intro to ECG

Question 1

cross-sectional view of the heart

Answer 1

inferior- lead 2, aVF, lead 3
anterior- V 1,2,3,4,
lateral- lead 1, V5, 6, aVL,

Question 2

QRS axis

Answer 2

Direction of average depolarisation in the heart
- dominated by left ventricular depolarisation Determined from limb leads

Angle determined relative to lead I Normal is -30 to +90 degrees
Axis is approximated by finding the lead with the most +ve QRS

Question 3

normal axis of QRS

Answer 3

Normal axis -30 to +90 degrees (positive QRS in I and II)

Question 4

abnormal axis of QRS

Answer 4

Left axis deviation -30 to -90 degrees
(positive QRS in I, negative in II and aVF

Right axis deviation +90 to +180 degrees (negative QRS in I, positive in aVF)

Question 5

extreme axis deviation of QRS

Answer 5

Extreme axis deviation +180 to -90 degrees (negative QRS in I and II, positive in aVR

Question 6

P/QRS/T morphology

Answer 6

The normal P wave is upright in the inferior leads The normal ST segment is flat
The normal T wave has the same polarity as the QRS

Question 7

nomenclature

Answer 7

P waves = positive, negative (inverted) or biphasic QRS

if first deflection negative = Q wave

positive deflection = R wave

any negative deflection after R = S wave

any further positive deflection = R’ capital letter = dominant wave small latter = non-dominant wave

ST segment = isoelectric, elevated or depressed
T waves = upright, inverted or flat
also concordant or discordant vs. QRS

Question 8

unipolar leads

Answer 8

Measure the potential variation at a single point Augmented limb leads: aVR, aVL, aVF Chest leads: V1 – V6

Question 9

bipolar leads

Answer 9

Measure the potential difference between two points Limb leads I, II and III
(I = RA-LA II = RA-LL III = LA-LL)

Question 10

ECG intervals: normal range s

Answer 10

PR interval <1 large square
<200ms

QRS < 3 small squares
< 120ms

QT interval < 11 small squares
< 440ms