Flashcards in cardiac conduction 3 Deck (19)
3 mechanisms leading to arrhythmia
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
isoelectric ST segment on the electrocardiogram which links the QRS to the T wave is isoelectric normally and corresponds to _____ of the action potential
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
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 _____
Endocardial and cells depolarize earlier than ____, but ___
repolarization is relatively slow in the endocardium