17.2 Class I: Sodium Channel Blockers
3 min read•june 18, 2024
are vital that regulate heart rhythms by slowing conduction and prolonging refractory periods. These Class I medications are subdivided based on their effects on duration, targeting various cardiac arrhythmias.
Nurses must understand the indications, adverse reactions, and drug interactions of sodium channel blockers. Careful monitoring, patient education, and collaboration with the healthcare team are crucial for safe and effective management of these powerful cardiac medications.
Class I: Sodium Channel Blockers
Characteristics of Class I sodium channel blockers
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- Class I antidysrhythmic drugs block sodium channels in cardiac cells
- Sodium channels enable rapid (Phase 0) of the cardiac
- Blocking sodium channels slows conduction velocity and prolongs the (time when cardiac cells cannot be re-excited)
- Class I drugs are subdivided based on their effects on action potential duration (APD)
- drugs moderately block sodium channels and prolong APD (, )
- drugs mildly block sodium channels and shorten APD (, )
- drugs strongly block sodium channels with minimal effect on APD (, )
- Slowing conduction velocity and prolonging the refractory period suppresses and , common mechanisms of dysrhythmias
Cardiac Electrophysiology and Class I Antidysrhythmics
- The cardiac action potential consists of depolarization (sodium influx) and (potassium efflux) phases
- Class I drugs primarily affect the depolarization phase by blocking sodium channels
- These medications can influence the refractory period, impacting the heart's ability to generate new action potentials
- By modifying , Class I drugs can suppress abnormal rhythms originating from ectopic foci or reentrant circuits
Indications and reactions of antidysrhythmic drugs
- Indications
- and fibrillation (abnormally fast heart rhythms originating in the ventricles)
- Supraventricular tachycardias (abnormally fast heart rhythms originating above the ventricles) (, )
- (PVCs) (early heartbeats originating in the ventricles)
- Adverse reactions
- (paradoxical worsening of dysrhythmias)
- Hypotension (low blood pressure) and negative inotropic effects (decreased heart contractility) due to
- Neurological symptoms (dizziness, confusion, tremors)
- Gastrointestinal disturbances (nausea, vomiting, diarrhea)
- Drug interactions
- Additive with other QT-prolonging medications (certain antibiotics, antipsychotics) increases risk of (a type of ventricular tachycardia)
- Increased risk of toxicity with drugs that inhibit (cimetidine, certain antifungals) by reducing drug clearance
- Enhanced negative inotropic effects when combined with other cardiodepressant drugs (beta-blockers, calcium channel blockers)
Nursing considerations for sodium channel blockers
- Assess baseline cardiac function and rhythm using ECG, vital signs, and physical examination
- Monitor for signs of drug toxicity or proarrhythmic effects
- ECG changes (, QT prolongation, new dysrhythmias)
- Hemodynamic instability (hypotension, bradycardia)
- Neurological symptoms (dizziness, confusion, tremors)
- Adjust dosage based on renal and hepatic function, as many Class I drugs are metabolized by the liver and excreted by the kidneys
- Administer medications as prescribed, ensuring proper dose, route, and timing
- Have emergency equipment readily available, including defibrillator and resuscitation medications
- Collaborate with the healthcare team to optimize therapy and manage potential complications
Patient education for Class I antidysrhythmics
- Emphasize the importance of taking medications as prescribed and not abruptly discontinuing therapy without consulting the healthcare provider
- Instruct patients to report any new or worsening symptoms (palpitations, dizziness, fainting)
- Advise patients to inform all healthcare providers about their antidysrhythmic medication use, especially before undergoing surgical or dental procedures
- Educate patients about potential drug interactions and the need to consult their healthcare provider before taking any new medications (over-the-counter products, herbal supplements)
- Encourage patients to maintain a heart-healthy lifestyle
- Regular exercise
- Balanced diet
- Stress management
- Avoidance of tobacco and excessive alcohol consumption
- Provide written educational materials and resources for additional information and support
Key Terms to Review (36)
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.
Antidysrhythmic drugs: Antidysrhythmic drugs are medications used to treat abnormal heart rhythms. They work by modifying the electrical impulses within the heart to maintain a normal rhythm.
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.
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.
Cardiodepression: Cardiodepression refers to the reduction or depression of cardiac function, specifically the contractile ability of the heart muscle. This term is particularly relevant in the context of Class I antiarrhythmic drugs, which are sodium channel blockers known to exhibit cardiodepressant effects.
Class IA: Class IA refers to a subgroup of antiarrhythmic drugs that work by blocking sodium channels in the heart. These drugs are used to treat certain types of abnormal heart rhythms, known as cardiac arrhythmias, by altering the electrical activity of the heart muscle.
Class IB: Class IB refers to a subgroup of sodium channel blockers, a class of antiarrhythmic drugs that work by inhibiting the sodium channels responsible for the rapid depolarization phase of the cardiac action potential. This subclass exhibits unique pharmacological properties compared to other sodium channel blocker classes.
Class IC: Class IC refers to a specific subgroup of sodium channel blockers, a class of antiarrhythmic drugs used to treat cardiac arrhythmias. These drugs work by inhibiting the flow of sodium ions through voltage-gated sodium channels in the heart, which helps to stabilize the electrical activity and prevent abnormal heart rhythms.
Depolarization: Depolarization is the process by which the electrical potential difference across a cell membrane is reduced, leading to the generation and propagation of an action potential. This term is particularly relevant in the context of conduction of electrical impulses and the mechanism of action of sodium channel blockers.
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).
Ectopic Foci: Ectopic foci refer to the presence of abnormal electrical impulse generation sites within the heart, outside of the normal pacemaker, the sinoatrial (SA) node. These ectopic foci can lead to cardiac arrhythmias and disrupt the normal heart rhythm.
Flecainide: Flecainide is an antiarrhythmic medication classified as a Class I sodium channel blocker. It is primarily used to treat certain types of serious ventricular and supraventricular arrhythmias.
Hepatic Metabolism: Hepatic metabolism refers to the biochemical processes that occur within the liver to break down, transform, and eliminate various substances, including drugs and other xenobiotics. It is a crucial aspect of pharmacokinetics, as the liver plays a central role in the metabolism and clearance of many medications.
Lidocaine: Lidocaine is a local anesthetic and antiarrhythmic drug used to treat ventricular dysrhythmias. It works by blocking sodium channels, thereby stabilizing the cardiac cell membrane.
Mexiletine: Mexiletine is a Class IB antiarrhythmic medication used to treat ventricular arrhythmias. It works by blocking sodium channels in the cardiac cells, stabilizing the cardiac membrane and reducing abnormal electrical activity.
Premature Ventricular Contractions: Premature ventricular contractions (PVCs) are abnormal heartbeats that originate in the ventricles, the lower chambers of the heart, before the normal electrical signal from the atria reaches them. These early, extra heartbeats disrupt the normal rhythm of the heart and can be an indicator of underlying heart conditions.
Proarrhythmia: Proarrhythmia is a condition where an antiarrhythmic drug paradoxically causes new or worsened cardiac arrhythmias. It often complicates the treatment of existing dysrhythmias.
Proarrhythmic Effects: Proarrhythmic effects refer to the potential for a medication or treatment to induce or worsen cardiac arrhythmias, which are abnormal heart rhythms. These effects can be a serious concern when using certain medications, particularly those that interact with the heart's electrical conduction system.
Procainamide: Procainamide is a Class I antiarrhythmic medication used to treat ventricular and atrial dysrhythmias. It works by blocking sodium channels, thereby slowing conduction and prolonging the cardiac action potential.
Propafenone: Propafenone is a Class IC antiarrhythmic drug used to treat certain types of serious irregular heartbeats. It works by blocking sodium channels in the cardiac cells, stabilizing the heart rhythm.
QRS Widening: QRS widening refers to an increase in the duration of the QRS complex on an electrocardiogram (ECG), which represents the electrical activation of the ventricles. This widening is an important indicator of abnormal ventricular conduction and is often associated with various cardiac conditions, particularly those involving the Class I: Sodium Channel Blockers.
QT Prolongation: QT prolongation is an electrocardiographic (ECG) finding characterized by an abnormally long time interval between the start of the Q wave and the end of the T wave, which represents the duration of ventricular depolarization and repolarization. This condition can increase the risk of potentially life-threatening cardiac arrhythmias, such as torsades de pointes, and is an important consideration in the context of various drug therapies.
Quinidine: Quinidine is a Class I antiarrhythmic drug that works by blocking sodium channels in the heart. It is used to treat various types of cardiac dysrhythmias, such as atrial fibrillation and ventricular tachycardia.
Reentrant Circuits: Reentrant circuits refer to a specific type of electrical circuit in which the electrical signal travels in a circular path, repeatedly re-entering the same tissue or structure. This concept is particularly important in the context of Class I: Sodium Channel Blockers, as reentrant circuits can contribute to the development and maintenance of certain cardiac arrhythmias.
Refractory Period: The refractory period is a crucial concept in the context of electrical impulse conduction and the mechanisms of action of certain drug classes. It refers to the period of time following the generation of an action potential during which a cell or tissue is unable to respond to a new stimulus, even if that stimulus would normally be sufficient to elicit a response.
Renal Excretion: Renal excretion is the process by which the kidneys remove waste products, excess water, and other unwanted substances from the bloodstream and eliminate them from the body through urine. This process is crucial for maintaining the body's homeostasis and is an essential component of both antiparasitic and anthelminthic drug metabolism, as well as the metabolism of Class I sodium channel blockers.
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.
Rythmol SR: Rythmol SR is an extended-release formulation of propafenone, a Class Ic sodium channel blocker used to treat certain types of serious irregular heartbeats (arrhythmias). It works by stabilizing the cardiac cell membrane and reducing excitability.
Sodium Channel Blockers: Sodium channel blockers are a class of medications that work by inhibiting the flow of sodium ions through voltage-gated sodium channels in the cell membranes. This action disrupts the generation and propagation of action potentials, which is crucial for the normal functioning of the cardiovascular and nervous systems.
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.
Xylocaine: Xylocaine, also known as lidocaine, is a local anesthetic and antiarrhythmic drug that works by blocking sodium channels. It is commonly used to treat ventricular arrhythmias during acute myocardial infarction.