CARDIOLOGY - ECG Monitoring (Week 3/4) Flashcards
Electrocardiogram
- a graphic representation of electrical activity/impulses of the heart
- produced by electrical currents in the atria and ventricles
What sorts of cardiac abnormalities are ECGs able to help with in identifying?
1) abnormal HRs, rhythms, conduction pathways
2) presence of hypertrophy or atrophy in portions of the heart
3) approximate location of ischemia/MI
What characteristics of the heart will ECGs not be able to provide information on?
mechanical info (confirmed by a pulse instead), BP
As per BLS, a cardiac monitor is warranted for patients exhibiting signs or symptoms of cardiovascular, respiratory or neurological compromise, which includes:
- All VSA patients except those who are obviously dead
- unconscious or altered LOC
- electrocution
- collapse or syncope
- suspected cardiac ischemia
- CVA
- OD
- major or multi-system trauma
- submersion injury
- hypothermia, heat exhaustion or heat illness
- moderate to severe SOB
- abnormal vital signs as per ALS PCS
- if requested by sending facility staff (for inter-facility transfers)
Who was the founding father of ECG and what did the research involve?
William Einthoven
- he suspended a silver wire between magnet poles and then two electrodes were placed on a guy, and also connected to the ends of the silver wire ⇒ the wire would then twitch to the rhythm of his heart
- also invented to the EKG machine
- projected light through a hole in magnet’s pole across a twitching wire ⇒ wire movements recorded on scrolling graph paper (series of distinct waves which represented a single cycle/heartbeat)
True or False. Paramedic evaluation requires ECG interpretation AND its relationship to clinical assessment of the patient/patient presentation (you cannot just rely on one or the other)
True
All of the following factors can affect ECG quality except:
a) patient movement
b) loose connections
c) electrode applied over soft area
d) frayed cable
e) dried out electrodes
c) electrode applied over soft area (bony areas affect ECG quality)
The ECG machine receives the voltage, amplifies and displays it on ___________ or transfers it to ____________.
oscilloscope screen; graph paper
viewpoints of electrical activity in the heart are known as
leads
The ECG machine measures ____________ flowing between ____ poles; a ______ pole and a _______ pole.
electrical current; two poles; negative, positive
Where does the ECG machine view electrical activity?
from the positive pole
Voltage can be displayed as _____ and represents electrical activity in a specific part of the heart. What can the voltage be seen as?
waves
a) isoelectric line
b) positive
c) negative
d) biphasic
Isoelectric line
No current detected and seen as a straight baseline on ECG tracing (absence of electrical activity in heart)
Positive waveform
- current is detected, seen as upwards deflection on ECG tracing
- represents an electrical impulse that’s moving towards a positive electrode
Negative waveform
- current is detected, seen as downwards deflection on ECG tracing
- represents electrical impulse moving away from positive electrode
Biphasic waveform
- current is detected
- seen as partly upward and partly downward deflection on ECG tracing
- represents electrical impulse that moves perpendicular to positive electrode
Limb lead placement
RA LA
RL LL
white on right, smoke over fire, green is ground
An ECG Lead can consist of what two options to create negative and positive poles?
a) 2 surface electrodes - one +ve and one -ve (standard limb leads)
b) 1 surface electrode and one reference point (augmented limb leads)
2 surface electrodes are known as ________ (bipolar, unipolar, multipolar).
Bipolar - because they use two electrodes of opposite polarity (one +ve and one -ve) to form a lead
1 surface electrode is known as ______ (bipolar, unipolar, multipolar).
unipolar - as it only uses ONE electrode of +ve polarity and no distinct negative pole (so just one +ve and one reference point to form a lead)
technically uses 3 electrodes (one positive electrode and the avg of the two negative electrodes)
Reference point
- also known as average; a combination of two negative electrodes between the positive electrode
- established between two negative poles which creates a negative field (central terminal), of which the heart (acting as negative pole) is at the center
Standard limb leads
- I, II, and III (bipolar)
- views the heart on a frontal place and records the difference in electrical potential between axis (imaginary line between +ve and -ve electrodes)
Vector vs Mean Vector
Vector: direction of depolarization in the heart
Mean Vector: the general/avg direction of depolarization in the heart
*measured from the AV node - also remember that the LV is thicker than the RV so the vector falls slightly more to the left than right down the middle of the interventricular septum (thicker = more Purkinje fibers)
Lead I
- assess electrical activity/views the lateral surface of the LV at a vantage point of 0º
- Records difference in potential between left arm and right arm
The mean vector for ventricular depolarization is ___________.
What is a normal range for mean vector in a patient?
- 59+ degrees (the perfect angle) - mean vector of ventricular depolarization
- mean vector points and to the left, normally between 0 and +90 deg
Lead II
- assesses electrical acivity/views inferior surface of the left ventricle at a vantage point of +60º
- measures the difference in potential between left leg and right arm
- offers the best view of the heart because it follows the general direction of depolarization (which is +59)
Lead III
- assesses electrical activity/views inferior surface of the LV at a vantage point of +120º
- records the difference in potential betweeen left leg and left arm
Augmented limb leads
- aVR, aVF, aVL (augmented voltage - right, foot, left)
- unipolar
- views the heart on a frontal plane and records the difference in electrical potential betwen axis (imaginary line between +ve and reference point with zero electrical potential at the center of the electrical field of the heart)
Lead aVF
- assesss electrical activity/views inferior surface of left ventricle from a vantage point of +90º
- records difference in potential between left leg and right arm/left arm
Lead aVL
- assesses electrical activity/views lateral surface of the LV from a vantage point of -30º
- measures difference in potential between left arm and right arm/left leg
Lead aVR
- distance recording electrode
- assesses activity from a vantage point of -150º (recording difference in potential between right arm and left arm/left leg
- pretty useless (doesn’t view any wall of the heart)
Precordial chest leads
- V1, V2, V3, V4, V5, V6 - unipolar
- views electrical activity in the heart on a transverse/horizontal plane
- six precordial leads are projected from +ve electrode through anterior chest wall (through AV node) and towards the back AND reference point with zero electrical potential at the center of the electrical field of the heart
Hexaxial reference system
diagram based on the first six leads of the 12 lead ECG. Augmented leads intersect at different angles than standard limb leads, which collectively produce six intersecting lines of reference creating the hexaxial reference system.
It is used to help determine the heart’s electrical axis in the frontal plane.
Precordial lead placement
V1 - 4th ICS to the right of the sternum
V2 - 4th ICS to the left of the sternum
V3 - directly between V2 and V4
V4 - 5th ICS at the left midclavicular line
V5 - 5th ICS at the left anterior axillary line
V6 - 5th ICS at the left midaxillary line
How is the 12-lead ECG displayed on ECG graph paper? Also indicate which wall of the LV each lead views.
Leads viewing lateral wall
I, aVL, V5, V6
Leads viewing inferior wall
II, III, and aVF
Leads viewing septal wall
V1 and V2 (remember, looking on tranverse plane)
Leads looking at anterior wall
V3, V4
Each small square on ECG is _____ mm.
Each large square on ECG is ______mm.
1mm x 1mm
5mm x 5mm
One small square is _____ secs.
One large square is ________ secs.
- 04 secs
- 2 secs
What is measured horizontally on an ECG paper?
time/duration (used to measure interval between or duration of specific cardiac events aka how much time it takes an electrical impulse to pass through a specific part of the heart)
What is measure vertically on an ECG graph?
Voltage (in mV) or amplitude (mm)
*note that voltage (mV) can be negative or positive value
Voltage or amplitude of 1 small square
0.1 mV - voltage
1 mm - amplitude
An ECG is recorded at standard paper speed which is:
25mm per second
Short vertical markings located on the top of the ECG paper represents what?
- marks 1 second intervals
- used as a method for HR calculations
Why is a 6-second strip used instead of a minute-long strip?
The most accurate way to determine the heart rate would be to run a minute -long rhythm strip and count every beat, but this would be extremely time-consuming and thus impractical.
THEREFORE, a 6 second strip (which is multiplied by 10) is much more efficient and commonly used in the field.
How does the voltage (potential difference) between poles get recorded and transferred to paper?
After ECG machine records voltage, the needle/pen of ECG moves a specific distance depending on voltage measured
An ECG machine’s sensitivity MUST be calibrated before use. When properly calibrated, what would you see?
A 1mV electrical signal that produces a deflection measuring exactly 10mm tall (2 large squares)
Calculate the following times based on the number of small/large squares on an ECG paper.
a) 1 small square
b) 5 small squares
c) 15 large squares
d) 30 large squares
e) 300 large squares
a) 0.04 sec
b) 0.2 sec
c) 3 seconds
d) 6 seconds
e) 60 seconds/1 minute
Complex components
set of waves seen on an ECG monitor, which represent an electrical impulse traveling through the electrical conduction pathway of heart, and include P, Q, R, S, T waves.
True or False. A cardiac cycle can be measured from the beginning of one P wave to the beginning of the next P wave
True. A cardiac cycle can be represented by a combination of the 5 waves (PQRST) representing a single heart beat
All waveforms begin and end at the _________.
isoelectric line
Each waveform seen on an oscilloscope screen or recorded on graph paper represents what
the conduction of an electrical impulse through certain parts of the heart
P wave represents
depolarization of both atria
*does not represent SA node - the activatin of the SA node occurs before the onset of the P wave
Where does the P wave start and end, and what does it typically look like?
Starts: with 1st positive (upwards) deflection from baseline
Ends: at point where it returns to baseline
- preceds QRS complex
- typically looks rounded (like a little bump)
Normal time and voltage for P wave
Time: 0.10 sec or less (2.5mm or less)
Voltage: 0.25mV or less (2.5mm or less)
1st half of P wave represents ____________.
2nd half of P wave represents ____________.
1st half: depolarization of the right atrium
2nd half: depolarization of left atrium
QRS complex represents
depolarization of both ventricles (which includes conduction from Bundle of His to Pukinje fibers into ventricular muscle)
mechanically, this is also the approximate beginning of mechanical systole of ventricles
QRS waveform may be:
a) positive
b) negative
c) biphasic
d) all of the above
d) all of the above
Where does the QRS complex start and end?
Starts: with 1st deflection from baseline
Ends: when last point of the complex flattens at, above, or below baseline (point at which the last wave of the complex begins to level out or distinctly changes direction at, above or below the baseline- observe when it looks like it’s going perpendicular)
Normal time for QRS complex
< 0.12secs (less than 3mm)
MEANING 0.12 = abnormal (it has be LESS than 0.12 secs)
QRS complex normally has what characteristics?
narrow and sharply pointed (when conduction is normal)
True or False. A QRS complex will not always have a Q, R, or S wave but it will see be called a QRS complex.
True.
even if there is just an R wave, it’s still a QRS complex
What waveform represents atrial repolarization?
Technically atrial repolarization happening during QRS complex but is overshadowed by ventricular depolarization therefore it is not seen
Q wave represents what
depolarization of the interventricular septum (physiological change - normal) or patological change (previous MI)
How does the Q wave present on ECG paper?
- the 1st negative deflection of the QRS (ALWAYS NEGATIVE)
- may NOT be present in all complexes
- only 1 Q wave in each
Normal physiological Q wave characteristics (excluding Lead III and AVR)
<0.04 seconds in duration (one small square)
AND
less than 1/3rd the height of the R wave in that lead
Abnormal pathologic Q wave characteristics
equal or > 0.04 seconds in duration
OR
more than 1/3rd the height of the R wave in that lead
*one possible cause is previous MI
Both R and S waves represent
simultaneous depolarization of the R and L ventricles
How is R wave represented as a waveform on ECG paper?
- 1st positive deflection of the QRS
- there may be more than one R wave in a complex
If there are multiple R waves, how are they denoted to help differentiate from other R waves?
Following upwards deflections are called:
- R’ (R prime) - 2nd R wave
- R’‘ (R double prime) - 3rd R wave
Upper case R’s used to designate waveforms of larger amplitude
Lower case r’s used to deisgnate waeforms of smaller amplitude
How is S wave represented as a waveform on ECG paper?
- negative deflection that follows the R
- may be more than 1 in a complex
- S wave can end above or below the isoelectric line
If there are multiple S waves, how are they denoted to help differentiate from other S waves?
Following downwards deflections are called:
- S’ (S prime) - 2nd S wave
- S’‘ (S double prime) - 3rd S wave
Upper case S’s used to designate waveforms of larger amplitude
Lower case s’s used to deisgnate waeforms of smaller amplitude
Morphology of the QRS complex can vary depending on what?
- lead from which you are viewing
- the individual patient
- abnormal pathology
*note that: although they may appear different it may be:
- “normal” for that individual
- suggestive of underlying conduction disturbance
If a QRS complex consists entirely of a positive waveform, it is referred to as:
R wave
If a QRS complex consists entirely of a negative waveform, it is referred to as:
a QS wave
T wave represents
repolarization of both ventricles
Voltage of T wave (normal parameters)
0.5mV or less in limb lead (5mm or less)
OR
1mV or less in chest leads (10mm or less)
Where does T wave begin and end?
Starts: with 1st (positive) deflection after the ST segment
Ends: at point it returns to baseline
Shape of T wave
normally rounded and slightly asymmetrical (should be taller than P wave but only concerning if it’s elongated OR almost as tall as QRS complex)
A T wave following an abnormal QRS complex (i.e _____ secs or more) is usually ______ in direction of the QRS complex.
When is this seen?
- 12 secs; opposite
i. e. when an abnormal QRS complex is predominantly negative, T wave will point up (or vice versa so if abnormal QRS complex is predominantly positive, T wave will point down)
seen in ventricular beats and bundle branch blocks
PR interval represents
time an impulse is conducted through the atria and AV node up to ventricular depolarization (i.e. from atrial depolarization ⇒ AV node ⇒ ventricular depolarization)
Normal parameters for PR interval
time: 0.12 - 0.20 seconds (considered prolonged if >0.20 seconds)
faster HRs may have PR intervals less than 0.12 secs
if abnormal, it indicates a disturbance in the electrical conduction pathway, specifically in AV node
Where does PR interval begin and end?
Starts: at beginning of P wave
Ends: at beginning of QRS complex
PR interval is dependent on what factors?
HR and conduction characteristics of AV node
QT interval represents
time from beginning of ventricular depolarization to the end of ventricular repolarization
Where does QT interval start and end?
Starts: at beginning of QRS complex
Ends: at the END of the T wave
The line that separates the absolute and relative refractory periods falls directly where?
What is the significance of this?
on the peak of the T wave
This means that beyond that point (the peak of the T wave), the heart may be able to respond to electrical stimuli (cardiac muscle is hard to stimulate but will response with enough stimuli)
R on T phenomenon
Lethal rhythm; when an impulse starts on the T wave (R wave superimposed on a T wave)
ST segment represents
early phase of repolarization of both ventricles
Where does ST segment start and end?
Starts: at end of QRS complex
Ends: at beginning of T wave
J point
Point at which the QRS complex and ST segment meet
True or False. The term “ST” is used regardless of whether the final wave of the QRS is an R or S wave.
True
How is the position of the ST segmented judged as abnormal/normal?
using baseline of PR interval as a reference
ST-segment deviation potential causes
myocardial ischemia
infarction
injury
(typically cardiac problems/cardiac disease related)
How does ST elevation present on ECG?
ST segment deviated above the baseline
How does ST depression present on ECG?
ST segment deviated below the
*seeing ST depression may indicate ST elevation is also happening
True or False. Artifact can mimic various cardiac dysrhythmias including ventricular fibrillation.
TRUE. therefore you need to evaluate patient before initiating any medicaiton intervention (do not just rely on ECG machine)
Artifact
Marks on ECG display caused by activities other then electrical activity of the heart
What are the 4 common causes of artifact?
1) 60 cycle interference
2) loose or broken ECG cables
3) patient movement/muscle activity
4) external chest compressions
60-cycle interference
grounding issue of an electrical component (the influence of other equipment/external source which is improperly grounded)
Long bizarre waves that look like nothing
loose or broken ECG cables
How does patient movement/muscle activity cause artifact?
things like shivering, tremors, seizures, tense muscles etc can cause ECG to look like lethal rhythms but REMEMBER to consider patient presentation
How would the following rhythm strip be considered artifact from patient movement/muscle activity?
some patients may be breathing very deeply causing artifact (work on coaching breathing in these situations to get a more acccurate reading)
peaked P waves (taller than normal P waves) may indicate
enlargement of right atrium
Notched P waves (“m-shaped”) may indicate
enlargement of LA
negative/inverted and absent P waves may indicate
electrical conduction that is initiated from the AV junction
Biphasic P waves may indiccate
enlargement of both atria (see only on 12-lead)
Biphase or absent T waves may be evidence for
heart muscle ishemia
or
changes in blood level of potassium
A T-wave greater than half the total heigh of the QRS complex is considered what?
considered hyperacute (elevated) and may indicate new ischemia of the cardiac muscle
An inverted T wave is frequently an indication of
cardiac ischemia
QT intervals are either normal or prolonged.
A normal QT interval is: ________.
A prolonged QT interval is _______ and may indicate:
Normal: less than one half of the R to R interval of that complex (typically < 0.44 seconds is normal)
Prolonged: >0.44 secs (or greater than half of R-R interval of that complex) and usually indicates problem within electrical conduction pathway of the heart
