Cardiac Physiology and Pharmacology

Question 1

Interaction between actin and myosin in myocytes is inhibited by what protein

Answer 1

Tropomyosin (effect of tropomyosin disinhibition is mediated by intracellular Ca+)

Question 2

Medications that exert their effects by altering intracellular Na currents

Answer 2

• Lidocaine
• Procainamide

Question 3

Medications that exert their effects by altering intracellular K currents

Answer 3

• Amiodarone
• Sotolol
• Ibutilide

Question 4

Medications that exert their effects by altering intracellular Ca currents

Answer 4

• Diltiazem

Question 5

Impact and MOA of decreased ATP, acidosis, and elevated lactate levels on vascular tone

Answer 5

Decrease vascular tone MOA: increased permeability of the ATP–sensitive K+ channel, resulting in hyperpolarization of the cell membrane that inhibits Ca entry into the cell.

Question 6

Pharmacologic agents that act via cyclic GMP

Answer 6

• Nitric Oxide
• Nitroglycerine
• Na Nitroprusside

Question 7

Pharmacologic agents that regulate intramyocyte Ca levels via cyclic AMP

Answer 7

Catecholamines with beta activity (epi, norepi, dobutamine)

Question 8

Describe ion fluxes at each point of the cardiac action potential

Answer 8

• 0: Depolarization with overshoot (inward Na influx)
• 1: Recovery (ceaseing of Na influx)
• 2: Plateau (inward Ca influx)
• 3: Repolarization (outward K efflux)

Question 9

Vaughn Williams Anti-arrhythmiac Classification

Answer 9

• Class I (Na channel blockers)
• Class II (Beta blockers)
• Class III (Prolong AP)
• Class IV (Block Ca entry)

Question 10

Class I Anti-arrhythmics

Answer 10

• Class Ia (long time constant for disassocatio from Na channel > drug accumulation in channel > slowed conduction/prolonged AP)
  
  • Procainamide
  • Quinidine
  • Disopyramide
• Class Ib (short time constant for disaccoation from Na channel)
  
  • Lidocaine
  • Mexiletine
• Class Ic (long time constant for disassocatio from Na channel > drug accumulation in channel > slowed conduction/prolonged AP)
  
  • Encainide
  • Flecainide
  • Propafenone

Question 11

Na channel blocker class that markedly decrease conduction velocity

Answer 11

Class Ic

• CAST study demonstrated higher incidence of sudden death with encainide and flecainide (not used commonly)
• Propafenone may be used for both atrial and venticular dysrhythmias.
  
  • beta-blocking and Na channel blocking effects
  • lengthens PR, QRS and QT intervals

Question 12

Na channel blocker that has little effect on conduction velocity in normal myocardial but slows conduction in ischemic myocardium

Answer 12

Lidocaine

• little effect on atrial tissue
• not recommended for shock resistent VT/VF

Question 13

Class III antiarrhythmics that are approved for the treatment of atrial fibrillation

Answer 13

• ibutilide (iv)
• dofetilide (po)

(carry risk of torsade de pointes)

Question 14

Class III antiarrhythmic that has both beta-blocker and K-channel blocker activity

Answer 14

Sotolol

(life threatening ventricular arrhythmias)

Question 15

What explains the effectivness of Class IV antiarrhythmics (verapimil and diltiazem) in treatment of supraventricular tachycardia

Answer 15

In SA and AV nodal tissue Ca channels contribute sinificantly to phase 0 depolarization, then the AV nodal refractory period is prolonged by Ca entry blockade.

Question 16

Drug that inhibits Na,K ATPase pump, leading to reduced intracelllular K