Interpretation of an ECG

Question 1

calculating Bp from an ECG

Answer 1

300 divide by the

number of big squares per R – R interval.

Question 2

QRS complex

Answer 2

<120 ms (0.12s) or wide >120 ms (0.12s)?

Question 3

P waves

Answer 3

<0.25mV, and upright in II III and AVF

Question 4

Arrhythmia - ATRIAL FIBRILATION

Answer 4

No discernible P waves and irregular QRS complexes

Question 5

Arrhythmia - Atrial flutter

Answer 5

p waves can be seen as a rate of 300 per minute giving a sawtooth appearance, 4 p waves per QRS complex

Question 6

nodal tachycardia

Answer 6

normal QRS but absent p waves

Question 7

ventricular tachycardia

Answer 7

after two sinus beats the rate increases to 150 per minute, the QRS complexes become broad a t waves are difficult to identify

Question 8

abnormal p wave - p-mitrale

Answer 8

Bifid P wave = left atrial hypertrophy

Question 9

abnormal p wave - p-pulmonale

Answer 9

Peaked P wave = right atrial

hypertrophy

Question 10

P-R Interval (Time Between Atrial and Ventricular Depolarisation)

Answer 10

Measure from the beginning of P to the beginning of Q wave

Normal range 120-200 ms (0.12-0.2 s)
Prolonged >200 ms (0.2 s) implies delayed AV conduction

Question 11

If>120ms(0.12s) in QRS interval

Answer 11

Ventricular Conduction Defects
 Bundle Branch Block
 Left and Right Bundle Branch Block

Question 12

Lowvoltage<5mm: in QRS complex

Answer 12

Hypothyroidism
 COAD
 Myocarditis
 Pericarditis and Pericardial effusion

Question 13

Left Ventricular Hypertrophy:

Answer 13

 RwaveinV5 >25mm or
 SumoftheS
wave in V1 and R wave in V5 or V6 >35mm
 Sokolow-Lyon index

Question 14

 Right Ventricular Hypertrophy:

Answer 14

 Dominant R wave in V1
 T wave inversion in V1 – V3 or V4
 Deep S wave in V6

Question 15

Significant Q Wave

Answer 15

> 40ms(0.04s)
 Depth>2mm.
 Present couple of hours/days after acute MI
 If present in lead III consider PE.

Question 16

QT interval

Answer 16

 Measure from start QRS to end of T wave – varies with rate.
 Corrected QTc Interval  QTc=QT/√RR
Normal 380-420 ms (0.38-0.42 sec)

Question 17

Prolonged QT Interval

Answer 17

 Acute Myocardial Ischaemia
 Myocarditis
 Bradycardia
 Head Injury
 Hypothermia
 U&E Imbalance (K+ Ca2+ Mg2+ )
 Congenital
 Drugs (Quinidine, Antihistamines, Macrolides, Amiodarone, Phenothiazines)

Question 18

ST Segment

Answer 18

 Time from the end of ventricular
depolarisation to the start of ventricular repolarisation
 Usually Isoelectric

Question 19

T Wave (Ventricular Repolarisation)

Answer 19

Abnormal if inverted in I, II and V4 -V6 (Ischaemia /Infarction)

Question 20

T Wave Digoxin effects

Answer 20

 T Wave inversion

 ST segment sloping depression

Question 21

Axis

Answer 21

(normal between -30° and +90°)

Question 22

Left Axis Deviation (-30°to -90°)

Answer 22

 Negative QRS deflections in II and III

 LV Hypertrophy, MI

Question 23

Right Axis Deviation

Answer 23

 Negative QRS deflections in I

 RV Hypertrophy, PE, MI

Question 24

MI ECG Changes

Answer 24

T wave peaking followed by T wave inversion
 ST segment elevation
 Appearance of new Q waves

Question 25

MI ECG Localizing the Infarct

Answer 25

 AnteriorInfarction:
 Any of precordial leads (V1 through V6)
 LateralInfarction:
 Leads I, AVL, V5 and V6
 InferiorInfarction:
 Leads II, III, and AVF
 PosteriorInfarction:
 Reciprocal changes in lead V1 (ST- segment depression, tall R wave)