ECG Basics

Question 1

ECG paper speed is ordinarily…

Answer 1

25 mm/sec

Question 2

small box = ___ sec

Answer 2

0.04 sec

Question 3

5 small boxes = 1 large box = ____ sec

Answer 3

0.20 sec

Question 4

P wave represents

Answer 4

atrial depolarization

Question 5

P wave duration is generally

Answer 5

<0.12 sec (3 small boxes)

Question 6

P wave amplitude

Answer 6

<0.25 mv (2.5 small boxes)

Question 7

PR interval includes

Answer 7

P wave + PR segment

Question 8

PR segment is

Answer 8

• measured from the begining of the P wave to the 1st part of the QRS complex (which may be a Q wave or R wave)

Question 9

PR interval includes…

Answer 9

time for atrial depolarization (P wave) & conduction through the AV nodes & the His-Purkinje system (which constitutes the PR segment).

Question 10

PR interval duration

Answer 10

0.12 - 0.20 sec (3 to 5 small boxes)

Question 11

Length of the PR interval changes with?

Answer 11

Heart rate

Question 12

PR interval is shorter at…

Answer 12

faster heart rates due to sympathetically mediated enhancement of atrioventricular (AV) nodal conduction

Question 13

PR interval is longer when…

Answer 13

the rate is slowed as a consequence of slower AV nodal conduction resulting from withdrawal of sympathetic tone or an increase in vagal input.

Question 14

QRS complex represents

Answer 14

ventricular depolarization

Question 15

Small Q waves are often seen in leads _______ as a result of initial septal depolarization.

Answer 15

I, aVL & V4 - V6

Question 16

Q wave in the QRS complex is…

Answer 16

the initial negative deflection.

Question 17

1st positive deflection of the QRS complex is

Answer 17

R wave

Question 18

R wave in the QRS complex represents

Answer 18

depolarization of the left ventricular myocardium.

NOTE: right ventricular depolarization is obscured because the left ventricular myocardial mass is much greater than that of the right ventricle.

Question 19

The small R wave in lead V1 represents

Answer 19

intial septal depolarization

Question 20

S wave in the QRS complex is the

Answer 20

negative deflection following the R wave

Question 21

S wave represents

Answer 21

terminal depolarization of the high lateral wall

Question 22

Lower case letters (q, r, or s) are used for…

Answer 22

relatively small amplitude waves of <0.5mV (<5mm with standard calibration)

Question 23

An entirely negative QRS complex is called a

Answer 23

QS wave

Question 24

QRS complex duration

Answer 24

0.06 - 0.10 sec (1.5 - 2.5 small boxes)

Question 25

Explain R wave progression & in what leads?

Answer 25

• R wave should progress in size across the precordial leads (V1 - V6).
• Normally there is a small R wave in lead V1 with a deep S wave.
• The R wave amplitude should increase in size until V4 - V6 while the S wave becomes less deep.

Question 26

ST segment occurs

Answer 26

after ventricular depolarization has ended & before repolarization has begun.

Question 27

J point

Answer 27

It is the intersection of the end of the QRS complex & the initial part of the ST segment.

Question 28

T wave represents

Answer 28

ventricular repolarization

Question 29

Why is the T wave asymmetrical & has a variable amplitude?

(T wave is broad, has slow upstroke & a more rapid downslope to the isoelectric lune following its peak)

Answer 29

This is because:
- the rate of repolarization is slower than depolarization.

Question 30

Difference in characteristics of T wave vs P wave

Answer 30

• Since the rate of repolarization is slower than depolarization, the T wave is broad, has a slow upstroke, & a more rapid downslope to the isoelectric line following its peak. Thus, the T wave is asymmetric & the amplitude is variable. - - In addition, the T wave is usually smooth up and down.
• If there is any irregularity on the T wave (bump, notch, rippled, etc) a superimposed P wave should be considered.

Question 31

QT interval consists of

Answer 31

• QRS complex
• ST segment
• T wave

Question 32

QT interval is primarily a measure of…

Answer 32

ventricular repolarization

Question 33

If the _____ duration is increased, this will lead to an increase in QT interval but doesn’t a change in ventricular repolarization.

Answer 33

• QRS complex

Question 34

A widened QRS must be considered if a ____________ is being evaluated.

Answer 34

prolonged QT interval

Question 35

The QT interval is dependent upon…

Answer 35

heart rate = shorter at faster heart rates & longer when the rate is slower.

Question 36

Clinicians also need to be mindful of the fact that since the QRS widens in the setting of a bundle branch block, the ____________ will also increase.

Answer 36

QT interval

Question 37

U wave may be seen in some leads especially the precordial leads…

Answer 37

V2 - V4

Question 38

U wave is more evident in some circumstances such as…

Answer 38

hypokalemia & bradycardia

Question 39

Normal QRS axis =

Answer 39

if the QRS is (+) (upright) in both leads I and II, then the axis falls between -30 & 90 degree which is normal.

Question 40

Left axis deviation =

Answer 40

If the QRS complex is is (+) in lead I but (-) in lead II, the it is left axis deviation (-30 to -90 degree).

Question 41

Right axis deviation =

Answer 41

If the QRS complexes are (-) in lead I and (+) in aVF, then it is right axis deviation (90 to 180 degree).

Question 42

Extreme axis deviation =

Answer 42

If the QRS complexes are (-) in both I & aVF, then the axis is extreme (180 to -90 degrees).

Question 43

8 steps in interpretating an ECG:

Answer 43

1. Rate
2. Rhythm
3. Axis
4. Intervals
5. P wave
6. QRS complex
7. ST segment T wave
8. Overall interpretation

Question 44

Short PR intervals may suggest of…

Answer 44

Wolff-Parkinson White syndrome

Question 45

Long QRS intervals represent…

Answer 45

• bundle branch block
• ventricular pre-excitation
• ventricular pacing
• ventricular tachycardia