Class I Antidysrhythmic medications

Antidysrhythmic medications help correct irregular heart rhythms. Class I antidysrhythmic medications, also known as sodium channel blockers, are divided into three groups which differ by how they impact electrical conduction and repolarization.

Class IA antidysrhythmics like quinidine, are used for atrial and ventricular dysrhythmias, as well as supraventricular dysrhythmias; whereas class IB antidysrhythmics, such as lidocaine, are used for acute ventricular dysrhythmias; and class IC antidysrhythmics, like flecainide, are used to treat the most serious, life-threatening ventricular dysrhythmias that have not responded to other antidysrhythmic medications.

Alright, so class I antidysrhythmics work by blocking sodium channels and reducing the influx of sodium into cardiac cells. This slows the electrical impulses through the heart’s conduction system, ultimately resulting in a slower, more regular heart rhythm.

The three medication subgroups have minor differences in how they affect the electrical impulses. First, class IA antidysrhythmics slow conduction and prolong repolarization; class IB antidysrhythmics slow conduction and shorten repolarization; and class IC antidysrhythmics prolong conduction with little or no effect on repolarization.

Now, even though antidysrhythmics are indicated to treat dysrhythmias, they tend to have pro-dysrhythmic properties, meaning they can make the dysrhythmia worse, or even cause new dysrhythmias. Other side effects of antidysrhythmic medications will vary depending on the subgroup.

So, quinidine can cause headaches, dizziness, bradycardia, and diarrhea. Some of the more severe effects include cardiotoxicity, including ventricular tachycardia, heart block, asystole, as well as arterial embolism. It can also cause cinchonism, which is an adverse effect of medications made from plant alkaloids from the cinchona bark, that causes symptoms like nausea, tinnitus, and visual disturbances.

On the other hand, lidocaine can cause drowsiness, anxiety, restlessness, and blurred or double vision; and more severe effects include hypotension, bradycardia, cardiac or respiratory arrest, and seizures.

Then, flecainide has a high potential to worsen existing cardiac dysrhythmias; and because it also decreases cardiac contractility, it can worsen or even cause heart failure.

As far as contraindications go, quinidine is contraindicated in patients with thrombocytopenic purpura and certain types of heart block. And because quinidine has anticholinergic effects, it should not be given to patients who are adversely affected by anticholinergic medications, like patients diagnosed with myasthenia gravis. Also, quinidine has a Black Box warning regarding increased mortality, especially when used in patients with structural heart disease, like in the heart valves and muscle.

Next, lidocaine is contraindicated in patients who have Stokes-Adams or Wolff-Parkinson-White syndrome, both of which can predispose patients to additional cardiac dysrhythmias; as well as patients with severe AV or SA block.

Flecainide is contraindicated in patients with cardiogenic shock, pre-existing second- or third-degree heart block, and structural heart disease. It also has Black Box warnings regarding its pro-dysrhythmic effects in patients with atrial fibrillation or flutter; and that it should never be used in patients who do not have a life-threatening ventricular dysrhythmia.

Lastly, all class I antidysrhythmics should be used with caution in patients with impaired liver and kidney function, and all antidysrhythmics are considered high alert medications, meaning the medications have an increased risk of causing significant harm if used in error.

Now, when caring for your patient who’s prescribed a class I antidysrhythmic, begin by performing a baseline cardiovascular assessment including vital signs, ECG, and laboratory tests results such as renal and liver function tests. Also be sure to place your patient on continuous cardiac monitoring and keep emergency equipment nearby. Following administration, assess your patient for side effects, and evaluate the effectiveness of antidysrhythmic therapy.

Then, when educating your patient about their medications, focus your teaching on safe self-administration. Teach them about the importance of taking their medications exactly as prescribed and to never stop their medication abruptly. Also, if your patient is prescribed quinidine, instruct them to avoid grapefruit juice, since it can increase quinidine’s absorption rate. Finally, review common side effects, ensure they understand when they should notify their health care provider, and remind them to keep all scheduled follow-up appointments.

Alright, as a quick recap.... Class I antidysrhythmic medications, also known as sodium channel blockers, are used in the treatment of cardiac dysrhythmias by altering electrical impulses in the heart’s conduction system. Class I antidysrhythmics have a variety of side effects including bradycardia and hypotension, and they can either worsen or cause new dysrhythmias.

Nursing considerations for class I antidysrhythmic medications include establishing a baseline assessment, monitoring for side effects, evaluating the effectiveness of therapy, and providing teaching for safe self-administration.