CVS 11 + 12 + 13 - ECG Flashcards
How is a depolarisation represented on an ECG? a repolarisation?
DEPOLARISATION:
Positive deflection= moving towards cathode (+ve)
Downward deflection= moving away from the cathode (+ve)
REPOLARISATION:
Downward deflection= moving towards cathode (+ve)
Positive deflection= moving away from the cathode (+ve)
–> Repolarising current is OPPOSITE polarity to depolarising current
What do P, QRS, T, Q, R, S waves represent?
P wave= atria contraction
QRS complex= ventricle contraction
T wave= ventricle repolarisation
Q wave= depolarisation of interventricular septum (towards –ve electrode)
R wave= ventricular depolarisation (towards +ve electrode)
S wave= depolarisation towards –ve electrode
Repolarisation of atria ‘buried’ in QRS of ventricle depolarisation
What is the Einthoven Triangle?
Triangle formed between lead I, II and III.
Lead I: Right arm to Left arm (one ‘L’ so lead I)
Lead II: Right arm to Left Leg (2 ‘L’)
Lead III: Left arm to Left Leg (3’L’)
Neutral: Right leg
Always ends on the Left side
Describe lead I
RA (-ve) to LA (+ve)
Gives a good view of depolarisation from right to left
QRS positive
Describe lead II
RA (-ve) to LL (+ve)
Depolarisation of heart is in this direction, so QRS nearly always positive
Describe lead III
LA (-ve) to LL (+ve)
Very little positive deflection as heart does not depolarize in this direction
How are augmented leads obtained?
Obtained by using the average voltage of two electrodes as the negative pole, and reading from the remaining electrode as the positive pole
aVR has right arm as positive electrode
aVL has left arm
aVF has left leg
What is a normal physiological value of the QRS axis?
+90 to -30 degrees
How do you work out the QRS axis?
Sum 2 vectors that are at right angles like Lead I and aVF.
Look at net positive deflection for QRS.
QRS = I + aVF (in vectors)
then calculate angle that the vectors form
What heart rate is considered bradycardia and tachycardia?
Bradycardia = < 60 bpm Tachycardia = > 100 bpm
What is the difference between segments and intervals?
Segments are isoelectric regions between two waveforms.
Interval is the time between the start of one wave and the start of the next.
What is the sweep speed of ECG?
25 mm/s
How wide is a small square and a large square and what time interval does that represent?
Small Square = 0.04 s (1 mm)
Large Square = 0.2 s (5 mm)
What’s the duration and amplitude of a normal P wave?
Duration = < 0.11 s Amplitude = < 2.5 mm
What is the duration of a normal PR interval?
0.12 - 0.2 s (=one large square max)
NOTE
PR interval has no clinical significance
What is the duration and amplitude of a normal QRS complex?
Duration = < 0.12 s Amplitude = < 25 mm
What is the duration and amplitude of a normal Q wave?
Duration = < 0.04 s Amplitude = < 25% of the total QRS complex
What is the duration of a normal QT interval?
0.38-0.42s
NOTE
Important as this is the start of the ventricles depolarising.
Long QT syndrome - predispose to arrythmias and sudden cardiac death.
What does a QRS complex with a large amplitude indicate?
Ventricular Hypertrophy
What are the ECG features of sinus tachycardia?
Normal waveforms - normal P wave, precedes each QRS complex.
Abnormally fast resting heart rate
Atrial and Ventricular Rate = 200 bpm
What are the ECG features of atrial fibrillation? Include atrial rate and ventricular rate in your answer.
ABSENT P WAVES (may get an oscillating baseline)
Irregular ventricular rhythm (duration between QRS varies) - irregularly irregular - v imp.
Could be high or normal ventricular rate
QRS complexes are normal
Atrial Rate = 350-600 bpm
Ventricular rate = 100-180 bpm
What are the ECG features of atrial flutter?
SAW-TOOTHED BASE LINE - ‘ flutter’
No isoelectric line - shows constant atrial activity
Regular ventricular rhythm - one in every few atrial depolarisations will get conducted down to the ventricles
QRS normal + regular ventricular rhythm
Atrial Rate = 250-350 bpm
Ventricular Rate = 150 bpm (with 2:1)
4:1 is also common
How is atrial fibrillation different to atrial flutter?
Atrial flutter has a more regular ventricular rhythm
What is atrioventricular nodal reentrant tachycardia?
When a local circuit is created within the AV node
What is atrioventricular reentrant tachycardia?
Local circuit is within the atria and the ventricles
What are the ECG features of AVNRT and AVRT?
Lots of QRS complexes
No clear P wave
QRS complexes are RAPID and IRREGULAR
You get simultaneous depolarisation of the atria and ventricles so you get instantaneous P wave and QRS complexes - P waves often burried into QRS or just after.
What happens in AVNRT?
Depolarisation is rotating within the AV node
Then it re-enters and causes simultaneous atrial and ventricular contraction
What is preexcitation syndrome and what is a defining feature of the ECG?
Defining Feature = DELTA WAVES aka slurred ventricular contraction (big).
Some people are born with a congenital connection between the atria and the ventricles called an ACCESSORY PATHWAY.
This allows early depolarisation of the ventricles leading to slurring of the QRS complexes - ventricular pre excitation.
This gives an abnormally short PR interval
What syndrome causes preexcitation syndrome?
Wolff-Parkinson-White Syndrome
What is the treatment to remove the accessory pathway?
Radio frequency ablation
What are the three types of atrioventricular nodal block and how do they vary?
Broad QRS complexes that are VOID OF ANY PATTERN
1st degree = prolonged PR interval 2nd degree (Mobitz type 1 and type 2) = some conduction gets there but it's slow 3rd degree = complete heart block
What is an ECG feature of grade 1 AVN block?
Prolonged PR interval but still 1 to 1 relationship between P wave and QRS complex. but in between nothing happens.
What is the difference between Mobitz type 1 and Mobitz type 2 atrioventricular nodal block?
2nd degree block = some of the beats from the atria do NOT reach the ventricles
Mobitz type I = gradual prolongation of the PR interval culminating in a dropped beat
Mobitz type II = fixed PR interval and then a dropped beat (you do NOT see gradually prolonging of the PR interval)
What is the ECG feature of 3rd degree atrioventricular nodal block?
There is NO conduction from atria to ventricles .
ECG shows COMPLETE DISSOCIATION between QRS complexes and P waves .
Ventricles fire on their own as a protective mechanism
What is the main ECG feature of bundle branch blocks?
QRS complex WIDENS and morphology changes.
It takes longer to depolarise the ventricles
How do you distinguish between RBBB and LBBB?
WilliaM MarroW
RBBB = V1 + V2 = rabbit ears
LBBB = V1 + V2 = deep S waves
What are the ECG features of ventricular tachyarrhythmia?
Rapid, regular, broad QRS complex pattern
What are the ECG features of ventricular fibrillation?
Broad QRS complexes that are VOID OF ANY PATTERN
How should the ST segment be?
‘isoelectric’
As elevated it may indicate myocardial infarction.
