Flashcards in ECG Deck (67):
How many electrodes are attached to the body?
How many leads are computed?
Which 2 planes do we view the heart in and which leads allow this?
Chest leads = horizontal/transverse plane
Limb leads = frontal/coronal plane
Which of the leads are unipolar?
Chest leads (C1-C6)
Augmented leads aVR, aVL and aVF
Which leads are bipolar?
I, II and III
Which bundle branch does conduction travel quicker down?
The left bundle branch
Depolarisation moving towards an electrode produces a...
Depolarisation moving away from an electrode produces a...
Repolarisation moving towards an electrode produces a ...
Repolarisation moving away from an electrode produces a...
What does the amplitude of the wave depend on?
How much muscle is depolarising
How directly towards or away from the electrode the excitation is moving
What does the p wave represent?
What does the q wave represent?
Septal depolarisation spreading to the ventricles
What does the R wave represent?
Main ventricular depolarisation
What does the S wave represent?
End ventricular depolarisation (travelling upwards)
What does the T wave represent?
Which lead do we use to assess rhythm?
Long rhythm strip
Usually from lead II
What is the standard speed of ECG machines and how does that correlate to squares?
5 large squares/sec
What does 1 large square represent?
5mm or 0.2secs
What does 1 small square represent?
1mm or 0.04 secs
If the rhythm is regular than how do we calculate it?
Divide 300 by the number of large squares in the R-R interval
If the rhythm is irregular, how do we calculate it?
Count the number of QRS complexes in 6 seconds (30 squares) then x10
How wide should the PR interval be?
0.12 - 0.20 secs
3 - 5 small squares
How wide should the QRS be?
Less than 3 small squares
What is the upper limit of the correct QT interval for males and females?
Males = 0.45 secs
Females = 0.47 secs
What is the basis of atrial fibrillation?
Multiple abnormal atrial pacemaker sites discharging randomly so impulse conducted irregularly to ventricles. The atria are quivering.
What does the PR interval indicate?
The time taken for conduction of impulse to ventricles.
What is first degree heart block and how do we spot it?
Slow conduction in AV node and His bundle due to ischaemia or degenerative change
PR interval is prolonged
Describe second degree heart block Type 1
Progressive lengthening of the PR interval till one P is not conducted, loss of a QRS.
Describe type 2 second degree heart block
PR interval is normal
Sudden lack of conduction to the ventricles - dropped QRS
High risk of progression to complete heart block
Describe complete (3rd degree) heart block
P waves normal but not conducted to ventricles
Ventricular pacemaker takes over
Rate is very slow (30-40bpm)
Wide QRS complexes
Requires urgent pacemaker insertion
Define ectopic foci
Abnormal pacemaker sites within the heart muscle that displays automaticity
Define ventricular tachycardia
A run of 3 or more consecutive ventricular ectopics
Which leads must we look in to assess structural abnormalities?
All 12 leads
Which leads view the inferior surface of the RV and LV?
Leads II, III and aVF
Which leads view the lateral surface LV and LA?
Leads I and aVL
Which lead views the atrial and ventricular cavities?
What do each of the chest leads face?
C1 and C2 = anteroseptal
C3 and C4 = anteroapical
C5 and C6 = anterolateral
What does sub-endocardial ischaemia cause in ECG?
Causes ST depression in leads facing the affected area(s)
What are the 3 ECG features of a fully evolved MI?
Pathological Q waves - myocardial necrosis
ST segment elevation - subepicardial injury
T wave inversion - ischaemia
(In ECG leads facing the infarcted area)
Describe pathological Q waves
More than 0.04s (I small square wide) and >2mm deep
Define the cardiac axis
The average (overall) direction of spread of ventricular depolarisation.
What is the normal cardiac axis?
-30 to +90 degrees
What can cause left axis deviation?
Left ventricular hypertrophy
Conduction blocks in the anterior part of the left bundle branch
What can cause right axis deviation?
Right ventricular hypertrophy
How will the QRS look in left axis deviation?
Lead I = upright QRS
Lead III = inverted QRS
How will the QRS look in right axis deviation?
Lead I = negative (inverted) QRS
Lead III = upright QRS
When can torsades de pointes occur?
In long QT syndrome
Describe torsades de pointes
Progressive twisting of the QRS complex
Changing amplitude of QRS in sinusoid all pattern
Irregular RR intervals
Heart rate = 150-300bpm
What do we use the Swartz score for?
To determine the likelihood that the patient had long QT syndrome
How does an early after depolarisation occur?
Repolarisation is interrupted by the reopening of VG calcium channels
How does a delayed after depolarisation occur?
A prolonged AP may cause elevated calcium load in cytoplasm. NCX expels calcium but allows 3 Na+ in for every calcium expelled which may be sufficient to trigger further AP.
What is Bachmann's bundle?
The interatrial tract to allow conduction to reach the LA.
What usually causes long QT syndrome?
Medication (often one that messes with K+ channels)
What are the other (non-medication) causes of long QT?
Excessive diarrhoea/vomiting causing loss of K+/Mg2+
Anorexia nervosa (decreased K+)
Thyroid dysfunction (decreased K+)
Structural heart disease
Where do we place C1?
4th ICS, right sternal border
Where do we place C2?
4th ICS, left sternal border
Where do we place C3?
Midway between C2 and C4
Where do we place C4?
5th ICS, mid-clavicle line on the left
Where do we place C5?
Midway between C4 and C6
Where do we place C6?
5th ICS, mid-axillary line on left
Where do we place the red limb lead?
Where do we place the yellow limb lead?
Where do we place the green limb lead?
Where do we place the black limb lead?
What is the formula for correct QT interval?
QT / square root of RR interval