ECG interpretation Flashcards
Describe SALI leads (and what arteries they relate to)
Septal - V1, V2 (also anterior) (LAD)
Anterior- V3, V4- (LAD)
Lateral V5, V6 (low), I and aVL (high) (LCx or LAD)
Inferior- II, III, and aVF (RCA and LCx)
What are the septal and anterior leads and what coronary artery does it relate to?
V1-V2
V3-4
Left anterior descending (LAD)
What are the lateral leads and what coronary artery does it relate to?
V5-V6 (low)
I and aVL (high)
Left circumflex or left anterior descending (LCx or LAD)
What are the inferior leads and what coronary artery does it relate to?
II, III, and aVF (RCA- about 80% and sometimes a dominant LCx 18%)
What is a normal PR interval?
0.12-0.20 (3-4 small squares
What does a delayed PR interval represent?
Delayed conduction through the AV node eg in heart block
What does a short PR interval represent?
Preexcitation syndromes (Eg accessory pathway syndromes like WPW) AV nodal (junctional) rhythm.
What does the P wave represent?
Atrial depolarisation
What is the duration of a normal P wave?
0.12 seconds (3 small squares)
In what lead is P wave biphasic?
V1
Where are atrial abnormalities most easily seen?
Atrial abnormalities are most easily seen in the inferior leads (II, III and aVF) and lead V1, as the P waves are most prominent in these leads.
What are the precordial leads?
Chest leads ie V1-V6
What is the normal amplitude of the P wave?
< 2.5 mm (0.25mV) in the limb leads
< 1.5 mm (0.15mV) in the precordial leads
The first 1/3 of the P wave represents the depolarisation of which atria- left or right?
The first 1/3 of the P wave corresponds to right atrial activation, the final 1/3 corresponds to left atrial activation; the middle 1/3 is a combination of the two.
What does P wave inversion in the inferior leads indicate?
P-wave inversion in the inferior leads indicates a non-sinus origin of the P waves
What is a normal duration for QRS complex?
Normal QRS width should be 2-3 small squares (0.08- 0.12)
What does a narrow QRS represent?
Narrow complexes (QRS < 100 ms) are supraventricular in origin.
What does a broad QRS complex represent?
Broad complexes (QRS > 100 ms) may be either ventricular in origin, or due to aberrant conduction of supraventricular complexes (e.g. due to bundle branch block, hyperkalaemia or sodium-channel blockade).
What leads are Q waves not normally seen in?
Under normal circumstances, Q waves are not seen in the right-sided leads (V1-3). They are pathological if seen in these leads.
What depth should Q waves be?
They should not be > 2 mm deep.
In relation to the QRS complex, under what size should the Q wave be?
They should not be > 25% of depth of QRS complex.
How wide should a Q wave be?
They should not be > 40 ms (1 mm) wide
What is the problem with a prolonged QT interval?
An abnormally prolonged QT is associated with an increased risk of ventricular arrhythmias, especially Torsades de Pointes.
What is the risk of shortened QT segment in congenital short QT syndrome?
Congenital short QT syndrome has been found to be associated with an increased risk of paroxysmal atrial and ventricular fibrillation and sudden cardiac death.
From where to where is the QT interval measured?
The QT interval is defined from the beginning of the QRS complex to the end of the T wave
What leads should the QT interval be measured in?
The QT interval should be measured in either lead II or V5-6
As a %, how long should the QT segment be compared to the RR interval?
A useful rule of thumb is that a normal QT is less than half the preceding RR interval
What can cause a prolonged QT (440)
Hypokalaemia Hypomagnesaemia Hypocalcaemia Hypothermia Myocardial ischemia ROSC Post-cardiac arrest Raised intracranial pressure Congenital long QT syndrome Medications/Drugs
WHat extra wave can hypokalaemia cause?
U wave
What is corrected QT interval (QTc)?
The corrected QT interval (QTc) estimates the QT interval at a standard heart rate of 60 bpm.
This allows comparison of QT values over time at different heart rates and improves detection of patients at increased risk of arrhythmias.
What is a normal QTc for men and for women?
QTc is prolonged if > 440ms in men or > 460ms in women
What does a QTc more than 500 put people at risk of?
QTc > 500 is associated with increased risk of torsades de pointes
What is considered a short QTc?
QTc is abnormally short if < 350ms
What can raised ICP cause in relation to T waves and QT interval?
A sudden rise in intracranial pressure (e.g. due to subarachnoid haemorrhage) may produce characteristic T wave changes (‘cerebral T waves’): widespread, deep T wave inversions with a prolonged QTc.
What can cause short QT?
Hypercalcaemia
Congenital short QT syndrome
Digoxin effect
What changes can digoxin cause on ECGs?
Digoxin produces a relative shortening of the QT interval, along with downward sloping ST segment depression in the lateral leads (‘reverse tick’ appearance), widespread T-wave flattening and inversion, and a multitude of arrhythmias (ventricular ectopy, atrial tachycardia with block, sinus bradycardia, regularized AF, any type of AV block).
What does ST depression indicate
Myocardial ischemia
What does ST elevation indicate
Myocardial infarction
What level of ST depression is significant
Horizontal or downsloping ST depression ≥ 0.5 mm (half a small square) at the J-point in ≥ 2 contiguous leads indicates myocardial ischaemia
ST depression of what amount is significant
ST depression ≥ 1 mm (one small square) is more specific and conveys a worse prognosis.
What can ST depression in localized to only high lateral and inferior leads mean?
ST depression localised to a particular territory (esp. inferior or high lateral leads only) is more likely to represent reciprocal change due to STEMI. The corresponding ST elevation may be subtle and difficult to see, but should be sought.
What is the pattern of depression and elevation in l main coronary artery occlusion
A pattern of widespread ST depression plus ST elevation in aVR > 1 mm is suggestive of left main coronary artery occlusion.
At what depth is T wave inversion significant
At least 1mm (one small square)and present in 2 waves that usually hAve upright Ts. ( T wave inversion is a normal variant in leads III, aVR and V1.)
How many small squares is significant for St elevation is limb leads and in precordial (chest) leads.
1 small square for limb, 2 small squares for precordial.
