L9 Heart- Mechanisms of Cardiac Arrhythmias

Question 1

Define cardiac arrhythmia.

Answer 1

Dysrhythmmias occur from alterations in impulse formation (pacemaker activity) and/or impulse conduction.

Question 2

Define altered automaticity and how it can cause cardiac arrhythmias.

Answer 2

Alterations in pacemaker rate that are mediate through changes in pacemaker mechanisms that normally exist in pacemaker cells (PM cells located within the specialized conduction system).
-Tachycardia or bradycardia

Question 3

Define re-entry of excitation and how it can cause cardiac arrhythmias.

Answer 3

Most common type of arrhythmia!
3 requirements: 
1. Geometry for conduction loop
2. Slow or delayed conduction
3. Unidirectional conduction block

Question 4

Define triggered activity and how it can cause cardiac arrhythmias.

Answer 4

Delayed after depolarizations (DAD) or Early after depolarizations (EAD)
-Can occur in atrial or ventricular tissues

Question 5

What are potential causes for altered automaticity?

Answer 5

Causes for tachycardia- NE, stimulants (amphetamines), ischemia, stretching (ventricular aneurysm), SSS, fever, hyperthyroidism
Causes for bradycardia- drugs (anti-arrhythmias, B-blockers, Ca antagonists, digatalis), barbiturates, anesthetics, ischemia/infarct, SSS, aging (fibrosis)

Question 6

What are potential causes for re-entry of excitation?

Answer 6

Ischemia
Infarction
Congenital bypass tracts (WPW)

Question 7

What are potential causes for DADs?

Answer 7

Digitalis toxicity
Elevated catecholamines
Rapid HR

Question 8

Define bradycardia and how it could look on EKG

Answer 8

HR

Question 9

Define tachycardia and how it could look on EKG

Answer 9

HR > 100bpm

EKG manifestations: sinus tachy, PAC, PVC, AT, VT, SVT

Question 10

What are early after-depolarizations (EADs) and what is the mechanism that causes them?

Answer 10

Related to prolonged AP, thought to be due to abnormal reactivation of slow inward Ca current

• Manifested at slow HRs b/c the slow HR lengthens the AP, leads to coupled beats
• Possible EKG manifestations= PAC, PVC, ATach or VTach

Question 11

What are delayed after-depolarizations (DADs) and what is the mechanism that causes them?

Answer 11

Caused by elevated INTRACELLULAR Ca

• Elevated intracellular Ca taken up by SR, SR overloaded with Ca means AP can trigger abnormal release of Ca.
• After AP ends, Ca removed from cell by exchanger, generating net inward current from Na
• Depolarizing inward current causes DAD
• If DAD hits threshold, AP generated
• Single beat or multiple beats generated, can lead to tachycardias

Question 12

Compare and contrast EADs and DADs

Answer 12

1

Question 13

What are 4 different anti-arrhythmic therapies?

Answer 13

Anti-arrhythmic drugs (Na, K, Ca channel blockers, B blockers)
Cardiac ablation
Cardioversion
ICD

Question 14

What are EKG manifestations of re-entry of excitation?

Answer 14

PAC/PVC
ATach or VTach
SVT
Atrial flutter
A Fib or V Fib

Question 15

What are potential causes EADs?

Answer 15

Acidosis (due to ischemia)
Hypokalemia
Quinidine (Ca channel blocker)
Slow HRs (bradycardia)

Question 16

What is the normal length of PR interval?

Answer 16

120-200ms

-1 deg. Heart block= longer than 200ms