Cardiac Conduction System & ECG (complete) Flashcards Preview

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Flashcards in Cardiac Conduction System & ECG (complete) Deck (16)
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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


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!


Describe the P wave

- Represents atrial depolarization


Describe the QRS complex

- Represents depolarization of ventricles


Describe the T wave

- Represents repolarization of ventricles
- When K+ channel takes over


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


Describe the QT interval

- Represents total duration of depolarization and repolarization


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


What are the three major mechanisms by which disturbances in cardiac conduction cause tachyarrhythmias?

1) Abnormal reentry pathways
2) Ectopic foci
3) Triggered activity


Describe abnormal reentry pathways as a mechanism leading to arrhythmia

- Most common cause of severe tachycardias
- Reentry occurs w/ unidirectional block and slowed conduction


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


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


What are the three types of atrioventricular block?

1) First Degree
2) Second Degree
3) Third Degree


Describe first degree AV block

- Conduction is delayed
- BUT all P waves conduct to the ventricles


Describe second degree AV block

Some P waves conduct --- not all


Describe third degree AV block

- No P waves conduct
- Ventricular pacemaker now needed