Cardiac Physiology and Conduction Disorders Flashcards
1
Q
cardiac cell types
A
- pacemaker - set rhythm of heart
- conducting - carry electrical signals
- contracting
2
Q
Threshold
A
- membrane potential where predominance of a given channel is open
- when you reach threshold, you open so many channels that you start an irreversible process that leads to contraction of muscle cell
3
Q
membrane channels in cardiac cells
A
- fast sodium
- slow sodium
- slow calcium
- potassium
4
Q
resting potential of pacemaker cells
A
- -55mv
- makes it easier to stimulate contraction
5
Q
resting potential of contracting cells
A
- -90mv
6
Q
how are pacemaker cells autorhythmic?
A
- LEAKY SODIUM CHANNELS!
- once the cell resets to -55, sodium immediately begins to leak in which makes it reach threshold again
7
Q
action potential of pacemaker cells
A
- rising phase (0): upstroke due to opening of voltage gated sodium/calcium channels
- repolarization (3): due to inactivation of sodium/calcium channels and opening of potassium channels
- resting (4): due to slow leak of sodium into cell
8
Q
threshold of pacemakers
A
-40mv
9
Q
purpose of the delay at the AV node
A
-to allow the filling of the ventricles - more blood in the ventricles = more CO
10
Q
conduction times (SA-AV, passage through AV)
A
- SA-AV = 0.03s
- passage through AV node = 0.13s
- total time = 0.16s from SA to ventricle
11
Q
AP of contracting cells
A
- 0: fast Na+ channels
- 1: K+
- 2: Ca++
- 3: K+
12
Q
pace of different cells
A
- SA node: 60-100 bpm
- AV node: 40-55 bpm
- Purkinje cells: 25-40 bpm
- the theory is that the fastest pacemaker will dominate the heart rate - this is usually the SA node
13
Q
control of rate
A
- autonomic NS control over pacemakers and conduction velocity
- parasympathetic slows activity
- SA nodal rate = 60-100
- our actual HR is usually a bit higher than the average rate at the SA node so this means that the dominant impact on the heart is the sympathetic activity form the nS
14
Q
EKG
A
- you are assuming when you see P waves that the atria contracted
- invented by Einthoven
- essentially measuring electrical current over the skin based on electrical activity of the heart
15
Q
Atrial flutter vs fibrillation
A
- flutter: ventricular rate is regular, only atria is fluttering - you see the sawtooth pattern
- fibrillation: muscle cells are not contracting together, contracting at all different times
