Flashcards in Cardiac Conduction System & ECG (complete) Deck (16)
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1
Describe the relationship between ventricular APs of individual cardiac myocytes and the surface electrocardiogram
- R wave => phase 0
- ST segment => phase 2
- T wave => phase 3
- Segment after T wave => phase 4
2
What is the sequence of the activation of the cardiac electrical conduction system?
- Upper portion of septum is depolarized from left to right
- then depolarization downward in the septum to the apex
- Depolarization from endocardium to epicardium
- Depolarization moves upward from apex in the free walls of both ventricles
- Depolarization of the base of the ventricles
OVERALL GOAL: to help push the blood in the correct direction!
3
Describe the P wave
- Represents atrial depolarization
4
Describe the QRS complex
- Represents depolarization of ventricles
5
Describe the T wave
- Represents repolarization of ventricles
- When K+ channel takes over
6
Describe the PR interval
- Index of conduction time across the AV node
- Depolarization pauses at the bundle of His after depolarization of atria and before that of ventricles
7
Describe the QT interval
- Represents total duration of depolarization and repolarization
8
Describe the effects of left or right bundle branch block on cardiac conduction
Right: QRS widening w/ delayed conduction to RV
Left: QRS widening w/ delayed conduction to LV
9
What are the three major mechanisms by which disturbances in cardiac conduction cause tachyarrhythmias?
1) Abnormal reentry pathways
2) Ectopic foci
3) Triggered activity
10
Describe abnormal reentry pathways as a mechanism leading to arrhythmia
- Most common cause of severe tachycardias
- Reentry occurs w/ unidirectional block and slowed conduction
11
Describe ectopic foci as a mechanism leading to arrhythmia
- when cells outside conduction system acquire automaticity
- and if depolarization rate exceeds that of SA node => abnormal rhythm
- Can be isolated ectopic beats or sustained arrhythmias
12
Describe the concept of triggered activity as a mechanism leading to arrhythmia
- abnormal afterdepolarizations may be triggered by the preceding AP
- Early afterdepolarization before AP => tachyarrhythmia
- Delayed afterdepolarizations appear after an AP => also triggers arrhythmias
13
What are the three types of atrioventricular block?
1) First Degree
2) Second Degree
3) Third Degree
14
Describe first degree AV block
- Conduction is delayed
- BUT all P waves conduct to the ventricles
15
Describe second degree AV block
Some P waves conduct --- not all
16
