ECGs 2 Flashcards
What is meant by the overall axis of the heart/ECG?
The overall direction of depolarisation of the heart
How can you imagine the layout of axis in the human body?
Imagine a stick man
Left arm = 0 degrees and is lead I
Feet = +90 degrees and is avF lead
Right arm = 180 degrees
Head = -90 degrees
What part of the ECG determines the axis of the ECG?
QRS complexes
What part of the ECG determines the axis of the ECG?
QRS complexes
Which 2 leads of the ECG determines the axis of the heart/ECG?
Lead I
AvF lead.
What is considered a normal axis of the heart?
Between -30 and 90 degrees
So generally in the left lower quadrant
How do you determine the axis of the heart using lead I and avF lead?
Lead I determines the horizontal axis of the vector
avF lead determines the vertical axis of the vector
How do you interpret lead I to determine the horizontal part of the vector to determine the axis?
Lead 1 the current normally runs to the left, this is the positive direction, to the right is the negative direction
So if the QRS in lead I is more positive than negative (more squares in the upward deflection than the downward deflection) it means the electrical current is going in the normal positive direction so to the left
How do you interpret avF to determine the vertical part of the vector to determine the axis?
In lead avF, the current normally runs downwards, so this is the positive direction
So if the QRS in lead avF is more positive than negative (more squares in the upward deflection than the downward deflection) the current is flowing in the positive direction so is going down the avF lead.
What degrees is considered left axis deviation?
Between -30 and -90 degrees
What degrees is considered right axis deviation?
+90 and 180 degrees So generally
What is the likely axis in this scenario:
-lead I QRS positive
-avF lead QRS is negative
+ Lead I means horizontal vector is left
- lead avF means upward vertical vector
So going top left quadrant so is left axis deviation
What is the likely axis in this scenario:
-lead I QRS negative
-avF lead QRS is positive
-ve lead I means depolarisation happening in opposite direction than normal so horizontal vector is right
+ve avF means depolarisation happening in normal direction so vertical vector is downwards
So overall depolarisation is going bottom right quadrant (+90 to +180) so is RIGHT AXIS DEVIATION
What can cause Right Axis Deviation?
Right ventricular strain likely due to a Massive PE
+
Left posterior fasicular block
What causes Left Axis Deviation?
Left ventricular strain
Left anterior fasicular block cause right
What are the 3 types of P waves?
Normal
P-mitrale
P-pulmonale
What does a p-mitrale wave look like?
Biphasic p wave (on first slide of notes)
What generally causes p-mitrale (biphasic p wave)?
What can cause this?
Left atrial enlargement
Mitral stenosis
What is p-pulmonale?
Tall peaked p wave where the p wave is greater than 2.5 small squares high
What generally causes p-pulmonale?
What can cause this?
Right atrial enlargement
Pulmonary hypertension, COPD, left sided heart failure causing right sided heart failure
What are the characteristic ECG findings of a massive pulmonary embolism?
S1Q3T3
Right Axis Deviation (Due to right ventricular strain)
Can get p-pulmonale but not always (due to right atrial enlargement)
What is meant by the characteristic S1Q3T3 seen on an ECG with a massive pulmonary embolism (PE)?
Deep S wave in lead I
Q wave in lead III
Inverted T wave in lead III
What type of patients do you commonly see p-pulmonale in?
COPD patients
What is the PR interval?
Time between the start of the P wave till the start of the QRS complex
What is represented by the PR interval?q
Time taken from the initiated depolarisation from the SAN to reach the AVN and travel down the bundle branches and the Purkinje fibres to the first ventricular depolarisation/contraction
When are there issues with a long PR interval?
When the PR is very long
There’s other conducting disease
Infective endocarditis on aortic valve (abscess in area where AVN is)
What causes a short PR interval/what does a short PR interval represent?
Short PR = very quick time between initial depolarisation of atria reaching the ventricles (means there’s an alternate pathway that is by passing the AVN)
An accessory pathway (Wolff Parkinson White Syndrome)
What type of wave will be visible on an ECG if theres an accessory pathway causing a shortened PR interval?
How does this look?
Delta wave
Slow upstroke/slurring of a wave before the QRS complex (top of page 2 in notes)
What is suggest if there is the presence of a Q wave in the QRS complex?
Patient has had a full thickness MI
What is the criteria for there being a Q wave?
Very first deflection must be down
Must be at least 1/4 of the depth of the subsequent R wave
The Q wave exists outside of leads III, II or avF since it’s normal to have Q. Waves here
How should the R wave change as you move through the chest leads?
R wave should progress so should get bigger and bigger
What is the voltage criteria for classifying left ventricular hypertrophy?
Need all 3 criteria:
-Count the squares of the S-wave in V1 or V2 (whichever is bigger) THEN count squares of R wave in V5 or V6 (whichever is bigger) then add the number of squares together. If its >35mm meets criteria
-any S or R waves on chest leads that are greater than 30mm
-R wave in lead I and avL > 14mm
What is indicated by a broad QRS?
Bundle Branch Block
What is a normal QRS complex?
Less than 3 squares
How do you assess whether a bundle branch block is either left or right?
Look at the chest leads V1-V6 at the Broad QRS complexes
What is the saying used to help determine the direction of bundle branch block?
WILLIAM MARROW
What does WILLIAM MARROW mean?
You look at the QRS complexes in leads V1 to to V6
V1 to V3 will either look like a W or M
V4 to V6 will either look like a W or M (opposite to V1 to V3)
Which name is used to show Left Bundle Branch block when looking at the chest leads?
WILLIAM
Which name is used to show Right Bundle Branch block when looking at the chest leads?
MARROW
How do you determine left bundle branch block using WILLIAM?
W.I.LL.IA.M
Look at the broad QRS complexes in V1-V3 it will look like a W
Look at the broad QRS complexes in V4-V6 it will look like an M
The way you can remember that WILLIAM is for LBBB is the 2 LLs in the middle
How do you determine right bundle branch block using MARROW?
M.A.RR.O.W
Look at the broad QRS complexes in V1-V3 it will look like an M
Look at the broad QRS complexes in V4-V6 it will look like an W
The way you can remember that MARROW is for RBBB is the 2 RRs in the middle
What are the 3 types of ST segments?
Normal
Elevated
Depressed
What are the 3 causes of ST elevation?
-MI (acute myocardial injury)
-pericarditis
-brugada syndrome
How does an ST elevation caused by an MI/acute myocardial injury?
Tombstone look to it
Regional to the area of damage with reciprocal changes in other leads
How does the ST elevation cased by pericarditis appear?
Saddle shaped elevated ST segment with pr depression
What is the difference between ST elevations caused by MI/acute Myocardial injury and pericarditis?
MI/myocardial injury:
-tombstone look that is specific to the area of damage
Pericarditis:
-saddle shaped ST segment with PR depression
What are the 2 types of ST depression that are dangerous/indicate coronary artery disease?
Horizontal ST depression
Downsloping ST depression
What are some types of pathological T waves that indicate an MI?
Biphasic T wave
Symmetrical T wave inversion
T wave triangular inversion
Asymmetrical T wave inversion is not dangerous
What is the QT interval?
How long it takes ventricles to repolarise
How do you identify the QT interval on an ECG?
Start of the Q wave to the end of the T wave
(Look at last page of notes if unsure)
What can QT prolongation cause?
Leads to torsades de pointes
What is the equation for working out QTc?
QT / square root of RR interval
Units = m/s
What is the RR interval?
Distance between the 2 peaks of the QRS
(Look at last page of notes if unsure)
