Cardiac Conduction, ECG, and Action Potential Flashcards
Pathway of electrical conduction
SA Node–>AV Node–>Ventricles–>Purkinje fibers–>Septum–>Apex–> The rest of the ventricular mass
ECG
Need to know how to draw this
PR Interval
120-200 BPM
Caused by heart block: Drugs, electrolytes
QRS Interval
80-120 BPM
Caused by Conduction abnormalities (Bundle Branch Block)
QT Interval
BPM varies but greater than 450 msec is considered tachycardia
Caused by repolarization abnormalities and ion channelopathies
PR Interval
This is the interval in which the electrical conduction moves through the AV node. Needs to be monitored when antiarrhythmic drugs are used.
QT Interval
This is the interval that represents ventricular repolarization and depolarization
It depends on heart rate
It uses the Bazett formula
BPM greater than 450 msec is considered tachycardia
What is dependent on Na+?
Atria and Ventricles
What is dependent on Ca+?
SA Node and AV Node
Impulse Generation “Leak”
During phase 4, there is a gradual increase in the slope caused by background Na+ and K+ channels that eventually lead to the start of one heartbeat. Making alterations on this slope will make alterations on cardiac pacing (heart rate)
Slope of Phase 4
Increasing the slope increases the automaticity (HEart rate)
Sympathetic activity increases heart rate
Cholinergic activity decreases the heart rate
Antiarrhythmic drugs make changes on the slope and ultimately the heart rate
Impulse Generation
SA node: 60-100 BPM
AV Node: 30-50 BPM
Ventricles: <30 BPM
Which one has the highest phase 4 slope?
SA Node
If the SA Node does not generate an electrical impulse, what would be the heart rate?
AV Node (30-50 BPM)
Effective or Absolute Refractory Period
The longest amount of time in which cells cannot be depolarized again
Relative Refractory period
The time in which cells can be depolarized again with a strong enough stimulus
What would a MOA be for an antiarrhythmic drug to decrease automaticity (heart rate)?
Act on Phase 4
What would a MOA be for an antiarrhythmic drug to decrease or slow down impulses.
Act on Phase 0
Antiarrhythmic classifications: Vaughan Williams
Class 1: Sodium Channel Blockers Class 2: Beta Blockers Class 3: Potassium Channel Blockers Class 4: Calcium Channel blockers Other: Adenosine, Atropine, Digitalis, Magnesium
AA MOA:
- Slow down conduction of AP
- Change the slope of phase 4
- Change threshold potential or maximum diastolic potential
What do Class IA drugs do?
Block open or inactivated sodium channels
Slow down conduction
Slow down phase 0 depolarization
Prolong action potential
