Class Ia

Question 1

describe general Class Ia Agents

Answer 1

Quinidine, procainamide, disopyramide

• Moderate binding to Na+ channels (phase 0 depoalrization)
• K+ channel blockage (delayed phase 3 repolarization)

–> PROLONG QRS and QT

• Ca2+ channel blocking effect at high doses (depressed phase 2 and nodal phase 0)

Question 2

Quinidine (MoA)

Answer 2

MoA: BLOCK RAPID INWARD Na+ Channel

–> Decreased Vmax of phase 0

–> slowed conduction

–> effects greasts at fast HR

ACTIONS: (dose dependent)

–> Block K+ channels = increase APD

–> block Alpha receptors = decrease BP

–> block M receptors = increase HR in intact subjects

Question 3

describe clinical app and adverse effects of QUINIDINE

Answer 3

• Applications:
• ONLY USED in REFRACTORY PATIENTS to

–> convert symptomatic AF or flutter

–> prevent recurrences of AF

• ADVERSE:

–> nausea vomiting, diarrhea (most common)

–> CINCHONISM (tinitus, hearing loss, blurred vision)

–> hypotension (due to alpha-adrenergic blockign effect)

–> proarrhythmic (torsades de pointes)

Question 4

procainamide (MoA)

Answer 4

• MoA:
• Block rapid inward Na+ channel –> slows conduction, automaticity, excitability
• blocks K+ channels = PROLONGS APD and REFRACTORINESS
• Cf. quinidine: procainamide has very little vagolytic acitivity and dose not prolong the QT interval to as great an extent

Question 5

describe the clinical apps and adverse effects of procainamide

Answer 5

USES:

• Ventricular - Life, threatening ventricular arrhythmias
• Supraventricular: acute tx of:

–> reentrant SVT, Atrial fibrillation, atrial flutter with Wolff-Parkinson-White syndrome.

ADVERSE:

–> Cardiac = arrhythmia aggravation, torsades de pointes

–> extracardiac = SLE-like syndrome (slow acetylators), GI nausea and vomiting (very common)

Question 6

Class IB agnets general

Answer 6

-Lidocaine

• “weak” binding to Na+ channels (weak effect on phase 0 depolarization due to rapid on-off receptor kinetics)
• Accelerated phase 3 repolarization (shorted APD and QT)
• TX in DIGITALIS and MI-INDUCED ARRHYTHMIA

Question 7

Lidocaine (MOA)

Answer 7

• Blocks OPEN and INACTIVATED Na+ channels (reduce Vmax)

–> shortens cardiac action potential in cases of ischemia or MI (more effective in ischemic tissues)

–> lowers the slope of Phase 4; altering threshold for excitability

• in abnormal conduction system it has variables effects

–> slows ventricular rate and potentiates infranodal block

** EXTENSIVE FIRST-PASS HEPATIC METABOLISM (IV USE)

–> need multiple loading doses and maintence infusion

Question 8

describe the clinical apps and adverse effects of lidocaine

Answer 8

• Second choic behind amiodarone for immediately life-threatening or symptomatic arrhythmias

–> innfective for prophylaxis of arrhythmias after MI

–> ineffects in atrial tissues

• ADVERSE:

–> CNS: rapid bolus = tinnitus, seizure; High dose = drowsiness, confusion, hallucinations, coma

–> cardiac function DECREASES –> decreased clearance and increase concentrations