CV Review Flashcards
What does the SA node do?
Initiates contraction (depolarizers about every second Or about 70 times per minute)
What does the AV node do?
Gateway for electrical impulse into ventricles (delays ventricular contraction)
Only way for an impulse to trigger ventricles in a healthy heart
What should we not use of someone has an AV block?
b-blockers or CCBs
What happens prior to conduction?
Heart muscle cells are ‘polarized’
- 80-90mV negative compared to outside of the cell
Ion pumps work to maintain this resting membrane potential (RMP)
What happens in phase 4?
Na+ is cleared from the cell and K+ loss(slows) diminishes negative charge
Eventually, an abrupt increase in Na permeability will occur when a certain ‘threshold potential’ is reached
What happens in phase 0?
Increase in permeability to sodium influx (into cell)
Calcium channels open around - 60 mV
What happens when you expose inside of muscle cell to calcium?
It contracts - you get contraction with every depolarization
What happens in phase 1?
Brief re-polarization from K escaping cell
What happens in phase 2?
Calcium continues to enter cell (started in phase 0)
Calcium enters through “L type” calcium channels
Calcium movement initiates muscle contraction
(CARDIAC MUSCLE CELL CANNOT CONTRACT HERE - ALREADY DEPOLARIZED)
What happens in phase 3?
Membrane remains permeable
Na and K ejected to ‘repolarize’ the cell
More calcium entry = …
Stronger contraction (inotropy/contractility)
Faster calcium entry = …
Faster contraction (chronotropy/heart rate)
What is an ECG?
Graph of electrical activity in heart
Detected by electrodes (leads) attached to the patient
The location of the “leads” allows different angles of the heart to be examined
6 or 12 leads are often used
What is the P-wave?
Depolarization of the atria(atrial contraction)
Normal duration = 0.12 seconds
What is the QRS?
Depolarization of ventricles
Normal duration < 0.12 seconds
