Chapter 1 Basic Principle, Rapid Interpretation of EKG's

Question 1

Scientific establishment of pumping of heart and electrical phenomena

Answer 1

• Kollicker and Mueller (1855)
• lay motor nerve to frogs leg over isolated beating heart
• leg would kick with each heartbeat

Question 2

Capillary electrometer

Answer 2

• created by Ludwig and Waller (1880’s)
• hearts rhythmic electrical stimuli can be monitored from a person’s skin
• capillary tube in a electric field that can detect faint electrical activity - find that fluid level in capillary tube moved with the rhythm of the subjects heart beat

Question 3

Invention of the 1st EKG machine

Answer 3

• Einthoven (1901)
• attaches two electrodes to a person skin
• ends of electrodes connect to ends of a silver wire passing through poles of a magnet
• projects a light bean through holes in the magnets poles across the silver wire which twitches to the rhythm of the subjects heartbeat
• creates shadow of distinct waves in repeating ycles
• names waves P, QRS, T

Question 4

Function of the EKG

Answer 4

Records the electrical activity of contraction of the heart muscle

Question 5

Charge Myocardial cells in resting state

Answer 5

• polarized

- interior of every cell is negatively charged (negative interior and positively charged outside surface)

Question 6

Charge myocardial cells during contraction

Answer 6

• depolarized

- interior become positive

Question 7

Depolarization of the myocardium

Answer 7

• an advancing wave of positive charges within the heart’s myocytes
• due to movement of Na+ through fast-moving Na+ chanels

Question 8

Upward deflection on EKG - meaning

Answer 8

Represents a depolarization wave moving toward a positive electrode

Question 9

Hearts dominant pacemaker

Answer 9

SA node

Question 10

Sinus rhythm

Answer 10

Normal pacing activity of SA node

Question 11

Automaticity

Answer 11

The generation of pacemaking stimuli

Question 12

Automaticity foci

Answer 12

Other focal areas of the heart that have automaticity

Question 13

Atrial depolarization (and contraction)

Answer 13

Spreading wave of positive charges within the atrial myocardial cells

Question 14

P wave

Answer 14

Upward deflection produced by depolarization of atria on EKG

Question 15

Function of atrio-ventricular valves - electrical conduction

Answer 15

Insulate the atria from the ventricles (making AV node the only conducting path between the atria and the ventricles)

Question 16

Timelapse at AV node

Answer 16

When wave of atrial depolarization enters the AV node depolarization slows producing a brief pause and allowing time for the blood in the atria to enter the ventricles (due to slow conducting Ca2+ ions)

Allows time for the blood to pass into the ventricles (takes time for blood to flow through the valves into the ventricles after the atria contract)

Produces flat baseline after each P wave

Question 17

Reason why depolarization conducts slowly through the AV node

Answer 17

Due to current being carried by slow-moving Ca2+ ions

Question 18

Ventricular conduction system

Answer 18

1) Bundle of His (penetrates the AV valves)
2) Bundle bifurcates in the interventricular septum into right and left bundle branches
3) Terminate in network of tiny filaments of purkinje fibers

Question 19

Purkinje fibers

Answer 19

• rapidly conducting fibers that form the right and left bundle branches and the bundle of His
• use fast-moving Na+ ions for the conduction of depolaization

Question 20

QRS complex

Answer 20

Corresponds to the depolarization of the ventricular myocardium on EKG

Question 21

Terminal filaments of the Purkinje fibers - location + what this means for direction depolarization of ventricles

Answer 21

Spread out just beneath the endocardium that lines both ventricular cavities
Ventricles epolarize from the lining towards the outside surface (epicardium)

Question 22

Relationship QRS to ventricular contraction

Answer 22

QRS complex represents only the beginning of ventricular contraction (a recording of ventricular depolarization which causes ventricular contraction)
Physical event of ventricular contraction lasts longer than the QRS complex

Question 23

Q wave

Answer 23

The first downward wave of the QRS complex

Often absent

Question 24

R wave

Answer 24

The first upward deflection of the QRS complex

Question 25

S wave

Answer 25

Any downward wave preceded by an upward wave

Question 26

QS wave

Answer 26

When there is only a downward deflection (no R wave) | Can't tell whether the deflection is a Q or S wave therefore is called a QS wave

Question 27

ST segment

Answer 27

The horizontal segment of baseline that follows the QRS complex Normally should be level with other ares of baseline (if it is elevated or depressed beyond the normal baseline level is sign of problem!)

Question 28

ST segment - what does represent

Answer 28

The plateau phase of ventricular repolarization (when K+ exit and Ca2+ entry are balanced) Ventricular repolarization is rather minimal during this segment

Question 29

What does the T wave represent

Answer 29

Represents the rapid phase of ventricular repolarization | Accomplished by K+ leading the myocytes

Question 30

Stages of EKG that ventricular systole corresponds to

Answer 30

Spans depolarization and repolarization of ventricles so from QRS to end of T wave I.e. the QT interval

Question 31

Why QT interval is a good indicator of repolarization

Answer 31

Snce repolarization comprises the most of the QT interval

Question 32

Long QT interval syndrome

Answer 32

- hereditary syndromes | - make people more vulnerable to rapid ventricular rhythms (why it is important to detect a prolonged QT interval)

Question 33

How does the QT interval vary

Answer 33

Varies with heart rate - with rapid heart rate both depolarization and repolarization occur faster Therefore precise QT interval measurements are corrected for rate (QTc values)

Question 34

What is considered a normal QT interval

Answer 34

-when it is less than half of the R-R interval at normal rates

Question 35

Smallest divisions on EKG strip

Answer 35

-one millimeter by one millimeter

Question 36

Large boxes

Answer 36

- denoted by heavy black lines on each side | - each side is 5 mm long (5 small boxes)

Question 37

Measure of voltage on EKG

Answer 37

The height and depth of a wave measured verticaly frm basline in mm -vertical amplitude is a measure of voltage

Question 38

Amplitude of a wave

Answer 38

The magnitude (in millimeters) of the deflection and is a measure of voltage

Question 39

Measuring elevation/depression of segments of baseline

Answer 39

Measured vertically in mm (just like measure waves)

Question 40

Conversion mm to mV

Answer 40

10 mm verticaly represents one mV

Question 41

Amount of time represented by the distance between two heavy black lines (5 small boxes)

Answer 41

0.2 of a second

Question 42

Amount of time represented by each small division

Answer 42

0.04 of a second

Question 43

How to determine the duration of any wave

Answer 43

Measure along its horizontal axis

Question 44

Leads in a standard EKG

Answer 44

- 12 separate leads | - six limb leads, six chest leads

Question 45

Placement of limb leads

Answer 45

-right arm -left arm -left leg (Placement of electrodes, two electrodes are used to record a lead, a different pair for each lead)

Question 46

Bipolar limb leads

Answer 46

- uses two electrodes: one positive, one negative - include lead I-III - this configuration is also called Einthoven's triangle

Question 47

Lead I

Answer 47

Positive electrode on left arm | Negative electrode right arm

Question 48

Lead II

Answer 48

Positive electrode left leg | Negative electrode right arm

Question 49

Lead III

Answer 49

Positive electrode left leg | Negative electrode left arm

Question 50

Bipolar limb leads moved to intersect at a centre point

Answer 50

There is a center of the triangle formed by the arrangement of the bipolar limb leads Can push limb leads so that they intersect this center point but still remain at same angles relative to each other (still yielding the same info)

Question 51

AVF lead

Answer 51

Uses left foot electrode as positive | Remaining two electrodes are channeled into a common ground that has a negative charge

Question 52

AVR lead

Answer 52

Right arm electrode is positive, remaining two electrodes negative

Question 53

AVL lead

Answer 53

The left arm is positive and the remaining two are negative

Question 54

Augmented limb (unipolar) organization

Answer 54

- intersect at different angles than those produced by bipolar limb leads (split the angled formed by the bipolar limb leads) - intersect at 60 degree angles

Question 55

Frontal plane

Answer 55

Arrangement of six limb leads; the bipolar leads superimposed over the augmented leads

Question 56

Importance of all six limb leads

Answer 56

All record a different angle (viewpoint) to provide a different view of the same cardiac activity

Question 57

Why do the waves look different in each lead

Answer 57

Recording the same cardiac activity in each lead but looks different because the heart's electrical activity is recorded from different angles for each lead

Question 58

Conventional grouping of limb leads

Answer 58

Latera leads and inferior leads To determine whether the depolarization is moving toward or away from the patients left side and whether it is directed inferiorly toward or away from the left foot

Question 59

Lateral leads

Answer 59

lead I, AVL

Question 60

Inferior leads

Answer 60

Lead II, III and AVF

Question 61

Position of chest leads

Answer 61

Cover the heart in its anatomical position within the chest Each lead is oriented through the AV node and projects through the patients back In the horizontal plane (cut body into top and bottom halves)