17.4 Class III: Potassium Channel Blockers
3 min read•june 18, 2024
are game-changers in treating dangerous heart rhythms. These drugs slow down the heart's electrical signals, giving cardiac cells more time to recover and preventing life-threatening arrhythmias.
While effective, these medications come with risks. Nurses must closely monitor patients for side effects like QT prolongation and watch for signs of trouble. Patient education is key to ensure proper use and prompt reporting of any issues.
Class III Antiarrhythmic Drugs: Potassium Channel Blockers
Features of potassium channel blockers
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- Prolong the duration and effective refractory period in cardiac cells
- Increase the time for cardiac cells to recover preventing premature contractions (early afterdepolarizations)
- Primarily used to treat ventricular arrhythmias
- Treat life-threatening rhythms such as and
- Examples of Class III
- , (), (), (), ()
Mechanism of Class III antiarrhythmics
- Block potassium channels, particularly the rapid component of the delayed rectifier potassium current ()
- Blocking slows leading to prolongation of duration and effective refractory period
- Indications
- Prevent and treat life-threatening ventricular arrhythmias (ventricular tachycardia, ventricular fibrillation)
- Maintain sinus rhythm in patients with or flutter
- Major side effects
- and risk of (polymorphic ventricular tachycardia)
- and due to prolonged repolarization
- with (, )
- with amiodarone (hypo- or )
- Gastrointestinal disturbances (nausea, vomiting, diarrhea)
- Visual disturbances with amiodarone (halos, blurred vision, photophobia)
Cardiac Electrophysiology and Antiarrhythmic Drug Action
- Action potential: The electrical signal that triggers contraction in cardiac cells
- Repolarization: The phase of the action potential where the cell returns to its resting state
- : Specialized proteins in cell membranes that control the flow of ions, crucial for generating action potentials
- : Abnormal heart rhythm caused by disruptions in the heart's electrical system
- Antiarrhythmic drugs: Medications designed to correct arrhythmias by modifying
Nursing considerations for channel blockers
- Assess baseline and ongoing ECG for QT interval prolongation
- Monitor for >500ms which increases risk of torsades de pointes
- Monitor electrolyte levels, particularly potassium and magnesium
- Correct any before and during therapy to reduce proarrhythmic risk
- Observe for signs and symptoms of (torsades de pointes)
- Watch for palpitations, syncope, or sudden cardiac arrest
- Administer medications as prescribed and educate patients on the importance of adherence
- Missed doses can lead to recurrence of arrhythmia
- Be aware of drug interactions that may increase the risk of adverse effects
- Avoid concomitant use of other (certain antibiotics, antipsychotics, antiemetics)
- Regularly assess and monitor liver, thyroid, and pulmonary function with amiodarone use
- Obtain baseline tests and monitor every 6 months
Patient education for antiarrhythmic medications
- Emphasize the importance of taking medications as prescribed and not discontinuing without consulting their healthcare provider
- Abrupt discontinuation can worsen arrhythmia
- Instruct patients to report any signs or symptoms of adverse effects
- Advise to alert provider for palpitations, dizziness, fainting, shortness of breath, vision changes, or gastrointestinal disturbances
- Advise patients to inform all healthcare providers about their antiarrhythmic medication use
- Crucial to avoid drug interactions and monitor for side effects
- Encourage regular follow-up appointments for monitoring of therapy effectiveness and adverse effects
- Typically every 3-6 months or more frequently if issues arise
- Discuss the importance of maintaining a heart-healthy lifestyle
- Engage in regular exercise, eat a healthy diet, manage stress, and stop smoking
- Educate patients on the potential for drug interactions and the need to consult their healthcare provider before starting any new medications, supplements, or herbal products
- Many compounds can affect metabolism of antiarrhythmics or exacerbate side effects
Key Terms to Review (47)
$I_{Kr}$: $I_{Kr}$ refers to the rapid component of the delayed rectifier potassium current, which is a crucial regulator of cardiac action potentials and heart rate. This potassium channel plays a vital role in the repolarization phase of the cardiac cycle, contributing to the maintenance of normal heart rhythm and function.
Action potential: An action potential is a rapid, temporary change in the electrical membrane potential of a cell. It is essential for the conduction of electrical impulses in cardiac and nerve cells.
Action Potential: An action potential is a rapid, transient electrical signal that propagates along the membrane of an excitable cell, such as a neuron or muscle cell. It is the fundamental unit of communication in the nervous system, allowing for the transmission of information between different parts of the body.
Amiodarone: Amiodarone is a Class III antiarrhythmic medication primarily used to treat and prevent various types of serious irregular heartbeats, such as ventricular tachycardia and ventricular fibrillation. It works by blocking potassium channels, which helps to stabilize the heart rhythm.
Amiodarone: Amiodarone is a complex antiarrhythmic drug that is primarily used to treat and prevent life-threatening cardiac arrhythmias. It works by blocking potassium channels, which affects the electrical activity of the heart, making it a key medication in the management of various dysrhythmias as well as in cardiac emergencies.
Antiarrhythmic Drugs: Antiarrhythmic drugs are a class of medications used to prevent and treat abnormal heart rhythms, or arrhythmias, by modulating the electrical activity of the heart. These drugs work to restore normal heart rhythm and function, thereby reducing the risk of complications associated with arrhythmias.
Arrhythmia: Arrhythmia is an abnormal heart rhythm that occurs when the electrical signals that coordinate the heart's contractions are disrupted. This can result in the heart beating too fast, too slow, or irregularly, affecting its ability to effectively pump blood throughout the body.
Atrial Fibrillation: Atrial fibrillation is an irregular and often rapid heart rate that can increase the risk of stroke, heart failure, and other heart-related complications. It occurs when the upper chambers of the heart (the atria) quiver instead of beating effectively, leading to an irregular and sometimes rapid heartbeat.
Atrial fibrillation with rapid ventricular response: Atrial fibrillation with rapid ventricular response (AFib with RVR) is a condition where the atria beat irregularly and frequently, leading to a fast heart rate in the ventricles. This can result in poor blood flow and increased risk of stroke.
Atrial Flutter: Atrial flutter is a type of cardiac arrhythmia characterized by a rapid, regular, and organized electrical activity in the atria of the heart. It is a common dysrhythmia that is closely related to the topics of introduction to dysrhythmias, as well as the various antiarrhythmic drug classes covered in this chapter.
Betapace: Betapace is a brand name for sotalol, a Class III antidysrhythmic drug that works by blocking potassium channels. It is used to treat life-threatening ventricular arrhythmias and maintain normal heart rhythm.
Betapace AF: Betapace AF is a brand name for sotalol, a Class III antidysrhythmic drug that acts as a potassium channel blocker. It is used to treat atrial fibrillation and atrial flutter.
Bradycardia: Bradycardia is a slower than normal heart rate, typically defined as fewer than 60 beats per minute in adults. It can be a sign of an underlying health issue or a side effect of certain medications.
Bradycardia: Bradycardia is a condition characterized by an abnormally slow heart rate, typically less than 60 beats per minute. This term is relevant in the context of various cardiovascular and pharmacological topics, as it can be a side effect or complication associated with certain medications and disease states.
Cardiac Electrophysiology: Cardiac electrophysiology is the study of the electrical activities and conduction system within the heart. It focuses on understanding the mechanisms that govern the heart's rhythmic contractions and the propagation of electrical impulses through the cardiac tissue, which are crucial for the heart's proper functioning.
Corvert: Corvert, also known as ibutilide, is a Class III antidysrhythmic drug that blocks potassium channels to treat atrial fibrillation and flutter. It is administered intravenously to convert arrhythmias to normal sinus rhythm.
Dofetilide: Dofetilide is a Class III antiarrhythmic drug that works by blocking potassium channels, thereby prolonging the action potential and refractory period in cardiac cells. It is primarily used to treat atrial fibrillation and atrial flutter.
Dronedarone: Dronedarone is an antiarrhythmic medication used to treat certain types of abnormal heart rhythms, specifically atrial fibrillation and atrial flutter. It works by blocking potassium channels among other mechanisms, which helps stabilize the heart's electrical activity.
ECG Monitoring: ECG (Electrocardiogram) monitoring is a non-invasive technique used to continuously record the electrical activity of the heart. It provides valuable information about the heart's rhythm, rate, and conduction, which is crucial for the management of various cardiac conditions, including those related to the effects of sodium channel blockers (Class I) and potassium channel blockers (Class III).
Electrolyte Imbalances: Electrolyte imbalances refer to abnormal levels of essential minerals, such as sodium, potassium, calcium, and magnesium, in the body. These imbalances can have significant impacts on various physiological processes, including cardiac function, fluid balance, and nerve and muscle function. Understanding electrolyte imbalances is crucial in the context of Class III potassium channel blockers, sodium-glucose cotransporter 2 inhibitors (SGLT2Is), and laxatives and stool softeners, as these medications can directly or indirectly influence electrolyte levels.
Heart Block: Heart block is a type of cardiac conduction disorder where there is an interruption or delay in the electrical impulses traveling from the atria to the ventricles, resulting in an abnormal heart rhythm. This term is particularly relevant in the context of dysrhythmias, as well as the mechanisms of action for various antiarrhythmic drug classes.
Hyperthyroidism: Hyperthyroidism is a condition in which the thyroid gland produces an excessive amount of thyroid hormones, leading to an overactive metabolism. This imbalance can have significant impacts on various bodily functions and is an important consideration in the context of hormonal therapy, potassium channel blockers, and thyroid-related disorders.
Hypothyroidism: Hypothyroidism is a condition in which the thyroid gland produces an insufficient amount of thyroid hormones, leading to a slowing of various metabolic processes in the body. This term is relevant across multiple topics, including osmolality, vitamins and minerals, mood stabilizers, potassium channel blockers, growth hormones, thyroid and parathyroid functions, thyroid and antithyroid drugs, and weight management.
Ibutilide: Ibutilide is a Class III antidysrhythmic drug used to treat atrial fibrillation and atrial flutter. It works by prolonging the action potential duration and refractory period through potassium channel blockade.
Ion Channels: Ion channels are specialized proteins embedded in the cell membrane that regulate the flow of charged particles, or ions, in and out of the cell. They play a crucial role in various physiological processes, including the generation and propagation of electrical signals in the body, as well as the maintenance of cellular homeostasis.
Liver Function Tests: Liver function tests (LFTs) are a group of blood tests that provide information about the state of a person's liver. These tests measure the levels of certain enzymes and proteins in the blood, which can indicate liver damage or disease.
Multaq: Multaq (dronedarone) is a Class III antiarrhythmic medication used to manage atrial fibrillation and atrial flutter by blocking potassium channels. It helps maintain normal heart rhythm in patients with these conditions.
Nexterone: Nexterone is a brand name for amiodarone used to treat and prevent various types of serious, life-threatening ventricular arrhythmias. It works by blocking potassium channels in the heart, prolonging the action potential and refractory period.
Pacerone: Pacerone is a brand name for amiodarone, a Class III antiarrhythmic medication used to treat various types of cardiac dysrhythmias by blocking potassium channels. It helps to restore and maintain normal heart rhythm.
Pneumonitis: Pneumonitis is a general term that refers to inflammation of the lungs, often caused by an immune response or exposure to irritants. It is a key concept in the context of both Biologic Response Modifiers and Potassium Channel Blockers, as these treatments can potentially induce this condition.
Potassium Channel Blockade: Potassium channel blockade refers to the inhibition or obstruction of potassium ion (K+) channels, which are essential for regulating the flow of potassium ions across cell membranes. This process has significant implications in the context of Class III antiarrhythmic drugs, as it can influence cardiac electrical activity and heart rate.
Potassium channel blockers: Potassium channel blockers are a class of antidysrhythmic drugs that inhibit the flow of potassium ions through cardiac cell membranes, prolonging repolarization and action potential duration. They are primarily used to treat various types of cardiac arrhythmias.
Proarrhythmia: Proarrhythmia is a term used to describe a medication or treatment that can actually induce or worsen cardiac arrhythmias, rather than the intended effect of preventing or treating them. It is a potentially serious adverse effect that can occur with the use of certain antiarrhythmic drugs, particularly those classified as Class III antiarrhythmic agents.
Pulmonary Fibrosis: Pulmonary fibrosis is a chronic and progressive lung disease characterized by the formation of scar tissue within the lungs, which can impair their ability to function properly. This condition is often associated with inflammation and can have significant implications in the context of the inflammatory response and anti-inflammatory drug treatments, as well as in the management of certain cardiac conditions through the use of potassium channel blockers.
Pulmonary Toxicity: Pulmonary toxicity refers to the adverse effects that certain drugs or substances can have on the lungs, leading to impaired respiratory function and potentially serious health consequences. This term is particularly relevant in the context of Class III Potassium Channel Blockers and Cardiac Emergency Drugs, as these pharmacological agents can interact with the pulmonary system and cause pulmonary-related side effects.
QT interval prolongation: QT interval prolongation refers to an abnormally extended duration of the QT interval, which represents the time between the start of the Q wave and the end of the T wave on an electrocardiogram (ECG). This condition can increase the risk of potentially life-threatening cardiac arrhythmias, particularly torsades de pointes, a type of ventricular tachycardia.
QT-Prolonging Agents: QT-prolonging agents are a class of drugs that can prolong the QT interval, the time between the start of the Q wave and the end of the T wave, in the heart's electrical activity. This can increase the risk of a potentially life-threatening heart rhythm disorder called torsades de pointes.
QTc: QTc, or corrected QT interval, is a measure of the time it takes for the ventricles of the heart to depolarize and repolarize. It is an important parameter in the assessment of cardiac function, particularly in the context of Class III: Potassium Channel Blockers, as it can be affected by these medications.
Repolarization: Repolarization is the process by which an excitable cell, such as a nerve or muscle cell, returns to its resting state after an action potential. It involves the restoration of the normal electrochemical gradient across the cell membrane, allowing the cell to become ready for another potential stimulus.
Sorine: Sorine is a brand name for sotalol, a medication used to treat certain types of irregular heartbeats (arrhythmias). It works by blocking potassium channels, helping to stabilize the heart's rhythm.
Sotalol: Sotalol is a medication used to treat and prevent abnormal heart rhythms by blocking potassium channels. It exhibits both beta-blocking and antiarrhythmic properties.
Thyroid Dysfunction: Thyroid dysfunction refers to a disruption in the normal functioning of the thyroid gland, which is responsible for producing hormones that regulate metabolism, growth, and development. This term is particularly relevant in the context of Class III: Potassium Channel Blockers, as certain medications in this class can impact thyroid function.
Thyroid Function Tests: Thyroid function tests are a group of diagnostic procedures used to assess the activity and health of the thyroid gland. These tests measure the levels of various hormones produced by the thyroid, providing valuable information about its function in the body. They are particularly relevant in the context of understanding the mechanisms and effects of potassium channel blockers, as well as the management of thyroid disorders through antithyroid drugs.
Tikosyn: Tikosyn (dofetilide) is an oral Class III antiarrhythmic medication primarily used to treat atrial fibrillation and atrial flutter. It works by blocking potassium channels, thereby prolonging the cardiac action potential.
Torsades de Pointes: Torsades de pointes is a potentially life-threatening type of ventricular tachycardia characterized by a distinctive twisting of the QRS complexes around the isoelectric line on an electrocardiogram. It is often associated with prolongation of the QT interval and can lead to ventricular fibrillation and sudden cardiac death if left untreated.
Ventricular Fibrillation: Ventricular fibrillation is a life-threatening cardiac arrhythmia characterized by rapid, disorganized, and ineffective contractions of the ventricles, leading to a loss of effective blood pumping by the heart. This condition is a medical emergency that requires immediate intervention to restore normal heart rhythm and prevent sudden cardiac death.
Ventricular Tachycardia: Ventricular tachycardia (VT) is a rapid, abnormal heart rhythm that originates in the ventricles, the lower chambers of the heart. It is a potentially life-threatening cardiac arrhythmia that can lead to decreased blood flow and cardiac arrest if not properly managed.