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Flashcards in cardiac conduction 3 Deck (19)
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3 mechanisms leading to arrhythmia

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


Abnormal reentry pathways can be present in the:

atria, ventricles, or the junctional tissue.


Reentry occurs when

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.


Ectopic foci occur when a

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.


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

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.


Arrhythmias due to this delayed afterpolarization are usually associated with

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


phase 0 of the action potential, which is due to

the fast sodium current.


the plateau in the AP is due to

balanced Ca influx with potassium efflux


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

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


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

phase 4 of the action potential.


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

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


R wave corresponds to __ of AP

phase 0


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

phase 2


an EKG

sums up all electrical from all over the heart



depolarization moving toward a positive electrode produces a positive defection


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

upright (+)

downward (-)


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 _____

same direction


Endocardial and cells depolarize earlier than ____, but ___

epicardial cells

repolarization is relatively slow in the endocardium


Although epicardial cells deploy later than endocardial cells, endocardial cells

their repolarization is very rapid and they repolarize sooner than