cardiac conduction 3

Question 1

3 mechanisms leading to arrhythmia

Answer 1

1. re-entry
2. ectopic foci
3. triggered activity

Question 2

Abnormal reentry pathways can be present in the:

Answer 2

atria, ventricles, or the junctional tissue.

Question 3

Reentry occurs when

Answer 3

1. there is a unidirectional block and slowed conduction through the reentry pathway.
2. After the slow reentry, the previously depolarized tissue has recovered and reentry into it will occur.
3. most common mechanism of serious tachycardias.

Question 4

Ectopic foci occur when a

Answer 4

focus of myocardium outside the conduction system acquires automaticity and if the rate of depolarization exceeds that of the sinus node an abnormal rhythm occurs.

These can be isolated “ectopic beats” or sustained tachyarrhythmias.

Question 5

In triggered activity, abnormal “afterpolarizations” may be triggered by:

Answer 5

1. the preceding action potential: an early afterpol when AP has only partially repolarized. This triggers tachyarrhythmis
2. Delayed afterpolarizations appearing after an action potential Is complete can also trigger arrhythmias.

Question 6

Arrhythmias due to this delayed afterpolarization are usually associated with

Answer 6

a delay in repolarization seen in the ECG as a “long QT interval”

Question 7

phase 0 of the action potential, which is due to

Answer 7

the fast sodium current.

Question 8

the plateau in the AP is due to

Answer 8

balanced Ca influx with potassium efflux

Question 9

The T wave of the ECG in which repolarization is occurring corresponds to

Answer 9

phase 3 of the action potential in which there is a rapid decrease in voltage as potassium efflux continues.

Question 10

The isoelectric segment after the T wave corresponds to ___ of AP

Answer 10

phase 4 of the action potential.

Question 11

during action potential repolarization in Phase 3, there is a decreasing or negative voltage change in the opposite direction from:

Answer 11

depolarization in Phase 0 but the T wave in the ECG and the R wave are in the same direction

Question 12

R wave corresponds to __ of AP

Answer 12

phase 0

Question 13

isoelectric ST segment on the electrocardiogram which links the QRS to the T wave is isoelectric normally and corresponds to _____ of the action potential

Answer 13

phase 2

Question 14

an EKG

Answer 14

sums up all electrical from all over the heart

Question 15

polarity:

Answer 15

depolarization moving toward a positive electrode produces a positive defection

Question 16

QRS will be ____ on the left sided leads and ____ on the right sided leads

Answer 16

upright (+)

downward (-)

Question 17

In each cardiac myocyte, repolarization is in the opposite direction of depolarization but in the normal ECG signal depolarization (the QRS) and depolarization (the T wave) are in the _____

Answer 17

same direction

Question 18

Endocardial and cells depolarize earlier than ____, but ___

Answer 18

epicardial cells

repolarization is relatively slow in the endocardium

Question 19

Although epicardial cells deploy later than endocardial cells, endocardial cells

Answer 19

their repolarization is very rapid and they repolarize sooner than