Chapter 2: Basic Electrophysiology

Front 1

What are the two categories of the cardiac cells?

Back 1

*Miocardial Cells (working or mechanical cells)
*Pacemaker Cells (electrical cells)

Front 2

What are myocardial cells?

Back 2

They are working or mechanical cells that contain contractile filaments.

Front 3

What are pacemaker cells?

Back 3

Specialized cells of the electrical conduction system responsible for the spontaneous generation and conduction of electrical impulses

Front 4

Major electrolytes that affect cardiac function

Back 4

*Sodium (Na+)
*Potassium (K+)
*Calcium(Ca++)

Front 5

What determines the cell's electrical charge?

Back 5

The differences of the electrolyte concentration.

Front 6

Normal cell charge

Back 6

*Excess of + ions on outside
*Excess of - ions on inside

Front 7

Membrane potential

Back 7

Difference in electrical charge across the membrane.

Front 8

Action potential

Back 8

Five-phase cycle that reflects the differences in the concentrations of the ions across the cell membrane at any given time.

Front 9

Two types of action potentials

Back 9

*Fast-response
*Slow-response

Front 10

Fast Response Action Potentials

Back 10

*Occur in cells of atria, ventricles, and Purkinje fibers.
*Occurs b/c of the presence of may Na+ channels that allow a rapid influx of Na+ when these channels are open and prevent influx when they are closed

Front 11

Slow Resonse Action Potentials

Back 11

*In SA and AV nodes
*Have slow Ca++ and slow Na+ channels
*Can sometimes occur anywhere in the heart, usually secondary to ischemia, injury or an electrolyte imbalance.

Front 12

Polarization (resting membrane potential)

Back 12

*Resting state, no electrical activity
*Intracellular ions include K+ and some anions (neg. charged ions)

Front 13

Depolarization

Back 13

*When the cardiac cell is stimulated.
*Inside of cell becomes more positive b/c of the entry of Na+ ions into the cell through Na+ membrane channels.
*Proceeds from endocardium to epicardium

Front 14

P Wave

Back 14

Atrial depolarization

Front 15

QRS Complex

Back 15

Ventricular depolarization

Front 16

PEA

Back 16

*Pulseless Electrical Activity
*Occurs when there is electrical activity on the monitor but no palpable pulse

Front 17

Repolarization

Back 17

*The diffusion of Na+ into the cell stops
*K+ is allowed to diffuse out of the cell, leaving the anions inside the cell.
*Occurs b/c of outward diffusion of K+
*Proceeds from epicardium to endocardium

Front 18

ST Segment

Back 18

Early ventricular repolarization

Front 19

T Wave

Back 19

Ventricular Repolarization

Front 20

Phases 1,2,3 of cardiac action potential

Back 20

Electrical Systole

Front 21

Phase 4 of the cardiac action potential

Back 21

Electrical Diastole

Front 22

Phase 0 of the cardiac action potential

Back 22

*Rapid depolarization phase / upstroke / spike / overshoot
*Begins when the cell receives an impulse.
*

Front 23

Phase 1 - Early Repolarization

Cardiac Action Potential Cycle

Back 23

*Fast Na+ channels partially close, slowing the flow of Na+ into the cell.
*K+ moves out of the cell rapidly
*Positive electrical charges within the cell decrease, producing a small negative deflection in the action potential.

Front 24

Phase 2 - Repolarization (Plateau Phase)

*Plateau = a raised flat area


Cardiac Action Potential Cycle

Back 24

*Occurs b/c of slow, inward movement of Ca++ and continued movement of K+ outward.
*Allows cardiac muscle to sustain an increased period of contraction.
*ST segment
*Is a part of the absolute refractory period.

Front 25

Phase 3 - Rapid Repolarization


Cardiac Action Potential Cycle

Back 25

*The cell rapidly completes repolariztion as K+ flows quickly out of the cell and the slow channels close, stopping the influx of Ca++ and Na+.
*The rapid efflux of K+ from the cell causes it to become progressively more electrically negative.
*T Wave

Front 26

Phase 4 - Resting Membrane Potential


Cardiac Action Potential Cycle

Back 26

*Return to the resting state
*Excess of Na+ inside the cell and excess of K+ outside the cell.
*Cell will remain in this state until the cell membrane is reactivated by another stimulus.

Front 27

Refractory Period

Back 27

The extent to which a cell is able to respond to a stimulus. Longer than contraction.

Front 28

Absolute Refractory Period

*aka Effective Refractory Period

Back 28

*Corresponds with the onset of the QRS complex to the peak of the T Wave and includes phases 0, 1, 2, and part of phase 3 of the cardiac action potential.
*Myocardial cell will not respond to further stimulation

Front 29

Relative Refractory Period

*aka Vulnerable Period

Back 29

*Corresponds w/ the downsloap of the T Wave
*Some cardiac cells have repolarized to their threshold potential and can be stimulated to respond (depolarized) to a stronger than normal stimulus.

Front 30

Supernormal Period

Back 30

*A weaker than normal stimulus can cause depolarization of cardiac cells.
*Extends from the terminal portion of phase 3 of the action potential to the beginning of phase 4
*End of T-Wave
*It is possible for cardiac dysrrhythmias to develop during this period.

Front 31

Four primary properties of cardiac cells

Back 31

Automacity, excitability, conductivity, and contractility

Front 32

Automacity

Back 32

Ability of cadiac pacemaker cells to spontaneously initiate an electrical impulse w/o being stimulated from another source.