Cardiac Conduction System and ECG

Question 1

Initial rapid upward deflection of R wave corresponds to ____ of the action potential

Answer 1

Phase 0 = fast inward INa current

Question 2

____ corresponds to Phase 0 = fast inward INa current of the action potential

Answer 2

Initial rapid upward deflection of R wave

Question 3

Which part of ECG is isolectric?

Answer 3

ST segmeent is isolectric

Question 4

What does ST segment correspond to on action potentiaL?

Answer 4

phase 2 plateau (when Ca2+ influx and K+ efflux balanced)

Question 5

What does phase 2 plateau correspond to on ECG

Answer 5

ST segment

Question 6

What does T wave on ECG correspond to on action potential

Answer 6

phase 3 of AP (rapid decrease in voltage as K+ efflux continues)

Question 7

What does isoelectric segment after T wave correspond to?

Answer 7

phase 4 of the action potential

Question 8

There must be Concordance between ____ and ___ on ECG

Answer 8

QRS and T wave in every ekg lead

Question 9

Why is there concordance between QRS and T? is there difference with an individual myocyte?

Answer 9

ventricular myocytes depolarize earliest must repolarize latest

discordance with individual myocyte

Question 10

what if there is no concordance between QRS and T

Answer 10

ischemia

ventricular hypertrophy

Question 11

Why is T wave longer than QRS segment?

Answer 11

repolarization requires more time than depolarization

Question 12

How does depolarization spread from cell to cell?

Answer 12

via gap junctions (formed by connexins that allow ions to pass from cell to cell)

Question 13

Path of electrical transmission in the heart…

Answer 13

1) SA node (where SVC enters the heart) = spontaneously depolarizes (automaticity)
2) travel from RA and then LA generating P wave

3) when reach AV node –> delay
4) pass to Bundle of His (extension of AV node)
5) Splits into left and right bundle for LV and RV
6) pass to purkinje fibers –> ventricles

Question 14

Valves on either side of AV _____ conduct electrical signal

Answer 14

DO NOT

Question 15

Why does signal delay when it reaches AV node?

Answer 15

allows atria time to contract before ventricles contract

Question 16

mean what?

P wave
QRS
T wave

Answer 16

atrial depol
ventricular depol
ventricular repol

Question 17

PR interval means

Answer 17

index of conduction

time across AV node

Question 18

QT interval means

Answer 18

total duration of depol & repol

Question 19

1st degree AV block

Answer 19

conduction delay but all P waves conduct to ventricles

PR prolonged

Question 20

2nd degree AV block

Answer 20

some P waves conduct but others don’t

Question 21

3rd degree AV block

Answer 21

complete block

no P waves conduct & ventricular pacemaker takes over

Question 22

Three mechanisms by which cardiac conduction cause tachyarrhythmias

Answer 22

abnormal reentry pathways

ectopic foci

triggered activity –> abnormal afterpolarizations

Question 23

abnormal reentry pathways present where

Answer 23

atria
ventricles
junctional tissue

Question 24

when does abnormal reentry pathway occur

Answer 24

unidrectional block and slowed conduction through reentry pathway
after slow reentry, previously depol tissue recovered

MOST COMMON MECHANISM OF SERIOUS TACHY

Question 25

ectopic foci

Answer 25

area of myocardium outside conduction system acquires automaticity

if rate of depol > SA node –> abnormal rhythm occurs

Question 26

triggered activity

Answer 26

abnormal afterpolarizations by preceding AP

early afterpolarization before AP fully repol –> tachyarrhythmia

delayed afterpol appear after AP is complete –> arrhythmia