Cardiac Conduction System and EKG II

Question 1

First degree block:

Answer 1

conduction delayed but all P waves conduct to the ventricles.

Question 2

Second degree block:

Answer 2

some P waves conduct, others do not.

Question 3

Third degree block:

Answer 3

none of the P waves conduct and a ventricular pacemaker takes over

Question 4

When the right bundle is blocked -

Answer 4

QRS widening with delayed conduction to the right ventricle

Question 5

When the left bundle is blocked –

Answer 5

QRS widening with delayed conduction to the left ventricle

Question 6

When left bundle fascicles are blocked

Answer 6

there are shifts in direction of depolarization but no QRS widening

Question 7

What are the 3 major disturbances in cardiac conduction that cause tachyarrhythmias?

Answer 7

• abnormal reentry pathways
• ectopic foci
• triggered activity

Question 8

mechanism of abnormal reentry pathways

Answer 8

present in the atria, ventricles or the junctional tissue. Reentry occurs when there is a unidirectional block and slowed conduction through the reentry pathway. After the slow reentry the previously depolarized tissue has recovered and reentry into it will occur.
**this is the most common mechanism of serious tachycardias

Question 9

mechanism of ectopioc foci

Answer 9

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

Question 10

mechanism of triggered activity

Answer 10

abnormal “afterpolarizations” may be triggered by the preceding action potential. Here, an early afterpolarization before the action potential has fully repolarized triggers tachyarrhythmia. Delayed afterpolarizations appearing after an action potential is complete can also trigger arrhythmias