Reading ECGs

Question 1

Calculating HR (normal rhythm)

Answer 1

No. large squares in one RR interval/300

Question 2

Calculating HR (irregular rhythm)

Answer 2

No. complexes on rhythm strip x 6

Question 3

P Waves

Answer 3

Present?
Followed by QRS?
Normal duration/size/shape?
If absent, any atrial activity?

Question 4

P Wave Abnormalities

Answer 4

Sawtooth baseline - flutter waves
Chaotic baseline - fibrillation waves
Flat line - no atrial activity
(absent w irregular rhythm = AF)

Question 5

Prolonged PR Interval

Answer 5

> 0.2s

AV delay/heart block

Question 6

Degrees of Heart Block

Answer 6

First degree
Second degree (Mobitz type I/Wenckebach +II)
Third degree (complete)

Question 7

First degree heart block

Answer 7

Prolonged PR interval

>200ms (5 smalll squares)

Question 8

Type I Second Degree Heart Block

Answer 8

Progressive prolongation of PR interval
Until atrial impulse is not conducted and QRS dropped
AV conduction resumes next beat and this repeats

Question 9

Type 2 Second Degree Heart Block

Answer 9

Consistent PR interval duration w intermittently dropped QRS
Intermittent QRS dropping usully follows repeating cycle
Every 3rd (3:1 block) or 4th (4:1 block) P wave

Question 10

Third Degree Heart Block

Answer 10

No elec communication between atria and ventricles
P waves/QRS have no association
Cardiac function maintained by junctional/vent pacemaker

Question 11

Escape Rhythms

Answer 11

Narrow complex 
- QRS<0.12s
- above bifurcation of Bundle of His
Broad complex
- QRS>0.12s
- below bifurcation of Bundle of His

Question 12

Shortened PR Interval

Answer 12

P wave originated from closer to AV node
OR
Atrial impulse gets to ventricle by faster shortcut (accessory pathway = delta wave = WPW syndrome)

Question 13

Height of QRS Complex

Answer 13

Small - <5mm in limb, <10 in chest

Tall - vent hypertrophy

Question 14

Delta Wave

Answer 14

Slurred upstroke of QRS complex

WPW syndrome = delta wave + tachyarrhythmias

Question 15

Q Waves

Answer 15

Isolated Q waves can be normal
Pathological 
- Q wave > 25% of R wave that follows it 
OR
- >2mm height, >40ms width
Assoc w previous MI

Question 16

R and S Waves

Answer 16

Assesses R wave progression across chest leads
Transition from S-R should be V3 or V4
Poor progression = previous MI or poor lead position

Question 17

J Point Segment

Answer 17

Where S wave joins ST segment

High take-off - normal but can look like ST elevation

Question 18

Key Points in J Point Segment

Answer 18

Benign early repol <50y (ischaemia >50y)
Normally J point raised w widespread STE in multiple territories
T waves raised (unlike STEMI)
ECG abnormalities don’t change (unlike STEMI)

Question 19

ST Elevation

Answer 19

> 1mm or in 2 or more contiguous limb leads
OR
2mm in 2 or more chest leads
Assoc w full-thickness MI

Question 20

ST Depression

Answer 20

> / 0.5mm in >/contiguous leads indicates myocardial ischaemia

Question 21

Tall T Waves

Answer 21

> 5mm in limb leads AND >10mm in chest leads
Assoc w
- hyperkalaemia (tall tented T waves)
- hyperacute STEMI

Question 22

Inverted T Waves

Answer 22

Normally inverted in V1 and lead III inversion is normal

Question 23

Causes of Inverted T Waves

Answer 23

• ischaemia
• bundle branch block (V4-6 in L, V1-3 in R)
• PE
• LV hypertrophy (lateral leads)
• hypertrophic cardiomyopathy (widespread)
• general illness

Question 24

Biphasic T Waves

Answer 24

2 peaks

Indicates ischaemia and hypokalaemia

Question 25

Flattened T Waves

Answer 25

Non-specific sign

May represent ischaemia or electrolyte imbalance

Question 26

U Waves

Answer 26

Not common
>0.5mm deflection after T wave (best seen in V2/3)
Larger the slower the bradycardia

Question 27

Causes of U Waves

Answer 27

Electrolyte imbalances
Hypothermia
Secondary to anti-arrhythmic therapy