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 t