ECG Basics And Interpretation Flashcards
Reference electrode is always
Positive
What do electrodes measure
Change in polarity
Waves are recorded as
Depolarization moves toward or away from electrode
Depolarizations moving towards an electrode
Positive
Depolarizations moving away from electrode are
Negative
Depolarizations moving towards an electrode
Negative
Repolarizations moving away from electrode
Positive
Moving at a right angle to electrode
Generates no wave
What do the electrodes ultimately measure
Sum and vector of everything
Most EKGs are what kind
12 leads
Limb leads
6
- 3 standard leads
- 3augmented leads
Requires a lead on each limb
Precordial leads
6
-arranged along chest wall
What do multiple leads allow
Entire heart to be viewed in (basically) 3D
Lead I
Left arm (+). Right arm (-)
Lead II
Right arm (-), legs (+)
Lead III
Left arm (-), legs (+)
Augmented leads
One +, other 2 are -
Up in atria
Precordial leads
Around heart at mid chest Gives horizontal view Used to localize infarcts Always have V in front of it Number gets bigger as you move towards the left
P waves in leads
Small and positive in the left and inferior leads
QRS in leads
- Large and positive R eaves are seen in left and inferior leads
- R wave progresses from negative to more positive through V1-V5
V1-V5, R wave gets taller (more +), breaks down during MI
T waves in leads
Variable, but positive in large R wave leads
How many beats on each lead?
2-3
What is a quick dirty diagnosis of morphology of heart
Mean electrical axis
Vector that shows where most depolarization occurs
Mean electrical axis
Shows most muscle mass is
Sum of all QRS vectors is usually
60 degrees
Why does the mean electrical axis go to 60 degrees normally?
Goes down and to the left because left ventricle is largest chamber
What happens if mean electrical axis changes?
The heart has changed shape
What changes in the heart would causes MEA to change
Hypertrophy/dilation in response to cardiac disease. Causes change in MEA because more muscle in heart needs to be treated
What are the two leads you need to look at when calculating MEA?
lead I and aVF
-covers all the ventricles
Where will aVF be positive?
Towards base
Where will Lead I be positive
Towards the left
Where will aVF be negative
Towards apex
Where will lead I be negative
Towards the right
Where is there normally overlap?
Bottom left, both leads are positive
Deviations of MEA are indicative of what
Structural changes
What are two functional changes of hte heart that will affect MEA?
Hypertrophy
Dilation
Heart cells get bigger
Hypertrophy
Response to hypertension
Heart will get thicker
Chamber gets bigger of heart
Dilation
Response to volume overload
What do both dilation and hypertrophy result in?
Shift towards THE AFFECTED area, usually the ventricles.
Why do atrial problems not normally showing in MEA changes?
Ventricles will hide the atrial dysfunction because the atria are smaller. Also, the left side can obscure right side changes
You receive an ECG with a positive R wave in lead I and a negative R wave in aVF. What is this persons MEA?
Left axis
You receive an ECG with a positive R wave in lead I and a negative R wave in AVF. Which of the following could result in such an ECG change?
Left ventricular hypertrophy, and maybe left atrial hypertrophy
Any alteration to normal rhythm, regularity, origin or condition of the heart beat
Arrhythmias
Are all arrhythmias bad?
Not all are dangerous, but some are fatal
Symptoms of arrhythmias
Palpitations and or sudden light-headedness
What can arrhythmias excacerbate?
Underlying conditions like heart failure
What do you do to diagnose arrhythmias?
Use rhythm strip. Gives a longer recording like 10s of lead II
How do you determine arrhythmia?
Rate and rhythm
How to determine rate
300/# of large squares between successive R waves.
What do you check when looking at rhythm?
Does it look normal
- P waves?
- QRS narrow or wide?
- 1:1 ratio between P and QRS?
- is it regular?
HR under 60BPM?
Bradycardia
Where does sunis bradycardia and tachycardia originate?
SA node
What kind of drug could cause sinus bradycardia?
M2 agonist
What changes on the EKG in bradycardia?
Lengthened PR interval
What does the lengthened PR interval on the EKG during bradycardia tell us?
Lengthened nodal delay
Which is worse, bradycardia or tachycardia?
Tachycardia
HR over 100 bpm
Sinus tachycardia
Is there a greater change in diastole or systole when the HR is increased?
Diastole, heart doesn’t stay relaxed long enough, decreased output because it didnt have proper time to fill
Rapid, irregular atrial depolarizations with a sawtooth pattern on EKG. Normal QRS
Atrial flutter
Why is the QRS complex normal in atrial flutter?
AV node refractory for most atrial depolarizations
What node is affected in atrial flutter
SA
No coordination of atrial depolarization. Irregular QRS
Atrial fibrillation
Why is the QRS irregular in A fib?
AV node will fire as soon as it is no longer in refractory. There is uncoordinated contraction between the atria and the ventricles
What kind of meds do you want to make sure someone with A fib is on?
Anticoagulants
Occur when depolarization is not conducted properly from atria to ventricle (AV node or bundle branches)
Conduction block
What is 1st degree conduction block?
- normal HR, but prolonged PR interval (>.2s)
- due to increased AV node delay
- can be seen in highly trained athletes. Each P wave has QRS, not a big deal. Prolonged pause between atrial and ventricular depolarization
What is 2nd degree conduction block?
- not all P waves are conducted via AV node
- P waves to QRS ratio is >1:1
- dropped beats (more P than QRS)
What are the types of 2nd degree conduction block?
- mobitz type I (Wenckebach)
- Mobitz type II
PR interval gets progressively longer until a beat is dropped
2nd degree conduction block: Mobitz type I (wenckebach)
PR interval is set, but still drop beats
Second degree conduction block: Mobitz type II
What is a 3rd degree conduction block?
No conduction via AV node between atria and ventricles
- both P waves and QRS have a regular rhythm but are not in sync.
- QRS can be wide
What does a wide QRS mean?
Ventricular origin of depolarization
What kind of conduction block kills every P wave as it tries to cross AV node?
3rd degree
What can ventricular arrhythmia lead to?
Ischemia
Disturbances arise from below the AV node and produce wide QRS and are life threatening
Ventricular arrhythmias
Ventricular tachycardia
- fast depolarization
- ischemic event
- no P waves
- can lead to fibrillation (still ejected a little blood but screwed up the filling of blood)
Ventricular fibrillation
- uncoordinated depolarization
- rapid death
- no ejection of blood
What kind of heart disturbance do you shock for
Ventricular arrhythmias
Disruption of oxygen delivery affects the EKG. What is this called?
Ischemia
What is something that can cause ischemia?
Atherosclerosis
Why does disruption of O2 delivery affect the heart?
Can’t make energy, cant pump ions for contraction
What is the first thing you will see if an ischemic attack is just happening
Peaked T waves, transitioning into inverted waves T waves.
- early sign
- reversible damage
What is a sign of hyperkalemia on an EKG?
Peaked T waves, transitioning into inverted T waves
What is the second thing you will see as ischemia progresses on the EKG?
ST-segment elevation
-approaching permanent damage
What is the third thing you see on EKG with old ischemic attacks or ones that are far along?
Q waves
- permanent damage
- also present with healed infarct
What does hyperkalemia resemble on EKG?
Early ischemia
Hyperkalemia affects on EKG
Progressive changes in QRS
- peaked T waves
- prolonged PR interval
- widens QRS, merges with T wave
Hypokalemia affects on EKG
- ST depression
- flattened T wave and long QT
- U wave
Why is EKG good for detecting ionic imbalances?
It is much quicker to do an EKG than it is to draw blood and wait for the results to return from the lab
What do you need to be able to do every time you read an EKG?
Check for:
- rate
- rhythm
- axis
- infarction
When you check rate on the EKG, what are you looking for?
Normal
Tachycardia
Bradycardia
When you check rhythm on EKG, what are you looking for?
Sinus or ventricular (1st-3rd degree blocks, fibrillation or flutter)
When you check axis on EKG, what are you looking for?
Determine the mean electrical axis (normal, left shift, right shift, intermediate shift) and predict pathology associated with that shift
When you are looking for infarction on EKG, what are you looking for
Is there active ischemia (peaked/inverted T waves), active infarction (ST-segment elevation), old/resolved infarct (Q waves)
What could result in widened QRS complex?
Sodium channel (Nav) blocker
