EGC Interpretation Basics

Question 1

Electrocardiogram (ECG)

Answer 1

Visual representation of the hearts electrical activity

Question 2

Arrhythmia

Answer 2

Without normal rhythm

Question 3

Dysrhythmia

Answer 3

Disturbance of rhythm

Question 4

Electrophysiology

Answer 4

Studies the electrical properties of biological cells and tissues

Question 5

Two functions for cardiac output

Answer 5

Electrical function, mechanical function

Question 6

Electrical function

Answer 6

Electrical impulses stimulate the heart to contract; initiated by pacemaker cells

Question 7

Mechanical function

Answer 7

Actual contraction of the heart to generate a palpable pulse; work of myocardial cells

Question 8

Two types of cardiac cells

Answer 8

Myocardial cells, pacemaker cells

Question 9

Myocardial cells

Answer 9

Form the muscular layers of the atrial and ventricular walls; contractile filaments, no spontaneous generation (no automaticity), rely on pacemaker cells for impulse
No impulse - No contraction

Question 10

Pacemaker cells

Answer 10

Specialized cells of the electrical conduction system that; found in SA node and AV junction, purkinje fibres.
Increased contraction Ca++ in the blood increase automaticity
Decreased contractions K+ decrease automaticity

Question 11

Four intrinsic properties of cardiac cells

Answer 11

Excitability (irritability), conductivity, automaticity, contractility

Question 12

Excitability (irritability)

Answer 12

Ability of cardiac muscles to respond to an outside stimulus; chemical, mechanical, electrical.
Cardiac muscle is electrically irritable because of ionic imbalance

Question 13

Conductivity

Answer 13

Ability of a cardiac cell to receive an electrical stimulus and conduct that impulse to an adjacent cardiac cell
Speed of conduction can be altered by factors such as sympathetic and parasympathetic stimulation

Question 14

Automaticity

Answer 14

Ability of pacemaker cells to initiate an electrical impulse without being stimulated from another source

Question 15

Contractility

Answer 15

The ability to contract/shorten in length

Question 16

What two avenues does electrical stimulation occur through?

Answer 16

Sympathetic response, parasympathetic response

Question 17

Response to sympathetic stimulation

Answer 17

Alpha 1 - arteries = constriction, Lungs = mild bronchoconstriction
Beta 1 - Heart = increased dromotropy, inotropy, chronotropy
Beta 2 - Lungs = smooth bronchial muscle dilation, Arteries = dilation

Question 18

What is released from the adrenal medulla during sympathetic stimulation?

Answer 18

Norepinephrine / epinephrine

Question 19

Depolarization

Answer 19

Myocardial cells are bathed in electrolyte solution, chemical pumps maintain the concentrations of ions within the cells, stimulus from the conduction system

Question 20

Repolarization

Answer 20

Closing of the sodium and calcium channels, restores the negative charge, sodium-potassium pump ( 3 Na+ out, 2 K+in)

Question 21

Cardiac action potential; phase 0

Answer 21

Depolarization, rapid influx of Na+, slow influx of Ca++, K+ leaves the cell, approx -90 millivolts to +30 millivolts

Question 22

Cardiac action potential; phase 1

Answer 22

Na+ slowly closes, Cl- enters the cell, K+ still leaving the cell. This results in a slight decrease in positive electrical charges in the cell. Approx +30 millivolts - 0 millivolts

Question 23

Cardiac action potential; phase 2

Answer 23

Plateau phase; Ca++ slowly enters cell, K+ slowly leaving cell, resulting in a similar positive and negative ion exchange across the cell membrane

Question 24

Cardiac action potential - Phase 3

Answer 24

Repolarization; Na+ and Ca++ channels close
K+ quickly leaving cell
Resulting in a more negative charge inside the cell

Question 25

Cardiac action potential- Phase 4

Answer 25

Resting membrane potential; sodium potassium pump
3 Na+ out, 2 K+ in
Resulting in relaxation of the cardiac muscle

Question 26

Refractory periods

Answer 26

Absolute, relative

Question 27

Absolute refractory period

Answer 27

Myocardial cell will not respond to a stimulus.
Corresponds with onset of QRS to peak of T wave. Phases 0,1,2, and part of 3

Question 28

Relative refractory period

Answer 28

Can be stimulated by a stronger than normal stimulus.
Corresponds with downslope of T wave