Electrocardiogram: EKG/ECG Flashcards
What is EKG?
Using surface electrodes to record the electrical activity of the heart
electrical activity correlates to mechanical function
Takes electrical “snapshots” of the heart at different angles
each electrical impulse = a cardiac contraction
What Information from EKG?
heart rate
heart rhythm
heart size
ischemia/infarction
drug and electrolyte abnormalities
Electrical impulse sequence =
starts with sinoatrial node -> Atrioventricular node ->
bundle of his ->
purkinje fibers ->
What is Isoelectric activity?
cardiac cells at rest, no relative movement of ions
What is Depolarization ?
muscle contraction due to movement of sodium, potassium, and calcium
What is repolarization ?
muscle relaxation due to return of sodium, potassium, and calcium to resting state
What is the normal conduction pathway?
SA Node sends an electrical impulse to the right and left atria
Atria contract and pump blood to the ventricles
Atrioventricular node (AV) stimulated – base of the right atrium
Slows the signal allowing time for the ventricles to fill
Electrical signal then travels down the bundle of His and branches to the right and left ventricles
Purkinje fibers at the base of the ventricles
Ventricular contraction
Two types of cardiac cells:
Conducting: 1%
Contracting: 99%
What is the EKG of Cardiac muscle cells at rest ?
(slight negative)
resting polarized state
What is the EKG of depolarization of the cells ?
(wave of positive or less negative due to sodium influx)
Endocardium to Epicardium -> contraction
What is the EKG of repolarization of the cells ?
(wave of negative or less positive due to potassium efflux)
Epicardium to Endocardium -> relaxation
Ventricular wall: epicardium and endocardium
Depolarization goes from the endocardium to epicardium
Repolarization is opposite and goes from the epicardium to endocardium
With contraction, blood is moved from:
Atrium to ventricles
Right ventricle to pulmonary circulation
Left ventricle to systemic circulation
Standard 12 lead EKG includes:
6 chest electrodes
4 limb electrodes
12 leads or views of the heart
Limb leads: I, II, III
Augmented leads: avr, avl, avf
Chest Leads: V1 – V6
Extremity electrode and placement:
RA (Right Arm) - Anywhere between the right shoulder and right elbow; modified to right anterior shoulder
LA(Left Arm) - Anywhere between the left shoulder and the left elbow; modified to left anterior shoulder
LL (Left Leg) - Anywhere below the left torso and above the left ankle; modified to LLQ
What are Limb leads?
Leads I, II and III
electrodes that form these signals are located on the limbs – one on each arm and one on the left leg – electrode on right leg is neutral and plays no role in the EKG other than completing the circuit
The limb leads form the points of what is known as Einthoven’s triangle
What is lead I ?
the voltage between the +LA electrode and -RA electrode
What is lead II ?
the voltage between the +LL electrode and the -RA electrode
What is lead III ?
the voltage between the +LL electrode and the -LA electrode
What are Augmented limb leads?
Leads aVR, aVL, and aVF
They are derived from the same three electrodes as leads I, II, and II
they use a central terminal created by a combination of inputs from two limb electrode
What is Lead augmented vector right (aVR) ?
combination of the left arm electrode and the left leg electrode
What is Lead augmented vector left (aVL) ?
combination of the right arm electrode and the left leg electrode
What is Lead augmented vector foot (aVF) ?
combination of the right arm electrode and the left arm electrode
Leads I, II, and III, augmented limb leads aVR, aVL, and aVF calculate what?
the heart’s electrical axis in the frontal plane = 6 views
Chest electrodes & leads:
v1, v2, v3, v4, v5, v6
Where does v1 go?
Fourth intercostal space on the right sternum
Where does v2 go?
Fourth intercostal space at the left sternum
Where does v3 go?
Midway between placement of V2 and V4
Where does v4 go?
Fifth intercostal space at the midclavicular line
Where does v5 go?
Anterior axillary line on the same horizontal level as V4
Where does v6 go?
Mid-axillary line on the same horizontal level as V4 and V5
What is the Isoelectric Line ?
no charge difference inside vs outside of cardiac myocyte, no movement of ions
What is depolarization?
primarily + sodium flowing into cells
What is repolarization?
primarily + potassium flowing out of cells
What is Positive deflection ?
wave of depolarization toward positive electrode
What is Negative deflection ?
wave of depolarization toward negative electrode
What is the importance of the 12 lead EKG?
translates electrical signal, depolarization, and repolarization into a visual representation of the heart’s mechanics and function
What is the importance of telemetry EKG?
Monitor heart rate and rhythm
Monitor ST segment changes
What is the importance of a holter EKG?
Portable ECG = typically worn 24+ hours for Dx purposes
Monitor heart rate and rhythm over several days to weeks
Correlate signs and symptoms to heart mechanics
P wave =
atrial depolarization
activation of the atria
Normally the right atrium depolarizes slightly earlier than left atrium since the depolarization wave originates in the sinoatrial node
P-R interval =
onset of the P wave to the start of the QRS complex
It reflects conduction through the AV node
normal PR interval: 120 – 200 ms (0.12-0.20s) = three to five small squares
1 small square = .04 seconds
Q wave =
septal depolarization
QRS =
ventricular depolarization
activation of the ventricles
QRS complex starts just before ventricular contraction
ST segment =
represents the isoelectric period when the ventricles are in between depolarization and repolarization
ST segment abnormality = cardiac ischemia
T wave =
ventricular repolarization
recovery wave
What are the EKG Complexes>
p wave
P-R interval
QRS complex
ST segment
T wave
what is an action potential?
electrical stimulation created by ion fluxes through specialized channels in the membrane of cardiomyocytes that leads to cardiac contraction = typically -90mV to 0mV
The action potential in typical cardiomyocytes is composed of 5 phases (0-4), beginning and ending with phase 4
Phase 4: The resting phase
resting potential in a cardiomyocyte is −90 mV due to a constant outward leak of K+
Na+ and Ca2+ channels are closed during resting phase
Phase 0: Depolarization
action potential is triggered by SA node
Fast Na+ channels open = Na+ leaks into the cell = less negative environment
Phase 1: Early repolarization
TMP is now slightly positive
Some K+ channels open = outward flow of K+ returns the TMP to approximately 0 mV
Phase 2: The plateau phase
Ca2+ channels are open = constant inward current of Ca2+
K+ channels open = outward current of K+
These two countercurrents are electrically balanced = the TMP is maintained at a plateau 0 mV throughout phase 2
Phase 3: Repolarization
Ca2+ channels inactivated = inward CA2+ flow stops
Outflow of K+ = TMP back towards resting potential of −90 mV to prepare the cell for a new cycle of depolarization
ECG voltage:
Small box: 1mm =.04 sec
Large box: 5mm =.20 sec
5 Large boxes = 1 second
Interpreting ECG: HR
Heart rate can be easily calculated from the ECG strip
When the rhythm is regular, the heart rate is 300 divided by the number of large squares between the QRS complexes
(300/5 = 60)
Heart rate determination
3 second marks:
Count number of Q wave peaks between 3 second marks = 15 large boxes
Multiple by 10 = HR
Rule of 300
Count number of boxes from one Q wave peak to the next
300/# of large boxes = HR
Used with normal rhythm HR
Normal sinus rhythm
Rate between 60 and 100 beats per minute (bpm)
SA Node in control
Rhythm is regular
dysrhythmia
Alteration in rate and rhythm
Ectopic Focus/Foci
> Excitable group of cells = lower Action potential threshold
> irritable cell
Causes of ectopic foci
ischema/hypoxia of myocardium
sympathetic discharge - anxiety, exercises
acidosis
alteration in electrolytes (decreased K+)
excessive stretch of myocardium
pharmacological agents
> SNS mimetics - caffeine
> anti-arrhythmic drugs
> digitalis
Recognizing normal from abnormal EKG
Pattern Recognition
Check QRS wave -size, shape, distance
Check P wave -size/shape
Check PR interval
Check T wave -size/shape
Check ST segment
P wave: Atrial Depolarization
Size and shape
P duration < 0.12 sec = less than 3 small boxes
P amplitude < 2.5 mm = <.25 mV
Tall P wave = right atria enlargement = right heart failure
Elongated p wave = myocardial fibrosis, atrial fibrillation
Elongated PR Interval =
delay in signal from atria to ventricles
check PR interval - will be <.2 seconds or 1 large box
QRS Wave: Ventricular depolarization
check QRS wave:
size (wider than 3 small blocks)
shape
distance between R waves (exercise)
What is the ST segment?
Depression measured in mm – each small box on EKG strip is one mm
Gives information about myocardial ischemia
ST Segment depression:
correlates with myocardial ischemia – non full thickness ischemia - unstable angina
ST Segment elevation:
correlates with myocardial infarction – coronary artery blockage - full thickness ischemia
St segment changes
Elevation = 4 small boxes
Depression = 3 small boxes
Normal sinus rhythm rate =
60-100 bpm
Bradycardia =
< 60 bpm
Tachycardia =
> 100 bpm
Premature ventricular contraction (pvc)
extra heartbeats that begin in one of your heart’s ventricles = These extra beats disrupt your regular heart rhythm
These extra contractions usually beat sooner than the next expected regular heartbeat And they often interrupt the normal order of pumping
Can manifest as a feeling of fluttering or a skipped beat in your chest
Premature ventricular contractions are common - They’re also called:
Premature ventricular complexes
Ventricular premature beats
Ventricular extrasystoles
Premature ventricular contractions can be associated with:
meds including decongestants and antihistamines
Alcohol/drugs
caffeine
tobacco
exercise
anxiety
Injury to the heart muscle from coronary artery disease, congenital heart disease, high blood pressure or heart failure
Unifocal PVC =
from one spot on the ventricle wall
Multifocal PVC =
from two or more spots on the ventricle wall
PVC rhythm =
Bigeminy: every other beat
Trigeminy: every third beat
Quadrageminy: every fourth beat
PVC Couplet:
two consecutive pvcs
Ventricular tachycardia =
> 3 pvcs in a row
VTach =
defined as 3 or more irregular heartbeats in a row, originating from the ventricle, a rate of more than 100 beats a minute
If VTach lasts for more than 6 seconds at a time, it can become life-threatening = V Fibrillation
Rapid heartbeat =
doesn’t give your heart enough time to fill with blood before it contracts again = reduced blood flow to the rest of your body
Ventricular fibrillation =
heart rhythm problem that occurs when the heart beats with rapid, erratic electrical impulses. This causes the ventricles to quiver uselessly, instead of pumping blood.
Significant drop in blood pressure limiting blood supply to your vital organs
an emergency that requires immediate medical attention
it is the most frequent cause of sudden cardiac death
automated external defibrillator (AED) necessary to reset the electrical rhythm
medications and implantable devices that can restore a normal heart rhythm
Atrial flutter =
the atria beat regularly, but faster than usual and more often than the ventricles
Example = four atrial beats to every one ventricular beat
Atrial fibrillation =
arrhythmia that can lead to blood clots, stroke, heart failure
At least 2.7 million Americans are living with AFib.
atria beat chaotically and irregularly — out of coordination with the ventricles
Atrial fibrillation symptoms =
often include heart palpitations, shortness of breath and weakness
Leads to cardiac compromise if frequency and duration are not addressed with medication
