Pharmacology · chapter 17 · Antidysrhythmic Drugs
Class I: Sodium Channel Blockers
The 14 things this section of the textbook says that you are most likely to be asked about — quoted word for word, not retold. Then 6 practice questions with the reasoning.
Key points
What sodium channel blockers do
Sodium channels are responsible for the depolarization of cardiac cells, and blocking these channels leads to slower conduction and a longer refractory period between impulses.
Class IA also blocks potassium
Blockage of potassium channels leads to a property called proarrhythmia, meaning the drugs have a propensity to cause other arrhythmias. Drugs that block potassium channels prolong the QT interval, which increases the risk for torsade de pointes.
Class IB is for ventricular rhythms
Class IB drugs block sodium channels with mild intensity. These drugs are exclusively used for ventricular arrhythmias.
Class IC is less proarrhythmic
Class IC drugs strongly block sodium channels but do not block potassium channels; thus, they are less proarrhythmic than class IA agents (King et al., 2023).
Quinidine versus quinine
Quinidine can easily be confused with quinine; nurses must be careful to avoid mixing up these drugs.
Quinidine: diarrhea and grapefruit
Clients should be educated on the potential for diarrhea and contact their provider if this occurs because it can lead to electrolyte abnormalities that can exacerbate arrhythmias. Clients who take quinidine should avoid grapefruit and grapefruit juice because of potential interactions.
Lidocaine CNS toxicity signs
Signs and symptoms to watch for include sedation and irritability (twitching), which could progress to convulsions and respiratory depression/arrest.
Never lidocaine with epinephrine for rhythm
Lidocaine with epinephrine should never be used as an antidysrhythmic agent.
Pill in a pocket
Propafenone is used off-label in a technique informally called “pill in a pocket.” This technique refers to a scenario in which a client who has symptomatic recurrent paroxysmal atrial fibrillation can keep propafenone on hand and take it as needed when they detect symptoms of atrial fibrillation.
Quinidine: what to monitor
The nurse will need to monitor the client’s ECG, complete blood count (CBC), and liver and kidney function.
Procainamide: lupus and blood dyscrasias
It has the potential to cause drug–induced lupus erythematosus–like syndrome as well as blood dyscrasias such as potentially fatal agranulocytosis, and it has been associated with increased mortality compared with placebo in certain populations.
Procainamide and hypotension
Procainamide can cause hypotension, so the nurse must be mindful of maximum infusion rates to minimize this possibility.
Flecainide and 1:1 AV conduction
Flecainide carries a warning because it can cause 1:1 AV conduction in atrial fibrillation/flutter. This means that the ventricles will beat once for each impulse in the atria, which is so fast that it can cause hemodynamic collapse.
IC drugs and structural heart disease
Flecainide and propafenone are contraindicated in clients with structural heart disease, such as heart failure or myocardial infarction, due to potentially fatal proarrhythmic effects and worsening of heart failure.
Terms to know
- proarrhythmia
- Blockage of potassium channels leads to a property called proarrhythmia, meaning the drugs have a propensity to cause other arrhythmias.
- sodium channel blockers
- Class I antidysrhythmic drugs are known as sodium channel blockers.
Practice questions
Stuck on select-all-that-apply? How to take them one option at a time.
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Every question here, with the answer
A client receiving an intravenous lidocaine infusion for a ventricular arrhythmia becomes drowsy and the nurse notices facial twitching. What does the nurse recognise?
- A normal response to a converted rhythm
- Expected sedation from the drug
- Signs of central nervous system toxicity
- Signs of hypoglycemia
Answer: Signs of central nervous system toxicity
Lidocaine can cause central nervous system toxicity; sedation and irritability with twitching are the warning signs and can progress to convulsions and respiratory arrest. Treating them as expected or unrelated delays action.
The pharmacy sends lidocaine with epinephrine for a client ordered IV lidocaine for ventricular tachycardia. What should the nurse do?
- Give it only if the client is in cardiac arrest.
- Give it at half the ordered rate.
- Give it, since the epinephrine will support blood pressure.
- Do not give it and obtain the correct IV lidocaine product.
Answer: Do not give it and obtain the correct IV lidocaine product.
Lidocaine with epinephrine should never be used as an antidysrhythmic; a death was reported when the wrong formulation was given. The nurse withholds it and gets the correct product, whatever the rate or situation.
A client starting quinidine asks what side effect to watch for at home. Which instruction is most important?
- Stop the drug if the pulse feels irregular.
- Drink grapefruit juice daily to improve absorption.
- Expect constipation and increase fiber.
- Report excessive diarrhea to the health care provider.
Answer: Report excessive diarrhea to the health care provider.
Quinidine commonly causes diarrhea, which can cause electrolyte abnormalities that worsen arrhythmias, so the client reports it. Grapefruit should be avoided, constipation is not the listed effect, and stopping the drug on one's own is not the teaching.
A nurse is caring for a client on a procainamide infusion. Which actions are appropriate? Select all that apply.
- Monitor the ECG, paying attention to the QT interval.
- Monitor levels of procainamide and N-acetyl procainamide.
- Stay within maximum infusion rates to limit hypotension.
- Monitor the complete blood count.
- Give it with lidocaine with epinephrine to prevent hypotension.
Answer: Monitor the ECG, paying attention to the QT interval., Monitor levels of procainamide and N-acetyl procainamide., Stay within maximum infusion rates to limit hypotension., Monitor the complete blood count.
Procainamide prolongs the QT interval, can cause blood dyscrasias and hypotension, and has an active metabolite, so the nurse monitors ECG, CBC and drug levels and respects maximum infusion rates. Lidocaine with epinephrine must never be used as an antidysrhythmic.
A health care provider plans to start flecainide. Which finding in the client's history should the nurse bring to the provider's attention?
- A previous myocardial infarction
- Controlled hypothyroidism
- Paroxysmal atrial fibrillation
- Seasonal allergies
Answer: A previous myocardial infarction
Flecainide and propafenone are contraindicated in structural heart disease such as myocardial infarction or heart failure because of fatal proarrhythmic effects. Paroxysmal atrial fibrillation is an indication, and the other conditions are not mentioned as concerns.
Which statements about class I antidysrhythmic drugs are accurate? Select all that apply.
- Propafenone must be taken every day to work as pill in a pocket.
- Class IB drugs are used only for ventricular arrhythmias.
- Procainamide is contraindicated in systemic lupus erythematosus.
- Quinidine can be confused with quinine.
- Class IC drugs block potassium channels more than class IA drugs.
Answer: Class IB drugs are used only for ventricular arrhythmias., Procainamide is contraindicated in systemic lupus erythematosus., Quinidine can be confused with quinine.
Quinidine and quinine are easily confused, procainamide is contraindicated in lupus, and class IB drugs are used exclusively for ventricular arrhythmias. Class IC drugs do not block potassium channels, and pill in a pocket means taking propafenone only when symptoms occur.
Where every quote comes from
Section 17.2 Class I: Sodium Channel Blockers of Pharmacology for Nurses by Tina Barbour-Taylor, Leah Mueller (Sabato), Donna Paris, Dorie Weaver, OpenStax, 2024. Read the whole section free at openstax.org.
The textbook is licensed under CC BY-NC-SA 4.0. This page quotes it word for word and adds the headings, the order and the practice questions; references to the book's figures and stray spaces left by its formatting are removed. The page is shared under the same licence. Nothing here is sold.