Mechanisms of Cardiac Arrhythmias Flashcards
What causes cardiac arrhythmias?
They are caused by disturbances in impulse formation, impulse conduction, or both.
Describe the mechanism of altered automaticity.
Alterations in pacemaker rate that normally exist in pacemaker cells.
What is tachycardia?
HR > 100 bpm
What is bradycardia?
HR < 60 bpm
What are some causes of tachycardia?
- Norepinephrine
- Stimulants
- Ischemia
- Ventricular aneurysm
What are some causes of bradycardia?
- Anti-arrhythmics
- Beta blockers
- Ca2+ antagonists
- Digitalis
- Barbituates
- Ischemia
- Aging (fibrosis)
What are EKG manifestations of tachycardia?
- Sinus tachycardia
- Premature atrial contraction
- Premature ventricular contraction
- Atrial/Ventricular tachycardia
- Supraventricular tachycardia
What are EKG manifestation of bradycardia?
-Sinus bradycardia
Describe the mechanism of reentry of excitation.
It is the most common arrhythmia and it is caused by electric signal circling around the heart.
What are the 3 requirements for reentry of excitation?
1 - Geometry for conduction loop
2 - Slow or delayed conduction
3 - Unidirectional conduction block
What are some possible causes of reentry of excitation?
- Ischmia
- Infarct
- Congenital bypass tracts (Wolf-Parkinson White)
Describe the mechanism of triggered activity.
Can occur in the atria or ventricles and are the result of Delayed Afterdepolarizations (DADs)
How are DADs caused?
They are due to elevated INTRACELLULAR [Ca2+] which is taken up by the SR. APs will cause an abnormal release of Ca2+ into the cell and it is extruded by Na/Ca exchanger. The incoming Na cause an inward current that can cause an AP if it reaches threshold.
What are Early Afterdepolarizations and how are they caused?
EADs are related to the elongation of the AP duration and it is believed to be due to abnormal activation of the inward Ca2+ current.
What is sinus tachycardia?
Fast HR caused by inspiration
