20.9e Sodium Channel Blockers (Class I)

sodium influx

All medications in this general class affect the (?) in phases 0 and 4 of fast potentials.

specialized conduction system

This slows the propagation of impulses down the (?), although it does not affect the SA or AV node.

Class IA medications

Class IA medications include (?).

repolarization rate

In addition to slowing conduction, these medications decrease the (?).

QRS complex

This widens the (?) and prolongs the QT interval as seen in an ECG.

procainamide

Although quinidine is usually considered the prototype for this class, we use (?) here because it is administered more frequently in emergency medicine.

atrial fibrillation with rapid ventricular response

Procainamide is indicated in the treatment of (?) and ventricular arrhythmias.

anticholinergic properties

Quinidine has a similar mechanism of action, but it also has (?) that can induce unintended tachycardias.

Class IB medications

Class IB medications include (?).

rate of repolarization

Unlike Class IA medications, Class IB medications increase the (?).

automaticity

They also reduce (?) in ventricular cells, which makes them effective in treating rhythms originating from ectopic ventricular foci.

other purposes

Several of the medications in this class are also used for (?).

Lidocaine

Lidocaine, the prototype, is frequently used with epinephrine as a local anesthetic, and phenytoin (Dilantin) is most commonly used as an antiseizure medication.

ventricular tachycardia

Lidocaine was once the medication of choice for treating (?) and ventricular fibrillation.

Prophylactic administration

(?) of lidocaine was once thought to benefit patients with myocardial infarction.

relatively ineffective

Recent studies, however, have shown it to be (?).

CNS side effects

When given in overdose, lidocaine has significant (?), including tinnitus, confusion, and convulsions.

Class IC medications

Class IC medications include (?).

conduction velocity

They decrease (?) through the atria and ventricles as well as through the bundle of His and the Purkinje network.

ventricular repolarization

Like the Class IA medications, Class IC medications delay (?).

proarrhythmic properties

Both medications, which are administered orally, are given to prevent recurrence of ventricular arrhythmias, but both also have (?); that is, they are likely to cause arrhythmias as well as treat them.

myocardial contractility

They also depress (?) and are therefore reserved for potentially lethal ventricular arrhythmias that do not respond to any other conventional therapy.

Moricizine (Ethmozine)

(?) is similar to the other Class I medications but has additional properties that exclude it from the other subclasses.

sodium influx

Like the other medications in this class, Ethmozine blocks (?) during fast potential depolarization, thereby decreasing conduction velocity, but it can also depress myocardial contractility.

ventricular arrhythmias

Like the Class IC medications, it is reserved for the treatment of (?) refractory to other conventional therapy.