of calcium ions, thus decreasing the ventricular response and decreasing the heart rate. These medications may be used to control heart rate associated with supraventricular tachycardias. Calcium channel blockers are also used to treat hypertension because they relax smooth muscle and cause vasodilation. See the “Antihypertensives” section later in this chapter for more information about their use in treating hypertension.

Mechanism of Action: Diltiazem inhibits calcium during depolarization to decrease the workload of the heart and increase oxygen supply to the myocardium. This medication will relax smooth muscle and decrease peripheral resistance.

Indications: Diltiazem is used to treat angina, hypertension, and supraventricular tachycardias.

Nursing Considerations: This medication is not given to hypotensive clients, clients with acute myocardial infarction, or clients with 2nd- or 3rd-degree heart block or sick sinus syndrome.

Side Effects/Adverse Effects: Diltiazem can potentially worsen signs and symptoms of heart failure due to the negative inotropic effect. Clients may experience bradycardia, worsening 1st-degree AV block, syncope, edema, hypotension, headache, dizziness, or hepatic injury.^[9]

Health Teaching & Health Promotion: Clients should be advised to closely follow the recommended dosing regimen. Clients or family members may need instruction on how to take a pulse rate and should report any pulse less than 50 bpm. Clients should also be advised that this medication may cause dizziness and visual changes. Clients may also notice orthostatic blood pressure decrease with position changes and should be advised to change positions slowly.

Clients should be advised to avoid grapefruit and sour orange juice during medication therapy. They should also monitor for gingival sensitivity and be sure to maintain good oral hygiene. Clients may also notice increased photosensitivity and should take protective measures.^[10]

Now let’s take a closer look at the medication grid for diltiazem in Table 6.6d.^[11] 

Table 6.6d Diltiazem Medication Grid

Adenosine

Adenosine is a unique medication given to clients who are experiencing paroxysmal supraventricular tachycardia. It is given all at once as a bolus in either a 6- or 12-mg dose to slow electrical conduction to restore a normal sinus rhythm.

Mechanism of Action: Adenosine will slow conduction through the AV node to restore normal sinus rhythm.

Indications: Adenosine is used to treat paroxysmal supraventricular tachycardia.

Nursing Considerations: This medication is an emergent type of medication. Use cautiously with geriatric clients with decreased cardiac function.

This medication is contraindicated with clients who have 2nd- or 3rd-degree AV block, sinus node disease, or any known hypersensitivity.

At time of administration, a nurse may see no electrical activity on an ECG for a brief few seconds before normal sinus rhythm is restored. The client should be warned they may feel extremely uncomfortable during this short period of time.

Side Effects/Adverse Effects: Clients receiving adenosine may experience prolonged asystole, arrhythmias, palpitations, facial flushing, hypotension, bronchospasm, shortness of breath, dizziness, seizures, loss of consciousness, numbness and tingling to upper extremities, and nausea.^[12]

Health Teaching & Health Promotion: Clients should be advised to closely follow the recommended dosing regimen. Clients or family members may need instruction on how to take a pulse rate and should report any abnormalities. Clients should also be advised that this medication may cause dizziness and visual changes. Clients may also notice orthostatic blood pressure decrease with position changes and should be advised to change positions slowly.

Clients should be advised to avoid grapefruit and sour orange juice during medication therapy. They should also monitor for gingival sensitivity and be sure to maintain good oral hygiene. Clients may also notice increased photosensitivity and should take protective measures.^[13]

Now let’s take a closer look at the medication grid for adenosine in Table 6.6e.^[14]

Table 6.6e Adenosine Medication Grid