Cardiovascular Clinical Pharmacology: Anti-arrhythmic Drugs

Vocabulary-style flashcards covering cardiac physiology, action potential phases, ECG patterns, and the Vaughan Williams classification of anti-arrhythmic drugs.

Automaticity

The ability of cardiac myocytes to be electrically excitable and generate electrical impulses spontaneously.

Sinoatrial node (SA node)

The pacemaker of the heart where the electrical impulse is generated to maintain a normal sinus rhythm of $60-100$ beats/min.

Phase 0 (Rapid Depolarisation)

The phase of the cardiac action potential characterized by the rapid inflow of $Na^+$ when voltage-gated fast $Na^+$ channels open.

Phase 1 (Partial Repolarisation)

The phase where the inward $Na^+$ current is deactivated and there is an outflow of $K^+$.

Phase 2 (Plateau)

A period of maintained depolarization due to $Ca^{2+}$ inflow through voltage-gated slow $Ca^{2+}$ channels and $K^+$ outflow through some $K^+$ channels.

Phase 3 (Repolarisation)

The phase resulting from the closure of $Ca^{2+}$ channels and the outflow of $K^+$ through additional voltage-gated $K^+$ channels.

Phase 4 (Pacemaker Potential)

Characterized by slow $Na^+$ inflow and the slowing of $K^+$ outflow.

Refractory Period

The period encompassing phases $1-3$ of the action potential when the cell does not respond to stimuli, even if they are strong.

P wave

The deflection on an ECG representing atrial depolarisation.

QRS complex

The deflection on an ECG representing ventricular depolarisation.

T wave

The deflection on an ECG representing ventricular repolarisation.

Bradycardia

A slow heart rate defined as less than $60$ beats/min.

Tachycardia

A fast heart rate defined as greater than $100$ beats/min.

Re-entry

A mechanism of arrhythmia where refractory tissue is reactivated due to a conduction block, causing an abnormal continuous circuit, such as in Wolff-Parkinson-White syndrome.

Class I Anti-arrhythmic Drugs

Drugs that bind to and block fast sodium channels responsible for rapid depolarization; they affect Phase $0$ and are used for atrial fibrillation, atrial flutter, and ventricular tachycardia.

Class IA Drugs

Sodium channel blockers like quinidine, procainamide, and disopyramide that increase the duration of the action potential ($\uparrow AP$).

Class IB Drugs

Sodium channel blockers like lidocaine and mexiletine that decrease the duration of the action potential ($\downarrow AP$).

Class IC Drugs

Sodium channel blockers like flecainide and propafenone that have no effect on the duration of the action potential ($\leftrightarrow AP$).

Cinchonism

A side effect of quinidine characterized by headache, dizziness, tinnitus, and deafness.

Lidocaine

A Class IB drug given only via the $IV$ route, it is the first choice for ventricular arrhythmias due to acute myocardial infarction, digitalis toxicity, or anesthesia.

Class II Anti-arrhythmic Drugs

Beta-adrenoceptor antagonists (beta-blockers) that reduce sympathetic activity, diminish phase $4$ depolarization, and depress automaticity.

Class III Anti-arrhythmic Drugs

Potassium channel blockers, such as amiodarone and sotalol, that selectively prolong repolarisation and the refractory period to suppress re-entrant rhythms.

Amiodarone

A Class III drug with a long half-life of $20-100$ days; long-term adverse effects include pulmonary fibrosis, thyroid dysfunction, and grey skin pigmentation.

Class IV Anti-arrhythmic Drugs

Calcium channel antagonists, mainly verapamil, which slow conduction through the SA and AV nodes and slow phase $4$ spontaneous depolarization.

Adenosine

A purine nucleotide with a half-life of less than $2$ seconds, given as a rapid $IV$ bolus to terminate supraventricular tachycardia (SVT).

Digoxin

A cardiac glycoside that increases inotropy (contractility) while decreasing chronotropy (heart rate) and increasing vagal tone.

Proarrhythmic Paradox

The phenomenon where anti-arrhythmic drugs trigger new or worse arrhythmias, such as palpitations or sudden cardiac death.

Atrial Flutter

A condition characterized by signals circling in the atria at a rate of $250-350$ beats/min, which precipitates CHF.

AV block

A type of heart block where electrical signals from the atria to the ventricles are delayed or blocked, resulting in bradycardia.

Asystole

A state where there is no heart beat.