Cardiac Arrhythmias

Question 1

What are the 3 requirements for re-entry of excitation?

Answer 1

1) Conduction loop geometry
2) Slow or delayed conduction
3) Unidirectional conduction block

Question 2

How might an increase in vagal nerve activity affect EKG recordings?

Answer 2

Vagus n. has direct effects on SA, AV, and atrial nodal tissues only. Thus, it may inhibit SA node pacemaker activity, thereby slowing HR, or it may slow AV node conduction and lengthen P-R interval.

Question 3

What are 3 major mechanisms by which dysrhythmias occur?

Answer 3

1) Altered automaticity (enhanced or depressed pacemaker activity)
2) Reentry of excitation
3) Triggered activity

Question 4

Cardiac arrhythmias result from disturbances in _____ or ______ or both.

Answer 4

impulse formation; impulse conduction

Question 5

What are the definitions of tachycardia and bradycardia in terms of heart rate?

Answer 5

• tachy: greater than 100 bpm

- brady: less than 60 bpm

Question 6

Alterations in pacemaker rate that are mediated through changes in pacemaker mechanisms that normally exist in pacemaker cells.

Answer 6

altered automaticity

Question 7

What are some possible causes of tachy-dysrhythmias?

Answer 7

• NE
• stimulants (amphetamines)
• stretching (ventricular aneurysm)
• electrolytes (hypokalemia)
• sick sinus syndrome, fever, and hypothyroidism

Question 8

What are some possible causes of brady-dysrhythmias?

Answer 8

• drugs (anti-arrhythmics, beta blockers, calcium antagonists, digitalis, barbiturates, anesthetics)
• ischemia or infarct
• sick sinus syndrome
• aging (fibrosis)

Question 9

True or false: re-entry of excitation can occur anywhere in the heart

Answer 9

true!

Question 10

What are possible causes of re-entry of excitation?

Answer 10

• ischemia
• infarction
• congenital bypass tracts (ex: WPW syndrome)

Question 11

Where can triggered activity occur?

Answer 11

in atrial or ventricular tissues

Question 12

Delayed After-Depolarization (DAD) is due to _______.

Answer 12

abnormally elevated intracellular [Ca2+]

Question 13

DADs are clinically documented with dysrhythmias resulting from ______.

Answer 13

digitalis toxicity

Question 14

What are the two types of triggered activity that we discussed in class?

Answer 14

• Delayed After-Depolarization (DAD)

- Early After-Depolarization (EAD)

Question 15

Are delayed after-depolarizations worse at high or low heart rates?

Answer 15

they’re worse at higher heart rates (more opportunities for Ca2+ to build up and cause one)

Question 16

Are early after-depolarizations worse at high or low heart rates?

Answer 16

low heart rates, as slow HR lengthens AP (and EADs are related to prolongation of AP duration)

Question 17

During which phase do DADs occur vs. EADs?

Answer 17

DADs- phase 4 (complete repolarization)

EADs- phase 2 or 3 (peak of AP and slow repolarization)

Question 18

What are some of the anti-arrhythmic therapies we discussed?

Answer 18

• drugs (Na+ channel blockers, K+ channel blockers, Ca2+ channel blockers, beta blockers)
• radio-frequency ablation (abnormal tissue “zapped” using heat)
• DC cardioversion (abnormal rhythm converted to normal rhythm using electricity)
• implantable cardio-verter defibrillator (ICD)

Question 19

What is essentially happening with brady-dysrhythmias?

Answer 19

the heart beats so slowly that other pacemakers become more relevant