Flashcards in Cardiac Electrophysiology Deck (101)
What are the 2 kinds of muscle cells in the heart?
What is the function of the conductive cells?
To rapidly spread APs over the entire myocardium and generate them spontaneously
Describe the conducting sequence as an AP spreads throughout the myocardium
1) SA node
3) AV node
4) Bundle of His
5) Purkinje system
What serves as the pacemaker of the heart?
The SA node
The AP spreads from the SA node to the right and left atria via what?
The atrial intermodal tracts
Slow conduction through the AV node ensures what?
That the ventricles have sufficient enough time to fill with blood before they are activated and contract
What does the term normal sinus rhythm mean?
That the pattern and timing of the electrical activation of the heart are normal
What are the 3 criteria that qualify a sinus rhythm as normal?
1) the AP must originate in the SA node
2) the SA node impulses must occur regularly at a rate of 60 to 100 impulses per minute
3) the activation of the myocardium must occur in the correct sequence and with the correct timing and delays
What is the membrane potential of cardiac cells determined by?
The relative permeabilities to ions and the concentration gradients for the permeant ions
What happens if the cell membrane has a high permeability to an ion?
That ion will flow down its electrochemical gradient and attempt to drive the membrane potential toward its equilibrium potential
The resting membrane potential of cardiac cells is determined primarily by what ions?
The conductance to K+ at rest is high and the resting membrane potential is close to the K+ equilibrium
What are the 2 mechanisms that can produce a change in membrane potential?
- there is a change in the electrochemical gradient for a permeant ion
- there is a change in conductance to an ion
What is threshold potential?
The potential difference at which there is a net inward current
What are the 3 characteristics of action potentials in the ventricles, atria, and Pukinje system?
- long duration
- stable resting membrane potential
How long is the action potential in the SA node, atria, ventricles, and Purkinje fibers?
- SA Node: 150 msec
- Atria: 150 msec
- Ventricles: 250 msec
- Purkinje fibers: 300 msec
The longer the action potential, the _____ cell is refractory to firing another action potential
Describe the plateau that occurs during the APs in the cells of the ventricles, atria, and Pukinje system.
The plateau is a sustained period of depolarization (due to an inward Ca2+ current) which accounts for the long duration of the AP and, consequently, the long refractory periods
Describe the 5 phases of the action potential in a ventricular, atrial, and Purkinje fiber
1) Phase 0, upstroke
2) Phase 1, initial repolarization
3) Phase 2, plateau
4) Phase 3, repolarization
5) Phase 4, resting membrane potential
Upstroke of what ion causes depolarization of the ventricles, atria, and Purkinje system?
What does upstroke cause?
Sodium flows inward during upstroke due to what?
The opening of activation gates on the Na+ channels
At the peak of the upstroke, what value is the membrane potential depolarized to?
about +20 mV
The rate of rise of the upstroke is called what?
What is dV/dT?
The rate of change of the membrane potential as a function of time
dV/dT depends on the value of the resting membrane potential, this dependence is called what?
When dV/dT is greatest, the rate of rise of the upstroke is _____.
When dV/dT is greatest, the resting membrane potential is most ____, or ___polarized
When dV/dT is lowest, the rate of rise of the upstroke is _____.
When dV/dT is lowest, the resting membrane potential is ___ ____, or ___polarized