Action potentials - picture questions

Question 1

What is repsonsible for Phase 0?

Answer 1

Voltage-gated Na channels open (Na influx)

Question 2

What is repsonsible for Phase 1?

Answer 2

Voltage-gated K channels begin to open (K+ efflux)

Question 3

What is responsible for Phase 2?

Answer 3

Ca²⁺ influx through voltage gated Ca²⁺ channels — Balances K efflux

Ca²⁺ triggers Ca²⁺ release from sarcoplasmic reticulum & myocyte contraction

Question 4

What is responsible for phase 3?

Answer 4

Massive K efflux due to opening of voltage-gated slow K channels & closure of voltage-gated Ca channels

Question 5

What is reponsible for Phase 4?

Answer 5

Resting potential: high K permeability thru K channels

Question 6

What classes of antiarrhythmics affect ventricular APs?

Answer 6

Class I: Na⁺channel blockers

Class III: K⁺ channel blockers

Question 7

What class of antiarrythmic drug is this and what are 3 examples?

Answer 7

Class Ia

Quinidine, Procainamide, Disopyramide

Question 8

What class of antiarrythmic drug is this? What are two examples?

Answer 8

Class IB

Lidocaine, Mexiletine

Question 9

What class of antiarrythmic drug is this? What are two examples?

Answer 9

Class IC

Flecainide & Propafenone

Question 10

Which of the class I is best post-MI? Which is contraindicated?

Answer 10

Class IB: Lidocaine, Mexiletine

**Preferentially affect ischemic or depolarized Purkinje/ventricular tissue

**Class IC: Flecainide, Propafenone **

Proarrhythmic

Question 11

What side effect is noted with quinidine?

Answer 11

Cinchonism: Headache and tinnitus

Question 12

What side effect is noted with procainamide?

Answer 12

Reversible SLE-like syndrome

Question 13

What side effect is noted with Disopyramide?

Answer 13

Heart failure

Question 14

What effect do K+ channel blockers have on the ventricular AP?

Answer 14

↑ AP duration

↑ Effective Refractory Period (ERP)

↑ QT interval

Question 15

What are examples of the class of drugs that have this effect?

Answer 15

Class III: K+ blockers

“AIDS”

Amiodarone

Ibutilide

Dofetilide

Sotalol

Question 17

What side effects does Amiodarone have?

Answer 17

Pulmonary fibrosis

Hepatotoxicity

Hypo/hyper - thyroidism

Corneal deposits

Skin deposits

Consitpation

Neurologic effects

Bradycardia➝Heart Block, CHF

Question 18

What is responsible for phase 0?

Answer 18

Opening of voltage gated Ca²⁺ channels (influx)

Question 19

What is responsible for phase 3?

Answer 19

Inactivation of Ca²⁺ channels

↑ activation of K⁺ channels — K⁺ efflux

Question 20

What is responsible for phase 4?

Answer 20

Slow diastolic depolarization

MP spontaneously depolarizes as Na⁺ conductance ↑ I_f

SLOPE DETERMINES HR

Question 21

What factors modulate the slope of Phase 4 repolarization in the pacemaker cells i.e. HR?

Answer 21

1. ACh/adenosine ↓ rate of diastolic depolarization
2. Catecholamines ↑ rate of diastolic depolarization
3. Sympathetic stimulation ↑ chance I_f channels will be open

Question 22

What classes of drugs effects SA/AV nodal conduction?

Answer 22

Class II: β blockers

Class IV: Ca²⁺ channel blockers

Question 23

What antiarrhythmic effects β-blockers exert on SA and AV nodal cells?

Answer 23

↓ slope of depolarization (Phase 4)

Prolonged repolarization at AV node

↓ nodal cAMP, ↓ Ca currents

↑PR interval

Question 24

What arrhythmias are β-blockers useful in treating?

Answer 24

SVT, slowing ventricular rate during a fib. and a flutter

Question 25

What effects do the Class IV antiarrhythmics have on SA/AV nodal conduction? What are two examples?

Answer 25

**Verapamil & Diltiazem** Slow rise of AP (Phase 0) Prolong repolarization at AV node (Phase 3)

Question 26

What arrhythmias are Ca channel blockers used to treat?

Answer 26

Prevent nodal arrhythmia - SVT Rate control in a. fib \*constipation, flushing, edema, CV effects (CHF, AV block, sinus node depression)

Question 27

Adenosine

Answer 27

↑K efflux - hyperpolarize cell - ↓I_Ca Diagnose/abolish SVT ~15 sec. action Flushing, hypotension, chest pain

Question 28

Mg²⁺

Answer 28

Effective in TdP and digoxin toxicity

Question 29

What does the P-wave represent? The PR interval?

Answer 29

Atrial depolarization Conduction delay thru the AV node (

Question 30

What does QRS complex represent?

Answer 30

Ventricular depolarization

Question 31

What does the QT interval represent?

Answer 31

Mechanical contraction of the ventricles

Question 32

What does the T wave represent?

Answer 32

Ventricular repolarization

Question 33

What two things cause a U wave?

Answer 33

Hypokalemia, bradycardia

Question 34

What meds will prolong the QT?

Answer 34

**Some Risky Meds Can Prolong QT** Sotalol Risperidone (antipsych) Macrolides Chloroquine Protease inhibitors (-navir) Quinidine (Class Ia, Class III) Thiazides

Question 35

What things can predispose one to TdP?

Answer 35

Long QT - drugs ↓K⁺, ↓ Mg²⁺, other abnormalities

Question 36

What are two causes of congenital long QT syndrome?

Answer 36

* Romano-Ward syndrome (AD) * Jervell and Lange-Neilson syndrome (AR) * sensorineural deafness

Question 37

What causes the delta wave seen here? What can this result in?

Answer 37

Abnormal fast accessory conduction pathway from atria to ventricle (bundle of kent) → *Early depolarization of the ventricles* Reentry circuit → SVT