1. Advanced Cardiac Care in the Streets Understanding EKGs Ray Taylor Valencia Community College
Electrophysiology

2. Notice All rights reserved.
Slide show used with permission only for the purposes of educating emergency medical providers (EMTs and Paramedics)
No portion of this presentation may be reproduced, stored in a retrieval system in any form or by any means (including but not limited to electronic, mechanical, photocopying etc.) without prior written permission from the author

3. Basic Electrophysiology
Objectives
State the two basic myocardial cell groups
Describe the function of each myocardial cell group
Discuss the four primary properties of cardiac cells
List the three major electrolytes that affect cardiac function

4. Basic Electrophysiology
Objectives [ continued ]
Describe the movement of ions
Describe cardiac depolarization
Describe cardiac repolarization
Define refractory period
Describe the absolute refractory period
Describe the relative refractory period

5. Cardiac Physiology Electrophysiology Cardiac Muscle Depolarization
Atrial
Ventricular
Excitatory and Conductive Fibers
Intercalated discs
Syncytium
Atrioventricular Bundle
Depolarization

6. Basic Cell Groups Specialized Pacemaker Cells
do not have the ability to contract
responsible for controlling rate and rhythm by coordinating regular depolarization
found in electrical conduction system of the heart
primary function is generation and conduction of electrical impulses

7. Basic Cell Groups The Myocardial Working Cells
responsible for generating the physical contraction of heart cells
muscular layer of atrial walls and thicker muscular layer of ventricular walls
primary functions are both contraction and relaxation
physical contraction of myocardial tissue actually generates blood flow

8. Basic Cell Groups
Threshold - point at which a stimulus will produce a cell response
“All or None” phenomenon - stimulus is strong enough for cardiac cells to reach threshold, ALL cells will respond to this stimulus or none will respond.
Syncytium

9. Cardiac Physiology Cardiac Cell Characteristics Properties
Automaticity
Excitability
Conductivity
Contractility

10. Primary Cardiac Cell Characteristics
1. Automaticity - [ electrical function ] ability of cardiac pacemaker cells to spontaneously generate own electrical impulses without external stimulation
2. Excitability - [ electrical function ] ability of cardiac cells to respond to electrical stimulus is also referred to as irritability

11. Primary Cardiac Cell Characteristics
3. Conductivity - [ electrical function ] ability of cardiac cells to receive an electrical stimulus and then to transmit the stimulus to other cardiac cells, so they function collectively as a unit
4. Contractility - [ mechanical function ] also referred to as rhythmicity, is the ability of cardiac cells to shorten and cause cardiac muscle contraction in response to an electrical stimulus

12. Major Electrolytes That Affect Cardiac Function
Myocardial cells bathed in electrolyte solutions
Electrolyte - substance or compound whose molecules dissociate into charged components, or ions.
Produce + charged ions [ cation ] and
- charged ions [ anion ] when placed in water

13. Three Major Cations That Affect Cardiac Function
Potassium [K+] - performs major function in cardiac depolarization and repolarization
Sodium [Na] - performs vital part in depolarization of myocardium
Calcium [Ca] - important function in depolarization and myocardial contraction

14. Movement of Ions Ionic difference on two sides of cell
Potassium ion -concentration greater inside cell
Sodium ion -concentration greater outside cell
Sodium-potassium exchange pump - active transport, potassium / sodium moved in and out of cell through cell membrane
During polarized or resting state, inside of cell electrically negative relative to outside of cell

15. Cardiac Depolarization
When impulse develops and spreads throughout the myocardium, changes occur in heart muscle fibers
Cardiac Depolarization - sodium ions rush into cell (fast channel), changing interior charge to + after cell stimulated
Calcium enters slow channel maintaining contraction
Cardiac Repolarization - sodium ions return to outside of cell, potassium returns to inside of cell

16. Cardiac Physiology/Ion Shifts
Cardiac Depolarization
Resting Potential
Action Potential
Repolarization

17. Terms to Remember
Resting Membrane Potential - state of cardiac cell- inside negative-outside positive
Action Potential - change in polarity; produces change in cell electrical charge caused by stimulation of myocardial cells

18. Terms to Remember
Syncytium - cardiac muscle cell groups that are connected together and function as a unit
Polarized State - resting state of cardiac cell, inside of cell is electrically negative relative to outside

19. Refractory Periods
Attempts to ensure muscle is totally relaxed before another action potential or depolarization can be initiated
Atrial muscle = 0.15 sec.
Ventricular muscle = 0.25 to 0.3 sec.
Period of rest is referred to as
Cardiac Repolarization

20. Two Stages of Repolarization
Absolute Refractory Period - cardiac cell unable to respond to new electrical stimulus, cannot spontaneously depolarize

21. Two Stages of Repolarization
Relative Refractory Period - repolarization is almost complete, cardiac cell can be stimulated to contract prematurely if stimulus is stronger than normal

22. Thank you!