Chapter 1 Basic Principle, Rapid Interpretation of EKG's Flashcards
Scientific establishment of pumping of heart and electrical phenomena
- Kollicker and Mueller (1855)
- lay motor nerve to frogs leg over isolated beating heart
- leg would kick with each heartbeat
Capillary electrometer
- 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
Invention of the 1st EKG machine
- 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
Function of the EKG
Records the electrical activity of contraction of the heart muscle
Charge Myocardial cells in resting state
- polarized
- interior of every cell is negatively charged (negative interior and positively charged outside surface)
Charge myocardial cells during contraction
- depolarized
- interior become positive
Depolarization of the myocardium
- an advancing wave of positive charges within the heart’s myocytes
- due to movement of Na+ through fast-moving Na+ chanels
Upward deflection on EKG - meaning
Represents a depolarization wave moving toward a positive electrode
Hearts dominant pacemaker
SA node
Sinus rhythm
Normal pacing activity of SA node
Automaticity
The generation of pacemaking stimuli
Automaticity foci
Other focal areas of the heart that have automaticity
Atrial depolarization (and contraction)
Spreading wave of positive charges within the atrial myocardial cells
P wave
Upward deflection produced by depolarization of atria on EKG
Function of atrio-ventricular valves - electrical conduction
Insulate the atria from the ventricles (making AV node the only conducting path between the atria and the ventricles)
Timelapse at AV node
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
Reason why depolarization conducts slowly through the AV node
Due to current being carried by slow-moving Ca2+ ions
Ventricular conduction system
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
Purkinje fibers
- 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
QRS complex
Corresponds to the depolarization of the ventricular myocardium on EKG
Terminal filaments of the Purkinje fibers - location + what this means for direction depolarization of ventricles
Spread out just beneath the endocardium that lines both ventricular cavities
Ventricles epolarize from the lining towards the outside surface (epicardium)
Relationship QRS to ventricular contraction
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
Q wave
The first downward wave of the QRS complex
Often absent
R wave
The first upward deflection of the QRS complex
S wave
Any downward wave preceded by an upward wave
QS wave
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
ST segment
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!)
ST segment - what does represent
The plateau phase of ventricular repolarization (when K+ exit and Ca2+ entry are balanced)
Ventricular repolarization is rather minimal during this segment
What does the T wave represent
Represents the rapid phase of ventricular repolarization
Accomplished by K+ leading the myocytes
Stages of EKG that ventricular systole corresponds to
Spans depolarization and repolarization of ventricles so from QRS to end of T wave
I.e. the QT interval
Why QT interval is a good indicator of repolarization
Snce repolarization comprises the most of the QT interval
Long QT interval syndrome
- hereditary syndromes
- make people more vulnerable to rapid ventricular rhythms (why it is important to detect a prolonged QT interval)
How does the QT interval vary
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)
What is considered a normal QT interval
-when it is less than half of the R-R interval at normal rates
Smallest divisions on EKG strip
-one millimeter by one millimeter
Large boxes
- denoted by heavy black lines on each side
- each side is 5 mm long (5 small boxes)
Measure of voltage on EKG
The height and depth of a wave measured verticaly frm basline in mm
-vertical amplitude is a measure of voltage
Amplitude of a wave
The magnitude (in millimeters) of the deflection and is a measure of voltage
Measuring elevation/depression of segments of baseline
Measured vertically in mm (just like measure waves)
Conversion mm to mV
10 mm verticaly represents one mV
Amount of time represented by the distance between two heavy black lines (5 small boxes)
0.2 of a second
Amount of time represented by each small division
0.04 of a second
How to determine the duration of any wave
Measure along its horizontal axis
Leads in a standard EKG
- 12 separate leads
- six limb leads, six chest leads
Placement of limb leads
-right arm
-left arm
-left leg
(Placement of electrodes, two electrodes are used to record a lead, a different pair for each lead)
Bipolar limb leads
- uses two electrodes: one positive, one negative
- include lead I-III
- this configuration is also called Einthoven’s triangle
Lead I
Positive electrode on left arm
Negative electrode right arm
Lead II
Positive electrode left leg
Negative electrode right arm
Lead III
Positive electrode left leg
Negative electrode left arm
Bipolar limb leads moved to intersect at a centre point
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)
AVF lead
Uses left foot electrode as positive
Remaining two electrodes are channeled into a common ground that has a negative charge
AVR lead
Right arm electrode is positive, remaining two electrodes negative
AVL lead
The left arm is positive and the remaining two are negative
Augmented limb (unipolar) organization
- 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
Frontal plane
Arrangement of six limb leads; the bipolar leads superimposed over the augmented leads
Importance of all six limb leads
All record a different angle (viewpoint) to provide a different view of the same cardiac activity
Why do the waves look different in each lead
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
Conventional grouping of limb leads
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
Lateral leads
lead I, AVL
Inferior leads
Lead II, III and AVF
Position of chest leads
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)
