ABG and ECG Tutorial Drama Flashcards
What is an ECG?
Sticky pads placed on a person, on their chest - detects the electrical activity of the heart from different planes / angles
The leads measure the direction of the electrical activity
ECG ‘deflections’ = differences in electrical potential between a cathode (+ve) and anode (-ve)
What are the advantages and limitations of ECGs?
Advantages = Cheap Pain free Quick Reproducible
Limitations =
Interpretations require skill
Need to be aware of the anatomical positioning of the heart
What is an isoelectric line?
No net change rather than no change
i.e. perpendicular line to place
What does the steepness and width of a deflection suggest?
Steepness = velocity Width = duration
What are the letters on wave?
P
QRS
T
What is the P wave?
Depolarisation from the right atrium, across to the left - SAN to AVN
Cardiac contraction initiated by the SAN
Should be <3 squares wide
Always inverted in aVR
What is the PR interval?
Depolarisation reaches AVN
Delay here to allow for ventricular filling
Slow signal with long duration - 3-5 small squares
What is the QRS complex?
Ventricular contraction
What is the Q wave?
Depolarisation continues down AVN, Depolarisation of septum
Downward deflection
What is the R wave?
Depolarisation of the ventricles
What is the S wave?
Final depolarisation of the ventricles
What is the ST segment?
Period between ventricular replorisation and depolarisation
What is the T wave?
Ventricular repolarisation
Should be <1 big square in limb leads, <2 in chest leads
What are the horizontal and vertical axis?
Horizontal = time Vertical = amplitude
Where are the electrodes V1-V6 placed?
V1 = 4th intercostal space at the right sternal edge V2 = 4th intercostal space at left border of the sternum V3 = Midway between V2 and V4 V4 = 5th intercostal space at midclavicular line V5 = Level with V4 at left anterior axillary line V6 = Level with V4-V5 at left midaxillary line
What are the aVR, aVL and aVF leads placed?
Ride Your Green bicycle
Red = Lead 1 = right arm to left arm Yellow = Lead II = right arm to left leg Green= Lead III = left arm to left leg
What is used to form the horizontal place?
V1-V6
What is the structures approach for looking at an ECG?
Check patient name and DOB
Check paper speed
Check signal quality - i.e. are the leads placed properly?
Check clinical contract of the ECG
Then check the ECG for the:
Rate
Rhythm
Axis
How is the rate calculated?
What does the rate indicate?
Count the number of r waves thoughtout the full durtaion of the rhythm strip of lead II, then multiply by 6 (for 60 seconds) to give bpm
OR 300/ number of large squares between the R waves (less used as rhythm is required ot be regular for this)
<60 = bradycardia >100 = tachycardia
What are the 3 types of rhythm?
Regular e.g. normal sinus rhythm
Regularly irregular e.g. heart block Mobitz Type II
Irregulrly irregular e.g. atrial fibrillation
What does sinus rhythm actually mean?
Default rhythm
How do you look for a sinus rhythm?
Ask 3 questions:
Are there p-waves?
Is each p-wave followed by a QRS wave?
Is each QRS wave preceded by a p wave?
What is the cardiac axis?
The average direction of electrical actvity though the vessels
Normal cardiac axis = between 2 o’clock to 6 o’clock (-30 to +90 degrees)
Why does the cardiac axis matter?
What does an axis deviation suggest?
Shows you whether there is an axis deviation
Axis deviation = intrinsic electrical problem e.g. a blockade in the left/right bundle branches) or the cardiac muscle increasing in size to compensate for demand
E.g. what might be a left axis deviation?
Left ventricular hypertrophy = left (muscular) acis deviation
Left ventricular muscle much larger in comparison = associated with grater degree of electrical activity
How can you calculate the axis?
Choose 2 leads that are perpendicular e.g. Leads I and aVF (or can use aVL and lead II)
Calculate the net amplitude of the QRS complex deflections (positive deflection above isoelectric line subtract negtaive deflection below isoelectric like) for both leads
e.g.
aVLnet deflection = 6.5mm
Lead I net deflection = 8mm
Each vector has a specific direction and length - this must be maintained
Perpendicular leads = right angle so you can use SOHCAHTOA
For lead I and aVL, use the TOA
angle = tan-1(opp/adj)
What is the alpha method of calculating axis?
Lead I and Lead II both positive = normal axis deviation
Lead I positive, lead II negative = left axis deviation
Lead I negative, Lead aVF positive = right axis deviation
Lead I and Lead aVF negative = extreme deviation
Whar is an interval VS segment?
Refers to length of a wave plus the isoelectric line that follows in
Segment = baseline between the end of one wave and the start of the next
What are some P-wave abnormalities?
P wave bifid in left atrial enlargement
P wave tall in large atrial enlargement
What are some QRS abnormalities?
Negative QRS in V1 = left ventricular hypertrophy
What are some ST segment abnormalities?
May be elevated or depressed
What is the QT interval?
Time taken for the end of ventricular depolarisation and end of ventricular repolarisation
What is the ECG flow chart?
Look at the other deck for the pic
What is A. fib?
What does atrial fibrillation look like on an ECG?
Chaotic electrical activity everywhere in the atria with no focus (as opposed to a focus of electricity generated from the SAN to AVN)
Absence of p-waves
Oscillating baseline
Irregularly irregular pulse (R-R interval very variable)
Increased risk of clot information within the atria (due to pooling of blood and turbulent flow) –> anticoagulation should be given
What does an atrial flutter look like on an ECG?
Abnormal p-waves
Regular saw tooth pattern
What is heart block?
Electrical signals from atria don’t conduct properly into the ventricles
Key measure of heart block = PR interval prolongation
What is first degree heart block?
Fixed prolongation of PR interval (>0.2s / >5 small squares)
What is second degree heart block?
Same as first degree but with occasional skipped QRS
What are the 2 types of second degree heart block?
Mobitz Type I = progressively prolonged PR interval until eventually there is a p-wave that is not followed by a QRS complex
Mechanism = reversible conduction block at AVN that progressively fatigues
Mobitz Type II = intermittently a p-wave is not followed by a QRS. Regular pattern of p-waves not followed by a QRS
Mechanism = failure of conduction at the level of His-Purkije system (usually due to structural damage)
What is third degree heart block?
No relationship between P waves and QRS complexes
P and QRS complex both come regularly, but there is no communication between the 2
What is ventricular tachycardia and how does it show on an ECG?
Regular broad QRS complex (wider than 3 small squares) and tachycardia (usually 100-200bpm) which originates from an ectopic focus (like atrial flutter)
Absent p-waves
Shockable rhythm
At risk of developing ventricular fibrillation
What is ventricular fibrillation and how does it show up on an ECG?
Irregular broad electrical activity (eate usualy >250bpm)
No p-waves
No recognisable QRS complex
Also a shockable rhythm
Need to defibrilate ASAP as there is no ventricular output in this rhythm
What are the possible ST segment changes on an ECG and what do they mean?
ST segment is supposed to be at the isoelectric line
ST elevation (>2mm above PR segment isoelectric line) = transmural infarction = tissue death by hypoperfusion e.g. coronary occlusion
ST depression (<2mm below PR segment isoelectric line) = subendocardial ischaemia = coronary insufficiency e.g. in exertional chest pain
Which leads correspond with which coronary arteries?
LCx = Lead 1, aVL, V5. V6
LAD = VI, V2, V3, V4
RCA = aVR, Lead II, Lead III, aVF
What happens if there is ST elevation in the anterior and lateral leads?
Anterolateral ST elevation MI (STEMI)
Also referred to as ‘tombstone’ ST elevation - as it looks like a tombstone and there is poor prognosis without rapid intervention
What is a basic ABG layout?
Patient ID, name, DOB
Oxygenation level at time take - e.g. on air? on oxygen?
FiO2 (e.g. 0.21 on room air, add on 1L = 0.24, and then every added 1L after that is +0.04)
temp
pH
pCO2
pO2
cHCO3-
BE
Na+
K+
Cl_
Ca2+
Hct tHb COHb O2Hb MetHb SO2
Glu
Lac
What is the importance of pO2 and pCO2?
Low PCO2 = respiratory failure
Can be divided into:
Type I RF = low pO2 and normal pCO2
Type II RF = low pO2 and high pCO2
What is the importance of pH?
Lets you know whether it is acidosis or alkalosis
What is the methodological approach for ABGs?
Low pH + high CO2 = respiratory acidosis
Low pH + low CO2 = metabolic acidosis with compensation
Low pH + high HCO3- = respiratory acidosis with compensation
Low pH + low HCO3- = metabolic acidosis
High pH + high CO2 = metabolic alkalosis with compensation
High pH + low CO2 = respiratory alkalosis
High pH + high HCO3- = metabolic alkalosis
High pH + low HCO3- = respiratory alkalosis with compensation
What happens if pH is normal but there is an abnormality with the CO2 and HCO3-?
This is fully compensated
What happens if the pH is outside the normal range but there is compensation from CO2 and HCO3-?
This is partial compensation
What is a bundle branch block and how does it show up on an ECG?
Problem with conduction in the Bundle of His = slower conduction of electricity e.g. if left bundle is blocked, only electricity travels down right side then travels up, then it must diffuse to the right side, so slight delay in contraction of the ventricles between the left and right (right contracts a little before the left)
Shows up on ECG are 2 QRSs joined together - a peak with 2 heads
What is a flat line on an ECG?
Asystole = non-shockable rhythm = pulseless electrical activity
Start CPR
