ECG interpretation

Question 1

Describe SALI leads (and what arteries they relate to)

Answer 1

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)

Question 2

What are the septal and anterior leads and what coronary artery does it relate to?

Answer 2

V1-V2
V3-4
Left anterior descending (LAD)

Question 3

What are the lateral leads and what coronary artery does it relate to?

Answer 3

V5-V6 (low)
I and aVL (high)
Left circumflex or left anterior descending (LCx or LAD)

Question 4

What are the inferior leads and what coronary artery does it relate to?

Answer 4

II, III, and aVF (RCA- about 80% and sometimes a dominant LCx 18%)

Question 5

What is a normal PR interval?

Answer 5

0.12-0.20 (3-4 small squares

Question 6

What does a delayed PR interval represent?

Answer 6

Delayed conduction through the AV node eg in heart block

Question 7

What does a short PR interval represent?

Answer 7

Preexcitation syndromes (Eg accessory pathway syndromes like WPW)
AV nodal (junctional) rhythm.

Question 8

What does the P wave represent?

Answer 8

Atrial depolarisation

Question 9

What is the duration of a normal P wave?

Answer 9

0.12 seconds (3 small squares)

Question 10

In what lead is P wave biphasic?

Answer 10

V1

Question 11

Where are atrial abnormalities most easily seen?

Answer 11

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.

Question 12

What are the precordial leads?

Answer 12

Chest leads ie V1-V6

Question 13

What is the normal amplitude of the P wave?

Answer 13

< 2.5 mm (0.25mV) in the limb leads

< 1.5 mm (0.15mV) in the precordial leads

Question 14

The first 1/3 of the P wave represents the depolarisation of which atria- left or right?

Answer 14

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.

Question 15

What does P wave inversion in the inferior leads indicate?

Answer 15

P-wave inversion in the inferior leads indicates a non-sinus origin of the P waves

Question 16

What is a normal duration for QRS complex?

Answer 16

Normal QRS width should be 2-3 small squares (0.08- 0.12)

Question 17

What does a narrow QRS represent?

Answer 17

Narrow complexes (QRS < 100 ms) are supraventricular in origin.

Question 18

What does a broad QRS complex represent?

Answer 18

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).

Question 19

What leads are Q waves not normally seen in?

Answer 19

Under normal circumstances, Q waves are not seen in the right-sided leads (V1-3). They are pathological if seen in these leads.

Question 20

What depth should Q waves be?

Answer 20

They should not be > 2 mm deep.

Question 21

In relation to the QRS complex, under what size should the Q wave be?

Answer 21

They should not be > 25% of depth of QRS complex.

Question 22

How wide should a Q wave be?

Answer 22

They should not be > 40 ms (1 mm) wide

Question 23

What is the problem with a prolonged QT interval?

Answer 23

An abnormally prolonged QT is associated with an increased risk of ventricular arrhythmias, especially Torsades de Pointes.

Question 24

What is the risk of shortened QT segment in congenital short QT syndrome?

Answer 24

Congenital short QT syndrome has been found to be associated with an increased risk of paroxysmal atrial and ventricular fibrillation and sudden cardiac death.

Question 25

From where to where is the QT interval measured?

Answer 25

The QT interval is defined from the beginning of the QRS complex to the end of the T wave

Question 26

What leads should the QT interval be measured in?

Answer 26

The QT interval should be measured in either lead II or V5-6

Question 27

As a %, how long should the QT segment be compared to the RR interval?

Answer 27

A useful rule of thumb is that a normal QT is less than half the preceding RR interval

Question 28

What can cause a prolonged QT (440)

Answer 28

``` Hypokalaemia Hypomagnesaemia Hypocalcaemia Hypothermia Myocardial ischemia ROSC Post-cardiac arrest Raised intracranial pressure Congenital long QT syndrome Medications/Drugs ```

Question 29

WHat extra wave can hypokalaemia cause?

Answer 29

U wave

Question 30

What is corrected QT interval (QTc)?

Answer 30

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.

Question 31

What is a normal QTc for men and for women?

Answer 31

QTc is prolonged if > 440ms in men or > 460ms in women

Question 32

What does a QTc more than 500 put people at risk of?

Answer 32

QTc > 500 is associated with increased risk of torsades de pointes

Question 33

What is considered a short QTc?

Answer 33

QTc is abnormally short if < 350ms

Question 34

What can raised ICP cause in relation to T waves and QT interval?

Answer 34

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.

Question 35

What can cause short QT?

Answer 35

Hypercalcaemia Congenital short QT syndrome Digoxin effect

Question 36

What changes can digoxin cause on ECGs?

Answer 36

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).

Question 37

What does ST depression indicate

Answer 37

Myocardial ischemia

Question 38

What does ST elevation indicate

Answer 38

Myocardial infarction

Question 39

What level of ST depression is significant

Answer 39

Horizontal or downsloping ST depression ≥ 0.5 mm (half a small square) at the J-point in ≥ 2 contiguous leads indicates myocardial ischaemia

Question 40

ST depression of what amount is significant

Answer 40

ST depression ≥ 1 mm (one small square) is more specific and conveys a worse prognosis.

Question 41

What can ST depression in localized to only high lateral and inferior leads mean?

Answer 41

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.

Question 42

What is the pattern of depression and elevation in l main coronary artery occlusion

Answer 42

A pattern of widespread ST depression plus ST elevation in aVR > 1 mm is suggestive of left main coronary artery occlusion.

Question 43

At what depth is T wave inversion significant

Answer 43

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.)

Question 44

How many small squares is significant for St elevation is limb leads and in precordial (chest) leads.

Answer 44

1 small square for limb, 2 small squares for precordial.