Master Class I Antiarrhythmics (Na+ Channel Blockers) Overview with Picmonic for Medicine

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Class I Antiarrhythmics (Na+ Channel Blockers) Overview

(1) Wand Ant-Tie-Arrhythmia-Drummer (Salt Shaker Channel Blocked)
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Class I Antiarrhythmics treat tachyarrhythmias by blocking fast Na+ channels and there are several subcategories of drug based on their specific effect on cardiac action potentials. These drugs are used to restore normal pacemaker and conduction activity, and are selective for depolarized tissue, which is known as state dependant. Class I antiarrhythmic drug's blockade of Na+ channels reduces rate of phase 0 depolarization and prolongs effective refractory period. This Na+ blockade also increases the threshold for firing within abnormal pacemaker cells. These drugs are contraindicated in hyperkalemic states, as excess potassium increases resting membrane potential and can produce a sodium-channel blockade so pronounced that asystole may result in patients taking Class I antiarrhythmics.
7 KEY FACTS
INDICATIONS
Arrhythmias
Broken Arrhythmia-drum

These drugs are indicated for arrhythmias, which generally refer to abnormal heart rate or regularity. They can be caused by either irregular impulse conduction or impulse generation.

Local Anesthesia
A-nest of Local Anethesia

Class I antiarrhythmics also have local anesthetic properties.

MECHANISM OF ACTION
Block or Slow Conduction
Slowed Snail-conductor

Class I drugs act by blocking fast sodium channels. This slows or halts conduction, especially within depolarized cells.

Block Na+ Channels
Block-guy Blocking Salt-shaker Channel

Blockage of Na+ channels reduces rate of phase 0 depolarization and prolongs effective refractory period.

Raise Threshold
Raised Blocks

Because of the Na+ channel blockage, these drugs increase the threshold for firing within abnormal pacemaker cells.

State Dependent
State Dependent Mine

The drugs in this class are state dependant, meaning they selectively depress tissue that is frequently depolarized, versus normally polarized tissue. This can include ischemic tissue.

CONTRAINDICATION
Hyperkalemia
Caution-tape Hiker-banana

These drugs are contraindicated in hyperkalemic states as they cause increased toxicity for all class I agents. This is because excess potassium increases resting membrane potential and can produce a sodium-channel blockade so pronounced that asystole may result.

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