17.6 Unclassified Antidysrhythmics

Atropine

Atropine is an anticholinergic agent approved for symptomatic bradycardia, among other indications. It works as an acetylcholine receptor antagonist, thus decreasing parasympathetic or vagal regulation of the heart rate. It is important to note that heart transplant recipients lack vagal innervation, so atropine does not work to treat bradycardia in these clients.

Atropine should be administered by rapid intravenous injection. Slow administration of atropine has been associated with paradoxical bradycardia (McLendon & Preuss, 2022) and should be avoided.

Digoxin

Digoxin is an older antidysrhythmic drug that was first approved in 1954 and is used for rate control of atrial fibrillation or atrial flutter. As an antidysrhythmic drug, it works by suppressing conduction through the AV node, slowing the rate of conduction and, thus, the ventricular heart rate. It does this by enhancing vagal (parasympathetic) stimulation of the heart. It is also approved for treatment of heart failure with reduced ejection fraction. Clients with heart failure and concomitant atrial fibrillation have few treatment options because many of the antidysrhythmic drugs are contraindicated. Therefore, given its approval for both disease states, digoxin is sometimes used for these clients.

Digoxin is available in both oral and intravenous dosage forms. Because it is eliminated by the kidneys and can accumulate in individuals with decreased kidney function, nurses must monitor renal function in clients who are taking digoxin.

Digoxin serum levels can be monitored; the reference range is 0.5–2.0 ng/mL. However, serum levels greater than or equal to 1.2 ng/mL may be associated with higher rates of mortality (Lopes et al., 2018). For clients who present with toxicity and particularly high digoxin serum levels (greater than 6–10 ng/mL), an antidote called digoxin immune fab (Digibind) can be administered to bind the digoxin and facilitate excretion. Many health care providers monitor the apical heart rate before administering digoxin, withholding it if the apical heart rate is less than 60 beats per minute.

Adenosine

Adenosine is another unclassified antidysrhythmic drug that is approved for treating paroxysmal supraventricular tachycardia. It works by enhancing potassium efflux and suppressing calcium influx into the cells of the AV node, slowing its conduction and extinguishing arrhythmias that originate there. Adenosine is available in an intravenous dosage form. It has an extraordinarily short half-life—less than 10 seconds. This short half-life necessitates specific administration to ensure that the drug will reach the systemic circulation before it is metabolized: It must be given as a rapid IV bolus by the peripheral intravenous route, either administered directly into a vein or into an IV injection port as close to the client as possible. It must be immediately followed by a rapid saline flush. Using a stopcock can help facilitate quick administration.

After administration of adenosine, clients will frequently experience a brief period of asystole on the ECG while concurrently experiencing a sensation of their heart stopping. This occurs because for a short period, conduction through the AV node (and thus the stimulus for ventricular contraction) is blocked. The nurse should tell the client about this expected effect to mitigate anxiety when the effect occurs. It is short lived due to the short half-life; prolonged asystole is very rare. Still, adenosine should be given only with continuous ECG monitoring at a facility with resuscitation measures available.

Table 17.11 lists common unclassified antidysrhythmics and typical routes and dosing for adult clients.

Adverse Effects and Contraindications

Atropine can cause anticholinergic adverse effects as an extension of its therapeutic effect. Some of the more serious adverse effects include tachycardia, acute glaucoma, pyloric obstruction, complete urinary retention in clients with benign prostatic hyperplasia, and formation of respiratory mucus plugs. Other common adverse effects include dry mouth, constipation, and blurred vision. Clients who cannot tolerate anticholinergic effects should avoid atropine. This caution includes individuals with myasthenia gravis or those with urinary retention because atropine can exacerbate their disease. Clients who have had a heart transplant should not rely on atropine to treat bradycardia because it may not have a therapeutic effect.

Digoxin should not be used in clients with baseline bradycardia or certain heart blocks because it can cause bradycardia as part of its therapeutic effect. Digoxin therapy has a propensity for toxicity, which is characterized by gastrointestinal upset, vision changes, dizziness, fatigue, and cardiovascular symptoms such as palpitations from premature ventricular contractions (Cummings & Swoboda, 2023).

Adenosine has a very short half-life, so adverse effects beyond the immediate period of administration are rare. However, immediately upon administration it is typical for clients to report skin flushing, sweating, nausea, and an impending sense of doom. It also can cause dyspnea (shortness of breath) and bronchoconstriction in susceptible individuals. Adenosine should not be administered to clients with second- or third-degree AV block or to those with bradycardia who do not have a pacemaker. Adenosine can cause AV block as an extension of its therapeutic effect.

Table 17.12 is a drug prototype table for unclassified antidysrhythmics featuring digoxin. It lists drug class, mechanism of action, adult dosage, indications, therapeutic effects, drug and food interactions, adverse effects, and contraindications.

Nursing Implications

The nurse should do the following for clients who are taking unclassified antidysrhythmics:

• Obtain a complete medication list to check for any drug interactions.
• Measure heart rate and blood pressure before administering the medication.
• Monitor for adverse effects, including electrolyte imbalances and changes in kidney function.
• Notify the health care provider if the client has baseline bradycardia and does not have a pacemaker.
• Use continuous cardiac monitoring in clients using these drugs.
• Provide client teaching regarding the drug and when to call the health care provider. See below for client teaching guidelines.