Electrophysiology of the heart Flashcards
What is the main difference between cardiac and skeletal muscle cells with respect to receptors?
Slow calcium channels
Is the cardiomyocyte permeable to sodium at rest?
No
Is the cardiomyocyte permeable to potassium at rest?
Yes
Where are the “funny” slow sodium channels located?
Nodal cells only
What allows the plateau phase to persist in cardiac myocyte AP?
- Slow calcium channels (calcium and sodium flux) 2. Decreased potassium permeability
When does the absolute refractory period begin?
Upstroke of phase 0
When does the absolute refractory period end?
Usually about midway through phase 3
What does the slope of phase 0 look like during relative refractory period?
Decreased slope
Is there a plateau phase during relative refractory period?
No
What is occurring at the sodium channel during the absolute refractory period?
Inactivation gate is closed
What is occurring at the sodium channel during the relative refractory period?
Inactivation gate is open but pore is closed
What occurs during phase 2 of the nodal cell AP?
- Calcium channels open 2. Slow / low slope of AP depolarization 3. No fast sodium channels
What is the effect of positive chronotrophs (eg norepinephrine) on cardiac AP?
- Increases permeability of nodal cells to sodium and calcium 2. Increases slope of phase 4 - threshold reached faster
What is the effect of negative chronotrophs (eg acetylcholine) on cardiac AP?
- Increase permeability of nodal cells to potassium (efflux) 2. Lower resting potential 3. Longer time to reach threshold (lower slope of phase 4)
What are the effects of potassium channel blockers?
- Increase AP duration and ERP2. Extends QT interval
What are the effects of calcium channel blockers?
- L-type slows rate of conduction at SA and AV nodes by delaying calcium entry
What are the effects of sodium channel blockers?
- Reduce phase 0 and slope of depolarization 2. Increases ERP
